Gene Expression in the Brain
The goal of the laboratory is to
understand the nervous system through
knowledge of the structure and properties of
proteins that mediate its functions. Our
general experimental approach is to use
selective cloning and other molecular
techniques to identify molecules of
interest, to define their structures, and,
ultimately, to test their functions. In
particular, we are interested in molecules
that are selectively expressed in neural
tissues or in specific neural cell types, on
the assumption that such molecules are
likely to mediate functions of importance to
the nervous system. These experimental
strategies have lead to the characterization
of two proteins, myelin-associated
glycoprotein and proteolipid protein, that
compose myelin, the insulating sheath that
is wrapped around axons; the proteolipid
protein gene was shown to be disrupted by a
single base mutation in the mouse mutant
jimpy, which is unable to synthesize myelin.
Other studies have focused on proteins
expressed in astrocytes, the predominant
cell type in the vertebrate brain; for
example, glial fibrillary acidic protein
(see figure) is a structural protein found
almost exclusively in astrocytes. A third
area of interest has been genes expressed in
neurons at critical stages of development,
such as axonal growth or synaptogenesis;
this work has included the analysis of the
expression of isotypes of tubulin and the
synapse-associated protein SNAP-25.
More recently, we have begun to analyze
gene expression in cells that play key roles
in the neural response to injury. Several
cell types are recruited following injury to
the central nervous system: microglia are
activated from a quiescent state,
circulating macrophages invade the injury
site, and astrocytes undergo a
characteristic proliferative and
morphological change ("reactive gliosis").
Our goals are to identify genes that encode
products essential for the injury response
and to characterize markers for these cell
populations. Using cultures of purified glia
cells as a source of mRNAs, we have applied
two complementary approaches to identify
cDNA clones encoding molecules of interest:
subtractive cloning and differential display
techniques. In particular, initial studies
have focused on the protein tyrosine kinase
and tyrosine phosphatase gene families,
which have been implicated in signal
transduction and cell differentiation
pathways. These studies are the starting
point for characterization of the
corresponding mRNAs and functional studies
of the encoded proteins. In addition to
providing potential marker proteins for the
various cell populations, these results
indicate diversity among the signaling
pathways utilized by the cells involved in
the neural response to injury. |
