Temporal profile of circadian clock gene expression in a transplanted suprachiasmatic nucleus and peripheral tissues

Nov 2, 2007The European journal of neuroscience

Timing of daily clock gene activity in transplanted brain clock and body tissues

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Abstract

The grafted suprachiasmatic nucleus (SCN) exhibited dynamic circadian expression rhythms of clock genes.

Transplanted SCN tissues restored behavioral circadian rhythms in SCN-lesioned mice.
Clock gene expression rhythms in the grafted SCN were similar to those in intact mice.
Phase relationships between the expression of clock genes and locomotor activity in grafted mice mirrored those observed in intact animals.
The phase angles between the grafted SCN and peripheral tissues in the liver, kidney, and skeletal muscles were maintained as in intact mice.
Amplitudes of mPeriod1 and mPeriod2 rhythms were reduced in peripheral tissues of SCN-grafted animals.

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The mammalian hypothalamic suprachiasmatic nucleus (SCN) is the master oscillator that regulates the circadian rhythms of the peripheral oscillators. Previous studies have demonstrated that the transplantation of embryonic SCN tissues into SCN-lesioned arrhythmic mice restores the behavioral circadian rhythms of these animals. In our present study, we examined the clock gene expression profiles in a transplanted SCN and peripheral tissues, and also analysed the circadian rhythm of the locomotor activity in SCN-grafted mice. These experiments were undertaken to elucidate whether the transplanted SCN generates a dynamic circadian oscillation and maintains the phase relationships that can be detected in intact mice. The grafted SCN indeed showed dynamic circadian expression rhythms of clock genes such as mPeriod1 (mPer1) and mPeriod2 (mPer2). Furthermore, the phase differences between the expression rhythms of these genes in the grafted SCN and the locomotor activity rhythms of the transplanted animals were found to be very similar to those in intact animals. Moreover, in the liver, kidney and skeletal muscles of the transplanted animals, the phase angles between the circadian rhythm of the grafted SCN and that of the peripheral tissues were maintained as in intact animals. However, in the SCN-grafted animals, the amplitudes of the mPer1 and mPer2 rhythms were attenuated in the peripheral tissues. Our current findings therefore indicate that a transplanted SCN has the capacity to generate a dynamic intrinsic circadian oscillation, and can also lock the normal phase angles among the SCN, locomotor activity and peripheral oscillators in a similar manner as in intact control animals.

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Temporal profile of circadian clock gene expression in a transplanted suprachiasmatic nucleus and peripheral tissues

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