Photoperiod-dependent regulation of gonadotropin-releasing hormone 1 messenger ribonucleic acid levels in the songbird brain

Abstract

Annual changes in day length induce marked changes in reproductive function in temperate zone vertebrates. In many avian species, in contrast to other seasonally breeding animals, plasticity in hypothalamic gonadotropin-releasing hormone – 1 (GnRH1) expression rather than (or in addition to) release governs changes in pituitary–gonadal activity. Investigations of the cellular and molecular mechanisms that govern GnRH1 plasticity were previously hindered by a collective inability of scientists in the field to characterize the gnrh1 cDNA in songbirds. We finally overcame this roadblock after data from the zebra finch (Taeniopygia guttata) genome project enabled us to rapidly clone the gnrh1 cDNA from hypothalamic RNA of zebra finches and European starlings (Sturnus vulgaris). Here, we review the original data that identified GnRH1 protein plasticity in the songbird brain and discuss earlier failed attempts to clone gnrh1 in these animals. Then, we present recent efforts, including our own, that successfully characterized gnrh1 in zebra finch and starling, and demonstrated dynamic regulation of gnrh1 mRNA expression, particularly in sub-populations of preoptic area neurons, in the latter. Overall, this paper highlights GnRH1 plasticity in the avian brain, and weaves into the narrative the previously untold story of the challenges to sequencing gnrh1 in songbirds.