PhD, University of Wisconsin, Madison
Associate Professor, Department of Biological Sciences, College of Liberal Arts & Sciences
Office: 3067 SELE
Web Site: Aixa Alfonso Departmental Page
Our main goal is to characterize the role of helix loop helix proteins in the specification and function of neurons. We use the soil nematode Caenorhabditis elegans (C. elegans) as a model system to attain this goal, and employ genetic, physiological/behavioral, pharmacological, biochemical and molecular approaches to address it. Our studies have revealed that total loss of function (lof) in hlh-3, a gene encoding an Achaete/Scute-like basic helix-loop-helix (bHLH) protein in C. elegans, result in abnormal terminal differentiation of neurons with sex-specific functions. In hermaphrodite both the hermaphrodite specific neurons (HSNs) and the ventral type C motor neurons (VCs) fail to acquire their terminal differentiation features. In particular the HSNs fail to reach the vulval muscles. As a result, hlh-3 (lof) mutant animals are egg-laying defective (Egl). hlh-3 (lof) mutant males in turn are defective in male-specific behaviors. We have shown that the effects in males are pleiotropic but in all instances we have looked hlh-3 function is necessary for the development and terminal differentiation of neurons with sex-specific roles, some of these neurons are sex-specific but others are not. Little is known about the transcription factors that control expression of molecules and orchestrate mechanisms necessary to coordinate differentiation of the nervous system in a sex-specific context. In particular bHLH proteins of the Achaete-Scute family, such as HLH-3, have not been previously implicated as direct regulators of these processes. Our work should help elucidate how this process can be regulated by such a transcription factor. Another project in my laboratory has been to characterize the role of the monomeric clathrin adaptor protein UNC-11 in the sorting and trafficking of the synaptic vesicle (SV) protein synaptobrevin. Synaptobrevin is an integral SV protein essential for synaptic transmission. This project involved the molecular and functional characterization of unc-11. We cloned the unc-11 genomic region and characterized five alternatively spliced, full-length cDNAs derived from it. The deduced protein sequence of these isoforms suggested that unc-11 encodes the nematode homologue to the mammalian neuronal specific adaptor protein AP180. We have shown that UNC-11 is an ortholog of AP180. In vivo UNC-11 is enriched in the nervous system but is also detected in some non-neuronal tissues. In vitro UNC-11 assembles bovine clathrin into cages. In the nervous system UNC-11 appears to have two functions, to sort the synaptic vesicle component synaptobrevin and to regulate synaptic vesicle size. As a result, unc-11 mutants are defective in synaptic release. Our goal has been to characterize the relationship between structure and function of different UNC-11 isoforms and determine their function as adaptors and clathrin assembly proteins. We also used the gene and its products as a foothold to characterize and identify other components (known or novel) involved in synaptic vesicle biogenesis. As such we have identified two UNC-11A binding proteins, Ce EAST and Ce Hrs/Hrs-2. Characterization of their temporal and spatial expression pattern revealed that these proteins are expressed ubiquitously and in a dynamic pattern. We are interested in analyzing their role in the trafficking of integral synaptic proteins.