Dnmt3aa but Not Dnmt3ab Is Required for Maintenance of Gametogenesis in Nile Tilapia ().

, a de novo methyltransferase, is essential for mammalian germ line DNA methylation. Only one is identified in mammals, and homozygous mutants of are lethal, while two paralogs, and , are identified in teleosts due to the third round of genome duplication, and homozygous mutants of and are viable in zebrafish. The expression patterns and roles of and in gonadal development remain poorly understood in teleosts. In this study, we elucidated the precise expression patterns of and in tilapia gonads. was highly expressed in oogonia, phase I and II oocytes and granulosa cells in ovaries and spermatogonia and spermatocytes in testes, while was mainly expressed in ovarian granulosa cells and testicular spermatocytes. The mutation of and was achieved by CRISPR/Cas9 in tilapia. Lower gonadosomatic index (GSI), increased apoptosis of oocytes and spermatocytes and significantly reduced sperm quality were observed in mutants, while normal gonadal development was observed in mutants. Consistently, the expression of apoptotic genes was significantly increased in mutants. In addition, the 5-methylcytosine (5-mC) level in gonads was decreased significantly, compared with that of and wild type (WT) gonads. Taken together, our results suggest that , not , plays important roles in maintaining gametogenesis in teleosts.