The transcriptome of chicken migratory primordial germ cells reveals intrinsic sex differences and hallmark germ cell genes

Primordial germ cells (PGCs) are germline-restricted embryonic cells, which form the functional gametes of the adult animal. The usage of avian PGCs in biobanking and producing genetically modified birds have driven research on the in vitro propagation and manipulation of these embryonic cells. In avian species, PGCs are hypothesized to be sexually undetermined at an early embryonic stage and undertake differentiation into an oocyte or spermatogonial fate dictated by extrinsic factors present in the gonad. However, chicken male and female PGCs require different culture conditions, suggesting that there are sex-specific differences, even at early stages. To understand potential differences between male and female chicken PGCs during migratory stages, we studied the transcriptome of circulatory stage male and female PGCs propagated in a serum-free medium.
We found that in vitro cultured PGCs were transcriptionally similar to their in ovo counterparts, with however, differences in cell proliferation pathways. Our analysis also revealed sex-specific transcriptome differences between male and female cultured PGCs, with notable differences in Smad7 and NCAM2 expression. A comparison of chicken PGCs with pluripotent and somatic cell types identified a set of genes which are exclusive to germ cells, enriched in the germplasm and associated with germ cell development.