Individuals with Angelman syndrome (AS) suffer sleep disturbances that severely impair quality of life. Whether these disturbances arise from sleep or circadian clock dysfunction is currently unknown. Here, we explored the mechanistic basis for these sleep disorders in a mouse model of Angelman syndrome (Ube3a mϪ/pϩ mice). Genetic deletion of the maternal Ube3a allele practically eliminates UBE3A protein from the brain of Ube3a mϪ/pϩ mice, because the paternal allele is epigenetically silenced in most neurons. However, we found that UBE3A protein was present in many neurons of the suprachiasmatic nucleus-the site of the mammalian circadian clock-indicating that Ube3a can be expressed from both parental alleles in this brain region in adult mice. We found that while Ube3a mϪ/pϩ mice maintained relatively normal circadian rhythms of behavior and light-resetting, these mice exhibited consolidated locomotor activity and skipped the timed rest period (siesta) present in wild-type (Ube3a mϩ/pϩ ) mice. Electroencephalographic analysis revealed that alterations in sleep regulation were responsible for these overt changes in activity. Specifically, Ube3a mϪ/pϩ mice have a markedly reduced capacity to accumulate sleep pressure, both during their active period and in response to forced sleep deprivation. Thus, our data indicate that the siesta is governed by sleep pressure, and that Ube3a is an important regulator of sleep homeostasis. These preclinical findings suggest that therapeutic interventions that target mechanisms of sleep homeostasis may improve sleep quality in individuals with AS.

Sleep loss can severely impair the ability to perform, yet the ability to recover from sleep loss is not well understood. Sleep regulatory processes are assumed to lie exclusively within the brain mainly due to the strong behavioral manifestations of sleep. Whole-body knockout of the circadian clock gene Bmal1 in mice affects several aspects of sleep, however, the cells/tissues responsible are unknown. We found that restoring Bmal1 expression in the brains of Bmal1-knockout mice did not rescue Bmal1-dependent sleep phenotypes. Surprisingly, most sleep-amount, but not sleep-timing, phenotypes could be reproduced or rescued by knocking out or restoring BMAL1 exclusively in skeletal muscle, respectively. We also found that overexpression of skeletal-muscle Bmal1 reduced the recovery response to sleep loss. Together, these findings demonstrate that Bmal1 expression in skeletal muscle is both necessary and sufficient to regulate total sleep amount and reveal that critical components of normal sleep regulation occur in muscle.DOI: http://dx.doi.org/10.7554/eLife.26557.001

Sex differences in spontaneous sleep amount are largely dependent on reproductive hormones; however, in mice some sex differences in sleep amount during the active phase are preserved after gonadectomy and may be driven by non-hormonal factors. In this study, we sought to determine whether or not these sex differences are driven by sex chromosome complement. Mice from the four core genotype (FCG) mouse model, whose sex chromosome complement (XY, XX) is independent of phenotype (male or female), were implanted with electroencephalographic (EEG) and electromyographic (EMG) electrodes for the recording of sleep-wake states and underwent a 24-hr baseline recording followed by six hours of forced wakefulness. During baseline conditions in mice whose gonads remained intact, males had more total sleep and non-rapid eye movement sleep than females during the active phase. Gonadectomized FCG mice exhibited no sex differences in rest-phase sleep amount; however, during the mid-active-phase (nighttime), XX males had more spontaneous non-rapid eye movement (NREM) sleep than XX females. The XY mice did not exhibit sex differences in sleep amount. Following forced wakefulness there was a change in the factors regulating sleep. XY females slept more during their mid-active phase siestas than XX females and had higher NREM slow wave activity, a measure of sleep propensity. These findings suggest that the process that regulates sleep propensity is sex-linked, and that sleep amount and sleep propensity are regulated differently in males and females following sleep loss.

Though stress causes complex sleep disruptions that are different in females and males, little is known about how sex influences the ability of stress to alter sleep. To date there have been no comprehensive examinations of whether effects of stress on sleep are sensitive to determinants of sex, such as reproductive hormones. Since restraint stress produces a sexually dimorphic increase in rapid eye movement sleep (REMS) amount in mice that is greater in males than females, in the current study we sought to determine whether estrogens and androgens influence the ability of restraint stress to alter sleep states. We removed the gonads from adult female and male C57BL/6J mice and implanted the mice with recording electrodes to monitor sleep-wake states. Gonadectomized females and males exhibited similar amounts of REMS in response to restraint stress. Mice were then implanted with continuous release hormone pellets. Females received 17β-estradiol and males received testosterone. Hormone replacement (HR) in females decreased the REMS response to restraint stress while HR in males increased the REMS response to restraint stress. The combined effects of HR in females and males restored the sex difference in the ability of restraint stress to alter REMS. These results demonstrate that sex differences in the effects of stress on REMS are dependent on reproductive hormones and support the view that endogenous or exogenous changes in the reproductive hormone environment influence sleep responses to stress.

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