Presence of the δ-MSH sequence in a proopiomelanocortin cDNA cloned from the pituitary of the galeoid shark, Heterodontus portusjacksoni

Abstract

Since a fourth MSH sequence, δ-MSH, has been detected in the proopiomelanocortin (POMC) gene of a dogfish and a stingray, members of superorder Squalea (class Chondrichthyes), it is possible that this novel MSH sequence might be a feature common to the POMC genes of all modern sharks and rays. As an initial step towards addressing this question, a full-length POMC cDNA was cloned and sequenced from the pituitary of the Port Jackson shark, Heterodontus portusjacksoni. The Port Jackson shark represents one of the oldest lineages in superorder Galea, and this superorder together with superorder Squalea form infraclass Neoselachii (the extant sharks and rays). The Port Jackson shark POMC cDNA has an open reading frame that is 1032 nucleotides in length and encodes the deduced amino acids sequences for β-endorphin, ACTH/α-MSH, β-MSH, γ-MSH, and δ-MSH. Port Jackson shark δ-MSH has 83% primary sequence identity with dogfish and stingray δ-MSH, and it appears that the δ-MSH sequence may have been the result of an internal domain duplication and reinsertion of the β-MSH sequence. The presence of the δ-MSH sequence in the POMC genes of representatives of both superorders of infraclass Neoselachii would indicate that the δ-MSH sequence must have been present in the ancestral euselachian shark that gave rise to the neoselachian radiation.