De novo assembly and characterization of the ovarian transcriptome reveal mechanisms of the final maturation stage in Chinese scallop Chlamys farreri

The objective of the present study was to characterize the pattern of gene expression at the last stage of ovarian maturation in Chlamys farreri. Dynamic transcriptomic analysis of ovaries was performed at four time points prior to ovulation, using the Illumina HiSeq 2500 platform. A total of 174,928 unigenes were obtained, among which 42,534 were annotated according to bioinformatics databases, such as NT, NR, Swiss-Prot, KOG, GO, and KEGG. Results from the transcriptome analysis revealed a time-dependent pattern of global transcriptional responses. When compared to the 0 d library, 99, 152, and 3248 differently expressed genes (DEGs) were obtained in the 3, 10, and 21 d libraries, respectively. Those three libraries shared only 10 DEGs, the majority of which were time-specific. Pairwise comparisons of each profile demonstrated that DEGs were related to hormone metabolism and receptors, cell division, gametogenesis, and vitellogenesis pathways. Notably, when adjacent sampling time point groups were compared, the only DEG throughout the experimental period was related to the G protein-coupled receptor signaling pathway. The present study provides the first dynamic transcriptomic analysis of C. farreri for evaluation of the molecular basis of gonadal maturation.