Two new genetically modified mouse alleles labeling distinct phases of retinal ganglion cell development by fluorescent proteins

During development, retinal progenitor cells (RPCs) take on different trajectories for distinct cell fates. Previous studies have identified key regulators involved in two key steps of retinal ganglion cell (RGC) genesis; Atoh7 functions in a subpopulation of RPCs to render them competent for the RGC fate, whereas Pou4f2 and Isl1 function to specify the RGC fate and promote RGC differentiation. Extensive research has been performed on the roles of these transcription factors in RGC development, but properties of these two phases they represent and the cellular context in which these two factors function have not been thoroughly investigated, largely due to the cellular heterogeneity of developing retina. In this paper, we describe two novel knock-in mouse alleles, Atoh7 zsGreenCreERT2 and Pou4f2 FlagtdTomato , which enabled us to label retinal cells in the two phases of RGC development by fluorescent proteins. In addition, the Atoh7 zsGreenCreERT2 allele also allowed for indirect labeling of RGCs and other cell types upon tamoxifen induction in a dose-dependent manner. Further, these alleles could be used to purify retinal cells of these different phases by fluorescence assisted cell sorting (FACS). Thus, these two alleles can serve as very useful tools for studying the molecular and genetic mechanisms underlying RGC formation.