We are using the nematode Caenorhabditis elegans to investigate
aspects of nerve cell development and function. The wealth of developmental,
anatomical, genetic, and molecular information available for C. elegans provides a powerful and
multifaceted approach to these studies. Our work has focused on the study of a
set of six neurons that are the sensory receptors for gentle touch (the touch
cells), to address two questions: 1) How is neuronal cell fate determined? and
2) What is the molecular basis of mechanosensation, a sensory modality that
underlies a variety of senses(e.g.,
touch, hearing, and balance)? We also work on neuronal degeneration,
microtubule structure and function, and channel structure and function.
Facilitating these studies is the development of new experimental methods, such
as Green Fluorescent Protein and reconstituted GFP as gene and protein markers,
a two component system (recCaspase) to selectively kill particular cells, a method to generate and insert temperature-sensitive strains for virtually any C. elegans gene and a method for cell-specific RNAi.
PubMed Listing of Dr. Chalfie's Publications
We initially approached touch cell development by
mutational analysis, obtaining more than 450 mutations (in 17 genes) that
produce a touch insensitive phenotype. These touch genes are needed for the
generation, specification, and function of the cells. The first two groups
contain genes that regulate touch cell development, and the last group
(function) contains genes that are developmental targets of this regulation.
Many of the genes that regulate touch cell differentiation are transcription
factors. In addition we have identified several other genes that in combination
with these genes specify the number and differentiation of the touch cells.
Twelve touch genes are needed for touch cell function. Using genetics,
molecular biology, and electrophysiology, we have identified a transduction
channel complex with proteins encoded by four of these genes that underlies the
touch response in these cells. Two of the proteins, MEC-4 and MEC-10, form the
pore of the channel; the other two proteins, MEC-2 and MEC-6 are
associated with the pore-forming proteins and are essential for channel
activity. MEC-2 is of particular current interest because it is part of a large
family of cholesterol-binding proteins. The
channel complex is localized as puncta along the touch receptor neuron process.
This localization requires components in the extracellular matrix. Two of these
components, MEC-1 and MEC-9 are made the touch cells; a third, the collagen
MEC-5, is not.
We are currently studying how these and other genes
expressed in these cells act to transduce touch. Our current model is that the
channel complex is associated with the extracellular matrix. This tethering can
lead to movement of the complex in the membrane leading to its opening.