Tranposable Element Control by TRIM28 Safeguards PGC Sex Determination Program [ATAC-Seq]

Transposable elements are increasingly appreciated as regulatory elements in early mammalian development, especially in cells which exhibit pluripotency. Mammalian primordial germ cells (PGCs) must exit latent pluripotency in a process termed determination before they are competent to differentiate and enter sex-specific developmental programs. Here, we find that determination is marked by large changes to the transposable element (TE) repertoire, a phenomenon driven by TRIM28, after which testicular and ovarian PGCs exhibit district transposable element repertoires. We find that loss of TRIM28 perturbs entry into determination as marked by expression of DAZL in a sex-specific manner, but does not result in a failure to downregulate markers of latent pluripotency, including SOX2 and NANOG in either sex. Despite downregulation of some early PGC markers, both ovarian and testicular PGCs fail to properly enter into their meiotic germ cell or prospermatogonial programs, respectively. Thus, we show that TRIM28-mediated reorganization of the TE repertoire is necessary to establish a PGC epigenome competent for proper germline commitment and gametogenesis.