Discipline: Biological Sciences
Onyinyechi Gift Ochiobi - University of Georgia
Co-Author(s): Devyn Oliver, Alison Philbrook, and Michael M. Francis, University of Massachusetts Medical School, Worcester, MA
Dendritic spines are small, dynamic protrusions that develop at excitatory synaptic sites on the dendrites of neurons. In mammals, dendritic spines are linked to learning and memory, and disruptions of these protrusions have been shown to be involved in several neurological disorders like autism, schizophrenia and Alzheimer’s disease. Although there are many studies on spine dynamics, our understanding of the genes involved in spine formation is very limited. In our laboratory, we identified dendritic spines in the model organism C. elegans, and generated a transgenic strain expressing GFP-tagged cholinergic receptors in the GABA DD motor neurons (AChR-GFP). We have focused our efforts on a single neuron, DD1, because the DD1 cell body and processes are spatially separated from the other DD neurons, enabling in vivo visualization of a single dendritic process. Cholinergic receptors in the DD1 dendrite are concentrated at the tips of spine-like dendritic protrusions and apposed by presynaptic vesicle markers, consistent with a synaptic localization. Using DD1 as a model, we are investigating genes that regulate dendritic spine formation. Using a spinning disc confocal microscope, we have found several candidate mutants with diffuse receptor distribution and we are now in the beginning stages of identifying these genes. Concurrently, we used a candidate gene approach to test how the genes pat-3 and lon-2, known axon guidance molecules, affect synapse development. Finally, we examined whether mutants that affect spine development also disrupt inhibitory signaling, using the acetylcholinesterase inhibitor aldicarb. We found that in pat-3 mutants, cholinergic receptors were diffusely clustered compared to wild type. Additionally, pat-3 mutants were hypersensitive to aldicarb, paralyzing faster compared to wild type. On the other hand, lon-2 mutants paralyzed slower. These results suggest that pat-3 may play a role in the expression of cholinergic receptors localized on dendritic spines, possibly altering dendritic spine morphology as well. For the future, we propose to use a heat shock promoter to temporally control expression of the pat-3 mutation. Regulated expression of mutant pat-3 at various life stages will provide a powerful tool in vivo for defining characteristics of dendritic spine morphogenesis.
References: Lai, K. O., & Ip, N. Y. (2013). Structural plasticity of dendritic spines: the underlying mechanisms and its dysregulation in brain disorders. Biochimica et Biophysica Acta (BBA)-Molecular Basis of Disease, 1832(12), 2257-2263.
Petrash, H. A., Philbrook, A., Haburcak, M., Barbagallo, B., & Francis, M. M. (2013). ACR-12 ionotropic acetylcholine receptor complexes regulate inhibitory motor neuron activity in Caenorhabditis elegans. The Journal of Neuroscience,33(13), 5524-5532.
Funder Acknowledgement(s): This study was fully funded by a NIH Grant #2 R25 HL092610-07 awarded to Deborah Harmon Hines, Ph.D., Program Director Summer Programs; Brian Lewis, Ph.D, Program Co-Director Summer Programs, University of Massachusetts Medical School, Worcester.
Faculty Advisor: Michael M. Francis,