A newly characterized melanotropin in proopiomelanocortin in pituitaries of an elasmobranch, Squalus acanthias.
Proopiomelanocortin (POMC) is a precursor for corticotropin (ACTH), three or fewer molecular types of melanotropin (MSH), and beta-endorphin. This protein is thought to have evolved by duplication of MSH genomic segments. Here we report that the POMC in the dogfish, an elasmobranch, contains a fourth type of MSH in addition to classical alpha-, beta-, and gamma-MSH. POMC cDNA was amplified by PCR from double-strand cDNA prepared from dogfish pituitary and ligated into lambdaZAP II. The POMC cDNA is composed of 1315 bp without a poly(A) tail. Northern blot analysis detected a 1.4-kb signal of dogfish POMC mRNA. An open reading frame of the POMC cDNA encodes 320 amino acids, including a signal peptide of 26 amino acids. The dogfish POMC includes gamma-MSH, ACTH, alpha-MSH, beta-MSH, and beta-endorphin at positions 50-61, 115-153, 115-127, 239-256, and 259-294, respectively. In addition to these classical peptides, a newly discovered MSH, which we have termed delta-MSH, is present in dogfish POMC at position (184-195). The four dogfish MSHs can be separated into two groups based on their sequence identities: one pair consists of alpha-MSH and gamma-MSH, and the other consists of beta-MSH and delta-MSH, suggesting that gamma-MSH and delta-MSH may have been duplicated evolutionarily from alpha-MSH and beta-MSH, respectively. gamma-MSH might first have appeared in early gnathostomes because it is absent in the most primitive vertebrate group, the agnathans. delta-MSH, which at this time is found only in chondrichthians, might have appeared after the divergence of chondrichthians from a lineage leading to osteichthyans and tetrapods.
Amemiya
Y
Y
School of Fisheries Sciences, Kitasato University, Sanriku, 022-0101, Japan.
Takahashi
A
A
Suzuki
N
N
Sasayama
Y
Y
Kawauchi
H
H
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D018076:DNA, Complementary / Q000032:analysis* / Q000737:chemistry; D004284:Dogfish / Q000235:genetics / Q000378:metabolism; D009074:Melanocyte-Stimulating Hormones / Q000737:chemistry / Q000235:genetics*; D008969:Molecular Sequence Data; D010902:Pituitary Gland / Q000737:chemistry*; D016133:Polymerase Chain Reaction; D011333:Pro-Opiomelanocortin / Q000737:chemistry / Q000235:genetics*; D017385:Sequence Homology; D000521:alpha-MSH / Q000737:chemistry / Q000235:genetics
D018076:DNA, Complementary; D000521:alpha-MSH; D011333:Pro-Opiomelanocortin; D009074:Melanocyte-Stimulating Hormones