Dr. Peter Lansdorp, Research Supervisor (Medicine)
Dr. Ann Rose, Research Supervisor (Medical Genetics)
Dr. Robert Kay (Medical Genetics)
Dr. Steven Jones (Medical Genetics)
EXAMINING COMMITTEE
Chair: Dr. Ross Macgillivray (Biochemistry)
Supervisory Committee: Dr. Peter Lansdorp, Research
Supervisor (Medicine), Dr. Ann Rose, Research Supervisor (Medical Genetics)
University Examiners: Dr. Don Riddle (Medical Genetics), Dr.
George Mackie (Biochemistry and Molecular Biology)
External Examiner: Dr. Shawn Ahmed, Department of Genetics.
University of North Carolina, Chapel Hill, NC, USA.
ABSTRACT
Mutations in genes that function in maintaining genome
stability, such as
those involved in DNA replication, DNA repair, or
cell-cycle checkpoints, may lead to extensive genetic alterations, leading to the so called
“mutator phenotype”. In Caenorhabditis elegans, the mutant strain dog-1(gk10)
displays such a phenotype. Molecular characterization of the strain revealed genome
wide deletions involving a very specific type of repeat, consisting of poly-G tracts
paired with poly-C tracts((G/C)n). Deletions have unique structural characteristics
and only occurred in roughly half of the (G/C)n tracts examined. DOG-1 contains
the seven signature motifs of a DExH-box helicase. Based on these
observations, a model was proposed in which the putative helicase DOG-1 is required for
unwinding secondary structures formed by G-rich DNA during lagging strand synthesis. In
the absence of functional DOG-1 such secondary structures may lead to deletions via
an unknown mechanism. Because telomeric DNA is capable of forming
secondary structure in vitro, dog-1(gk10) was examined for telomere defects. In
order to be able to measure telomere length in C. elegans with higher
sensitivity and accuracy a PCR-based technique, called STELA was adapted to C.
elegans thereby enabling chromosome specific telomere length measurement from
as few as a single worm. Telomere length analysis using this technique revealed
the presence of short telomeres thatwere clearly distinct from the bulk
telomere length distributions in different wild-type strains. This suggests
that processes other than end-replication losses and telomerase-mediated
lengthening contribute to telomere length heterogeneity in C. elegans. An
increased frequency of such short outlying telomeres was observed in the
telomerase mutant trt-1, indicating that besides replicative loss, telomerase
is also required for preventing large scale loss of telomeric DNA. Analysis of
telomere length in dog-1(gk10) using STELA showed no significant shortening of
average telomere length or increased frequency of short telomeres. Therefore,
DOG-1 appeared to be required specifically for the maintenance of (G/C)n tracts
within the genome.
PUBLICATIONS
Cheung, I., Schertzer, M., Baross, A., Rose, A.M.,
Lansdorp, P. M. & Barid, D.M. (2004) Strain-specific telomere length revealed by single
telomere length analysis in Caenorhabditis elegans. Nucleic Acids Res. 32, 3383-3391.
Cheung, I., Schertzer, M., Rose, A. & Lansdorp, P. M.
(2002) Disruption of dog-1 in Caenorhabditis elegans triggers deletions upstream of
guanine-rich DNA. Nat. Genet. 31, 405-409.
PRESENTATIONS
2005/5 Characterization of the telomerase mutant, trt-1,
in C. elegans. Cold
Spring Harbor Meeting on Telomeres and Telomerase, Cold
Spring Harbor, NY (oral presentation)
2004/11 Studies of Telomere Biology in C. elegans Using
Single Telomere Length Analysis (STELA). AACR special conference on the Role of
Telomeres
and Telomerase in Cancer Research, San Francisco, CA.
(Oral presentation)
2004/8 Strain-specific telomere length revealed by single
telomere length analysis in Caenorhabditis elegans. West Coast Worm Meeting, Santa
Barbara, CA. (Poster)
2004/5 Strain-specific telomere length revealed by single
telomere length
analysis in Caenorhabditis elegans. 4th Canadian Symposium
on Telomeres and Telomerase, Sherbrooke, Quebec. (Oral
presentation)
2003/11 The putative C. elegans helicase DOG-1 is required
for genomic stability. 2003 BC Cancer Agency conference, Vancouver, BC. (Oral presentation)
2003/3 The putative C. elegans helicase DOG-1 is required
for genomic stability. Gordon Conference on Biology in Aging, Ventura, CA.
(Poster)
2002/5 Genetic instability and telomere shortening in a C.
elegans helicase. 3rd Canadian Symposium on Telomeres and Telomerase, Vancouver,
BC.
(Oral presentation)
AWARDS
2003/9-present CIHR Canada Graduate Scholarship Doctoral
Award MSFHR Incentive Award
2002/9-2003/8 Roman M Babicki Fellowship
2001/1-2002/8 UBC University Graduate Fellowship
GRADUATE STUDIES
Field of
Study: genomic instability and telomere biology
