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 the UNC-11/AP180 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 should 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 the HLH-3 protein (a transcription factor) has a role in the differentiation of sex specific neurons in both hermaphrodites and males. In hermaphrodites HLH-3 is necessary for the differentiation of the egg-laying motor neurons (HSNs) and in the absence of hlh-3 function mutant hermaphrodites are egg-laying defective (Egl) (Doonan et al., 2008). Mutant males are defective in specific mating steps and it appears some of the male-specific neurons mediating these behaviors are also affected in the differentiation (unpublished). Our emphasis is on characterizing how hlh-3 is regulated and identifying its downstream targets.
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.