Oxytocin/Vasopressin-Like Peptide in the Central Nervous System and Ovaries of the Mud Crab Scylla olivacea

Oxytocin (OT)/vasopressin (VP)-like peptide has been reported in invertebrates as a single peptide with various common names. This peptide was suggested to be a primitive form of the oxytocin and vasopressin present in vertebrates. In this study, the full mRNA sequence of the OT/VP-like peptide was annotated in the central nervous system (CNS) transcriptome of the mud crab <i>Scylla olivacea</i>through the National Center for Biotechnology Information (BioProject ID: PRJNA1006859). The sequence contained 607 bp corresponding to 158 amino acids. Multiple alignment and phylogenetic tree analyses suggested that the OT/VP-like peptide of <i>S. olivacea</i> is most similar to that of <i>Scylla paramamosain</i>. Reverse transcription polymerase chain reaction (RT-PCR) analysis indicated that the mRNA was expressed in the eyestalks, brain, ventral nerve cord (VNC), ovaries, and other peripheral organs. Real-time qPCR revealed that the highest expression levels of this mRNA occurred in the CNS and ovaries of the crabs bearing stage I ovaries. Using the conserved region CFITNCPPGGKRSGGLMSTLGR to produce antibody, the OT/VP-like peptide was detected in neuronal clusters 6/7, 8, 11, and 14/15 and in neuropils of the brain, as well as the neurons and neuropils of the VNC, including the subesophageal (SEG), thoracic (TG), and abdominal (AG) ganglia. In the ovaries, immunoreactivity of this peptide occurred in the ooplasm of the oocytes of immature ovaries, and it was detected near the cell membranes of oocytes of mature ovaries. This work supports the neuro-endocrine study of an economically important mud crab species and could be helpful in aquaculture management.