The mPer1 clock gene expression in the rd mouse suprachiasmatic nucleus is affected by the retinal degeneration

Endogenous rhythms of mammals are controlled by the clock located in the suprachiasmatic nucleus (SCN). The molecular mechanism of a clock involves transcription/translation-based feedback loops in which the expression of the so called "clock genes" is suppressed periodically by their protein products. Previous studies reported influence of the eye itself on the circadian oscillation of the SCN, apart from the well-known photic readjustment of the central clock. With this in mind, we decided to analyze the mPer1 clock gene expression in the retinally degenerate (rd) mouse SCN by means of immunohistochemical techniques. Our objective was to detect possible alterations of the daily endogenous oscillation of PER1 protein in the SCN of these rd mice, as well as to make clear whether or not this protein was involved in the resetting of the central clock in a manner similar to wild-type animals. We found that the endogenous levels of PER1 protein were reduced in the SCN of rd mice throughout the 24-h cycle, which suggests that loss of classic photoreceptors influences somehow the main mechanism of the SCN clock. Light stimulation induced a parallel increase of Per1 expression at the subjective night, but not at the subjective day, in both rd and wild-type mice. Therefore, SCN readjustment by light in the rd mice occurs with a pattern similar to wild-type controls, despite the reduced PER1 protein levels detected. The effect of retinal degeneration on the circadian system and the possible interactions between the retinal and the SCN clocks are discussed.