MRG-1, a mortality factor-related chromodomain protein, is required maternally for primordial germ cells to initiate mitotic proliferation in C. elegans

We identified MRG-1, a Caenorhabditis elegans chromodomain-containing protein that is similar to the human mortality factor-related gene 15 product (MRG15). RNA-mediated interference (RNAi) of mrg-1 resulted in complete absence of the germline in both hermaphrodite and male adults. Examination of the expression of PGL-1, a component of P granules, revealed that two primordial germ cells (PGCs) are produced during embryogenesis in mrg-1(RNAi) animals, but these PGCs cannot undergo mitotic proliferation, and they ultimately degenerate during post-embryonic development. Zygotic RNAi experiments using RNAi-deficient hermaphrodites and wild-type males demonstrated that MRG-1 functions maternally. Moreover, immunoblot analysis using mutant animals with germline deficiencies indicated that MRG-1 is synthesized predominantly in oocytes. These results suggest that MRG-1 is required maternally to form normal PGCs with the potential to start mitotic proliferation during post-embryonic development.