Cloning and characterization of the SSB-1 and SSB-4 genes expressed in zebrafish gonads.

The protein of the gustavus (gus) gene has a typical SOCS box domain and repeats in the splA and RyR (SPRY) domains. GUS can interact with Vasa and is necessary for the specification of germ cells. We cloned two zebrafish genes, SSB-1 and SSB-4 (SPRY domain SOCS box proteins). Phylogenetic analysis shows that zebrafish SSB-1 and SSB-4 are clustered into clades of SSB-1-like and SSB-4-like genes from other species. RT-PCR analysis of tissues revealed that zebrafish SSB-1 and -4 are expressed in the ovary and testis. We investigated the spatial expression patterns of zebrafish SSB-1 and -4 in embryos from the two-cell stage to 72 h postfertilization (hpf) using whole-mount in situ hybridization. SSB-1 and -4 transcripts were present in all blastomeres during the early embryonic stages, but the genes differ in their expression pattern. SSB-4 mRNA was located in the region of the primordial germ cells in 24 and 72 hpf embryos, but SSB-1 mRNA was not detected at these stages. We hypothesize that SSB-4 plays a role in the early development of germ cells.