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 RORα, RORβ and RORγ and of the nuclear retinoid receptor RXRα in the pancreas and islet of rats. Immunohistochemistry of rodent islets detected nuclear receptor expression. The RORα and RORβ signals were visualised in α-cells, whereas that of RORγ was largely confined to β-cells. RXRα was expressed throughout the islets. Quantitative RT-PCR revealed circadian expression in the rat pancreas for RORγ, RORα and RXRα, but not for RORβ. Circadian expression of RORγ mRNA was verified in mouse pancreas and in rat INS-1 β cells by serum shock experiments. The results point to differential and circadian expression and thus cell-type-specific functions of RORα and RORγ in islet cells secreting glucagon or insulin.