| Chinese mitten crab(Eriocheir sinensis), which is widely distributed in the Yangtze River, Liao River, Ou River and other waters, mainly grows in the Yangtze River in China. Due to stock introduction blindly, the genetic exchange among the populations of different waters has become more frequently in recent years. Therefore, it has become a top priority to conduct selective breeding. This study analyzed the genetic characters of3base stocks by microsatellite technology, and useful information would be accumulated for further study of selective breeding. In recent years, a common phenomenon that one age old crabs become precocious ccurred in the process of aquaculture. Precocity severely restricted the development of crab aquaculture and has caused great losses to the production. In this study, we hypothesize that the variants of the MIH are associated with the precocity of Eriocheir sinensis. To address this hypothesis, we sought to identify new polymorphisms of the MIH gene, then genotyped all the SNPs in precocious and normal crab populations, and evaluated the associations between these meaningful SNPs and the precocity of Eriocheir sinensis.In order to select excellent germplasm of Eriocheir sinensis,16pairs of microsatellite primers were used to analyze the genetic characters of3base stocks which were collected from Chongming Tuanjiesha of Yangtze River Delta, Yangzhong section, and Jingjiang, Liuhe, Jiang Pu sections of Yangtze River respectively. The results showed that the genetic diversity indices of the3stocks are high with average expected heterozygosities (He) as0.7014, and the average observed heterozygosities (Ho) of the three stocks were higher than the average expected heterozygosities (He) in the all16microsatellite loci. The average observed heterozygosities (Ho) of the three stocks were0.7750,0.7457and0.7917, and the average expected heterozygosities (He) were0.7050,0.7029, and0.6964respectively. The first stock had the highest He, while the third stock had the lowest value, but there was no significant difference among the three stocks (P>0.05). The fixation indices (Fis) were used to evaluate the inbreeding or outcrossing of the3stocks, and the negative values were observed at almost all16microsatellite loci for the3stocks. The Hardy-Weinberg equilibrium (D) among the three stocks ranged from-0.3794to0.9666, and there were heterozygous reduction at five locus in each of these stocks. The pairwised genetic distance among the three stocks ranged from0.0321to0.0384. The Ds between the first and second stock was smaller (0.0321) than any others and it can be inferred that the genetic exchange between them was more frequent. Overall, the three base stocks in the present study had relatively higher genetic diversities, and it was suitable for selective breeding.Molt-inhibiting hormone (MIH), an important regulator of steroidogenesis, inhibits the synthesis of ecdysteroid in Y-organ (YO) and plays a significant role in the regulation of molting and postembryonic development of crustacean. Because unsuccessful molting have been widely observed in precocious crabs, we investigated whether genetic variants of the MIH gene are associated with precocity of Eriocheir sinensis. Thirty individual DNA samples were sequenced to search for SNPs in the control regions and coding regions of the MIH gene.12SNPs and10SNPs were selected from control regions and coding regions, respectively. In contron regions, there are5SNPs (SNP A196A, SNP G230C, SNP G305C, SNP C323G and SNP T372C) located in the5’-flanking region and7SNPs (C2677G, SNP G2759A, SNP T2807G, SNP T3032T, SNP C3042T, SNP A3088T and SNP A3095T) located in the3’-UTR of the MIH gene. In coding regions, there are3SNPs (SNP C422G, SNP G1714A and SNP C2529T) located in the exon regions and7SNPs (SNP C2384T, SNP C2387T, SNP T2410G, SNP G2415T, SNP T2416A, SNP A2430C and SNP C2466C) located in the intron regions.21SNPs(except SNP T3032T) were selected for the individual genotyping in a two-stage association study. We found that a SNP A3088T in the3’-UTR and a SNP C2466C in the intron regions of MIH gene were significantly associated with precocity of Eriocheir sinensis. The combined additive model result of SNP A3088T is OR=1.469(95%CI1.169-1.844, P=0.001), and combined codominant model(TT) result of SNP C2466C is OR=0.613(95%CI0.386-0.975, P=0.039). However, no significant associations were observed between the other19SNPs and precocity of Eriocheir sinensis. To our best knowledge, this is the first association study between various SNP genotypes and phenotype attributes in Eriocheir sinensis. Our findings suggest that the SNP A3088T and SNP C2466C may be candidate markers for effective marker-assisted selection to decrease the precocity of Eriocheir sinensis in future studies. |
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