Characterization of de novo DNA methyltransferase dnmt3 regulating sterility in female allotriploid fish

Meiosis is under strict surveillance by checkpoints, which impairment could cause sterility directly via forming defective gametes. DNA methyltransferases, regulating DNA methylation dynamically, are critical for meiosis in mammals. However, little is known about de novo DNA methyltransferases regulating sterility in fish. Here, we firstly compared the gene expression of meiotic key genes in sterile and fertile fish and proved the pachytene arrest of oocytes in allotriploid fish. Based on this result, dnmt3 was cloned and found to be highly expressed in the gonad, especially in oocytes, but expressed relatively weak in the ovaries of sterile allotriploid fish when compared with fertile diploid and allotetraploid fish. Furthermore, two kinds of important hormones of HPG axis, human chorionic gonadotrophin (hCG) and estradiol (E2), were used to examine the relationship between HPG axis and dnmt3 in regulating sterility in allotriploid fish. We found that E2 treatment increased the expression of dnmt3 but decreased msh4, while hCG treatment had no influence on the two genes. Meanwhile, E2 treatment not only increased the whole genome DNA methylation level but also increased the DNA methylation level of CpG island on msh4 gene. Taken together, our results suggest that the epigenetic regulation is involved in sterility in female teleost. These results may be useful in the fields of reproductive biology and genetics as well as in aquaculture breeding.