Effects Of Light On Circadian Expression Of Clock Related Genes In Suprachiasmatic Nucleus And Lymphocytes

Biorhythm is one of the most common phenomena in nature. Disturbance of biorhythm, especially circadian rhythm, will cause malaise and even disease. Basis of rhythmic structure is circadian clock, which is located at suprachiasmatic nucleus(SCN) and pineal gland in mammal. The molecular basis of which is composed of a series of genes and their corresponding protein products. In the present study, we determine the clock and melatonin receptor subtypes ( mt 1 , mt2 ) genes in suprachiasmatic nucleus (SCN) and lymphocytes at different time points of specific light regimes. The aim of this study is to investigate the effects of light on circadian expression of these clock related genes, and to explore possible roles and mechanisms of these genes in regulation of the diurnal rhythm.SD rats were housed in different regimes for at lest three weeks before experiment. Animals of 3 weeks anaesthetized by ether in set conditions, were sampled from the SCN and blood every four hours in a circadian day. Lymphocytes were separated from the blood with Ficoll, and mRNA were extracted from the samples. The method of semiquantitative reverse transcription polymerase chain reaction (RT-PCR) was used to determine the clock, mt1 and mt2 mRNAs for eachsample. Circadian parameters were analysed by the cosine method, and by the F test to judge the statistics significance.The results show that these three genes represent circadian rhythms in different regimes in SCN, while they only show markedly circadian rhythms in constant dark in lymphocytes. On the basis of relationship of the peak phases of the genes rhythms in different light regimes, It can be concluded that:(1) Circadian expression of the clock gene varied with the appearence of light, namely the light signal, but not the light regime.(2) Both the circadian clock and the light signal may affect the circadian expressions of the mt1 and mt2 genes. The mt1 is more sensitive to variation with the structure of light and dark, but the mt2 is more affected by the time length of light exposure.(3) Molecular circadian oscillators may also exist in lymphocytes, with a complicated relationship with the SCN. Circadian information may be possibly transferred from the center to the peripheral tissues.