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Neuroscience Graduate Program at UCSF
Neurotransmitter Transport; Molecular genetics of ethanol sensitivity and tolerance
There are two areas of research in our laboratory. One is the identification and characterization of vesicular transporters that mediate the packaging of neurotransmitters into synaptic vesicles. A second project involves the genetic basis of sensitivity and behavioral adaptation to ethanol in the nematode Caenorhabditis elegans.
The exocytotic release of neurotransmitter is dependent on vesicular transport. Nevertheless, many of the proteins responsible for transport and the mechanisms regulating transport remain unknown. We have used a genetic approach to identify the vesicular GABA transporter of C. elegans. unc-47 mutant animals show increased accumulation of GABA in all GABAergic neurons, suggesting that they have a defect in transmitter release. Further pharmacological studies were consistent with a defect in vesicular packaging of GABA. unc-47 proved to encode a protein with multiple transmembrane domains which colocalizes with synaptic vesicles in GABAergic neurons. A rat homologue of unc-47, rVGAT, was then identified and found to be expressed in GABAergic neurons in rat brain. When expressed in PC12 cells, rVGAT was shown to confer GABA transport into synaptic-like microvesicles. unc-47 and rVGAT appear to be the first identified members of a novel family of vesicular transporters.
An additional 12 genes with sequence similarity to unc-47 have been identified in C. elegans. In collaboration with Erik Jorgensen's laboratory, we are attempting to define the substrates and bioenergetics of these putative transporters. Several of the unc-47-related genes appear to be likely to encode novel vesicular neurotransmitter transporters. As with unc-47, the further characterization of these genes may again lead to the identification of vertebrate homologues and to a better understanding of neurotransmitter packaging.
We have also found that unc-47 and rVGAT are related to a larger family of primitive amino acid transporters. Seven genes in Saccharomyces cerevisiae have sequence similarity to unc-47. Our results have revealed that these genes encode a new class of intracellular amino acid transporters in yeast that are bioenergetically and pharmacologically similar to the neuronal vesicular transporters. Further genetic and biochemical studies will allow us to understand the mechanisms regulating these transporters and the signals responsible for transporter localization.
A second area of research in the laboratory involves the identification and characterization of genes in C. elegans that mediate the acute and chronic behavioral responses to ethanol. Exposure to ethanol interferes with complex behaviors in many model systems, but it has been difficult to correlate effects of ethanol on behavior with observations of its effects on specific molecular targets. Recently, studies in Drosophila have suggested a link between ethanol sensitivity and a learning pathway. To better understand the effects of ethanol, we have identified a number of mutants in C. elegans that are resistant to ethanol intoxication or defective in the behavioral adaptation that occurs with prolonged ethanol exposure. Different sets of genes appear to mediate these processes. A molecular analysis of these genes may lead to a greater understanding of ethanol abuse and tolerance.
Link to Publications via PubMed
McIntire SL, Reimer RJ, Schuske K, Edwards R, Jorgensen E: Identification and Characterization of the Vesicular GABA Transporter. Nature 389:870-876, 1997.
McIntire SL, Jorgensen E and Horvitz HR: Genes required for GABA function in Caenorhabditis elegans. Nature 364:337-341, 1993.
McIntire SL, Jorgensen E, Kaplan J and Horvitz HR: The GABAergic nervous system of Caenorhabditis elegans. Nature 364:334-337, 1993.
McIntire SL, Garriga G, White J, Jacobsen D and Horvitz HR: Genes necessary for directed axonal elongation or fasciculation in C. elegans. Neuron 8:307-322, 1992.
Steven McIntire, M.D./Ph.D.
Phone
510-985-3100
Office Location
Ernest Gallo Clinic & Research Center
5858 Horton Street,
Suite 200
Emeryville, CA 94608
Other Websites
PIBS Website
Biomedical Sciences Graduate Program