The human vasopressin-oxytocin gene family: no evidence for additional neurophysin-related genes

Over the last 20 years several observations at the peptide level have indicated the possible existence of additional members of the vasopressin (VP)-oxytocin (OT) gene family in mammals. In this study, the human genome was analyzed for the existence of genes structurally related to the VP and OT genes. Human genomic blots probed under low stringency conditions with exon B of the human OT gene, that codes for the conserved constant region of neurophysin, revealed the presence of two distinct bands in addition to the known VP and OT gene fragments. Five clones were obtained from a library of genomic EcoRI fragments ranging from 4-8 kb, that comprised both low stringency signals, by low stringency hybridization with the OT exon B probe. One clone of 7 kb hybridized at high stringency conditions to bands of the same size as previously detected with OT exon B on a human genomic blot. However, no similarity was observed between the open reading frames of this clone and the neurophysin portion of the OT gene. Another clone of 4.8 kb was identical to a fragment of the gene for the human bone morphogenetic factor hBMP-6, a member of the TGF-ß family. The hBMP-6 gene was not detected by low stringency hybridization of the human genomic blot with the OT exon B probe. No significant similarity was found between the amino acid sequences of human OT neurophysin and hBMP-6. Therefore, no evidence can be provided that the human genome contains additional neurophysin-related genes. This finding suggests that if additional vasopressin and oxytocin-like peptides exist, they will not be transcribed from genes with close similarity to the VP and OT genes.