| Sturgeons(Acipenseridae)is one of Chondrostei in the world,which plays an important role in the evolutionary process of vertebrate.In recent years,the worldwide sturgeons have been listed as endangered species by Convention on International Trade in Endangered Species of Wild Fauna and Flora(CITES)because of habitat destruction and overfishing.At present,complete artificial propagation of most of sturgeons has been achieved,but late maturation and long lifespan would hinder the rapid development of sturgeon industry.Researches on the molecular mechanism of gonadal development in sturgeons would not only broaden the understanding of gonadal development in fish,but also contribute to the breeding of sturgeons.In additional,it would further contribute to the development of the sturgeon industry and the conservation of endangered sturgeon.At present,a series of achievements have been made in the studies on gonadal development and regulation mechanism in sturgeons,but the specific molecular mechanism is still unknown in sturgoens.In this study,Amur sturgeon(Acipenser schrenckii)and Yangtze sturgeon(Acipenser dabryanus)as the research subjects,the gonadal differentiation and development of sturgeons were preliminarily discussed by the transcriptome sequencing and foxl2 expression pattern.The main results are as follows:1.Comparative analysis of transcriptome sequencing between ovary and testis from Amur sturgeonGonadal transcriptomes from 10(five of each sex)individuals from two-year-old Amur sturgeon.99919 transcripts were obtained,and,52842 genes for Swissprot protein database,33066 genes for GO database and 15156 genes for KEGG database were respectively annotated.19690 differentially expressed transcripts were found between male and female gonads,in which the sex-related genes mainly included transcription factors(dmrt1,sox9 and foxl2)and transforming growth factors(amh,bmp15 and gdf9).Through KEGG pathway enrichment analysis,a total of 56 pathways were significantly enriched,in which the gonadal development related pathways are Progesterone-mediated oocyte maturation,Oocyte meiosis,Ovarian steroidogenesis and Gn RH signaling pathway.And,18 differentially expressed genes were found in the ovarian steroid synthesis pathway.The results showed that bmp15,cyp1a1,gdf9,hsd17b1 and foxl2 were highly expressed in ovaries,and cyp1b1,hsd3b1,and cyp17a1,fshr,ldlr,lhr and sox9 were highly expressed in testis.Subsequently,the expression patterns of 18 differentially expressed genes were analyzed,and it was concluded that the synthesis of estrogen in ovary would be inhibited in two-year old Amur sturgeon,but the synthesis of androgens in the testis might be not affected.2.The time of histological sex differentiation in Yangtze sturgeonIn this study,paraffin and HE staining were performed on the gonad tissues from Yangtze sturgeon at 30-1317 dah(days after hatching),and the time of sex differentiation was determined according to its histological analysis results.Two types of gonads were observed in Yangtze sturgeon at 100 dah that the germinal epithelium of ovaries was plicated,while germinal epithelium of gonads was smooth,which indicated that the histological sex differentiation time of Yangtze sturgeon was about at 100 dah.In addition,the germ cells of individuals at 1317 dahhave been divided into primary oocytes at small growth phase,and the sections from the testis at 1317 dah were filled with extended sperm.The result showed that the development of ovarian was later than the testis at this point.The results would provide a foundation for further study on the regulation mechanism of gonad differentiation and development.3.Cloning and expression analysis of foxl2 gene in Yangtze sturgeonc DNA sequence of Yangtze sturgeon foxl2 was obtained by RACE,of which length is 2260 bp with 918 bp of open reading frame and encoding 305 amino acids.Foxl2 protein shared high homology(>70%)with other vertebrate by multiple sequence alignment.Phylogenetic analysis showed that the Yangtze sturgeon foxl2 was clustered with Cartilaginous fishes as a branch.It showed that foxl2 was abundantly expressed in ovary of Yangtze sturgeon,and was not or weakly detected in other tissue by q PCR.Subsequently,expression of foxl2 was clearly detected in female gonads at 30 dah(The female sex specific marker of Yangtze sturgeon developed in our laboratory was used).And its expression gradually increased with ovary development after 80 dah,and significantly increased at 130 days.The expression of foxl2 reaches the highest level at705 dah with germ cell proliferation,following the expression decreased at 1317 dah with the differentiation of germ cell,but it showed weakly expression in testis of Yangtze sturgeon.This study suggested foxl2 may play an important role of sexual differentiation in Yangtze sturgeon,and maintain and promote ovarian development,as well as provide a foundation for the further studies on understanding the mechanism of sex differentiation. |
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