Calcium-Dependent Regulation of Neural Fate in Development and Disease

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PROJECT SUMMARY/ABSTRACT Mutations in the calcium channel Cav1.2 and downstream calcium signaling proteins in the calcineurin (CaN)/ NFAT pathway, in particular the kinase Dyrk1a, have been reproducibly associated with neuropsychiatric disorders, including autism spectrum disorders (ASD). These genetic findings implicate calcium signaling dysfunction in psychiatric disease and underscore a critical gap in our knowledge of how calcium signals are initiated and transduced in the developing brain. Our long-term goal is to understand how intracellular calcium elevations in neural progenitor cells (NPCs) direct their differentiation into neurons and glia, with an eye towards uncovering how mutations in calcium signaling proteins alter their developmental functions to promote disease. In this proposal, we focus on two distinct aspects of calcium signaling: detectors and sensors that initiate calcium responses to extrinsic cues or depletion of intracellular calcium stores, and molecular pathways that act as downstream transducers of calcium signals. We have found that utilization of two disease-relevant Cav1.2 exons is dynamically regulated in the embryonic cortex, and that an ASD-associated mutation in Cav1.2 prevents this developmental splicing switch in channel transcripts, which in turn alters the differentiation of specific cortical neuron subtypes. Similarly, we have also found that splicing of STIM2, a calcium sensor involved in store operated calcium entry (SOCE) in response to ER calcium depletion, is developmentally regulated to generate two isoforms with opposing effects on SOCE. Altering the relative levels of these isoforms in NPCs using in utero electroporation bidirectionally modulates cell cycle exit in vivo. Finally, in mice bearing a forebrain-specific deletion of Dyrk1a, a kinase that antagonizes CaN/NFAT signaling, we have observed broad misregulation of NPC function and differentiation. Building on these published and preliminary studies, the central objective of this proposal is to interrogate specific mechanisms by which intracellular calcium signals link extracellular cues with intrinsic differentiation programs and to elucidate how alternative splicing refines these signals. The proposed studies will test the hypotheses that calcium entry, regulated by precisely-timed exon utilization, orchestrates differentiation programs in the developing cortex (Aim1), and that downstream cell type-specific calcium signaling via the CaN/NFAT pathway is a key mechanism involved in the regulation of NPC function and differentiation (Aim2). This research will broadly impact the field of developmental neuroscience by elucidating the developmental regulation of calcium signaling in differentiating cells, building a foundation for future studies aimed at understanding how extracellular cues and intracellular calcium dynamics converge to regulate brain development. Our results will also have significant translational potential by providing new insights into mechanisms underlying the pathophysiology of psychiatric disorders.