RESUMEN
Circadian clocks regulate various aspects of photoreceptor physiology, but their contribution to photoreceptor development and function is unclear. Cone photoreceptors are critical for color vision. Here, we define the molecular function of circadian activity within cone photoreceptors and reveal a role for the clock genes Bmal1 and Per2 in regulating cone spectral identity. ChIP analysis revealed that BMAL1 binds to the promoter region of the thyroid hormone (TH)-activating enzyme type 2 iodothyronine deiodinase (Dio2) and thus regulates the expression of Dio2. TH treatment resulted in a partial rescue of the phenotype caused by the loss of Bmal1, thus revealing a functional relationship between Bmal1 and Dio2 in establishing cone photoreceptor identity. Furthermore, Bmal1 and Dio2 are required to maintain cone photoreceptor functional integrity. Overall, our results suggest a mechanism by which circadian proteins can locally regulate the availability of TH and influence tissue development and function.
Asunto(s)
Factores de Transcripción ARNTL/genética , Relojes Circadianos/genética , Células Fotorreceptoras Retinianas Conos/metabolismo , Hormonas Tiroideas/metabolismo , Factores de Transcripción ARNTL/metabolismo , Envejecimiento , Secuencia de Aminoácidos , Animales , Relojes Circadianos/efectos de los fármacos , Regulación de la Expresión Génica/efectos de los fármacos , Yoduro Peroxidasa/química , Yoduro Peroxidasa/genética , Yoduro Peroxidasa/metabolismo , Ratones Noqueados , Opsinas/metabolismo , Proteínas Circadianas Period/metabolismo , Células Fotorreceptoras Retinianas Conos/efectos de los fármacos , Triyodotironina/farmacología , Yodotironina Deyodinasa Tipo IIRESUMEN
PURPOSE: Ambient light is both a stimulus for visual function and a regulator of photoreceptor physiology. However, it is not known if light can regulate any aspect of photoreceptor development. The purpose of this study was to investigate whether ambient light is required for the development of mouse rod photoreceptors. METHODS: Newborn mouse pups (C57BL/6) were reared in either cyclic light (LD) or constant dark (DD). Pups were collected at postnatal day (P)5, P10, P17, or P24. We performed retinal morphometric and cell death analysis at P5, P10, and P17. Rhodopsin expression was assessed using immunofluorescence, Western blot, and quantitative RT-PCR analysis. Electroretinograms were performed at P17 and P24. Radioimmunoassay and ELISA were used to follow changes in thyroid hormone levels in the serum and vitreous. RESULTS: In the DD pups, the outer nuclear layer was significantly thinner at P10 and there were higher numbers of apoptotic cells at P5 compared to the LD pups. Rhodopsin expression was lower at P10 and P17 in DD pups. Electroretinogram a-waves were reduced in amplitude at P17 in the DD pups. The DD animals had lower levels of circulating thyroid hormones at P10. Light-mediated changes in thyroid hormones occur as early as P5, as we detected lower levels of total triiodothyronine in the vitreous from the DD animals. Drug-induced developmental hypothyroidism resulted in lower rhodopsin expression at P10. CONCLUSIONS: Our data demonstrate that light exposure during postnatal development is required for rod photoreceptor development and that this effect could be mediated by thyroid hormone signaling.