Molecular pathways regulating astrocyte morphogenesis and function

SUMMARY Astrocytes are the most abundant glial cell type in the human brain and are critical for central nervous system (CNS) development and function. Mature astrocytes are unusually elaborate cells, with an intricate and ramified morphology. Their numerous fine cellular processes interact closely with synapses, neuronal cell bodies, axons, blood vessels, and other glial cells throughout the CNS. Through these interactions, astrocytes fulfil diverse functions to support and enhance neuronal activity, maintain CNS homeostasis, and modulate circuits. Underscoring the importance of proper astrocyte development, defects in astrocyte growth or loss of astrocyte complexity are implicated in many neurological diseases, including Alexander's disease, autism, and epilepsy. However, it remains poorly understood how astrocytes develop their intricate morphological associations and regulate neural circuit function. Our long-terms goals are to understand how astrocyte acquire their remarkable morphology, target their processes to synapses, and use these cell-cell contacts to modulate brain function. We recently performed a genetic screen in Drosophila to identify new regulators of astrocyte development, and uncovered a novel gene, Trapped in endoderm 1 (Tre1), as required for astrocyte morphogenesis. We find that loss of Tre1 leads to severely reduced astrocyte complexity in vivo, resulting in decreased infiltration of the synaptic neuropil. Tre1 encodes a G protein-coupled receptor (GPCR) with no known function in the CNS. This proposal will use a synergistic combination of molecular-genetic tools available in Drosophila and zebrafish along with new tools we have generated and in vivo imaging to: determine how Tre1 regulates astrocyte morphogenesis, function, and animal behavior in Drosophila (Aim 1); elucidate signaling pathways upstream and downstream of Tre1 activation (Aims 1+2); and define the evolutionary conservation of Tre1 in vertebrates (Aim 3). Our work will provide exciting new insights into the mechanisms regulating astrocyte development and function in vivo and lay the foundation for understanding astrocyte growth and dysfunction in human disease.