Expression Regulation Of Estrogen Receptor Genes On Growth Differences Between Males And Females In Representative Fish Species

Gender dimorphism is common in fish,and some fish species have significant differences in male and female growth rates,which shows species specificity.For example,the growth rates of females in loach(Misgurnus anguillicaudatus)and tongue sole(Cynoglossus semilaevis)are significantly larger than that of males;however,in yellow catfish(Pelteobagrus fulvidraco)and tilapia(Oreochromis niloticus),males grow significantly faster than that of females.The 17β-estradiol had been reported to play an important role in regulating the feeding behavior and regulating energy balance in the mammals through estrogen receptor,thereby controlling the body weight of the individual.However,it is not clear whether the estrogen receptor also plays roles in regulating fish females and males’ growth.In this study,we select M.anguillicaudatus as our main research object,which has significant differences in male and female growth.Together with analysis on C.semilaevis,P.fulvidraco and O.niloticus,we hope to clarify whether estrogen receptor genes play an important role in fish females and males’ growth.The results from the present study could lay a foundation for exploring the function of estrogen receptor genes in the regulation of fish growth and development.The main results are as follows:1.Cloning and analysis of c DNA sequences of estrogen receptor genesThrough gene cloning,the c DNA core sequences of M.anguillicaudatus ERα,ERβ1and ERβ2 genes were obtained,which were 1821 bp,1008 bp,and 1197 bp,respectively,of which the ERα gene obtained the complete CDS sequence and was composed of 607 amino acid residues.The phylogenetic tree was constructed by comparing the amino acid sequence information of the ER family genes with the Ensemble or Gene Bank database of six fish and four exogenous ER family members.M.anguillicaudatus has the closest relationship with zebrafish,and then gathers together with other carps,and has a far relationship with mammals.This evolutionary relationship is consistent with the taxonomic status of various species in traditional morphology.It indicates that thefunction of each ER gene is also conserved throughout the evolution process.These results provide a theoretical basis for the role of ERs in the development of M.anguillicaudatus.2.The dynamic expression of estrogen receptor genes in regulating the growth difference between males and females M.anguillicaudatusQuantitative RT-PCR was used to detect the expression of ER genes in five growth stages of diploid loach as well as diploid and tetraploid adults.The results showed that three genes were differentially expressed in brain,muscle,liver,and gonadal tissues of male and female individuals before and after sexual maturity.Among them,the expression of ERα in brain,muscle and gonad tissues of male individuals was significantly higher than that of females(P<0.05),and the expression in female liver tissues was generally higher than that in males(P<0.05).The expression levels of ERβ1and ERβ2 in testis tissue were always in high level.Comparison results between different ploidy showed that the expression of three ER genes in the diploid brain tissue was significantly higher than that of the tetraploids,and the expression levels of males were higher than females,with the expression of ERα being the most significant.The results of this study indicated that regardless of the difference between ploidy and sex growth,ERαappears to have relatively higher expression in the brain tissue of slower growing(diploid,male)individuals.Therefore,we speculate that the ERα gene in brain tissues has a certain inhibitory effect on the growth rate of individual fish.3.The commonness of estrogen receptor genes in regulating the growth difference between fish males and femalesTwo comparing groups were set up as: the M.anguillicaudatus and C.semilaevis with females growing faster than males,and the P.fulvidraco and O.niloticus with males growing faster than females.The period of significant difference between males and females was selected and quantitative RT-PCR was used to detect the expression of estrogen receptor related genes in the tissues of male and female individuals.The results showed that ERα/ERβ1/ERβ2 was differentially expressed between male and female in various tissues,and both were relatively highly expressed in female liver and testis.Among them,the ERα gene was relatively highly expressed in the brain tissues of male M.anguillicaudatus and C.semilaevis and in the brain tissues of female P.fulvidraco and O.niloticus.This indicates that ERα gene had significantly higher expression in the brain tissues of slower growth gender,which validates our conclusion about the ERα gene has a certain inhibitory and regulatory effect on the growth rate of individual fish.The results initially proved that the expression of ERα gene in brain tissue may have a certain commonality in inhibiting the growth rate of individual fish.