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R. E. Rosenstein, D. Fernandez, P. Sande, M. Chianelli, H. Aldana Marcos, N. de Zavalía; Clock Gene Expression in the Golden Hamster Retina: Endogenous Rhythmicity, Localization and Influence of the Suprachiasmatic Nuclei. Invest. Ophthalmol. Vis. Sci. 2008;49(13):177.
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The mammalian retina contains single or multiple intrinsic circadian oscillators that can be entrained by light cycles. The aim of the present work was to investigate circadian variations of two clock-gene proteins (BMAL1 and CLOCK), their localization, and the influence of the suprachiasmatic nuclei on these rhythms.
Male Golden hamsters were kept under a photoperiod of 14 h of light-10 h of darkness (LD, lights on at 06.00 h), with free access to food and water. In some experiments, animals were kept in constant darkness (DD) for 48 h. In one group of animals, bilateral thermic lesions of the suprachiasmatic nuclei (SCN) were performed. After surgery, SCN-lesioned animals were exposed to a light-dark cycle for 15 days, and then transferred to constant darkness for 24 h. BMAL1 and CLOCK levels were assessed by Western blotting of nuclear and cytosolic fractions from hamster retinas excised at midday, midnight, subjective midday or subjective midnight. BMAL1 and CLOCK localization was examined by immunohistochemistry.
Nuclear levels of BMAL1 and CLOCK were significantly higher at midday than at midnight (p<0.01), while in the cytosolic fraction no changes were observed. A similar profile was observed in animals kept in constant darkness, as well as in SCN-lesioned animals. In both cases, nuclear levels of these proteins were significantly higher at subjective midday than at subjective midnight (p<0.01). BMAL1 and CLOCK were localized in ganglion cell layer
These results indicate significant circadian variations of BMAL1 and CLOCK nuclear levels in the hamster retina, which are regulated by a local circadian clock, presumably located in retinal ganglion cells.
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