Identification of European starling GnRH-I precursor mRNA and its seasonal regulation.
Songbirds show dynamic seasonal changes in their reproductive activities during the year. Gonadotropin-releasing hormone-I (GnRH-I) is critical for the control of reproduction in vertebrates. The molecular mechanisms controlling reproduction are not well understood in songbirds, largely because the GnRH-I precursor polypeptide gene was unknown until now. Here, we report the complete sequence and seasonal regulation of GnRH-I precursor polypeptide mRNA in a songbird, European starling (Sturnus vulgaris). The translated starling GnRH-I precursor polypeptide contained an amino acid sequence that can be processed into chicken GnRH-I peptide (pEHWSYGLQPG-NH(2)). However, the overall homology of GnRH-I precursor polypeptide (including a 23 amino acid signal peptide, the decapeptide hormone and Gly-Lys-Arg cleavage site followed by 55 amino acid GnRH-associated peptide sequences) between starling and chicken was only 58%. GnRH-I mRNA and GnRH-I peptide were observed to be co-localized in the preoptic area of sexually mature birds using in situ hybridization and immunocytochemistry. GnRH-I mRNA exhibited large variance in photosensitive birds, and converged to a high level in photostimulated birds. Subsequently, GnRH-I mRNA decreased to below detectability in most of the photorefractory birds. Changes were also observed in GnRH-I peptide levels, although changes in GnRH-I peptide were not as marked. Our data indicate that GnRH-I mRNA synthesis commences but is variable in photosensitive birds, stabilizes in photostimulated birds, then ceases when birds become photorefractory. Finer-scale investigation into temporal regulation of GnRH-I precursor polypeptide mRNA will provide insight into its regulation by environmental, social and physiological cues.
Department of Integrative Biology and Helen Wills Neuroscience Institute, University of California at Berkeley, 3060 Valley Life Sciences Building #3140, Berkeley, CA 94720-3140, USA. ubukat@berkeley.edu
Takayoshi
T
Ubuka
Penelope A
PA
Cadigan
Ariel
A
Wang
Jennifer
J
Liu
George E
GE
Bentley
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001921:Brain / Q000378:metabolism; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics; D005260:Female; D005786:Gene Expression Regulation; D007987:Gonadotropin-Releasing Hormone / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D006066:Gonads / Q000033:anatomy & histology; D008297:Male; D008969:Molecular Sequence Data; D009474:Neurons / Q000166:cytology / Q000378:metabolism; D010775:Photic Stimulation; D011301:Preoptic Area / Q000166:cytology / Q000378:metabolism; D011498:Protein Precursors / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D012621:Seasons; D046749:Starlings / Q000235:genetics* / Q000378:metabolism
D018076:DNA, Complementary; D011498:Protein Precursors; C050866:progonadoliberin I; D007987:Gonadotropin-Releasing Hormone