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.