Differential expression of two Piwil orthologs during embryonic and gonadal development in pufferfish, Takifugu fasciatus

Piwil was an important regulator gene in germ cell division during gonadal development. Two Piwi-like genes, Piwil1 and Piwil2, were first cloned from T. fasciatus. The full-length cDNAs of Piwil1 and Piwil2 were of 2933 and 3394 bp, respectively. Piwil1 and Piwil2 possessed an open reading frame (ORF) of 2565 and 3138 bp, encoding 854 and 1045 amino acids, respectively. The tissue distribution analysis demonstrated that Piwil1 and Piwil2 were expressed at higher levels in gonad compared to other tissues (brain, liver, gill, etc.). The time-course dynamic expressions of Piwils during embryonic indicated that Piwil1 and Piwil2 were mainly enriched in the early embryonic development. In testis, the expression of Piwil1 and Piwil2 increased at first but then decreased at mRNA and protein levels. However, the expression of Piwil1 and Piwil2 in the ovary showed a downward trend from the beginning. In addition, the expression levels of Piwil1 and Piwil2 were weak in mature testes or ovaries. The immunohistochemistry analysis revealed that Piwil1 and Piwil2 were abundantly expressed in cytoplasm of spermatogonia, spermatocytes, oocyte I and oocytes II, which were mainly presented in the early stages of gonadal development. Our results suggested that Piwil was related to the differentiation of germ cells, and might play an important role in embryonic development. Therefore, our findings provided valuable information of Piwils in the reproductive cycle of T. fasciatus.