Meeting Abstract

S10.5  Tuesday, Jan. 6  Molecular and Endocrine Mechanisms of Vertebrate Photoperiodic Response YOSHIMURA, T.; Laboratory of Animal Physiology and Avian Bioscience Research Center, Graduate School of Bioagricultural Sciences, Nagoya University takashiy@agr.nagoya-u.ac.jp

Animals living outside the tropics use changes in photoperiod to adapt to seasonal changes in environment, but the molecular mechanisms underlying photoperiodic response are not fully understood. The Japanese quail is a robust model for the study of these mechanisms because of its rapid and dramatic response to changes in photoperiod. Local thyroid hormone catabolism within the mediobasal hypothalamus (MBH) by thyroid hormone-activating enzyme (DIO2) regulates the seasonal reproduction. Rapid induction of DIO2 gene expression in the ependymal cells (EC) lining ventrolateral walls of third ventricle of the MBH was the earliest event yet recorded in the photoperiodic signal transduction pathway. To address the identity of the photoperiodic transduction pathway, we have dissected the molecular dynamics of gene expression regulating photoinduced thyroid hormone catabolism using a chicken high-density oligonucleotide microarray. We identified two waves of gene expression. The first was initiated ~14 h after dawn of the first long day and included increased thyrotropin (TSH) beta subunit expression in the pars tuberalis of the pituitary gland; the second occurred ~4 h later and included increased DIO2 expression. TSH receptor was found in the EC of the MBH and intracerebroventricular administration of TSH to short day quail stimulated gonadal growth, and expression of DIO2. This TSH induced expression of DIO2 was shown to be mediated through a thyrotropin receptor-cAMP signaling pathway by the promoter analysis. Increased pars tuberalis TSH therefore appears to trigger long day photoinduced seasonal breeding.