A genetic approach was used to investigate whether the emergence of circadian rhythms in murine pups is dependent on a functional maternal clock. Arrhythmic females bearing either the mPer1/Per2 or mPer2/Cry1 double-mutant genotype were crossed with wild-type males under constant darkness. The heterozygous offspring have the genetic constitution for a functional circadian clock. Individual pups born to arrhythmic mPer1/Per2 and mPer2/Cry1 mothers in constant darkness without external zeitgeber developed normal circadian rhythms, but their clocks were less synchronized to each other compared to wild-type animals. These findings indicate that development of circadian rhythms does not depend on a functional circadian clock in maternal tissue, extending previous findings obtained from pups born to SCN-lesioned mothers.
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