Non-Visual Opsin 3 Localizes with Microtubules During Mitosis and is Essential for Cytokinesis

Opsin photoreceptors are responsible for the absorption of light, transduce information about daily lighting conditions and provide vision. Opsins are also involved in diverse non-visual functions such as the circadian clock. The non-visual opsin 3, also known as encephalopsin, is expressed in skin and its functions remain poorly defined. The expression of opsin 3 in human skin tissue was evaluated by immunohistochemistry, in keratinocytes and melanocytes by immunodetection. Opsin 3 and β-tubulin colocalization was performed during the keratinocyte mitotic phase. Opsin 3-siRNA transfection was used in primary keratinocytes and successful transfection was confirmed by immunodetection. These results show that opsin 3 was detected in the epidermis of human skin, both in keratinocytes and melanocytes. Opsin 3 colocalize with β-tubulin during the mitotic phase and participate in keratinocyte cell division. Opsin 3 protein expression was reduced after transfection with opsin 3-siRNA; inhibition of opsin 3-siRNA reduces keratinocyte cell proliferation and promotes the apparition of binucleated cells. This study highlights an unconventional function of opsin 3 in extra-ocular cells. Opsin 3 appears to be involved in the regulation of late cytokinesis in keratinocytes, and therefore in the maintenance of epidermal homeostasis.