Discovery of molecular mechanisms of identified cycling genes using a gene chip in the suprachiasmatic nucleus

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We identified cycling 101 genes in the suprachiasmatic nucleus(SCN) using a gene chip. Next, using in situ hybridization, we examined whether these genes expresses rhythmically or not in the SCN and detected rhythmic expression of some genes. The SCN showed oscillatory expression of ID2 in both LD and DD, high during the night, low during the day. We suggested that ID2 works as a negative regulator of the transcription and may be good candidate for the modulator of Per transcription.In addition, Dexras1 and HSPa5 mRNA expression showed circadian rhythm, peaked during night and these genes expression were found predominantly in the dorsomedial portion of the SCN(DMSCN).We investigated expression profiles of Per genes in the rat SCN in steady light-dark condition by in situ hybridization method, with special reference to the induction in the ventrolateral portion of the SCN(VLSCN). In the LD condition, the onset of the Pen and Per2 genes expression in the SCN began 30 minutes after lights on, while the VLSCN did not expression Per genes until 2hours after lights on in DD. Therefore, it is likely that the expression of Per genes during the early daytime is caused by the exposure to light during subjective night. These findings suggest that the involvement of Per genes in the daily synchronization of the circadian clock to environment time. Also, we demonstrate that an abrupt shift in the LD cycle disrupts the synchronous oscillation of circadian components in the rat SCN. The VLSCN, photoreceptive region, shifted rapidly, but the DMSCN were relatively slow to shift. This dissociation and slow resynchronization of endogenous oscillators within the SCN after an LD cycle shift suggests a mechanism for the physiological symptoms that constitute jet lag. Then these finding suggested that there are potential two oscillators in the SCN.