HSP90B1, a thyroid hormone-responsive heat shock protein gene involved in photoperiodic signaling

In order to further advance the understanding of genes involved in avian photoperiodic signaling, a chicken hypothalamic cDNA microarray was made to identify changes in gene expression in the whole hypothalamus of juvenile male domestic chickens after 4 days' photostimulation. The most robust change was a depression in heat shock protein 90B1 (HSP90B1) expression. This observation was confirmed using quantitative PCR, and it was subsequently demonstrated that the depression in HSP90B1 expression first occurs in the anterior hypothalamus after 1 day's photostimulation, and was also depressed in the anterior and basal hypothalamus after 4 days' photostimulation. Four days after an intravenous injection of thyroxine (T4), an avian photomimetic, in short day birds, HSP90B1 expression was depressed in the anterior, but not in the basal hypothalamus. Depressed HSP901 expression after photostimulation or T4 treatment was associated with increased GnRH-I mRNA and plasma LH. HSP90B1 is abundant throughout the brain where it occurs in glial cells, and is involved in regulating white matter plasticity. It is suggested that photoperiodically depressed hypothalamic HSP90B1 may affect glial function in photoperiodic signaling pathways in the neuroendocrine system. This is the first report of a thyroid hormone-responsive gene involved in photoperiodic signaling.