Figure 2.

Human and mouse germ cell development and associated genes. Primordial germ cells (PGCs, marked as green) can be recognized for the first time at the extraembryonic region of epiblast in mouse (at ~E6.25) and a layer between epiblast and visceral endoderm in human (at ~2 to 3 weeks of gestation) during gastrulation. These cells migrate towards the genital ridge during embryo turning, and simultaneously undergo extensive epigenetic reprogramming. Upon arrival at the genital ridge, PGCs are dispersed in the female genital ridge and organized to make a winding tubular pattern in male genital ridge. Multiple scRNA-seq studies in various stages of germ cell development were performed to elucidate cellular diversity, and critical gene expression signatures in developing germ cells, terminating mitosis and entering meiosis. Stage-specific genes identified by scRNA-seq are noted. SSC: spermatogenic stem cells, diff-SPG: differentiating spermatogonium.