Nonmammalian OT-family peptides

Abstract All nonmammalian tetrapods, lungfish, and coelacanths have mesotocin (MT) while ray-finned fish have isotocin (IT). Batoids and holocephalans have glumitocin and OT, respectively, but sharks have two distinct peptides. From cartilaginous fish to birds, OT family peptide genes are located on the same chromosome with the VT gene in tail-to-head orientation. Cyclostomes do not have an OT family peptide. OT family peptides are implicated in salt and water balance, but are less potent when compared with vasotocin. The widespread distribution of MT and IT receptors suggests their diverse functions. Similar to mammalian OT, contributions of MT and IT to social and sexual behaviors are implicated. Knockdown of MT produces female-specific deficits in gregariousness, pair bonding, and nest cup ownership in finches. ITR-KO zebrafish exhibited reduced social recognition. In the medaka, IT and ITR gene KO individuals revealed that IT/ITR1 signaling plays a role in the mate choice for familiar individuals in a sex-dependent manner.