Cell Type-Specific Expression Profiling of Clock Cells and Glia
Genome-wide studies of circadian transcription or mRNA translation have been hindered by the presence of heterogeneous cell populations in complex tissues such as nervous system. We have recently developed Drosophila strains that permit cell-specific and genome-wide studies of protein translation. We have used these strains, together with NexGen (RNA-seq) sequencing analysis, to identify hundreds of mRNAs that exhibit cycles of ribosome association (i.e., translation) in circadian clock cells of adult Drosophila (Huang et al, 2013 ). Some of these clock cells are glial astrocytes which communicate with the circadian neuronal circuitry. In recent studies, the lab has performed similar translational profiling studies of developing (Huang et al, 2015 ) and mature (adult) astrocytes. These studies revealed significant similarities between the gene expression profiles of fly and mammalian glial astrocytes, emphasizing the conservation of cellular and molecular mechanisms that regulate behavior in vertebrates and invertebrates. They point to Drosophila as an excellent genetic model for understanding the glial regulation of neuronal circuits and behavior. As circadian and sleep mechanisms are conserved between Drosophila and humans, our studies have considerable significance for understanding pathophysiological changes that affect these processes.
Brain Glial Cells Behavior
An important goal of contemporary neuroscience research is to define the neural circuits and synaptic interactions that mediate behavior. Mechanisms regulating circadian behavior and sleep, both rhythmic behaviors, are remarkably similar in Drosophila and mammals. The molecular biology of the circadian clock, for example, is virtually identical in flies and mammals including humans (Jackson, 2011 ). In mammals, sleep is regulated by homeostatic and circadian processes, and the same is true of Drosophila sleep, which has characteristics in common with human sleep. In mammals and Drosophila, the neuronal circuits controlling circadian behavior or sleep have been the subject of intensive investigation, but roles for glial cells in the networks controlling rhythmic behavior have only begun to be defined in recent studies. Our lab was the first to document an important role for glial cells in the physiological regulation of circadian behavior (Suh and Jackson, 2007 ; Ng et al., 2011 ). Others have shown that mammalian astrocytes regulate sleep homeostasis. Our more recent studies have utilized Drosophila astrocyte gene expression profiling as a basis for RNAi-based genetic screens to discover glial factors regulating circadian behavior (link to Ng and Jackson, 2015 ) or sleep. In similar studies, we have performed a genome-wide screen for small Drosophila non-coding RNAs (microRNAs) that regulate circadian behavior. That screen has revealed a number of microRNAs and target RNAs that are required in adult astrocytes for normal circadian behavior. Ongoing studies in the lab are focused on a number of glial factors that regulate Drosophila circadian behavior or sleep.
Figure 1. A novel glial protein regulating Drosophila sleep is trafficked to glial processes (green), consistent with secretion.