Characterization of H3 methylation in regulating oocyte development in cyprinid fish

Histone post-modifications are important epigenetic markers involved in multiple cellular processes via regulation of gene transcription or remodeling of chromatin structure. Oocyte development is a critical process under rigorous control to prevent the generation of aberrant gametes. However, the regulatory mechanism of oocyte early development is not well-understood due to the tiny size and poor distinguishability of the gonad in juvenile stages. Here, two cyprinid hybrid fishes, a sterile allotriploid fish and a gynogenetic hybrid fish with delayed oocyte development, provided research models to investigate the mechanisms involved. We used cytogenetic and molecular methods to confirm the pachytene arrest of oocytes in allotriploid fish and gynogenetic hybrid fish. On the basis of these developmental differences, we screened 21 different histone H3 modifications by ELISA and found that four modifications(H3 K4 me3, H3 K9 me3, H3 K79 me, and H3 K79 me3) differed significantly in the two cyprinid hybrid fishes. Changes in histone methylation at the three residues(H3 K4, K9, K79) were caused by specific methyltransferases and demethylases. Our results provide new insights into the epigenetic regulation of oocyte early development in fish, a process critical for understanding of reproductive biology and with practical applications in the aquacultural breeding industry.

An improved hybrid bream derived from a hybrid lineage of Megalobrama amblycephala(♀)×Culter alburnus(♂)

Distant hybridization is an important technique in fish genetic breeding.In this study,based on the establishment of an allodiploid fish lineage(BT,2n=48,F_(1)–F_(6))derived from distant hybridization between female Megalobrama amblycephala(BSB,2n=48)and male Culter alburnus(TC,2n=48),and the backcross progeny(BTB,2n=48)derived by backcrossing female F_(1) of BT to male BSB,an improved hybrid bream(BTBB,2n=48)was obtained by backcrossing BTB(♀)to BSB(♂).Moreover,the morphological and genetic characteristics of BTBB individuals were investigated;BTBB was similar to BSB in appearance but had a higher body height than BSB.The study results regarding chromosome numbers and DNA content indicated that BTBB is a diploid hybrid fish.The 5S rDNA and Hox gene of BTBB were inherited from the original parents.Gonadal development in BTBB was normal.On the other hand,BTBB had a faster growth rate,higher muscle protein level,and lower muscle carbohydrate level than BSB.Hence,bisexual fertile BTBB is promoted and can be applied as a high-quality fish,and it can also be used as a new fish germplasm resource to develop high-quality fish further.Thus,this study is of great significance for fish genetic breeding.