Molecular cloning of proopiomelanocortin cDNA from an elasmobranch, the stingray, Dasyatis akajei.

Recently, we have characterized a new MSH (named delta-MSH) which joins the group of MSHs (alpha, beta, gamma) in dogfish proopiomelanocortin (POMC). The present study has confirmed the presence of delta-MSH in POMC of another member of the elasmobranchian order, the stingray, Dasyatis akajei, by cDNA cloning from pituitary mRNAs. Overlapping partial cDNA clones corresponding to stingray POMC were amplified by PCR from single-strand cDNA prepared from pituitary poly (A)(+) RNA. Excluding the poly A tail, stingray POMC cDNA consists of 1077 base pairs (bp). It contains a 912-bp open reading frame encoding a signal peptide of 24 amino acids (aa) and a POMC of 280 aa. gamma-MSH, alpha-MSH, ACTH, delta-MSH, beta-MSH, and beta-endorphin are located at POMC (50-61), (115-127), (115-153), (182-193), (226-242), and (245-280), respectively. The stingray POMC is smaller than that of the dogfish POMC (294 aa) mainly due to the absence of a sequence of 11 consecutive aa between delta-MSH and beta-MSH. delta-MSH has been found only in the elasmobranchs and, therefore, delta-MSH might have evolved after the divergence of chondrichthians from the ancestral vertebrate lineage and before divergence of sharks and rays.