Abstract
Objectives: Previously, we reported a light-dependant phenotype incircadian regulation in PER3 knockout (Per3-/-) mice. These mice also showed altered sleep architecture and elevated activity levels inthe second half of the dark period. In humans, a polymorphism inPER3 has been associated with diurnal preference, sleep homeo-stasis, and cognitive decline in response to sleep loss. We generated humanised knock-in (KI) mice expressing two variants of the human polymorphism and investigated activity patterns in response to different photoperiods. We also further investigated gene expression profiles of Per3-/- and KI mice during an ultradian light exposure paradigm.
Methods: Male and female C57Bl/6 mice, expressing either the 4- or 5- repeat of the human variable number tandem repeat in PER3 (Per34/4 and Per35/5) were exposed to short (8 h), intermediate (12 h) and long (16 h) photoperiods, as well as constant light.Transitions between the conditions were mixed between animals,such that the response to a new photoperiod could be analysed,taking into account different light-histories. Behavioural activity was recorded as running wheel revolutions. In addition, we subjected Per3-/- and KI mice to an ultradian light-dark cycle (3.5 h L–3.5 h D) and analysed whole genome RNA expression at CT 16, in an ultradian light episode.
Results: Significant differences between male and female activity were seen. Female mice showed more activity in the second half of the dark period, and overall 24-h activity levels were more than 1.5-fold higher in females. These differences were seen in all genotypes. In constant darkness, both male and female Per34/4 mice showed increased activity in the second half of the dark period, compared toWT and Per35/5 mice. The behavioural responses to photoperiods were diverse, with KI mice appearing to adjust more rapidly to a new photoperiod. Whole genome RNA expression in Per3-/-and KI mice was altered compared to WT mice, and similar pathways were affected in both Per3-/-and KI mice.
Conclusion: Here we show behavioural data on a novel humanised mouse model of PER3. In mice, this polymorphism associates with altered activity, especially in the transition between photic conditions.We also observed a consistent difference between male and female activity. This emphasizes the need to not only use transgenic mice but also to include both sexes in animal models of human conditions.