Six novel gonadotropin-releasing hormones are encoded as triplets on each of two genes in the protochordate, Ciona intestinalis.
GnRH is the key regulator of the reproductive axis in vertebrates, but little is known about GnRH before the origin of vertebrates. We have identified two genes encoding GnRH in a protochordate, Ciona intestinalis, thought to be related to the ancestral animal that gave rise to vertebrates. Each gene, Ci-gnrh1 and Ci-gnrh2, encodes in tandem three GnRH peptides, each of which is unique compared with known forms. Ci-gnrh1 encodes three peptides and contains no introns, whereas Ci-gnrh2 encodes three more peptides but has two introns. This is the first report in which more than one GnRH peptide is encoded on a single gene. The Ciona genes reveal consensus promoter elements that are conserved compared with human GNRH1. Both tunicate genes are expressed as mRNA early and throughout development, measured at the stages of four-cell, gastrulation, tail release, and tail resorption. In a closely related tunicate species, Ciona savignyi, we used in silico analysis to identify two similar genes encoding six peptides, only one of which is unique compared with C. intestinalis. Immunohistochemistry showed that at least one GnRH peptide was in the nerve net that surrounds the dorsal strand. Synthetic forms of the seven novel tunicate peptides induced release of gametes in adult tunicates. In contrast, the peptides did not activate the human GnRH-I receptor or cause release of LH in a rat pituitary cell assay. These data provide insight into the structural evolution of the GnRH peptides and their genes and show a functional role for GnRH in tunicate spawning.
Adams
Bruce A
BA
Department of Biology, University of Victoria, Victoria, British Columbia, Canada V8W 3N5.
Tello
Javier A
JA
Erchegyi
Judit
J
Warby
Carol
C
Hong
Doley J
DJ
Akinsanya
Karen O
KO
Mackie
George O
GO
Vale
Wylie
W
Rivier
Jean E
JE
Sherwood
Nancy M
NM
D000375:Aging / Q000502:physiology; D000595:Amino Acid Sequence / Q000235:genetics; D000818:Animals; D001665:Binding Sites / Q000235:genetics; D002938:Ciona intestinalis / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D003429:Cross Reactions; D005854:Germ Cells / Q000502:physiology; D007987:Gonadotropin-Releasing Hormone / Q000235:genetics* / Q000276:immunology / Q000378:metabolism; D006801:Humans; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000276:immunology / Q000378:metabolism; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic / Q000502:physiology; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D011966:Receptors, LHRH / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics; D024363:Transcription Initiation Site; D018911:Trinucleotide Repeats
D010446:Peptide Fragments; D012333:RNA, Messenger; D011966:Receptors, LHRH; D014157:Transcription Factors; D007987:Gonadotropin-Releasing Hormone