| Macrobrachium rosenbergii is one of the main freshwater economic shrimps in China.Due to the long-term focus on growth as the main breeding direction and the single target trait for introduction,the degradation of germplasm resources such as reduced disease resistance and precocious maturity is a common problem in industry,which greatly limits the seed and breeding industry developing of M.rosenbergii.Study on the developmental regularity of gonads in M.rosenbergii is helpful for artificial intervention at the key periods of its growth and reproduction,furtherly contributing to improve the individual size,fecundity and survival rate of shrimp seedlings,which is the premise of cultivating excellent parents during selective breeding.In this study,we used paraffin sections,morphological data analysis and transcriptome sequencing to investigate the histology of gonadal development,the relationship between gonadal development and growth,and the regulatory mechanism of gonadal development in M.rosenbergii.The main results are as follows:1.The results of gonad morphology and histological observation showed that: the composition and distribution of germ cells at different development stages displayed regularity with the development of the gonads.Ovarian development can be divided into 8 stages and testis development can be divided into 4 stages.The external morphological development of the ovary was highly synchronized with the internal histological changes.As the maturity of the ovary increases,the germ cells in different stages form a circular distribution from the germinal zone outward.The ovarian volume,germ cell size and gonadal index（GIS）increase slowly in stages I to III,and mainly accumulated the number of germ cells;stage IV～VII ovarian volume,germ cell size and GIS increased rapidly,and the process of germ cell proliferation was accompanied by rapid accumulation of nutrients.The development stages of germ cells in the ovary can be inferred based on the color,volume,and pigment pattern of the ovary.The synchrony of testis morphology and histological development was low;Stage I testis was developed mainly for the improvement of individual reproductive functions.The testes at stage Ⅱ,Ⅲ,and Ⅳ were developed for strengthening ability of individual reproductive.2.Statistical analysis was carried out on the gonadal index of individuals with different culture periods and the occurrence frequency of individuals with different gonadal development stages.The results showed that:ovary development with the increase of culture time can be divided into three stages: the germ cell accumulation stage（83d-90d）,the endogenous yolk synthesis stage（97d-104d）,and exogenous yolk synthesis stage（111d-146d）.There was no regular variation in male gonad index and individual frequency in different testis developmental stages.Correlation analysis and path analysis were carried out on 13 phenotypic traits such as body length and body weight.The results showed that: ovary development restricted the growth of body weight and length of carapace in female shrimps,but the growth of abdominal length was not inhibited,which may be related to the increase of individual fertility by expanding abdominal volume.Testis development did not inhibit the individual growth of male shrimps.The key phenotypic traits which affecting the body weight of M.rosenbergii were different for different sexes at the same growth stage or different growth stages.The results of determination degree analysis showed that the multiple correlation coefficient between retained traits and body mass reached0.99,indicates that key traits affecting body mass have been identified.3.146,537 unigenes were obtained through transcriptome sequencing of testis and ovary at different developmental stages.Unigene N50 is 2008 bp with an average length of 1144 bp.The results of differential gene expression analysis showed that there were 468,339 and 7933 genes differentially expressed in the comparison group among the different developmental stages of ovary,among different developmental stages of testis,and between testis and ovary,respectively.A total of 13 signaling pathways related to gonad development,including insulin synthesis,oocyte maturation,and steroid biosynthesis,were obtained by KEGG enrichment analysis.The pathways mainly involved biological processes such as hormone metabolism regulation,sex cell proliferation and development,and amino acid metabolism.Analysis of the common differentially expressed genes in the above pathways show that severial genes including insulin-like growth factor 1 receptor（IGF1R）,heat shock protein 90（Hsp90）,cyclooxygenase（COX）were highly expressed during vitellogenin synthesis,which may be involved in yolk protein synthesis.In the process of yolk accumulation and oogenesis,calmodulin（Ca M）gene is highly expressed during the testis development and may play an important regulatory role in the process of spermatogenesis.The morphological and histological regularities of sexually mature gonad development of M.rosenbergii were obtained in this study,and the correlation between growth and gonad development was also analyzed,and a large number of differentially expressed genes related to gonad development were screened.The present results can provide a reference for learning the growth status of individuals from the perspective of gonad development in the process of nursery production and commercial shrimp culture,and also provide a theoretical basis for further exploration of the analysis and regulation mechanism of gonad development in M.rosenbergii. |
