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Photoperiodic regulation of sleep

Primary Supervisor: Dr Ko-Fan Chen, Department of Genetics and Genome Biology

Secondary supervisor: Professor Flaviano Giorgini

PhD project title: Photoperiodic regulation of sleep

University of Registration: University of Leicester

Project outline:

General background: Sleep is an evolutionarily conserved behaviour regulated by cellular mechanisms and environmental factors. Using animal models such as the fruit fly and mice, the cellular mechanisms that control sleep, such as circadian clock, has been studied intensely. On the other hand, less is known about how environmental factors modify sleep.

Changes in photoperiod (i.e. day length) are a daily feature of middle and high latitude environments. Adjustment of sleep-wake profiles according to the current photoperiod allows animals to maintain their temporal niches across the 24-hour day. We and others have recently showed that photoperiod modifies sleep quantity and quality in the fly (1). Moreover, such modification requires neuronal activity of photoreceptors in the fly eyes. Intriguingly extreme photoperiods were shown to modify photoreceptor activity via branches of a kinase-signalling network called the integrated stress response (ISR)(2). Cellular stressors such as protein aggregates and reactive oxidative stress trigger ISR and modulate downstream gene transcription. Furthermore, altered ISR levels in the fly neurons modify sleep, suggesting that the ISR is a potential cellular mechanism linking environmental day length to sleep.

Aim: Using the versatile genetic and imaging tools available in the fruit fly, this PhD project aims to investigate the role of the ISR and other novel molecular mechanisms in photoperiodic regulation of sleep.

Objectives and Methods: Experiments will be conducted under five photoperiods (from 0 to 24 hours, with 8-hour increments) to investigate the following question-oriented research objectives: 1. Which subset of photoceptors are required for photoperiod-mediated sleep changes? Using video- and infrared beam-based behaviour assays and state-of-art transgenic binary expression systems in the fly, the sleep profile of flies with activated or inhibited subsets of photoreceptors will be recorded under different photoperiods. 2. How do the neuronal activity and ISR levels of photoreceptors correlate with sleep profiles at different photoperiods? Using transgenic fluorescent reporters, the level of ISR, synaptic structural changes and synaptic release properties of photoreceptors will be recorded by confocal microscopy across several time points during the five photoperiods. 3. What molecular mechanisms in the eye report changes in photoperiod? Aggregate-prone proteins and the RNAi constructs against genes in the ISR pathways will be expressed acutely in the fly eyes to manipulate ISR levels. Fly sleep in these conditions will be recorded to investigate the role of ISR in photoperiod-mediated sleep changes. Eye transcriptomes will also be collected for the five photoperiods. The identified differentially expressed genes will be knocked down in the fly eyes via somatic-CRISPR and RNAi technology. The effect of these manipulations on sleep will be tested in order to unbiasedly identify genes associated with photoperiodic regulation of sleep.

Significance: Photoperiod is an important environmental factor that has been shown to modify sleep quality and quantity. However, the underlying neurogenetic mechanisms remain largely unclear. Using the powerful genetic toolkit available in fruit flies, this PhD project provides a unique opportunity to begin investigating this knowledge gap. The results obtained may also offer insight into the prevalent sleep disturbances associated with the artificially extended photoperiod in modern “24-7” human society.

References:

  1. K. F. Chen, S. Lowe, A. Lamaze, P. Kratschmer, J. Jepson, Neurocalcin regulates nighttime sleep and arousal in Drosophila. eLife. 8 (2019), doi:10.7554/eLife.38114.
  2. A. T. Moehlman, A. K. Casey, K. Servage, K. Orth, H. Krämer, Adaptation to constant light requires Fic-mediated AMPylation of BiP to protect against reversible photoreceptor degeneration. eLife. 7, e38752 (2018).

BBSRC Strategic Research Priority:Understanding the Rules of Life: Neuroscience and behaviour

    Techniques that will be undertaken during the project:

    • Drosophila Genetics
    • Video-based behaviour assay
    • Ex vivo brain imaging
    • RNA-Seq
    • Immunohistochemistry

    Contact: Dr Ko-Fan Chen, University of Leicester