Steroid responsive regulation of IFNγ2 alternative splicing and its possible role in germ cell proliferation in medaka.

Interferon gamma (IFNγ) is an active player in estrogen dependent immuno-regulation of fish. The present work was aimed to characterize the alternatively spliced isoforms of IFNγ2 in the gonadal sex development in medaka. Phylogenetic analysis demonstrated that IFNγ2a and 2b were clustered with fish specific interferon gamma. Our in vitro promoter and mini-genome analysis data confirmed that alternative splicing of IFNγ2 is regulated by estrogens and androgens. Tissue distribution, quantitative PCR and ISH data demonstrated ubiquitous expression of IFNγ2a, while IFNγ2b was only expressed predominantly in female germ cells than males. This was further confirmed by germ cell specific GFP signals in the IFNγ2b-GFP over-expressed embryos and specific induction of IFNγ2b expression in the BrdU positive cells. All together our data suggest that steroid responsive alternatively spliced IFNγ2b isoforms might have some indirect roles in germ cell proliferation and thus can be an important candidate for immuno-reproductive interaction studies.