DEVELOPMENTAL EXPRESSION OF RZR-BETA, A PUTATIVE NUCLEAR-MELATONIN RECEPTOR MESSENGER-RNA IN THE SUPRACHIASMATIC NUCLEUS OF THE RAT

RZR beta is a member of the retinoid Z receptor (RZR) family of orphan receptors, and its expression is brain-specific. Recently, it was rep orted that the distribution of RZR beta mRNA is partially coincident w ith melatonin binding sites and that RZR beta is a putative nuclear re ceptor of melatonin. Using in situ hybridization, we investigated the developmental expression of RZR beta mRNA in the suprachiasmatic nucle us (SCN) of the rat, which is considered as circadian pacemaker. The R ZR beta mRNA was first found in the dorsomedial portion of the SCN at embryonic day 20, and RZR beta mRNA expression in the dorsomedial SCN continued until postnatal day 60. This result suggests that RZR beta p lays specific roles as a transcription factor in the dorsomedial SCN b ut not in the ventrolateral SCN during development and throughout post natal life.