Circadian regulation of cell outputs

New York University, New York NY

Investigators

Linked publications, trials & patents

Abstract

Enter the text here that is the new abstract information for your application. This section must be no longer than 30 lines of text. Circadian clocks drive a range of rhythmic cellular outputs to control 24hr rhythms in behavior and physiology. These outputs include rhythms in cell size and shape, but the mechanisms are not well-understood. Circadian pacemaker neurons, hepatocytes and intestinal epithelial cells all show 24hr rhythms in cell size and shape, while fibroblasts show circadian rhythms in actin dynamics during wound healing. We study the circadian control of cell size and shape using the Drosophila s-LNv circadian pacemaker neurons. The structure of neurons makes them excellent cells to visualize changes in shape. In addition, the relative simplicity of the Drosophila brain permits visualization and quantification of s-LNv projections, and Drosophila genetics allows precise spatial and temporal manipulation of s-LNv gene expression. We plan to study 3 areas that address key aspects of control of circadian changes in cell shape. Growth factors and other signals induce immediate early gene (IEG) transcription in most cells. Neuronal firing is typically the relevant signal for IEGs in neurons. In Area 1, we will study a transcriptional program activated by the opposite signal in s-LNvs: absence of neuronal activity. Neuronal inactivity activates transcription of toy, which encodes the fly Pax6 transcription factor. Toy then activates transcription of Pura, which encodes a GEF that increases Rho1 activity to retract s-LNv projections via the actin cytoskeleton. Mutations in Pura that prevent s-LNvs from changing shape cause long period behavioral rhythms, underlining the importance of rhythmic s-LNv shape changes for accurate 24hr rhythms. We will dissect the inactivity-regulated gene expression pathway, and test if it functions in different cells – including broadly across the brain during sleep. This gene regulatory network may also be activated when growth factors are removed from fibroblasts to ensure they do not progress through subsequent cell cycles. In Area 2, we focus on the function of Pura as a GEF. Pura activates Rho1, which in turn activates effectors including Rho Kinase. However, Pura itself is an in vitro target of Rho Kinase. Post-translational regulation of Pura could function either in a feedforward loop to lock Pura / Rho1 in an active state, or via negative feedback to limit the activity of Pura / Rho1 and ensure that s-LNv projections do not over-retract. We will test these ideas in vivo in s-LNvs. Our findings should have broad implications for control of Rho family GTPase activity, which is important in processes such as mitosis, cell movement and phagocytosis as well as cell morphology. Area 3 focuses on connections between cells: How do cells know which other cells to interact with? This question is of general importance, but is especially important in the nervous system. We will build on our novel connectomics assay to understand the cell adhesion molecule code that s-LNvs use to make and break connections with downstream cells as they change structure.