Cellular and Genetic Origins of Astrocytes

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DESCRIPTION (provided by applicant): The human brain is made up of neurons and glia. Glia comprise about 90% of brain cells and are involved in devastating disorders such as multiple sclerosis, seizures and Alzheimer's disease. We know little about development of the most prevalent glial cells called astrocytes. This proposal will identify fundamental mechanisms by which neural stem cells give rise to astrocytes. It is also intended to generate useful markers to investigate roles for astrocytes during development and in human disease. The goal of the proposed research is to identify a set of genetic markers for development of astrocytes and to map their cellular origins in the central nervous system. The underlying hypothesis to be tested is that astrocytes develop from heterogeneous locations in the developing CMS. We have three specific aims: Specific Aim 1 is to identify and characterize activity of transcription factors that uniquely mark and may regulate astrocyte development. In preliminary work, we have interrogated the mammalian transcriptome to identify transcription factors that co-localize with astrocytes in the developing spinal cord. Expression analysis and gain- and Ioss-of-function screens will be conducted to prioritize generation of antibodies to transcription factors that mark and may regulate astrocyte lineage heterogeneity in the CNS. Specific Aim 2 is to develop cell type- and stage-specific markers for fibrous and protoplasmic astrocytes. We have developed fluorescent activated cell sorting (FACS) protocols for acute harvest of gray matter astrocytes and analysis by expression profiling. By sorting cells from Gensat transgenic mice that express green fluorescent protein (GFP) in (1) pan-astroglial and (2) white matter astrocyte compartments, we will identify markers specific for fibrous astrocytes, protoplasmic astrocytes and astrocyte precursors in various CNS regions. Specific Aim 3 is to determine whether astrocyte diversity correlates with developmental site of origin in the embryonic spinal cord and brain. We will use a cohort of cre/lox transgenic mice to fate map heterogeneous progenitor domains for astrocytes and their ultimate cellular origins in the embryonic CNS. Based on information obtained in Aims1/2, we will generate a floxed conditional reporter transgenic mouse Iine that will express the FACS-selectable marker GFP exclusively in astroglia. This will enable acute purification of astrocyte subsets for further discrimination of astrocyte heterogeneity. PUBLIC HEALTH RELEVANCE These studies will elucidate the mechanisms by which neural stem cells give rise to astrocytes and provide useful genetic tools for understanding the diverse roles of astrocytes in human development, with practical implications for diagnosis and treatment of human disorders such as epilepsy, brain cancer and neurodegeneration.