Initial demonstration of rhythmic Per gene expression in the hypothalamus of a non-mammalian vertebrate, the house sparrow

In mammals, the major pacemaker controlling circadian rhythmicity is locate d in the hypothalamic suprachiasmatic nuclei which are characterized by spe cific molecular features including the expression of three homologues of th e Drosophila clock gene period (per). Until now, no comparable structure ha s been unambiguously described in the brain of any nonmammalian vertebrate. We cloned the PAS-domain of the Per2 gene in the house sparrow (Passer dom esticus), a model organism in circadian research. Hypothalamic expression o f posserPer2 (pPer2) showed a marked diurnal rhythm in the suprachiasmatic nucleus, a cell group located in the anterior hypothalamus directly above t he optic chiasm and adjacent to the third ventricle. Additionally, pPer2 wa s diurnally expressed in the lateral hypothalamus. This first demonstration of rhythmic clock gene expression in the hypothalamus of a nonmammalian ve rtebrate provides basic information for future research on the evolution of circadian pacemaking systems. NeuroReport 12:1167-1170 (C) 2001 Lippincott Williams & Wilkins.