Molecular cloning of proopiomelanocortin cDNA in the ratfish, a holocephalan

Proopiontelanocortin (POMC) is a precursor for several pituitary hormones including adrenocorticotropin (ACTH), melanocyte-stimulating hormone (MSH) and endorphin (END). Fish POMCs in four taxonomic classes, Cephalaspidomorphi (lampreys), Chondrichthyes (cartilaginous fish), Sarcopterygii (lobe-finned fish), and Actinopterygii (ray-finned fish) have been identified. However, two essential species, ratfish in Chondrichthyes and hagfish in Agnatha, are still missing in the evolutionary image of this molecule. The present study reports analysis of POW cDNA in the ratfish, Chimaera phantasma, which belongs to another subclass in the Chondrichthyes. Partial cDNA clones were amplified by PCR from single-strand cDNA prepared on total RNA from a complex of pituitary and hypothalamus, and subsequently overlapped to obtain a full-length sequence. Ratfish POW cDNA consists of 1294 bp excluding the poly(A) tail. It encodes a signal peptide of 25 amino acids and POW of 300 amino acids. gamma-MSH, ACTH, alpha-MSH, delta-MSH, beta-MSH, and beta-END are located at prePOMC (76-87), (120-158), (120-132), (212-227), (275-290), and (293-325), respectively. delta-MSH, originally found in elasmobranch POMCs, was also present in ratfish POW, suggesting this structure might have appeared after the divergence of chondrichthians from the ancestral lineage. Thus, we demonstrated the common occurrence of four MSHs in chondrichthian POW and established a clear understanding of the molecular evolution of POW in gnathostomes. (C) 2003 Elsevier Inc. All rights reserved.