Sandra M. Leal
The central nervous system (CNS) is a vast network built upon thousands of precisely interconnected neurons. Remarkably, this specialized system maintains the fidelity of neurotransmission and promotes the execution of simple and complex behaviors. Many neurological, neurodegenerative, and psychiatric disorders, including epilepsy, Parkinson’s disease, and schizophrenia, result from genetic defects that disrupt the organization and function of the nervous system. Thus, my broad, long-term research goal is to understand the basic mechanisms that coordinate the proper formation and organization of the CNS. To achieve this challenging goal, our laboratory employs the fruitfly, Drosophila melanogaster, as a powerful model system in which we can apply a battery of genetic, molecular, cell biological, and behavioral approaches to study CNS development and function in far greater detail than is possible in higher organisms. Further, a completely sequenced fly genome, the conservation of neural networks, and the advent of functional comparative genomics will enable us to translate our basic research in flies to higher organisms. At present, approximately 75% of identified genes implicated in the etiology of human diseases share an orthologous or related gene in the fruitfly. Thus, the simple fruitfly harbors the potential to help advance therapies to treat human diseases.
During embryonic CNS development in both flies and humans, formation of a neural circuit requires the functional integration of three processes: 1) neuronal specification, 2) axon pathfinding, and 3) synaptogenesis. Neuronal specification involves the generation of unique neuronal subtypes at specific times and locations in the nerve cord and brain of developing embryos. Axon pathfinding involves the subsequent ability of neurons to extend axons towards their targets, while synaptogenesis is a process by which axons form and sustain synaptic connections with their targets. These processes are highly complex and despite decades of research, the exact molecular mechanisms and genetic programs that mediate them are not completely understood. Thus far, preliminary results from a forward genetic screen I undertook in Drosophila have yielded a large number of gene candidates encoding some growth factor, neurotransmitter receptor, and cell cycle proteins that may play vital roles in regulating neuronal specification, axon pathfinding, and/or synaptogenesis. While we continue to identify these gene candidates, our lab is also functionally characterizing a pair of new neural fate specification genes identified from the forward genetic screen: neuromancer-1 (nmr-1) and neuromancer-2 (nmr-2).
Specifically, we are deciphering the genetic and molecular basis of nmr-1 and nmr-2 function as neural specification determinants. nmr-1 and nmr-2 belong to a large family of T-box transcription factor genes governing many developmental processes throughout all metazoan species. Although the roles of T-box genes in embryonic patterning, organogenesis, and limb development have been well characterized, their roles in regulating CNS development remain largely unexplored. As a postdoctoral fellow, I generated antibody probes to assay Nmr-1 and Nmr-2 protein expression in the CNS and together with other specialized tools developed in Drosophila, determined that Nmr-1- and Nmr-2 are expressed within interneuronal populations of the embryonic nerve cord. Very recently, the embryonic stem cell lineages that give rise to Nmr-1- and Nmr-2-positive interneurons have also been identified, completing the descriptive analyses of these T-box genes within the Drosophila embryonic CNS (Leal et al., in press 2008).
As a new investigator, my research will shift towards understanding nmr-1 and nmr-2 function in regulating CNS development. Studies on neuronal specification in Drosophila and vertebrates have identified a growing number of conserved transcription factors that act in a combinatorial manner to specify the fates of individual neurons. Based on these findings, it is plausible that nmr-1 and nmr-2 are members of a combinatorial transcription factor code that regulate gene expression within interneuronal subtypes where variation among subtypes is dependent upon permutations of distinct transcription factors. Generally, transcriptional regulation of gene expression also depends upon the interaction of transcription factors with co-regulatory proteins to activate or repress gene expression. However, completely deciphering Nmr-1 and Nmr-2 function in the context of neuronal specification requires not only an identification of co-regulatory effectors, but also the identification of downstream target genes since these genes have the potential to regulate specific neuronal properties including neurotransmitter synthesis and axon pathfinding behaviors. Given the complexity of this regulatory network, our lab is undertaking two major research goals: 1) to identify nmr-1- and nmr-2-interacting genes as well as Nmr-1- and Nmr-2-interacting proteins and 2) to identify nmr-1 and nmr-2 downstream gene targets. These comprehensive analyses will provide insight into the mechanisms by which nmr-1 and nmr-2 function as transcriptional regulators to specify neuronal fates and functions during CNS development.
Leal, S.M., Qian, L., Lacin, L., Bodmer, R., and Skeath, J.B. Neuromancer-1 and Neuromancer-2 Regulate Cell Fate Specification in the Developing Embryonic CNS of Drosophila melanogaster. Developmental Biology, in press (2008).
Neckameyer W.S. and Leal, S.M. Biogenic amines as circulating hormones in insects. In, “Hormones, Brain, and Behavior”, Academic Press, D. Pfaff, A. Arnold, A. Etgen, S. Farbach, R. Moss, and R. Rubin, Eds., in press (2008).
Leal, S., Kumar, N., and Neckameyer, W. GABAergic modulation of motor-driven behaviors in juvenile Drosophila and evidence for a non-behavioral role for GABA transport. Journal of Neurobiology. 61:189-208, 2004.
Leal, S.M. and Neckameyer, W.S. Pharmacological evidence for GABAergic regulation of specific behaviors in Drosophila melanogaster. J. Neurobiol. 50:245-261, 2002.