280. Photo inhibited heat shock protein 108 gene expression in the chicken hypothalamus

In domestic juvenile chickens kept on short days, photoinduced luteinsing hormone (LH) release, and by inference gonadotrophin-releasing hormone (GnRH) release, are readily detectable within 4 days of photostimulation.2 The molecular mechanisms responsible for the rapid photoinduced release of LH and GnRH in avian species are unknown. It has been suggested that it might involve a cascade of gene expression associated with an increase in cfos in the basal hypothalamus and glial cells in the median eminence.1 A microarray was made consisting of known genes of interest and clones obtained from a hypothalamic short day/long day subtractive library. An experiment was undertaken to determine if this reproductive neuroendocrine microarray could detect new targets for study in the chicken model of photostimulated GnRH release. The microarray was interrogated with hypothalamic RNA from juvenile chickens showing an increase in plasma LH after 4 days of photostimulation. Six genes were identified as showing changes in expression after photostimulation on the microarray. However, only one gene, encoding heat shock protein 108 (HSP108), could be confirmed by quantitative competitive RT-PCR. The expression of this gene decreased both in the hypothalamus and the optic tectum. Treatment of short day juvenile chickens with thyroxine, to mimic the effects of photostimulation, resulted in LH release and depression of HSP108 expression in the anterior but not the basal hypothalamus. Immunocytochemical analyses showed that HSP108 is widely distributed in the brain including glial-like cells with terminals in the median eminence. HSP108 is suggested as a candidate protein involved in the regulation of gonadotrophin release from the median eminence by glial cells. (1)Meddle SL and Follett BK (1995) Photoperiodic activation of fos-like immunoreactive protein in neurones within the tuberal hypothalamus of Japanese quail. Journal of Comparative Physiology [A] 176(1), 79–89.(2)Sreekumar KP and Sharp PJ (1998) Ontogeny of the photoperiodic control of prolactin and luteinizing hormone secretion in male and female bantams (Gallus domesticus). General and Comparative Endocrinology 109(1), 69–74.