Hamlin, Joyce L.
Primary Appointment
Professor and Chair, Biochemistry and Molecular Genetics
Education
- BA, Biology, Case Western Reserve University
- PhD, Molecular Biology, University of California at Los Angeles, Los Angeles, CA
- Fellowship, Protein Chemistry, University of California at Irvine, Irvine, CA
- Fellowship, Cell Biology, Princeton University, Princeton, NJ
Contact Information
PO Box 800733
Jordan, 6240
Telephone: 434-924-5858
Email: jlh2d@virginia.edu
Website: http://www.people.virginia.edu/~jlh2d
Research Interests
Control of Mammalian Chromosomal DNA Replication, and DNA Damage, Repair and Genetic Instability in Cancer
Research Description
<b>Biochemistry, Molecular Biology, and Genetics<br/>
Cell and Developmental Biology</b><br/>
Our laboratory is interested in the control of mammalian chromosomal replication.
It has been known for a long time that DNA replication initiates at multiple sites
termed "origins of replication" along each DNA fiber. However, the precise
location or properties of even a single origin had not been determined. Several
years ago, we localized the first mammalian origin, which lies within the 55 kb
spacer region between the DHFR and 2BE2121 genes. This spacer is characterized
by the presence of a centered matrix attachment region (MAR). Using a two-dimensional
gel electrophoretic technique to precisely identify initiation sites, we have
shown that the origin corresponds to a very broad zone of potential sites scattered
throughout the intergenic region. There are several genetic elements whose functions
could contribute to the regulation of origin activity in this locus (e.g., a replicator,
the promoters of the two flanking genes, the MAR). To identify the responsible
controlling elements, we have devised a novel homologous recombination strategy
to specifically knock out or mutagenize any fragment within the intergenic region
or the two flanking genes. Our recent studies suggest that both the promoter and
the 3' end of the DHFR gene are required for proper origin function. Surprisingly,
however, the MAR is required to effect sister chromatid separation shortly after
the origin fires. Our long-range goals are to define the initiation reaction in
molecular terms by identifying both the cis- and trans-regulatory elements that
participate, and to reconstitute initiation in vitro.
<br/><br/>To gain insight into whether the DHFR origin is typical of other mammalian
origins, we have recently devised a very efficacious strategy for isolating
all of the active origins in the human genome. The resulting library has been
shown to be essentially pure. By comparing the sequences of the origin clones
to the human genome database, we will be able to determine their distribrutions
vis-a-vis active genes, and whether or not they share common sequence motifs.
<br/>
<b>Cancer Research - Molecular Medicine</b> <br/>
We are interested in the mechanism by which cells amplify DNA. DNA sequence
amplification is an important phenomenon that only occurs in tumor cells, which
usually lack critical damage-sensing pathways. Most human tumors have amplified
one or more cellular oncogenes, which are thought to confer a selective growth
advantage over surrounding normal cells. Thus, it is important to determine
how gene amplification occurs. In fluorescence in situ hybridization studies,
we have shown that the very first amplification events are mediated by chromosome
breaks, followed by sister chromatid fusion, bridge formation, and further breaks.
Thus, it is now clear why cells that lack the ability to sense DNA damage (i.e.,
breaks) are able to amplify oncogenes, while normal cells cannot. We are devising
new strategies to examine the products of the earliest amplification events
at the nucleotide sequence level to determine why and how cell breaks and fusions
occur. Our goal is to identify steps in the amplification process that could
be targets for chemotherapy.
<br/><br/><b>Cell and Molecular Biology Training Program</b><br/>
Our laboratory is interested in the control of mammalian chromosomal replication.
It has been known for a long time that DNA replication initiates at multiple
sites termed "origins of replication" along each DNA fiber. However,
the precise location or properties of even a single origin had not been determined.
Several years ago, we localized the first mammalian origin, which lies within
the 55 kb spacer region between the DHFR and 2BE2121 genes. This spacer is characterized
by the presence of a centered matrix attachment region (MAR). Using a two-dimensional
gel electrophoretic technique to precisely identify initiation sites, we have
shown that the origin corresponds to a very broad zone of potential sites scattered
throughout the intergenic region. There are several genetic elements whose functions
could contribute to the regulation of origin activity in this locus (e.g., a
replicator, the promoters of the two flanking genes, the MAR). To identify the
responsible controlling elements, we have devised a novel homologous recombination
strategy to specifically knock out or mutagenize any fragment within the intergenic
region or the two flanking genes. Our recent studies suggest that both the promoter
and the 3' end of the DHFR gene are required for proper origin function. Surprisingly,
however, the MAR is required to effect sister chromatid separation shortly after
the origin fires. Our long-range goals are to define the initiation reaction
in molecular terms by identifying both the cis- and trans-regulatory elements
that participate, and to reconstitute initiation in vitro.
<br/><br/>To gain insight into whether the DHFR origin is typical of other mammalian
origins, we have recently devised a very efficacious strategy for isolating
all of the active origins in the human genome. The resulting library has been
shown to be essentially pure. By comparing the sequences of the origin clones
to the human genome database, we will be able to determine their distribrutions
vis-a-vis active genes, and whether or not they share common sequence motifs.
<br/><br/>We are also interested in the mechanism by which cells amplify DNA. DNA sequence
amplification is an important phenomenon that only occurs in tumor cells, which
usually lack critical damage-sensing pathways. Most human tumors have amplified
one or more cellular oncogenes, which are thought to confer a selective growth
advantage over surrounding normal cells. Thus, it is important to determine
how gene amplification occurs. In fluorescence in situ hybridization studies,
we have shown that the very first amplification events are mediated by chromosome
breaks, followed by sister chromatid fusion, bridge formation, and further breaks.
Thus, it is now clear why cells that lack the ability to sense DNA damage (i.e.,
breaks) are able to amplify oncogenes, while normal cells cannot. We are devising
new strategies to examine the products of the earliest amplification events
at the nucleotide sequence level to determine why and how cell breaks and fusions
occur. Our goal is to identify steps in the amplification process that could
be targets for chemotherapy. <br/>