Regulation of neuronal polarity and acquisition of neuronal fate in C. elegans

The work that goes on in my laboratory attempts to elucidate the mechanism(s) involved in (1) sorting and trafficking of neuronal specific proteins (cell biology) and (2) specification of neuronal identity (development and differentiation). Our approach has been to isolate and characterize mutations that disrupt these processes with the goal of understanding the role of the wild type products in the process. Specifically we use the soil nematode Caenorhabditis elegans (C. elegans) as a model system to analyze (1) the role of the clathrin adaptor protein UNC-11 (C elegans AP180) in the trafficking of the synaptic vesicle (SV) protein synaptobrevin (SNB) and (2) the role of basic helix loop helix proteins such as HLH-3 in the specification of motor neurons.

Our analysis of unc-11 mutants has revealed that this protein is necessary to regulate the assembly of clathrin coats and is involved in the trafficking or sorting of the integral SV protein SNB (Nonet et al., 1999). Synaptobrevin is essential for generating fusion-competent SVs; it is one of the three components in the complex that mediates SV fusion. The observation that UNC-11 has a role in trafficking and sorting of SNB is novel and has raised additional questions with respect to the mechanism by which this clathrin assembly protein promotes the trafficking or sorting of this essential SV protein. Moreover, since all cells have proteins homologous to UNC-11 [AP180 is in the nervous system and CALM is in the trans-Golgi network (TGN) and at the plasma membrane of all cells (Tebar et al., 1999)], and SV formation and SV recycling are specialized types of membrane recycling, then, our studies will also shed light into the mechanisms of the fundamental process of membrane trafficking and protein sorting by this family of monomeric assembly proteins in cells in general.

Our analysis of hlh-3 mutants has revealed that this protein has a role in the differentiation of the egg-laying motor neurons HSN and possibly VC4 and VC5. Although hlh-3 is expressed through out embryonic development its expression becomes restricted to the HSNs and VCs in the fourth larval stage. The fact that hlh-3 mutants are egg-laying defective suggests that HLH-3 is necessary for the differentiation of these neurons. Our emphasis is on defining the site of action of the gene and identifying the downstream targets.

Representative Publications

Tokarev, A., Alfonso, A., and Segev, N., 2009. Chapter 1: Overview of Intracellular Compartment and Trafficking Pathways. In Trafficking Inside Cells: Pathways, Mechanisms and Regulation, Landes BioScience Springer.

Doonan, R., Hatzold, J., Raut, S, Conradt, B. and Alfonso, A., 2008. HLH-3 is a C. elegans Achaete/Scute protein required for differentiation of the hermaphrodite-specific motor neurons. Mechanisms of Development 125:883-893.

Ved, R., Saha, S., Westlund, B., Perier, C., Burnam, L., Sluder, A., Hoener, M., Rodrigues, C.M., Alfonso, A., Steer, C., Liu, L., Przedborski, S. and Wolozin, B., 2005. Similar patterns of mitochondrial vulnerability and rescue induced by genetic modification of alpha-synuclein, parkin, and DJ-1 in Caenorhabditis elegans. J Biol. Chem. 280(52):42655-42668.