Targeted disruption ofPparγ1promotes trophoblast endoreplication in the murine placenta

In murine placentas, peroxisome proliferator-activated receptor (PPAR) γ1, a nuclear receptor, is abundant at the late stage of pregnancy (E15–E16), but its functional roles are still elusive because PPARγ-full knockout embryos die early (E10). We generated mice disrupted in only Pparγ1 , one of the two major mRNA splicing variants of PPARγ1. Pparγ1- knockout embryos developed normally until 15.5 dpc, but their growth was retarded thereafter and they did not survive. At 15.5 dpc, in the wild-type placentas, intense PPARγ-immunostaining was detected in sinusoidal trophoblast giant cells (sTGCs), a cell lineage that coordinates the maternal blood microcirculation in the labyrinth, whereas they were absent in the knockouts. Although Pparγ1 -knockout placentas were normal in morphology, we observed severely dilated maternal blood sinuses in the labyrinth. The Pparγ1 -knockout sTGCs had abnormally large nuclei, an enhanced endocycling phenotype, indicating insufficient differentiation. RNA-sequencing of the placentas showed increased expression of genes coding for nucleosome assembly factors. Labyrinthine gene expressions for atypical E2Fs and cyclin E, key drivers for endocycling, were increased >3-fold. These findings suggested that PPARγ1 plays a key role in endocycle termination.