Rare minnow (Gobiocypris rarus) is an emerging model fish in China, and the development of its gonads is still elusive. Germ cell-specific genes are conserved in animals. Dead end (Dnd) was first documented as a germ granule component in zebrafish. Here, we report the cloning and expression profile of dnd in rare minnow. RT-PCR results showed that dnd is expressed specifically in the gonads of both sexes, is maternal in origin and is expressed continuously during embryogenesis. Dnd mRNA could be detected exclusively in the germ cells of the testis and ovary. Temporal expression of dnd mRNA is similar to that of vasa and dnd in zebrafish during embryogenesis. Taken together, dnd mRNA is restricted to the germ cells of rare minnow.

In this study, a homologous gene named plzfa was identified and characterized in medaka Oryzias latipes. Oryzias latipes plzfa was detected in all the tissues including brain, gill, muscle, liver, intestine, kidney, spleen, testis and ovary using reverse transcriptase (RT)-PCR. plzfa was detected in the oocytes of the ovary and in the spermatogonia and somitic cells of the testis by in situ hybridization. plzfa had a maternal origin with continuous and dynamic expression during embryonic development. plzfa was observed in the brain, neural rod and sensor organs including the eyes, ears and nose during embryogenesis. plzfa was also detected in the neural crest, somite, pectoral fin, intestine and skin. These results indicate that plzfa is a pleiotropic gene that may play major roles in various tissues.

Protein arginine methyltransferase 5 (Prmt5), conserved from yeast to humans, catalyzes arginine's dimethylation in proteins. Prmt5 is necessary for embryonic development in mice because it maintains embryonic stem cells. However, the embryos of zebrafish (Danio rerio) remain viable with a deficiency in germ cells and sexual development after the knockout of prmt5. Therefore, it was considered whether prmt5 is dispensable during embryogenesis in fish. Medaka (Oryzias latipes), another model fish organism, was used in this experiment. The medaka prmt5 was mutated with Transcription Activator-Like Effector Nucleases (TALEN) causing the premature stopping of transcription. None of the homozygous prmt5 mutant fish were viable, only the heterozygous offspring survived. Quantitative reverse transcription-polymerase chain reaction (qPCR) results showed a significant decrease in octamer-binding transcription factor 4 (oct4), homeobox transcription factor nanog (nanog), vasa, B-cell CLL/lymphoma 2 (bcl2), and the ratio of bcl2 to bax (bcl2 associated x), and a significant increase in caspase3 and caspase8 in the embryos of the heterozygous prmt5 mutant compared with that of the wild type. The results showed that the mutation of prmt5 caused down-regulation of the genes functioning in stemness and up-regulation of the genes in the cascade of cell death. These results suggested that prmt5 is necessary for embryogenesis via maintaining stemness and repressing apoptosis in medaka.