Increased FOXL2 Expression Alters Uterine Structures and Functions

Increased FOXL2 Expression Alters Uterine Structures and Functions | bioRxiv /* */ /* */ <!-- <!-- /*! * yepnope1.5.4 * (c) WTFPL, GPLv2 */ (function(a,b,c){function d(a){return"[object Function]"==o.call(a)}function e(a){return"string"==typeof a}function f(){}function g(a){return!a||"loaded"==a||"complete"==a||"uninitialized"==a}function h(){var a=p.shift();q=1,a?a.t?m(function(){("c"==a.t?B.injectCss:B.injectJs)(a.s,0,a.a,a.x,a.e,1)},0):(a(),h()):q=0}function i(a,c,d,e,f,i,j){function k(b){if(!o&&g(l.readyState)&&(u.r=o=1,!q&&h(),l.onload=l.onreadystatechange=null,b)){"img"!=a&&m(function(){t.removeChild(l)},50);for(var d in y[c])y[c].hasOwnProperty(d)&&y[c][d].onload()}}var j=j||B.errorTimeout,l=b.createElement(a),o=0,r=0,u={t:d,s:c,e:f,a:i,x:j};1===y[c]&&(r=1,y[c]=[]),"object"==a?l.data=c:(l.src=c,l.type=a),l.width=l.height="0",l.onerror=l.onload=l.onreadystatechange=function(){k.call(this,r)},p.splice(e,0,u),"img"!=a&&(r||2===y[c]?(t.insertBefore(l,s?null:n),m(k,j)):y[c].push(l))}function j(a,b,c,d,f){return q=0,b=b||"j",e(a)?i("c"==b?v:u,a,b,this.i++,c,d,f):(p.splice(this.i++,0,a),1==p.length&&h()),this}function k(){var a=B;return a.loader={load:j,i:0},a}var l=b.documentElement,m=a.setTimeout,n=b.getElementsByTagName("script")[0],o={}.toString,p=[],q=0,r="MozAppearance"in l.style,s=r&&!!b.createRange().compareNode,t=s?l:n.parentNode,l=a.opera&&"[object Opera]"==o.call(a.opera),l=!!b.attachEvent&&!l,u=r?"object":l?"script":"img",v=l?"script":u,w=Array.isArray||function(a){return"[object Array]"==o.call(a)},x=[],y={},z={timeout:function(a,b){return b.length&&(a.timeout=b[0]),a}},A,B;B=function(a){function b(a){var a=a.split("!"),b=x.length,c=a.pop(),d=a.length,c={url:c,origUrl:c,prefixes:a},e,f,g;for(f=0;f<d;f++)g=a[f].split("="),(e=z[g.shift()])&&(c=e(c,g));for(f=0;f<b;f++)c=x[f](c);return c}function g(a,e,f,g,h){var i=b(a),j=i.autoCallback;i.url.split(".").pop().split("?").shift(),i.bypass||(e&&(e=d(e)?e:e[a]||e[g]||e[a.split("/").pop().split("?")[0]]),i.instead?i.instead(a,e,f,g,h):(y[i.url]?i.noexec=!0:y[i.url]=1,f.load(i.url,i.forceCSS||!i.forceJS&&"css"==i.url.split(".").pop().split("?").shift()?"c":c,i.noexec,i.attrs,i.timeout),(d(e)||d(j))&&f.load(function(){k(),e&&e(i.origUrl,h,g),j&&j(i.origUrl,h,g),y[i.url]=2})))}function h(a,b){function c(a,c){if(a){if(e(a))c||(j=function(){var a=[].slice.call(arguments);k.apply(this,a),l()}),g(a,j,b,0,h);else if(Object(a)===a)for(n in m=function(){var b=0,c;for(c in a)a.hasOwnProperty(c)&&b++;return b}(),a)a.hasOwnProperty(n)&&(!c&&!--m&&(d(j)?j=function(){var a=[].slice.call(arguments);k.apply(this,a),l()}:j[n]=function(a){return function(){var b=[].slice.call(arguments);a&&a.apply(this,b),l()}}(k[n])),g(a[n],j,b,n,h))}else!c&&l()}var h=!!a.test,i=a.load||a.both,j=a.callback||f,k=j,l=a.complete||f,m,n;c(h?a.yep:a.nope,!!i),i&&c(i)}var i,j,l=this.yepnope.loader;if(e(a))g(a,0,l,0);else if(w(a))for(i=0;i (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0];var j=d.createElement(s);var dl=l!='dataLayer'?'&l='+l:'';j.src='//www.googletagmanager.com/gtm.js?id='+i+dl;j.type='text/javascript';j.async=true;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-M677548'); Skip to main content Home About Submit ALERTS / RSS Search for this keyword Advanced Search New Results Increased FOXL2 Expression Alters Uterine Structures and Functions View ORCID Profile Rong Li , View ORCID Profile San-Pin Wu , Lecong Zhou , View ORCID Profile Barbara Nicol , John P. Lydon , View ORCID Profile Humphrey H-C Yao , View ORCID Profile Francesco J. DeMayo doi: https://doi.org/10.1101/2020.03.06.981266 Rong Li 1 Reproductive and Developmental Biology Laboratory, National Institute of Environmental Health Sciences, Research Triangle Park , NC Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Rong Li San-Pin Wu 1 Reproductive and Developmental Biology Laboratory, National Institute of Environmental Health Sciences, Research Triangle Park , NC Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for San-Pin Wu Lecong Zhou 2 Integrative Bioinformatics, National Institute of Environmental Health Sciences, Research Triangle Park , NC Find this author on Google Scholar Find this author on PubMed Search for this author on this site Barbara Nicol 1 Reproductive and Developmental Biology Laboratory, National Institute of Environmental Health Sciences, Research Triangle Park , NC Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Barbara Nicol John P. Lydon 3 Department of Molecular and Cellular Biology, Baylor College of Medicine , Houston, TX Find this author on Google Scholar Find this author on PubMed Search for this author on this site Humphrey H-C Yao 1 Reproductive and Developmental Biology Laboratory, National Institute of Environmental Health Sciences, Research Triangle Park , NC Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Humphrey H-C Yao Francesco J. DeMayo 1 Reproductive and Developmental Biology Laboratory, National Institute of Environmental Health Sciences, Research Triangle Park , NC Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Francesco J. DeMayo For correspondence: demayofj{at}niehs.nih.gov Abstract Full Text Info/History Metrics Supplementary material Preview PDF Abstract Transcription factor FOXL2 exhibits an increase in mRNA levels in eutopic endometrial biopsy in endometriosis patients. While FOXL2 is known of regulating sex differentiation and reproductive function, the impact of elevated FOXL2 expression on uterine physiology remains unknown. To answer this question, we generated mice with over expression of FOXL2 (FOXL2 OE ) in the female reproductive tract by crossing Foxl2 LsL/+ with the Pgr cre model. FOXL2 OE uterus showed severe morphological abnormality including abnormal epithelial stratification, blunted adenogenesis, increased endometrial fibrosis and disrupted myometrial morphology. In contrast, increasing FOXL2 levels specifically in uterine epithelium by crossing the Foxl2 LsL/+ with the Ltf icre mice resulted in the eFOXL2 OE mice with uterine epithelial stratification but without defects in endometrial fibrosis and adenogenesis, demonstrating a role of the endometrial stroma in the uterine abnormalities of the FOXL2 OE mice. Transcriptomic analysis of 12 weeks old Pgr cre and FOXL2 OE uterus at diestrus stage showed a positive correlation of FOXL2 OE uterine transcriptome with human endometrium of endometriosis patients. Furthermore, we found FOXL2 OE mice were sterile. The infertility was caused in part by a disruption of the hypophyseal ovarian axis resulting in an anovulatory phenotype. The FOXL2 OE mice failed to show decidual responses during artificial decidualization in ovariectomized mice which demonstrates the uterine contribution to the infertility phenotype. These data supported that aberrantly increased FOXL2 expressions in the female reproductive tract can disrupt ovarian and uterine functions, particularly, may be involved in the progressions of endometriosis. Introduction Endometriosis is a hormone dependent disease in which uterine endometrial cells grow outside the uterus. The most accepted hypothesis of the origins of endometriosis is that it is the peritoneal deposition of endometrial tissue from the retrograde menses that is not cleared by the body [ 1 ]. Endometriosis affects about 10 percent of women in the United States [ 2 ]. This disease results in pelvic inflammation, pain and infertility and is a significant women’s health issue. In women with endometriosis the eutopic endometrium and ectopic extrauterine tissues display altered gene expression signatures [ 3 ], including higher expression levels of Forkhead Box L2 ( FOXL2 ) [ 4 , 5 ]. Studying the role FOXL2 plays in regulating the biology of the reproductive tract will aid in understanding the cause of endometriosis and the development of treatments for this disease. Forkhead Box L2 (FOXL2) is a transcription factor which contains a forkhead domain and a polyalanine tract. In addition to the human endometrium, FOXL2 is also expressed in the ovaries, the pituitary, including the gonadotrophs and some thyrotropes [ 4 , 6 , 7 ]. Germline mutation in FOXL2 has been associated with the blepharophimosis-ptosis-epicanthus inversus syndrome (BPES), characterized by eyelid malformation with or without primary ovarian insufficiency in humans [ 8 ]. Similarly, Foxl2 −/− mice display premature ovarian failure [ 9 , 10 ]. Ablation of Foxl2 at different stages of ovarian development demonstrated that Foxl2 is a major regulator for the sex differentiation and maintenance of the ovary from the embryonic stage to adulthood [ 11 – 13 ]. In the pituitary, gonadotroph specific deletion of Foxl2 in mice led to subfertility in both females and males due to Follicle-stimulating hormone (FSH) deficiency [ 14 ]. Both in vitro and in vivo models suggest that FOXL2-SMADs complexes can bind at the Follicle Stimulating Hormone Subunit Beta ( Fshb ) promoter to regulate its transcription [ 15 – 19 ]. FOXL2 also plays an important role in cancer development. It can suppress proliferation and promote apoptosis [ 20 , 21 ]. Its mutation is present in most adult type granulosa-cell tumors and cervical cancers [ 20 , 22 , 23 ]. Taken together, FOXL2 is pivotal for the regulation of reproductive development and the hypophyseal-ovarian axis. There are limited studies about FOXL2 functions in the uterus. FOXL2 is detected in the stroma and glandular epithelium of cow uterus throughout the estrous cycle with much higher levels during luteolysis, as progesterone treatment decreases its expression [ 24 ]. FOXL2 is also detected in the stroma and myometrium of mouse uterus, and conditional deletion of Foxl2 by Pgr cre reduced the stroma compartment while altering myometrial thickness and disrupting myometrial morphology [ 25 ]. In contrast, a recent study reported that FOXL2 is mainly detected in the epithelium and myometrium but not stroma in the mice [ 26 ]. In order to investigate the role of FOXL2 in embryo implantation, FOXL2 expression has been attenuated or enhanced in human endometrial cancer cell lines resulting in disruption of embryo attachment in vitro [ 26 ]. Despite of the contradictory expression patterns of FOXL2 in the uterus, these studies all suggested that FOXL2 may play a crucial role in endometrial homeostasis and function. The goal of this work is to investigate the consequences of increased FOXL2 expression in the reproductive tract by employing the mouse model of uterine FOXL2 overexpression, Pgr cre Foxl2 LsL/+ (FOXL2 OE ) and Ltf icre Foxl2 LsL/+ (eFOXL2 OE ) mice. FOXL2 OE mice displayed multiple changes in uterine morphology, including impaired adenogenesis, altered uterine epithelial differentiation, increased collagen deposition and altered myometrial integrity, while eFOXL2 OE mouse uteris only showed epithelial stratification. Transcriptome of three months old FOXL2 OE uterus is positively correlated with human endometrium with endometriosis. FOXL2 OE mice were infertile with defective ovaries. The disrupted uterine functions were indicated by the abolishment of decidual responses upon artificial decidualization. Material and methods Mice The Rosa26-CAG-LSL-Foxl2 mice with FOXL2 overexpression (named as Foxl2 LsL/+ in this paper), and Pgr cre mice were described previously [ 13 , 27 ]. Ltf icre mice were kindly provided by Dr. Sudhansu K. Dey [ 28 ]. Foxl2 LsL/+ mice were crossed with Pgr cre mice to generate Pgr cre Foxl2 LsL/+ mice, FOXL2 overexpression in female reproductive tract (FOXL2 OE ). To generate uterine epithelial FOXL2 overexpression mice, eFOXL2 OE , Foxl2 LsL/+ mice were crossed with Ltf icre mice. All the mice were maintained on 129Sv and C57BL/6J backgrounds. All animal studies were conducted in accordance with the Guide for the Care and Use of Laboratory Animals published by the National Institutes of Health and animal study protocols approved by the Institutional Animal Care and Use Committee (IACUC) at the National Institute of Environmental Health and Sciences. Breeding Trial 8 weeks old Pgr cre control mice and FOXL2 OE mice (N=6 for each genotype) were mated with stud males for 6 months. The copulation plug and delivery date for the first generation were recorded, and the pups delivered and survival rate were checked daily. Tissue collection Postnatal Day (PND) 21, 3 months old (3M), 8 months old (8M) Pgr cre and FOXL2 OE mouse ovary and uterus were collected at diestrus stage (N=6). The samples were fixed in 4% PFA, dehydrated, cleared and embedded in paraffin for histology and immunohistochemistry. The blood was collected from 3M diestrus Pgr cre and FOXL2 OE mice for serum hormone analysis. 3M Pgr cre (N=3) and FOXL2 OE (N=4) diestrus uterus were used for RNA-seq (N=3-4). 3M Ltf i cre and eFOXL2 OE females were mated with stud males. The morning the plug was detected was defined as pregnancy day 0.5. The Ltf icre and eFOXL2 OE mice (N=6) were sacrificed at pregnancy day 3.5, the uterus were collected and embedded in the paraffin. Superovulation PND21 Pgr cre and FOXL2 OE mice were injected with 3.25 IU of equine chorionic gonadotropin (eCG). 48h later, the mice were injected with 2 IU human chorionic gonadotropin (hCG). After 16h, the mice were sacrificed. The blood was collected for the serum hormone analysis. The oviducts were flushed for oocyte counting. The ovaries were fixed for paraffin embedding. N=6. Serum hormone analysis The blood was collected by retroorbital bleeding. After clotting at room temperature (RT) for 1h, the blood samples were centrifuged at 2000g at RT for 10min. The supernatant was collected into a new tube and stored at −80ºC. The serum samples were shipped to The Center for Research in Reproduction Ligand Assay and Analysis Core, University of Virginia for luteinizing hormone, Follicle-stimulating hormone, estradiol and progesterone analysis. N=6. Artificial decidualization Pgr cre and FOXL2 OE mice were ovariectomized at 6 weeks old. After 2 weeks, the mice were subcutaneously (s.c.) injected with 100ng 17β-estradiol (E8875, Sigma) each day for three consecutive days, rested for two days, then given daily s.c. injections of 1mg progesterone (P0130, Sigma) and 6.7ng 17β-estradiol for three days. On the third day, 50ul corn oil was injected into one uterine horn 6h after the hormone injections. The mice were maintained with daily s.c. injections of 1mg progesterone and 6.7ng 17β-estradiol for five days, and the uteri were collected at the 6 th day. The uterine horns of both the oil injected and uninjected side were weighed. N=6. Histology and Masson’s trichrome staining Paraffin embedded tissues were sectioned at 5 μm and a subset of sections were stained with hematoxylin solution, Harris modified (Sigma-Aldrich) and eosin (Sigma-Aldrich) for histology. A subset of sections was submitted to NIEHS histology Core for Masson’s trichrome staining. N=3. Immunohistochemistry and immunofluorescence 5μM paraffin sections were dewaxed and rehydrated for immunohistochemistry. After antigen retrieval, endogenous peroxidase blocking and serum blocking, they were incubated with primary antibody at 4ºC overnight, including FOXL2 (1:600, ab5096, abcam), HIS tag (1:300, ab9108, abcam), ESR1 (1:100, ACA054C, Biocare Medical), PGR (1:400, 8257, Cell signaling), FOXA2 (1:400, 8186, Cell signaling), P63 (1:800, 39692 Cell signaling), KI67(1:1000 ab15580 Abcam). For immunohistochemistry, on the second day, the slides were incubated with 1:500 biotin-conjugated ant-rabbit (BA-1000 Vector laboratories), anti-goat (BA-9500 Vector laboratories) secondary antibody for 1h at room temperature respectively, followed by the ABC reagent (PK-6100 Vector laboratories) for 1h at room temperature. Signal was developed by DAB (SK-4105 Vector laboratories) for 30s. The slides were counterstained with hematoxylin, dehydrated, cleared and mounted by Permount medium (Thermo Fisher, Waltham, MA USA). The images were taken using Axiocam microscope camera (Zeiss). N=3. For immunofluorescence, on the second day, the slides were incubated with Alexa Fluor® 647 goat anti-rabbit secondary antibody (1:300, ab150079, Abcam) for 1h at RT. The slides were mounted by ECTASHIELD® Antifade Mounting Medium with DAPI (H1200, Vector laboratories). The images were taken under Zeiss 710 confocal microscopy. RNA-seq analysis Total RNA was isolated from 3 months old Pgr cre and FOXL2 OE diestrus uteri using RNeasy mini kit (Qiagen). The library was prepared using TruSeq RNA Library Prep kit (Illumina) and subsequently sequenced using Nextseq 500. The sequencing reads with Quality score <20 were filtered using a custom perl script. The adaptor sequence was removed using cutadapt (v1.12). The reads were aligned to mm10 genome using STAR aligner (v2.5.2b) and counted using featureCounts (v1.5.0-p1) function in Subread program. The differential expressed genes (DEG) between Pgr cre and FOXL2 OE were identfied using R package “DESeq2”. The threshold was set as “maximal FPKM>=1, unadjusted p=1.5 (up-regulated) or =<−1.5 (down-regulated)”. The RNAseq data is deposited to NCBI Gene Expression Omnibus repository (GEO accession number) GSE140047. The functions of the DEG were analyzed by Ingenuity Pathway Analysis (IPA, Qiagen) and DAVID Functional Annotation Bioinformatics Microarray Analysis [ 29 , 30 ]. Statistical analysis The normality of the data was tested by Kolmogorov–Smirnov test. The equal variance of the data was tested by Levene’s test. The total number of pups, the number of ovulated oocytes, the serum levels of progesterone, 17β-estradiol, FSH and LH, the number of uterine glands, and the uterine gland penetration were compared by two tail, student’s t test. The significance was set at p<0.05. Results Increased endometrial FOXL2 expression in a subset of patients with endometriosis Molecular profiles of eutopic endometrial tissues from 34 healthy human subjects and 28 patients who had minimal or mild endometriosis were examined to determine the relative expression level of FOXL2 between the two cohorts [ 5 ]. Normalized expression values of FOXL2, detected by the probe set 220102_at, were extracted directly from the series matrix file for comparison (GSE51981). The endometriosis specimens of this cohort exhibit higher levels of FOXL2 expression compared with healthy endometrial biopsies (Suppl. figure 1A). Notably, in another cohort, FOXL2 levels are comparable in endometrial tissues between healthy and endometriosis subjects, but increased in the ectopic endometriosis tissues [ 4 ], suggesting that the elevation of FOXL2 expression occurs in the ectopic and/or eutopic endometriosis tissues. Based on these findings, we generated uterine Foxl2 overexpression mice to model the observation on human and investigate the impact of increased FOXL2 expression in the uterus. Foxl2 transgene expression in the mouse uterus Increased Foxl2 expression was achieved by crossing mice with a conditionally active transgene, Foxl2 LsL/+ [ 13 ] with the Pgr cre allele [ 27 ] generating the Pgr cre/+ Foxl2 LsL/+ (FOXL2 OE ) mouse. Immunohistochemical analysis was used to detect the expression of endogenous FOXL2 and the Foxl2 transgene in the mouse uterus. In wild type mice,FOXL2 expression was observed in the endometrial stroma and blood vessels, and to a lesser extend in the epithelial and myometrial compartment of the uterus (Suppl. Fig. 1B-D) as previously reported [ 25 ]. The analysis of the uterine expression of the Foxl2 transgene in the FOXL2 OE , showed an increased expression in a subset of uterine luminal and glandular epithelium, and sporadic staining in the myometrium (Suppl. Fig. 1E-G). Due to the fact that FOXL2 is already highly expressed in the endometrial stroma cells of the Pgr cre mice, it is difficult to distinguish the endogenous FOXL2 from the expression of the Foxl2 transgene. Since the HIS Tag epitope was incorporated into the Foxl2 transgene, the expression of the transgene in the endometrial stroma was determined by immunofluorescence staining for His tag [ 13 ]. Compared to the Pgr cre mouse uterus (Suppl. Fig, 1 H-J), HIS tag displayed strong nuclear staining of the FOXL2 transgene in all compartments of the uterus (Suppl. Fig. 1K-M). This analysis demonstrated that the Foxl2 transgene was expressed in not only the epithelial and myometrial compartment but also the stroma. Abnormal uterine morphology by Uterine FOXL2 overexpression Macroscopic examination of the uterus showed that at PND21 the uterine size of the Pgr cre and FOXL2 OE were comparable ( Fig. 1A, D ). However, the uteri of FOXL2 OE mice was thinner compared to the control mice at 3 and 8M at diestrus stage ( Fig. 1B, C, E, F ). Histological analysis identified alterations in all compartments of the uterus. Analysis of the uterine epithelium showed altered uterine epithelial cell differentiation. p63 is a marker for epithelial stratification [ 29 ]. While the control Pgr cre mice showed a uterine epithelium lined with a single layer of columnal cells ( Fig. 1G-I ), the FOXL2 OE showed the presence of basal cells with P63 positive staining in glandular and luminal epithelium ( Fig 1J-O ). In addition to the altered uterine epithelial differentiation there was altered uterine gland morphology indicating a defect in adenogenesis. Download figure Open in new tab Fig. 1. FOXL2 oe mice displayed thin uterus and stratified uterine epithelium. The representative uterine images of Pgr cre (A-C) and FOXL2 oe mice (D-F) at PND21 (A, D), 3M (B, E), and 8M (C, F). The uteri were much thinner in FOXL2 oe mice compared to Pgr cre mice at 3 and 6M. Basal cell marker, P63, staining in the uterus of Pgr cre (G-I) and FOXL2 oe mice (J-O) at PND21 (G, J, M), 3M (H, K, N), and 6M (I, L, O). P63 positive basal cells in the uterus indicates epithelium stratification. They were found at the basal side of some luminal epithelium (J-L) and some glandular cells (M-O) in the FOXL2 oe uterus. PND: postnatal day; M: months old. Arrow indicates stratified epithelium. *p<0.05. N=3 for each genotype and age group. Adenogenesis in rodents is a hormone independent process prior to puberty but is maintained by estrogen after puberty [ 31 ]. In the FOXL2 OE uterus, pre-pubertal gland development was already impaired at PND21, demonstrated by a decrease of the gland number and by the decreased penetration of the glands into the stroma ( Fig, 2A, D, G, J, K ). The defect in adenogenesis became more pronounced during the post-pubertal period. The Pgr cre mice showed a remarkable increase in both the number of glands and gland penetration into the stroma compared to PND21. In contrast, the uterine glands of the FOXL2 OE remained at a lower number and few of them were able to penetrate the stroma. The impaired adenogenesis may result from a defect in gland growth or from the uterine stroma not providing the appropriate milieu for gland development. ( Fig. 2B, C, E, F, H-K ). Download figure Open in new tab Fig. 2. Disrupted adenogenesis in FOXL2 oe mice. FOXA2 labeled glands in Pgr cre (A-C) and FOXL2 oe (D-I) uterus at PND21 (A, D, G), 3M (B, E, H) and 8M (C, F, I). The number of glands were calculated in two cross sections per mouse, in total 3 mice (J). The penetration of glands was defined as the closest distance of the glands to the adjacent luminal epithelium, and calculated in one longitudinal section per mouse, in total 3 mice (K). PND: postnatal day; M: months old. *p<0.05. In order to determine the impact on FOXL2 expression on the endometrial stroma biology, the composition of the stromal extracellular matrix of the mouse uterus, Pgr cre and FOXL2 OE mouse uteri was examined by Masson’s trichrome staining. Blue staining indicating collage deposition was increased with age in both Pgr cre and FOXL2 OE mice ( Fig. 3A-F ). But at each age, the blue staining was much stronger in FOXL2 OE uterus suggesting increased collagen deposition ( Fig 3A-F ). The changes in the composition of the extracellular matrix may impede the ability of the glands to fully develop. Download figure Open in new tab Fig. 3. Stroma fibrosis and defective myometrium in FOXL2 oe mice. Masson’s trichrome staining in Pgr cre (A-C) and FOXL2 oe (D-F) uterus at PND21 (A, D), 3M (B, E), 8M (C, F). Increased blue staining in the stroma of FOXL2 oe uterus suggested increased collagen deposition. αSMA staining in Pgr cre (G-I) and FOXL2 oe (J-O) uterus at PND21 (G, J, M), 3M (H, K, N), 8M (I, L, O). The thickness of muscle layers was reduced and the inner muscle layer was discontinued in the FOXL2 oe uterus. PND: postnatal day; M: months old. Arrow indicates the discontinued muscle layer. N=3 for each genotype and age group. In addition to the impact of Foxl2 transgene expression on the uterine endometrium the transgene also affected the morphology of the myometrium. Immunohistochemistry was conducted to assay the expression of alpha smooth muscle actin (α-SMA), one of the common markers of mature myometrium [ 8 ]. The α-SMA positive myometrial cells were identified in both Pgr cre and FOXL2 OE mouse uterus with no obvious changes of its staining intensity ( Fig. 3G-O ). However, while the myometrium of Pgr cre mouse uteri showed the inner layer of myometrium to be a continuous layer of circular smoother muscle surrounding the endometrium ( Fig. 3G-I ), the inner smooth muscle layer of the FOXL2 OE mouse myometrium was discontinued at several loci ( Fig. 3J-O , arrows). This abnormality was detected in the FOXL2 OE not the Pgr cre uterus as early as PND21 ( Fig. 3G, J, M ), and remained at 3M ( Fig, 3H, K, N ) and 8M ( Fig. 3I, L, O ). The outer longitudinal smooth muscle layer increased proportionally with age in control mice from PND21 to 8M ( Fig. 3G-I ). The increase is dramatically diminished in the FOXL2 OE mice, resulted in hypotrophic muscle layer at 8M ( Fig. 3L, O ). Altered uterine epithelial differentiation but not adenogenesis, stromal fibrosis or myometrial structures by Epithelial FOXL2 overexpression The FOXL2 OE mouse uterus exhibited FOXL2 overexpression in all the uterine compartments. In order to investigate the impact of altered FOXL2 functions specifically in the uterine epithelium, we bred the FOXL2 LSL mice with the uterine epithelial Ltf i cre to generate epithelial overexpressing FOXL2, eFOXL2 OE , mice. Ltf i ce expresses Cre recombinase specifically in the uterine epithelium [ 28 ], FOXL2 and HIS-tag staining confirmed the FOXL2 overexpression is limited in a subset of luminal and glandular epithelium of eFOXL2 OE uterus (Suppl. Fig. 2). Uterine morphology was assayed at D3.5 of pregnancy. The gross uterine morphology was similar between Ltf icre and eFOXL2 OE females ( Fig. 4A, B ). The thread like uterus observed in FOXL2 OE mice ( Fig. 1D-F ) was not found in eFOXL2 OE mice. Histological analysis of the uterus of the eFOXL2 OE mice showed epithelial stratification with the presence of P63 positive basal cells, which was also observed in the FOXL2 OE mouse uterus ( Fig. 4C, D ). Unlike the FOXL2 OE , eFOXL2 OE mouse uteri did not show any alteration in the number of uterine glands, as determined by FOXA2 staining ( Fig. 4E, F ), or in the uterine stromal fibrosis, as determined by Masson’s trichrome ( Fig. 4G, H ); or in their myometrium morphology, as determined by αSMA staining ( Fig. 4I, J ). These suggested that epithelial overexpression of FOXL2 impacted uterine epithelial stratification, but uterine gland development, stromal fibrosis and myometrial morphology were mainly affected by the extraepithelial overexpression of FOXL2. Based on this, FOXL2 OE mouse were used for further study of the impacts of FOXL2 overexpression in uterine transcriptome and functions. Download figure Open in new tab Fig. 4. eFOXL2 oe exhibited epithelium stratification but no adenogenesis, stroma fibrosis and myometrial defects. The representative uterine images of Ltf i cre (A) and eFOXL2 oe mice (B) at Pregnant D3.5. P63 (C, D), FOXA2 (E, F), Masson’s trichrome (G, H), and αSMA (I, J) staining in Ltf i cre (C, E, G, I) and eFOXL2 oe (D, E, H, J) uterus. Basal cells with P63 positive staining was detected in the luminal and glandular epithelium of eFOXL2 oe uterus. No changes were observed in FOXA2 labeled uterine glands, Masson’s trichrome staining, and αSMA labeled muscle layers. Arrow indicates stratified epithelium. N=3. Foxl2 transgene impact on the uterine transcriptome In order to determine the impact of the Foxl2 transgene expression on the mouse uterus at the molecular level, RNA seq was conducted on the uteri of Pgr Cre and FOXL2 OE of three months old. Since uterine transcriptome largely depends on the hormone regulation, we collected all the uteri at diestrus stage. In total, 3515 genes were differentially expressed in the FOXL2 OE compared to the Pgr cre uterus (1746 upregulated and 1769 downregulated genes, respectively, Fig. 5A , the detailed gene list is in supplement excel file). Ingenuity pathway identified multiple signaling pathways altered in the FOXL2 OE uterus ( Fig 5B , the full list of the altered pathways is in supplement excel file). The altered pathways included pathways regulating cell proliferation (cyclins and cell cycle regulation and estrogen-mediated S-phase entry, enhanced role of CHK proteins in cell cycle checkpoint control), extracellular matrix production (inhibition of matrix metalloproteases, suppressed collage receptor, GP6 and Hepatic Fibrosis/Hepatic Stellate activation), and Wnt/β-catenin signaling. These pathways likely contribute to the altered epithelial and stroma phenotype observed in the FOXL2 OE mouse uterus. Here we would like to mention that several collagen genes in the GP6 pathways were decreased in FOXL2 OE uterus such as Col1a1 , Col6a1 . In contrast, the collagen degradation genes in the inhibition of matrix metalloproteases were also suppressed in FOXL2 OE uterus, such as MMP2, MMP15. These results suggested that the inhibition of the matrix degradation may be the major reason for the increased collagen deposition in the FOXL2 OE uterine The RNA-seq results identified several critical genes that are known to have an important role in the uterine phenotypes. We next validated the protein expression of selected genes. Since genes involved in cell cycle regulation were altered, Ki67 expression was assayed. As expected, Ki67 expression was decreased in our RNA-seq results (FC=−5.86, p<0.001), and immunohistochemistry confirmed the decreased protein levels of KI67 in both the epithelial and stromal compartments of the FOXL2 OE uterus ( Fig. 6A, B ). Esr1 and Pgr are the major receptors for ovarian hormones and regulators of uterine function [ 32 ]. Our RNA-seq results showed mRNA levels of Esr1 (FC=1.51, p<0.001) was increased and Pgr (FC=−1.26, p=0.035) was decreased in the FOXL2 OE uterus. Immunohistochemistry showed much higher expressions of ESR1 ( Fig 6C, D , solid arrow) and much lower levels of PGR ( Fig. 6E, F , open arrow) in the FOXL2 OE uterine epithelium. In the stroma, much more cells with weak ESR1 and PGR expression were found in the FOXL2 OE uterus compared to the Pgr cre uterus ( Fig. 6C-F , open arrow). Download figure Open in new tab Fig. 5 Transcriptomic changes of Pgr cre and FOXL2 oe at 3M diestrus stage (p 1.5, <−1.5). Heating map showed cluster of differentially expressed genes in Pgr cre and FOXL2 oe (A). Ingenuity pathway analysis identified top altered signaling pathways (B). DAVID analysis indicates top altered cellular processes using up-regulated genes (C) and down-regulated genes (D). N=3-4. Download figure Open in new tab Fig. 6. Protein expressions of KI67, ESR1 and PGR in FOXL2 oe uterus at 3M diestrus stage. Immunohistochemistry of KI67 (A, B), ESR1 (C, D), PGR (E, F) in Pgr cre (A, C, E) and FOXL2 oe (B, D, F) uterus. In the Pgr cre uterus, KI67, ESR1 and PGR was expressed in the nucleus of most epithelium and stroma cells. In the FOXL2 oe uterus, ESR1 was sporadically increased in the epithelium, PGR and KI67 was decreased in the epithelium of the FOXL2 oe uterus. Solid arrow indicates cells with strong staining. Open arrow indicates cells with weak staining. N=3. As mentioned above, FOXL2 is increased in several human endometriosis tissues [ 4 , 5 ]. To investigate the possible correlation of the FOXL2 mouse model with the human endometriosis, we used Nextbio [ 33 ] to determine if the FOXL2 transcriptome correlated with transcriptome of any human endometrial data sets. This analysis identified a significant positive correlation of the FOXL2 OE transcriptome with multiple human endometriosis transcriptome data sets (GSE7305, GSE5108, GSE87809, GSE51981, GSE4736, Fig. 7A , Suppl. Fig. 3A-D), including human endometrosis tissues compared to the normal normal endometrium and ectopic compared to eutopic endometriosis tissues [ 5 , 34 – 37 ]. As expected, a positive correlation of the transcriptome was established in the dataset GSE51981 (Suppl. Fig 3C), in which the increased Foxl2 mRNA levels were identified in the human endometrium with endometriosis compared to the normal human endometrium (Suppl. Fig. 1A). Among them, the most correlated data set was collected from the human ovarian endometriosis tissues that was compared to the control endometrium of the same patients using microarray analysis revealing 5864 up-regulated and 6361 down-regulated genes ( Fig. 7A , [ 35 ]). We found 1816 genes were common between the two data sets. Of these, 1152 (63%) genes showed expression changes in the same direction. We analyzed the functions of the 1816 overlapping genes using IPA and DAVID and identified several common pathways between these two data sets ( Fig 7B, C ). These pathways were regulation of cell proliferation and death, cellular matrix, cell migration and adhesion, regulation of immune system process, vasculature development, and pathways that can be associated with epithelium differentiation problems such as tube and gland development. These are pathways which are known to be critical for the progression of endometriosis [ 38 – 40 ]. Download figure Open in new tab Fig. 7. FOXL2 oe transcriptomic was positively correlated with human endometriosis. The most positively correlated human endometrium transcriptome determined by Nextbio was the comparison between ovarian endometriosis tissue with control endometrium in the same patient (GSE7305 [ 35 ], A). The number of up- and down-regulated genes were labeled accordingly near the up and down arrows. The number of overlapped genes between both datasets were plotted in the venn diagram. The significance of the overlap was showed below the venn diagram. Furthermore, the 1816 overlapping genes were divided into four groups based on its up- or down regulated in either dataset. The significance and number of overlapped genes in these four groups were displayed in the bar graph. The IPA (B) and DAVID (C) analysis of the 1816 overlapping genes between FOXL2 oe and human endometriosis identified multiple altered pathways that may relate with endometriosis. Infertility in FOXL2 OE mice As we already observed multiple uterine functions in the FOXL2 OE mice, we decided to investigate the impact of the Foxl2 transgene expression by a 6-month breeding trial. Adult Pgr cre and FOXL2 OE female mice were placed with a male mouse and allowed to breed for 6 months. During the six months, Pgr cre females produced 36±2.35 pups/ female, while FOXL2 OE females produced no offspring ( Fig. 8A ), This demonstrated that the FOXL2 OE female mice were infertile. In order to determine the cause of infertility, female mice were examined for the presence of a postcoital vaginal plug after being placed with a male mouse. No copulation plug was ever detected in FOXL2 OE females during the breeding trial. Since mating occurs in female mice during the estrus stage of the cycle, the ability of the FOXL2 OE mice to undergo a normal estrus cycle was analyzed by vaginal cytology over a two-week period. We found FOXL2 OE female mice did not show the presence of a vaginal estrus cycle and were in a constant state of diestrus ( Fig 8B, C ). Analysis of estrogen and progesterone levels in the FOXL2 OE mice reveals that they were comparable with those of Pgr cre mice in the diestrus stage (Suppl. Fig. 5A, B). This confirmed the continuous diestrus stage in the FOXL2 OE mice not only reflected on the vagina cytology but also by the ovarian hormone levels. Download figure Open in new tab Fig. 8. FOXL2 oe mice were infertile with abolished decidual responses. All the Pgr cre mice but none of the FOXL2 oe mice delivered any pups during 6-month breeding trial (A). Representative pictures of estrous cycle showed continuous diestrus in FOXL2 oe mice (C) in contrast to the estrous cycle showed in Pgr cre mice (B) during 14-day period. Representative ovarian histology pictures of Pgr cre (D-F) and FOXL2 oe (G-I) virgin mice at diestrus stage at the age of PND21 (D, G), 3M (E, H) and 8M (F, I). FOXL2 oe ovaries were depleted of corpus luteum. The representative pictures of the hormone primed uterus after 5-day oil injections in the Pgr cre (J) and FOXL2 oe (K) mice. The weight ratio of the oil injected side over the un-injected side uterine horn (L) confirmed the decidualization occurred in all the Pgr cre but none of the FOXL2 oe mice. Arrow indicates the oil injected side. D: diestrus; P: proestrus; Me: metestrus; E: estrus; PND: postnatal day; M: months old; CL: corpus luteum. Arrow indicates oil injected uterine horn. n=6 for each genotype and age group. Altered ovarian function in FOXL2 OE mice The estrus cycle of mice is driven by steroid hormones produced by the ovaries. Since Pgr is transiently expressed the ovarian corpus luteum [ 41 ], we examined the ovaries to determine whether the acyclicity was caused by any ovarian defects. At PND21, the ovaries contained most small and medium follicles in both Pgr cre and FOXL2 OE mice ( Fig. 8D, G ). At 3M and 8M, the ovaries of Pgr cre mice showed follicles at different stages and multiple corpora lutea ( Fig. 8E, F ). However, the FOXL2 OE mouse ovaries showed normal follicular development until antral follicle but complete absence of corpora lutea ( Fig. 8H, I ). The lack of corpora lutea in the FOXL2 OE could be intrinsic to the ovary or could be due to a defect in neuroendocrine regulation of the ovulatory process. In order to determine the reason for the lack of corpora lutea in the FOXL2 OE mice, we first investigated the expression of the Foxl2 transgene in these mice. At 3M, both Pgr cre and FOXL2 OE ovaries from the mice in diestrus showed high levels of endogenous FOXL2 in the small and medium follicles (Suppl. Fig. 4A, B). However, His-Tag staining detected no strong nuclear staining in Pgr cre and FOXL2 OE ovaries suggesting no Foxl2 transgene expression in FOXL2 OE mouse ovaries (Suppl. Fig. 4C, D). Therefore, the ovarian phenotype may not be due to ovarian expression of the Foxl2 transgene since the follicles could not develop to a stage where the Pgr cre would activate the expression of the transgene. We next examined if the ovarian phenotype could be rescued by administering a super ovulatory regimen of gonadotropins to mice. We found 7/10 Pgr cre and 3/10 FOXL2 OE ovulated in response to the superovulation of gonadotropins. Pgr cre mice that ovulated produced 34.3±4.5 oocytes and FOXL2 OE mice that ovulated produced 8.3±3.8 oocytes (Suppl. Fig. 4I). All mice showed corpora lutea in the ovary (Suppl. Fig. 4G, H, J), and Foxl2 transgene expression was identified by His-tag in the peri-ovulatory follicles and the corpus luteum of the FOXL2 OE mice (Suppl. Fig. 4F, H). Although the ovulation capability was reduced in the FOXL2 OE mice, the formation of corpus luteum in the FOXL2 OE mice indicates that the corpus luteum can and does form in FOXL2 OE ovary under the appropriate hormone stimulation. Since one major function of the corpus luteum is progesterone synthesis, we checked the serum progesterone levels of one litter of 21 days old mice after superovulation to test whether these corpus lutea were functional. Both the Pgr cre and four FOXL2 OE mice displayed increased progesterone levels in comparison to the diestrus mice with no difference between the Pgr cre and FOXL2 OE mice (Suppl Fig. 5A, E). This indicated that FOXL2 overexpressed corpus luteum capable of producing progesterone. Based on these results, we proposed that the cause of the FOXL2 OE ovarian dysfunctions was a defect in neuroendocrine control of ovulation. To evaluate the functions of the pituitary, the direct upstream regulator of ovary, we assayed the serum levels of two gonadotropins produced by the pituitary: Follicle stimulating hormones (FSH) and Luteinizing hormone (LH) showed no difference in serum levels (Suppl Fig. 5C, D). Although the pituitary is capable of production FSH and LH in the FOXL2 OE mice, we have not ruled out that the appropriate cyclic regulation of these gonadotropins is altered. This determination is beyond the focus of this report as the primary focus is the investigation of the phenotypic consequences of the Foxl2 transgene on the mouse uterus. Impaired ability of the FOXL2 OE uterus to undergo a decidual reaction It is true that the ovarian defects led to the infertility of the FOXL2 OE mice, but considering the multiple uterine morphological changes, it is possible that the uterine functions might also be altered. Since one major function of the uterus is to accommodate the embryo implantation by decidualization, the ability of the uterus to undergo a decidual reaction was assayed. The decidualization of the uterine stroma, which involves both stroma and epithelial signaling, is critical is to support pregnancy [ 42 ]. To avoid the ovary defects, female Pgr Cre and FOXL2 OE mice were ovariectomized and administered an ovarian hormonal regimen combined with trauma to one uterine horn to assess the decidual response. The control mice showed an increase in the uterine size of the traumatized horn as compared to the untraumatized horn indicative of a decidual response ( Fig. 8J, L ). In contrast, the size of the traumatized horn of the FOXL2 OE mice did not increase at all indicating the complete absence of a decidual response ( Fig. 8K, L ). This demonstrates that altered FOXL2 expression impairs the hormonal differentiation of the uterus necessary to support pregnancy. Discussion In this study we found FOXL2 overexpression in PGR expressing cells severally impaired uterine structures and functions. These mice showed altered uterine epithelial differentiation, disrupted adenogenesis, altered endometrial stroma extracellular matrix, impaired myometrium development. In contrast, the epithelial specific FOXL2 overexpression only led to epithelial stratification suggesting the importance of extraepithelial FOXL2 contribution in the uterine phenotypes. Since FOXL2 expression is increased in humans with endometriosis we compared the FOXL2 OE uterine transcriptome with the transcriptome of endometriosis patients and identified positive correlations between FOXL2 OE uterine transcriptome and multiple transcriptome of endometriosis patients. Additionally, the female FOXL2 OE mice were sterile with constant diestrus. The ovaries showed no signs of ovulation or corpora lutea formation which can be rescued by superovulation implying hypohpyseal gonadal axis defects. The uterus cannot respond to the decidual cue under the appropriate hormone priming patterns. All these results demonstrate a pleiotropic role of FOXL2 overexpression in female reproductive system. Since we observed constant diestrus in FOXL2 OE mice in which stage estrogens and progesterone are at relatively low levels, it is natural to assume that these low levels of ovarian hormones might explain some of the FOXL2 OE uterine phenotypes. However, the uterus of the FOXL2 OE mouse does not phenocopy what is observed in the ovariectomized mouse models. First ovariectomy has never been positively correlated with epithelium stratification, instead, estrogen is required for vagina epithelium stratification [ 43 ]. The stratification was also observed in the mice with epithelial specific overexpression of FOXL2 indicating a phenotype of uterine origin. Second, neither ovariectomy nor ablation of PGR and ESR1 impair prepubertal adenogenesis as observed in the FOXL2 OE mouse [ 44 – 46 ]. Since ovariectomy does impair post-pubertal glandular development, the alteration in ovarian hormone production may be partly responsible for the reduction of adenogenesis at 3 and 8M. Third, ovariectomy has been reported to decrease collagen deposition in the uterus [ 47 ]. Finally, the reduced ovarian hormone might account for the hypotrophic myometrium but not the discontinued smooth muscle layer [ 48 ]. According to these evidences, we conclude that the FOXL2 OE uterine defects are of uterine origin. The stratified squamous uterine epithelium has been observed in both FOXL2 OE and eFOXL2 OE uterus suggest epithelial Foxl2 transgene expression is sufficient to induce the epithelial differentiation phenotypes. Previous studies reported multiple mouse models with enhanced estrogen signaling may stimulate the uterine stratification [ 49 – 52 ]. Considering the low estradiol scenario in this FOXL2 OE mice which are at continuous diestrus stage, alternative pathways might be involved. In our studies we found that the Wnt/β-catenin pathway was suppressed in the 3M FOXL2 OE mouse uterus. Wnt/β-catenin signaling interacts with multiple estrogen signaling [ 53 , 54 ]. Mice with either Pgr cre/+ induced deletion of β-catenin in Pgr cre/+ Ctnnb1 dd mice [ 55 ], or with global knockout of Wnt7a [ 56 ] mice exhibit epithelium stratification in the uterus. It is possible that FOXL2 can promote epithelial stratification through suppressing the Wnt/β-catenin pathway. The FOXL2 negative regulation on Wnt/β-catenin has also been reported in other studies. Pgr cre/+ induced deletion of FOXL2 upregulates Wnt4 and Wnt7a in the mouse uterus at PND25 [ 25 ]. FOXL2 and β-catenin have been shown opposite functions on cell proliferation in ovarian cells [ 57 ]. Normal gland development in the eFOXL2 OE uterus suggested that epithelial FOXL2 overexpression does not impair adenoegenesis. For the pre-pubertal adenogenesis, it is possible that stroma FOXL2 exert its effects also through Wnt/β-catenin signaling, which has been identified to be important for the pre-pubertal adenogenesis [ 58 – 61 ]. For the post-pubertal adenogenesis, it is also true that that low levels of estradiol might inhibit the gland growth, but one unique phenotype in FOXL2 OE mice is the severely impaired penetration of the glands into the stroma. It is possible that without the appropriate penetration, the glands cannot elongate and branch further leading to a decrease in the number of glands. The increased collagen deposition may act as the physical obstacle of gland penetration, suggesting the importance of the endometrial stroma extracellular matrix in allowing normal uterine gland development. Increased collagen deposition was also found in the Pgr cre induced Transforming Growth Factor Beta Receptor 1 (TGFBR1) or Smoothened (SMO) overexpression mouse models [ 62 – 64 ]. However, these studies did not exclude potential confounding factors from the ovary, so it is still unclear whether the uterine TGFBR1 and SMO are the major players. One study using FOXL2−/− male mice shows retarded cartilage and bone formation [ 65 ], suggesting a positive role for FOXL2 in regulation of cartilage formation. Our study presents a direct evidence showing that uterine FOXL2 overexpression may increase collagen deposition. The inhibition of matrix metalloprotease signaling is mainly composed of matrix degradation related genes. This signaling is enhanced in the 3M FOXL2 OE uterine transcriptome indicates that FOXL2 can also increase collagen through inhibition of collagen degradation. A previous study also reported a disorganized smooth muscle layer in Pgr cre induced FOXL2 knockout mice [ 25 ], and together with our study, these observations indicate that appropriate FOXL2 levels are required for the myometrium development. Similarly, either deletion or overexpression of TGFBR1 leads to disrupted smooth muscle layers suggesting the subtle roles of TGFβ pathways [ 64 , 66 ]. Additionally, overexpressed TGFBR1 also reduced pre-pubertal adenogenesis [ 58 ], Since the FOXL2-SMAD4 complexes acted synergistically in the pituitary [ 15 , 19 ], it is possible that FOXL2 also collaborated with the TGFβ pathways in regulation of myometrium development. Endometriosis is prevalent in women at reproductive age [ 2 ], but the pathologic mechanisms leading to the disease remain unclear. FOXL2 overexpression has been found in human endometriotic lesions [ 4 ]. Our FOXL2 overexpression mouse model further indicates a positive correlation with human endometriosis. Pathways including fibrosis, inflammation, cell adhesion and migration are among those that have been shown to be involved in regulating endometriosis progressions [ 38 , 67 ], and were altered in the uterine transcriptome of the 3 months old FOXL2 OE mice. Immunohistochemistry also showed decreased progesterone receptor in the FOXL2 OE uterus. This is consistent with the protective role of progesterone in endometriosis [ 68 ], and the lower progesterone receptor in endometrotic lesions compared to the eutopic endometrium [ 69 , 70 ]. This study has identified a FOXL2 signature that may contribute to the endometriotic phenotype observed in patients. The defect in the estrus cycle and ovarian function in the FOXL2 OE is most likely due to a disruption of the hypohpyseal gonadal axis. The Foxl2 transgene is detected in the ovary of the FOXL2 OE mouse, yet FOXL2 OE mice were able to respond to exogenous gonadotropins and ovulate and produce normal levels of progesterone. The presence of corpus luteum in the super ovulated ovary suggested that the FOXL2 overexpression in the ovary did not affect its ability to develop a corpus luteum. Although we could not detect any changes in normal circulating gonadotropins this could not rule out the impact of FOXL2 on pituitary function. Since deletion of FOXL2 has been reported to affect gonadotropin production by the pituitary leading to ovarian defects, the alteration of FOXL2 expression may disrupt the timing of gonadotropin release necessary to stimulate appropriate follicular development and ovulation [ 14 , 71 ]. The precise effects of FOXL2 overexpression on pituitary development requires further investigation. In addition to the structure alterations, the failure of the FOXL2 OE uterus to respond to the decidual cue indicates the functions of the uterus to support pregnancy were also impaired. Ovariectomy with exogenous hormone treatment eliminates the ovarian effects and indicates an intrinsic uterine defect. It is possible that the structure abnormality might lead to the function defects. The stratified epithelium may lose its ability to support the pregnancy. Previous studies identified several mutant mouse models with epithelium stratification were infertile, such as Pgr cre/+ Ctnnb1 dd mice [ 55 ], Wnt7a−/− [ 56 ] mice, and Pgr cre/+ Sox17 dd mice [ 49 ]. However, since these mice exhibited multiple phenotypes, it is still too presumptions to link the epithelial stratification with pregnancy failure. In contrast, the presence of functional glands is well known to be critical for uterine decidualization probably through LIF signaling [ 72 – 74 ]. The severely retarded adenogenesis in the FOXL2 OE uterus might be one of the major players in the failed decidualization. Besides, endometrial decidualization is promoted by mesenchymal-epithelial transition (MET) [ 75 ], while fibrosis is positively correlated with epithelial-mesenchymal-transition (EMT) [ 76 ]. Therefore, the exaggerated fibrosis observed in the FOXL2 OE uterine stroma might also blunt the decidualization through inhibiting the MET process. Our study first reported that the Pgr cre induced Foxl2 transgene expression can alter the uterine structures and functions, including adenogensis, epithelium stratification, collagen deposition, and myometrial development. It provides a model to investigate the role of the stroma extracellular matrix in uterine gland development. It also provides new evidence to positively correlate FOXL2 overexpression with endometriosis progression. Further studies are required to identify the underlying mechanism and the therapeutic potentials of FOXL2 in human. Acknowledgments The authors acknowledge the Epigenomic and DNA Sequencing Core, The DNTP Clinical Pathology Core, the Integrative Bioinformatics Supportive Group, the Fluorescence Microscopy and Imaging Center and the Comparative Medicine Branch at NIEHS for their research support. The authors acknowledge Research in Reproduction Ligand Assay and Analysis Core, University of Virginia for serum analysis. The authors appreciated Dr. Tianyuan Wang’s consultation on bioinformatic analysis, Mr. Linwood Koonce for mouse colony management, Ms. Mita Ray for sharing the reagent, and Dr. Sylvia Hewitt for the constructive input on the paper and Ms. Janet DeMayo for the proof reading. Footnotes Summary Sentence: FOXL2 overexpression in the uterus induced epithelial stratification, blunted adenogenesis, increased fibrosis, and disrupted myometrium leading to impaired decidual responses and a similar transcriptome with human endometriosis. Grant support: This work was funded by an Intramural Research Program of the National Institute of Health (NIH) Z1AES103311-01 to F.J.D. and a NIH / National Institute of Child Health and Human Development (NICHD) RO1 HD042311 to J. P. L. Reference 1. ↵ Sampson , J.A. , Metastatic or Embolic Endometriosis, due to the Menstrual Dissemination of Endometrial Tissue into the Venous Circulation . Am J Pathol , 1927 . 3 ( 2 ): p. 93 – 110 43 . OpenUrl PubMed Web of Science 2. ↵ Giudice , L.C. , Clinical practice. Endometriosis . N Engl J Med , 2010 . 362 ( 25 ): p. 2389 – 98 . OpenUrl CrossRef PubMed Web of Science 3. ↵ Burney , R.O. and L.C. Giudice , Pathogenesis and pathophysiology of endometriosis . 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Confalonieri , Epithelial(-)Mesenchymal Transition in the Pathogenesis of Idiopathic Pulmonary Fibrosis . Medicina (Kaunas) , 2019 . 55 ( 4 ). Back to top Previous Next Posted March 07, 2020. Download PDF Supplementary Material Email Thank you for your interest in spreading the word about bioRxiv. NOTE: Your email address is requested solely to identify you as the sender of this article. Your Email * Your Name * Send To * Enter multiple addresses on separate lines or separate them with commas. You are going to email the following Increased FOXL2 Expression Alters Uterine Structures and Functions Message Subject (Your Name) has forwarded a page to you from bioRxiv Message Body (Your Name) thought you would like to see this page from the bioRxiv website. Your Personal Message CAPTCHA This question is for testing whether or not you are a human visitor and to prevent automated spam submissions. Share Increased FOXL2 Expression Alters Uterine Structures and Functions Rong Li , San-Pin Wu , Lecong Zhou , Barbara Nicol , John P. Lydon , Humphrey H-C Yao , Francesco J. DeMayo bioRxiv 2020.03.06.981266; doi: https://doi.org/10.1101/2020.03.06.981266 Share This Article: Copy Citation Tools Increased FOXL2 Expression Alters Uterine Structures and Functions Rong Li , San-Pin Wu , Lecong Zhou , Barbara Nicol , John P. Lydon , Humphrey H-C Yao , Francesco J. 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