During metazoan central nervous system (CNS) development, neural precursor cells undergo multiple rounds of asymmetric cell divisions producing either neuronal or glial progenitor cells with each division. Underpinning the formation of these uniquely fated neural cells are integrated gene expression regulatory networks that establish distinct functional cellular identities. The objective of this project is to identify and characterize transcription factor cis-regulatory networks controlling cell-identity decisions in the developing CNS. Although much is known about early developmental decision leading to the formation of neural precursor cells, little is understood about subsequent cell fate decisions that generate the unique functional identities of neurons or glia. The identification and functional characterization of the molecules and pathways/circuits underlying these cell-fate decisions remain a central goal of neurobiology. We have discovered that in the developing Drosophila CNS most, if not all, neural precursor cells transition through a series of synchronized gene expression programs during their asymmetric divisions. These temporal windows of gene expression are marked by the sequential expression of different transcription factors that, in turn help establish unique neural cell types. Our studies have revealed that the temporal domains are part of a global CNS regulatory network that coordinates cell fate-determining events in both the developing embryonic brain and in the ventral cord. These studies have also demonstrated that when cultured in isolation, Drosophila neural precursor cells maintain the correct temporal shifts in transcription factor gene expression. This cellular independence provides evidence that once neural lineage development is initiated no additional signaling cues between stem cells or adjacent tissues are required to trigger this cascade of regulatory gene expression. More recent studies from our lab have identified the cis-regulatory enhancers that control the expression of specific transcription factor genes during different temporal windows of neural precursor cell lineage development. Our evolutionary comparative DNA sequence analysis of these enhancers have revealed that they contain clusters of conserved DNA sequence blocks and many of these genus invariant sequences contain DNA-binding sites for transcription factors. Functional analysis of the conserved cis-regulatory DNA that controls one of the earliest expressed cell-identity determinants, the Zn-finger Nerfin-1 transcription factor, and the enhancers that regulates a late expressing cell-determinant, the Zn-finger gene castor, reveals that their dynamic expression in the developing nervous system is controlled by multiple independent enhancers that regulate different aspects of their spatial and temporal expression patterns. Using a new set of comparative genomics tools that we have developed (described in our accompanying project Identification of Functionally Related Drosophila cis-Regulatory DNA NS009413-02) we have identified additional early neural precursor enhancers based on their shared conserved sequences with nerfin-1 enhancer. We have also used these comparative genomic tools to identify potential Castor regulated enhancers that contain highly conserved DNA-binding sites for the Castor transcription factor. We are currently pursuing the characterization of these enhancers to determine if their cis-regulatory behavior is altered in different mutant transcription factor backgrounds. Additional information and publications describing this work can be obtained at our web site (http://intra.ninds.nih.gov/investigators.asp).
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