Two new forms of gonadotropin-releasing hormone in a protochordate and the evolutionary implications.
The neuropeptide gonadotropin-releasing hormone (GnRH) is the major regulator of reproduction in vertebrates. Our goal was to determine whether GnRH could be isolated and identified by primary structure in a protochordate and to examine its location by immunocytochemistry. The primary structure of two novel decapeptides from the tunicate Chelyosoma productum (class Ascidiacea) was determined. Both show significant identity with vertebrate GnRH. Tunicate GnRH-I (pGlu-His-Trp-Ser-Asp-Tyr-Phe-Lys-Pro-Gly-NH2) has 60% of its residues conserved, compared with mammalian GnRH, whereas tunicate GnRH-II (pGlu-His-Trp-Ser-Leu-Cys-His-Ala-Pro-Gly-NH2) is unusual in that it was isolated as a disulfide-linked dimer. Numerous immunoreactive GnRH neurons lie within blood sinuses close to the gonoducts and gonads in both juveniles and adults, implying that the neuropeptide is released into the bloodstream. It is suggested that in ancestral chordates, before the evolution of the pituitary, the hormone was released into the bloodstream and acted directly on the gonads.
Powell
J F
JF
Department of Biology, University of Victoria, BC Canada.
Reska-Skinner
S M
SM
Prakash
M O
MO
Fischer
W H
WH
Park
M
M
Rivier
J E
JE
Craig
A G
AG
Mackie
G O
GO
Sherwood
N M
NM
D000595:Amino Acid Sequence; D000818:Animals; D005075:Biological Evolution; D002645:Chickens; D004220:Disulfides; D005399:Fishes; D017952:Ganglia, Invertebrate / Q000737:chemistry; D007987:Gonadotropin-Releasing Hormone / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification; D008322:Mammals; D008969:Molecular Sequence Data; D009420:Nervous System / Q000737:chemistry*; D009928:Organ Specificity; D017386:Sequence Homology, Amino Acid; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D014561:Urochordata / Q000235:genetics / Q000502:physiology*
D004220:Disulfides; D007987:Gonadotropin-Releasing Hormone