Expression of jun family genes in rat retinal cells: regulation by light/dark cycle

The expression of jun family genes in the retina of rats raised under a 12 h light/12 h dark cycle (LD 12:12) was examined by in situ hybridization histochemistry. c-jun and jun B mRNAs were found to be expressed in the inner nuclear layer (INL) which consists of horizontal, bipolar and amacrine cells and in the ganglion cell layer (GCL) which consists of ganglion cells and displaced amacrine cells and this expression was induced following the onset of the light. The expression of both mRNAs reached maximal levels by 30 min and then declined to low levels 2 h after light onset. In contrast, high levels of jun D mRNA were constitutively expressed and this expression was not confined to the INL and the GCL since it was also present in the ONL. Together with our previous report that c-fos was expressed transiently in the INL and the GCL after the onset of the light period and constitutively in the ONL throughout the dark period, the colocalization of c-fos with c-jun, jun B and jun D in the INL and the GCL after light onset and with jun D in the ONL during the dark period suggests that Jun and Fos proteins form an active AP-1 transcription factor which plays a key role in gene regulation in retinal cells.