Cyclin B protein undergoes increased expression and nuclear relocation during oocyte meiotic maturation of the freshwater prawn Macrobrachium rosenbergii and the Chinese mitten crab Eriocheir sinensis

Potential role for the germ cell-specific Rad21 in early meiosis of oocyte and spermatocyte in the Chinese mitten crab Eriocheir sinensis

Rad21/Rec8 family proteins are vital for sister chromatid segregation in mitosis and homologous recombination in meiosis, but no molecular data are available in crustacean species. In this study, a germ cell-specific Rad21 named EsRad21 was identified in the crab Eriocheir sinensis. EsRad21 mRNA has an open reading frame of 2310 base pairs (bp) encoding a 769 amino acids (aa) protein. RT-PCR showed that EsRad21 mRNA was particularly expressed in testis and ovary. The RT-qPCR results further revealed that the EsRad21 mRNA exhibited similar expression pattern in gonads at various developmental stages. EsRad21 mRNA expression level was the highest in testis at early spermatogenesis stage and ovaries at previtellogenesis stage, thereafter decreased significantly at middle spermatogenesis and vitellogenesis, and finally reach the lowest level at late spermatogenesis and vitellogenesis. In situ hybridization (ISH) analysis showed that EsRad21 mRNA was exclusively expressed in germline cells, but not in gonadal somatic cells. Notably, hybridized signal was detected on chromosomes of metaphase spermatocytes. EsRad21 is thus an underlying helpful indicator of the early phases of germ cell development. RNAi knockdown of EsRad21 downregulated the expression of other meiosis-related genes like Smc5-Smc6 and SPO11 and resulted in high mortality of individuals after 24 h post injection of EsRad21 dsRNA. Taken together, our results showed a potential role for EsRad21 in early meiosis of oocytes and spermatocytes in E. sinensis. This is the first report on the molecular characterization of the Rad21 transcript in a crustacean species.

Comparative Transcriptome Reveals the Potential Modulation Mechanisms of Spfoxl-2 Affecting Ovarian Development of Scylla paramamosain

Previously, we reported the identification, tissue distribution and confirmed the roles of Spfoxl-2 in regulating vitellogenin (vtg) expression in Scylla paramamosain. Here, we primally analyzed its potential target genes in the ovary with RNAi and RNA-Seq technology. By comparing the transcriptome data of two groups (ovaries that injected with EGFP and Foxl-2 siRNA, respectively), we found 645 DEGs (differentially expressed genes), including several conserved crucial genes involved in ovarian development, such as vtg, vitellogenin receptor (vtgR), adenylate cyclase (AC), cyclinB, and cell division cycle 2 (cdc2). In addition, these DEGs were also enriched in pathways related to ovary development, including relaxin signaling pathway, ovarian steroidogenesis, and progesterone-mediated oocyte maturation. Moreover, several genes were selected for qRT-PCR to validate the accuracy of the bioinformatic result. To the best of our knowledge, the current study was the first report about foxl-2 function through comparative transcriptome analysis in crustacean species, which identified not only relevant genes and pathways involved in ovarian development of S. paramamosain, but also provided new insights into the regulatory mechanisms of foxl-2 at the molecular level in crustacean.