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.
Ubuka
Takayoshi
T
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
Cadigan
Penelope A
PA
Wang
Ariel
A
Liu
Jennifer
J
Bentley
George E
GE
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