Figure 1

Expression pattern and mutant phenotype of proteins involved in TE repression in the developing male germline in mice. The germline genome gets heavily demethylated as primordial germ cells (PGCs) colonize the genital ridges around 10.5 d.p.c. After sex determination, male PGCs become prospermatogonia (ProSpg) and get remethylated from 13.5 d.p.c. to birth, at the formation of spermatogonial stem cells (SSC). This period coincides with an accumulation of TE-derived piRNAs and a peak of expression of de novo DNA-methyltransferases Dnmt3L and Dnmt3A, PIWI proteins MILI and MIWI2 and their respective associated Tudor proteins TDRD1 and TDRD9. Other proteins with an important role in supporting piRNA biogenesis are also present in ProSpg, Maelstrom (MAEL) and GASZ. Some of these proteins are expressed at later stages of spermatogenesis. Mutations in these genes results in male sterility, with male germ cells ending their progression at the pachytene stage.