Molecular evolution of peptide tyrosine-tyrosine: primary structure of PYYfrom the lampreys Geotria australis and Lampetra fluviatilis, bichir, python and desert tortoise

Peptide tyrosine-tyrosine (PYY) has been isolated from the intestines of tw o species of reptile, the desert tortoise Gopherus agassizii (Testudines) a nd the Burmese python Python molurus (Squamata), from the primitive Actinop terygian fish, the bichir Polypterus senegalis (Polypteriformes) and from t wo agnathans, the Southern-hemisphere lamprey Geotria australis (Geotriidae ) and the holarctic lamprey Lampetra fluviatilis (Petromyzontidae). The pri mary structure of bichir PYY is identical to the proposed ancestral sequenc e of gnathostome PYY (YPPKPENPGE(10)\DAPPEELAKY(20)\YSALR HYINL30\ITRQRY). Tortoise and python PYY differ by six and seven residues, respectively, fro m the ancestral sequence consistent with the traditional view that the Test udines represent an earlier divergence from the primitive reptilian stock t han the Squamates. The current views of agnathan phylogeny favor the hypoth esis that the Southern-hemisphere lampreys and the holarctic lampreys arose from a common ancestral stock but their divergence is of a relatively anci ent (pre-Tertiary) origin. The Geotria PYY-related peptide shows only two a mino acid substitutions (Pro(10) --> Gln and Leu(22) --> Ser) compared with PYY from the holarctic lamprey Petromyzon marinus. This result was unexpec ted as Petromyzon PYY differs from Lampetra PYY deduced from the nucleotide sequence of a cDNA (Soderberg et al. J. Neurosci. Res. 1994;37:633-640) by 10 residues. However, a re-examination of an extract of Lampetra intestine revealed the presence of a PYY that differed in primary structure from Pet romyzon PYY by only one amino acid residue (Pro(10) --> Ser). This result s uggests that the structure of PYY has been strongly conserved during the ev olution of Agnatha and that at least two genes encoding PYY-related peptide s are expressed in Lampetra tissues. (C) 1999 Elsevier Science B.V. All rig hts reserved.