Compression of daily activity time in mice lacking functionalPerorCrygenes

Feb 18, 2014Chronobiology international

Shortened daily active periods in mice missing key body clock genes Per or Cry

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Abstract

mPer2(Brdm1) mutant mice did not compress their activity time in response to varying night lengths.

Wild-type and mPer1(Brdm1) mutant mice showed compression followed by decompression of activity time when exposed to a full L:D 18:6 photoperiod.
mCry1 and mCry2 knockout mice displayed clear and systematic compression of activity time under skeleton photoperiods.
Both mPer1(Brdm1) and mPer2(Brdm1) mutants poorly adjusted to skeleton photoperiods.
One mPer2(Brdm1) mutant mouse that did adjust did not exhibit activity time compression.
Findings suggest that deletions of mCry1 and mCry2 do not hinder the ability to adjust to day length.

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The adjustment of daily activity time (α) to the varying night length in nocturnal creatures was one of the functions originally attributed to a putative dual oscillator structure of circadian pacemakers in mammals. In two experimental approaches, we tested whether this ability is compromised in mice with functional deletions of one of the four circadian clock genes. First, we tested the capability of α compression by long days in mPer1(Brdm1) and mPer2(Brdm1) mutant mice. When exposed to a full L:D 18:6 photoperiod, wild-type and mPer1(Brdm1) mutant mice show compression followed by decompression of α in DD. mPer2(Brdm1) mutant mice did not compress their activity time. The interpretation of these data is, however, complicated by masking due to light. We, therefore, embarked on a second experiment, exploiting skeleton photoperiods. The skeleton photoperiod was changed stepwise from 0 to 24 h, and mCry1 and mCry2 knockout mice were now included in the design. We observed clear and systematic compression of α in wild-type and mCry1 and mCry2 knockout mice. mPer1(Brdm1) and mPer2(Brdm1) mice both poorly entrained to the skeleton photoperiod. The single mPer2(Brdm1) mutant mouse that did entrain did not show α compression. The results show that neither mCry1 nor mCry2 deletions compromise adjustment to day length, consistent with our earlier conclusions on period lengthening in constant light (Spoelstra & Daan, 2008). The mPer2(Brdm1) mutant behaves aberrantly and appears not to respond to the delaying action of light in the late subjective day.

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Compression of daily activity time in mice lacking functionalPerorCrygenes

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