Ovarian transcriptome analysis of Mactra chinensis provides insights into genes expressed during the intermediate and...

Enhancing the production of aquatic animals is very important for fishery management and aquaculture applications. Ovaries have important functions in producing oocytes and hormones. The Chinese clam (Mactra chinensis) is a nutritious saltwater shellfish. Significant biochemical changes take place during the sexual maturation of M. chinensis; however, the genetic mechanisms of this process are unclear. Transcriptome sequencing can determine gene expression changes as development occurrs. In the present study, transcriptome sequencing was used to produce a comprehensive transcript dataset for the ovarian development of M. chinensis. The different ovarian developmental stages were determined using hematoxylin-eosin staining. There was identification of 54,172 unigenes at the intermediate stage and 63,081 at the ripening stage, and 80,141 all-unigenes were assembled to determine the molecular mechanism of ovarian development in M. chinensis. Quantitative real-time PCR for nine mRNAs confirmed the RNA-seq data. Functional annotation of the transcripts indicated there were important pathways in ovarian development, such as those involving the vitellogenin gene. Six pathways associated with ovarian development were identified: estrogen signaling pathway, GnRH signaling pathway, progesterone-mediated oocyte maturation, ovarian steroidogenesis, steroid hormone biosynthesis, and steroid biosynthesis. Significant upregulation of protein kinase alpha (PKA) and calmodulin (CAM) in four of the pathways indicates that PKA and CAM are active in M. chinensis ovarian development during maturation. Results of the present study provide the first comprehensive transcriptomic resource for M. chinensis ovaries, which will increase understanding of the molecular mechanisms underlying sexual maturation and promote molecular nutritional studies of M. chinensis.