- Sensing and signaling environmental stress
-Organization of the neuromuscular junction - roles in C. elegans motility and human Limb-Girdle Muscular Dystrophy
Much of biology has been studied under highly controlled environments that reflect "ideal" conditions. However, most cells and organisms do not live under such conditions and are constantly facing environmental challenges from changing temperature, water availability, oxidative states, and exposure to various natural and man-made toxins. Our goal is to to define the molecular 'systems' that allow organisms to interact with their environment and activate appropriate physiolgical responses. Since the environment plays a major role in the etiology of many human diseases, our studies will provide important insights into the mechanisms of gene-environment interactions and could provide therapeutic mechanisms for treating a variety of environmentally influenced diseases.
We carry out our studies using genetic and genomic approaches in the nematode C. elegans. Worms make an outstanding model for studying the effects of the environment since their native environment is the soil, where they are exposed to all types of environmental stressors and toxins. Since worms are optically transparent, the expression of environmentally regulated GFP reporters are convenient phenotypic indicators for the activation state of stress responsive signaling pathways. These reporters, coupled with the powerful genetics of the worm, provide phenotypic assays for the selection of mutants affecting environmentally regulated signaling pathways. By characterizing these mutants, we hope to understand how C. elegans engages its environment and activates appropriate gene expression programs.
Coordinated motility drives many aspects of cellular and organismal movement. Movement is generated by the coordinated activation of excitatory and inhibitory neurotransmitter receptors at the neuromuscular junction (NMJ). NMJ dysfunction underlies many human disease states, such as myasthenia gravis and NMJ proteins are a common target of biological weapons, such as the nerve gas sarin. Because the anatomy and molecular biology of the synapse is conserved from worms to humans, C. elegans is a tremendous genetic system in which to define the molecular mechanisms of synaptic function.
We are utilizing genetic, genomic, electrophysiological, and mechanical engineering approaches to explore the mechanisms regulating C. elegans post-synaptic function. Through these studies, we have discovered a novel role for the C. elegans Dysferlin homolog fer-1. fer-1 was originally described as a gene that affected spermatogenesis in C. elegans. We have recently shown that fer-1 is expressed in muscle, where it functions to regulate the activity of post-synaptic acetylcholine receptors. In collaboration with the Khurana Lab at UPENN, we have also found that the synaptic function(s) of Dysferlin are also conserved in mice. These findings have led us to hypothesize that the Dysferlin protein plays an evolutionarily conserved role in the regulation/organization of post-synaptic neurotransmitter receptors. This hypothesis has significant translational implications, which we are currently testing in mouse models of the disease.
Through our studies of fer-1, we discovered that worms carrying mutations in genes affecting synaptic transmission frequently exhibit relatively normal movement. We reasoned that while their movement might be superficially normal, the mechanics of movement was likely to be altered. To test this hypothesis, we are collaborating with Dr. Paulo Arratia and Dr. Prashant Purohit in the UPENN Department of Mechanical Engineering to quantiatively describe the mechanics of C. elegans motility. Using fluid mechanics, MATLAB-based image quantification, and mathematical modeling approaches, we have been able to demonstrate that C. elegans fer-1 mutants do indeed generate less muscle force than wild type animals. Currently, we are utilizing this technology to perform biomechanical 'profiling' of many different NMJ mutants. We hypothesize that multiparametric biomechanical profiling will provide a powerful phenotypic tool for the quantiative analysis of C. elegans motility mutants.