The Dimorphism Of Growth Hormone Regulation By 17β-estradiol In Spotted Scat (Scatophagus Argus)

Growth hormone（Gh）is an essential endocrine factor that regulates somatic growth.Spotted scat（Scatophagus argus）is a famous marine aquaculture species in China with a typical sexual growth dimorphism in which females grow faster and larger than males.In order to analyze the mechanism of regulating growth differences between the females and males,the following research was performed,and the results are as follows.1.The expression patterns of Gh in pituitary glandBased on the qPCR analysis,gh mRNA was mainly expressed in the pituitary gland and weakly in the gonads and hypothalamus.Furthermore,gh mRNA expression in the pituitary gland was significantly higher in females than in males,suggesting a dimorphic expression pattern.In addition,spotted scat Gh polyclonal antibody was produced for this study.Western blot analysis of gonads showed that the molecular weight of spotted scat Gh was about 21 k Da.Immunohistochemistry（IHC）in pituitary glands showed that Gh was mainly expressed in the proximal pars distalis（PPD）,and a few cells were distributed in the rostral pars distalis（RPD）.2.Study on the molecular mechanism of estrogen regulating the expression of gh dimorphismIn previous studies,estrogen and androgen were injected into female fish in vivo.The expression level of gh in pituitary of the estrogen-injected group was significantly higher than that in the control group.In contrast,the expression gh in the androgen-treated group was not significantly different from the control.It is indicated that estrogen may be one of the internal reasons that affect the dimorphic expression of gh in female and male spotted scat.Based on this,we injected 4.0μg/kg of exogenous estrogen（17β-Estradiol,E₂）in vivo in females and males fish at the age of24 months.The qPCR results showed that,in the pituitary gland,gh mRNA expression in female and male fish was significantly up-regulated.But the expression of estrogen receptor（Estrogen receptors,Er）era and erβ2 mRNA in female and male fish were decreased.In the liver,the expression of igf1 and ghr1 mRNA was significantly decreased in E₂-injected female and male spotted scat.The erαmRNA expression significantly increased in male fish;however,no significant difference was observed in female fish.The results suggested that E₂might directly or indirectly regulate gh mRNA expression in the pituitary.The transcriptome sequencing of the pituitary was performed in female and male fish after 17β-estradiol injection.Results showed a total of 329,247,007 clean reads and 23,466 annotated genes.208 genes were significantly differentially expressed compared to the control group in pituitary of female and male fish.According to Kyoto Encyclopedia of Genes and Genomes（KEGG）pathway analysis,in the E₂-FP group,DEGs were significantly enriched in Histidine metabolism and p53 signaling pathway terms.And in the E₂-MP group,DEGs were significantly enriched in Glutathione metabolism terms.qPCR and transcriptome results showed that,some growth-related genes such as junbb、mstn2、insm1a and gap43 could respond to estrogen.3.The effect of estrogen feeding on the growth of spotted scatEstrogen mixed with diet was used to feed the undifferentiated spotted scat fry.We observed its growth status and detected the expression level of growth-related genes in the GH/IGF1 axis.The results showed that at 6 months,the body length and weight of both female and male spotted scat in E₂treatment group were significantly lower than those of the control group.The qPCR results showed that at 6 months,gh mRNA expression in the pituitary gland of female fish was significantly up-regulated in the E₂300 group and significantly down-regulated at 12 months.There was no significant difference in the expression level of gh mRNA in the pituitary gland at the age of 6 and 12 months in male fish.In summary,1).gh mRNA expression in the pituitary gland was significantly higher in females than in males.This may be one of the internal reasons for the growth dimorphism between female and male fish.2).E₂reduced hepatic sensitivity to Gh as well as reduced the production of Igfs.In addition,E₂may indirectly affect the expression level of gh mRNA by regulating the expression of growth-related genes,thus affecting the growth of vertebrates.3).Exogenous estrogens may inhibit the growth axis by down-regulating the expression levels of some growth-related genes in the liver,thus inhibiting spotted scat growth.This study has potential application value in sex control breeding and the production of mono-sex fingerlings of spotted scat.