Differential and day-time dependent expression of nuclear receptors RORα, RORβ, RORγ and RXRα, in the rodent pancreas and islet

The retinoic-acid-related receptor family of orphan receptors (RORs) act as transcriptional activators or repressors. One of their functions involves integrated actions within circadian oscillators, particularly of the periphery. The present paper describes differential expression of the orphan receptors ROR alpha, ROR beta and ROR gamma and of the nuclear retinoid receptor RXR alpha in the pancreas and islet of rats. Immunohistochemistry of rodent islets detected nuclear receptor expression. The ROR alpha and ROR beta signals were visualised in alpha-cells, whereas that of ROR gamma was largely confined to beta-cells. RXR alpha was expressed throughout the islets. Quantitative RT-PCR revealed circadian expression in the rat pancreas for ROR gamma, ROR alpha and RXR alpha, but not for ROR beta. Circadian expression of ROR gamma mRNA was verified in mouse pancreas and in rat INS-1 beta cells by serum shock experiments. The results point to differential and circadian expression and thus cell-type-specific functions of ROR alpha and ROR gamma in islet cells secreting glucagon or insulin. (C) 2012 Elsevier Ireland Ltd. All rights reserved.