Cloning of the Maternal Effector Gene org and Its Regulation by lncRNA ORG-AS in Chinese Tongue Sole (Cynoglossus semilaevis)

Maternal effector genes (MEGs) encode maternal RNA and protein, accumulating in the cytoplasm of oocytes. During oocyte development, MEGs participate in oocyte meiosis and promote oocyte development. And MEGs can also regulate maternal transcriptome stability and promote maternal–zygotic transition (MTZ) in early embryonic development. Long noncoding RNAs (lncRNAs), as new epigenetic regulators, can regulate gene expression at both the transcriptional and post-transcriptional levels through cis- or trans-regulation. The oogenesis-related gene org is a germ-cell-specific gene in fish, but the role of org in embryonic development and oogenesis has rarely been studied, and the knowledge of the lncRNA-mediated regulation of org is limited. In this study, we cloned and identified the org gene of Chinese tongue sole (Cynoglossus semilaevis), and we identified a lncRNA named lncRNA ORG-anti-sequence (ORG-AS), located at the reverse overlapping region of org. The results of qRT-PCR and FISH demonstrated that org was highly expressed during the early stages of embryonic development and oogenesis and was located in the cytoplasm of oocytes. ORG-AS was expressed at low levels in the ovary and colocalized with org in the cytoplasm of oocytes. In vitro experiments showed that overexpression of ORG-AS inhibited org expression. These results suggest that org, as a MEG in C. semilaevis, participates in the MTZ and the oogenesis. The lncRNA ORG-AS negatively regulates the gene expression of org through trans-regulation. These new findings broaden the function of MEGs in embryonic development and the oogenesis of bony fish and prove that lncRNAs are important molecular factors regulating org.