Phone: 301-594-7419
Fax: 301-402-3095
Biography:
Dr. Florence Davidson received her Ph.D. from the University of California at San Diego, where she studied the structure and mechanism of phospholipase A2 with Dr. Edward Dennis. She received postdoctoral training in the laboratory of Dr. H. Gobind Khorana at the Massachusetts Institute of Technology, studying the mechanism of light-induced conformational change in rhodopsin. She then completed further postdoctoral work with Dr. Hermann Steller, also at M.I.T., studying the molecular genetics of apoptosis in Drosophila. She joined the Laboratory of Biochemistry in March, 1998.
Research:
Molecular Mechanism of Apoptosis in Terminally Differentiated Neurons
Apoptosis is a gene-directed form of cell death
that is essential to the correct development and maintenance of multicellular
organisms. When properly regulated, apoptosis eliminates cells that are
injured, extranumerous, or have completed or failed their biological programs.
Inappropriately stimulated apoptosis leads to tissue degeneration. Inappropriate
inhibition leads to cancer. Our goal is to determine the molecular mechanism
of apoptosis in a model system relevant to human disease. The biological
process we are studying is the premature apoptosis of photoreceptor neurons
in the retinas of adult Drosophila melanogaster. The flies we are studying
are born with apparently normal retinas, but display age dependent degeneration
of the retina in response to light. This phenomenon mimics a number of
human retinopathies that cause blindness, and is due in some cases to the
exact same mutation in homologous proteins of the two organisms. We have
chosen to use Drosophila as a model organism because it is well-suited
to biochemical and genetic techniques of investigation. A large body of
evidence indicates that all animal cells regardless of phyla contain a
common core program for apoptosis. This core program is stimulated by different
signals in different cells. Among all possible cells in which apoptosis
can be investigated, terminally differentiated cells lack the complicating
factor of a cell cycle. So, the analysis of cell death is simpler therein.
Retinal photoreceptor neurons have the additional advantage of large relative
abundance and easy accessibility for both functional assays and genetic
manipulation. About 30 % of all cases of autosomal dominant retinitis pigmentosa
(ADRP) are caused by mutations in the coding region of the human rhodopsin
gene. When expressed in heterologous systems, most of these mutant proteins
apparently misfold. In studies of the relationship between rhodopsin domains
that are important for folding and their role in light-activated conformational
change, I found that a conserved extracellular pair of cysteines previously
thought to be essential for folding could actually be mutated to alanines
with no significant effect on ground state structure. Characterization
of these mutants revealed that the conserved disulfide bond of the serpentine
receptor superfamily regulates the formation and decay rates of the physiologically
active signaling intermediate, without affecting stabilities or kinetics
of earlier conformational intermediates. By contrast, larger amino acid
substitutions at these sites did cause misfolding upon COS cell expression.
It was subsequently found that some of these
mutations of the conserved cysteine pair cause early and severe ADRP. Moreover,
the equivalent mutations in fly rhodopsin cause autosomal dominant retinal
degeneration. I found that the mode of cell death induced by these and
other mutations in photosignaling proteins of Drosophila was apoptosis.
Apoptosis in these systems was light dependent and could be blocked by
expression in transgenic flies of the caspase inhibitor protein p35. We
therefore know that the mechanism of cell death includes caspase activation.
Our ongoing work is aimed at identifying the upstream and downstream components
of this pathway. For this we will be using a combination of molecular biological,
genetic and biochemical techniques. The rescue observed with p35 was functional
as well as morphological, and this holds out the promise of therapeutic
benefits arising from the discoveries we are able to make in this system.
Citations:
Davidson, FF, et al. Proc Natl Acad Sci 1994;91:4029-33.
Davidson, FF, et al. Nature 1998; 391: 587-91.
Mollaaghababa, R, et al. Proc Natl Acad Sci 1996;93:11482-6.
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This page was last updated on June 20, 2001, by Zoraida
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