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BIOGRAPHY:
Dr. Rubinstein is Investigator, Institute for Research on Genetic Engineering and Molecular Biology (CONICET), National Council of Science and Technology, and Professor, Department of Biology, University of Buenos Aires, Argentina. He received a Ph.D. in chemistry in 1989 from the School of Exact and Natural Sciences, University of Buenos Aires, and conducted postdoctoral research at the Vollum Institute, Oregon Health Sciences University, in Portland. In 1998 he received the Bernardo A. Houssay Prize from the Argentine Society for Biology and the Young Investigator Award from the International Society for Neurochemistry. This is his second HHMI International Research Scholar award. His current project involves functional studies of the D2 and the D4 dopamine receptors in the central nervous system, using mouse molecular genetics.
RESEARCH ABSTRACT SUMMARY:
The Modular Architecture of the Proopiomelanocortin Gene Promoter
Controls Neuronal-Specific Expression in the Brain
The proopiomelanocortin (POMC) gene is expressed at significant
levels in neurons of the arcuate nucleus of the hypothalamus and in
pituitary melanotrophs and corticotrophs. Neuronal processing of the
POMC prohormone produces melanocortins and beta-endorphin to activate
satiety and analgesia, respectively, whereas pituitary ACTH triggers a
widespread stress response, stimulating glucocorticoid release.
Pituitary-specific expression of the POMC gene is controlled by
cis-acting regulatory elements proximal to the TATAA box, and we
have demonstrated that neuronal-specific expression requires upstream
distal sequences. We have identified 4 kb present in the 5' flanking
region of the mouse POMC gene that targets eutopic expression of
reporter genes to POMC hypothalamic neurons. Comparison of this region
with the human POMC locus led us to the identification of two highly
conserved sequences we named nPOMC1 and nPOMC2. By using a
deletion/truncation analysis in transgenic mice, we showed that these
sites were critical for POMC gene expression in the brain. We have also
observed transgenic expression of EGFP in the dentate gyrus of the
hippocampus controlled by cryptic sequences dispensable for pituitary
or arcuate expression. The number of EGFP-positive cells in the dentate
gyrus increased after prolonged free running and decreased with age,
paralleling neurogenesis. EGFP-positive neurons had immature
properties, including short spineless dendrites and small action
potentials. Colocalization with BrdU indicated that EGFP-labeled
granule cells were approximately two weeks postmitotic. EGFP-labeled
cells expressed the neuronal marker PSA-nCAM, but not the glial marker
GFAP nor the interneuron marker parvalbumin. Thus, hippocampal
expression of EGFP driven by mouse POMC sequences is specific for
immature granule cells and provides a suitable marker with which to
study the integration of newly born granule cells into the adult
hippocampal circuitry. Taken together, these results demonstrate that
the POMC promoter contains scattered cis-acting regions that
function as independent modules to control cell-specific expression in
different cell types.
Photo: Dominic Chaplin, Pine Creek Pictures
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