Human chorionic gonadotropin suppresses expression of Piwis in common carp (Cyprinus carpio) ovaries

Piwi proteins are required for germline maintenance and gonad development. In this study, the cDNAs encoding Piwil1 and Piwil2 were cloned and sequenced from the common carp. The full-length cDNA of Piwil1 and Piwil2 were 3114 and 3421bp, encoding 858 and 1034 amino acids including PAZ domain and PIWI domain, respectively. In addition, the Piwil1 and Piwil2 proteins shared high homology with other teleosts. Reverse transcriptase PCR revealed that the Piwi mRNAs were exclusively expressed in adult testes and ovaries. Using real-time PCR, expression study of different developmental profiles showed that Piwil1 and Piwil2 were down-regulated during pre-ovulation. Further, human chorionic gonadotropin treatment in ovaries (in vivo) and in cultured ovaries cells (in vitro) resulted in down-regulation of Piwi RNAs. These results suggest that the decreased expression which was regulated by hormone plays a crucial role during ovarian differentiation and development.