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Duncan M Baird

Publications and source records attributed to Duncan M Baird.

11 recordsLinked to original sources
PubMed2026

Mitotic microhomology-mediated break-induced replication promotes chromoanasynthesis.

Chromoanasynthesis is a form of complex chromosomal rearrangement (CCR) commonly detected in cancers and congenital disorders, but the mechanism underlying its generation remain elusive. Here we develop a single-molecule long-read DNA sequencing approach to characterise ultra-complex mutational events, consistent with chromoanasynthesis, occurring at shortened telomeres and sub-telomeric DNA double-strand breaks in human cells. Our data reveal that chromoanasynthesis is generated by microhomology-mediated break-induced replication (MM-BIR), occurring specifically in mitosis. Surprisingly, this mitotic pathway involves a collaboration between microhomology-mediated end-joining (MMEJ) and BIR, where MMEJ proteins initiate a Polδ-dependent BIR pathway that is regulated by PIF1, POLD3 and PCNA. This pathway is highly prone to template switching and can generate dramatic amplification of genomic loci in a single event. Our findings help explain the extreme mutagenic nature of chromoanasynthesis and establish mitotic MM-BIR as a key driver of CCRs, with important implications for the origin of cancers and congenital disorders.

Humans↗
PubMed2006

Telomeres.

The role that telomere biology may play in the human ageing process is of a significant interest to many laboratories around the world. In this, the first of a series of yearly reviews on telomeres and ageing, I review a small selection of papers published between July 2005 and June 2006 that maybe of direct relevance to the gerontology research community.

Aging↗
PubMed2006

Structural stability and chromosome-specific telomere length is governed by cis-acting determinants in humans.

Single telomere length analysis (STELA) of the XpYp telomere has revealed extensive allelic variation and ultra-short telomeres in senescent cells. Superimposed on end-replication losses are additional mutational events that result in large-scale changes in telomere length. In order to establish if the dynamics of the XpYp telomere are typical of human telomeres, here we describe an analysis using STELA of the telomeres of 2p, 11q, 12q, 17p and XpYp. The dynamics of telomere loss (erosion rates and stochastic length changes) was conserved among 2p, 11q, 12q and XpYp within the same cell strains and was dependent on the replicative kinetics of the cells in culture. However, of the telomeres analysed, the telomere of 17p was more stable with a striking paucity of large-scale length changes, and exhibited the shortest recorded allelic distribution (300 bp) in senescent cells and displayed a general, but not absolute, trend towards being the shortest telomere. Ectopic over-expression of hTERT homogenized both allelic and chromosome-specific telomeric distributions. However, telomerase-expressing cancer cells displayed both allelic variation and chromosome-specific telomere length, with 17p displaying the shortest allelic telomere length. Although other telomeres in the genome may share the properties of 17p, these data suggest that physiological levels of telomerase allow differential telomere length regulation and indicate the presence of cis-acting factors that govern both telomeric stability and chromosome-specific telomere length in the presence of telomerase.

Alleles↗
PubMed2005

Telomere instability in the male germline.

Telomeres play a key role in upholding the integrity of the genome, and telomerase expression in spermatogonial stem cells is responsible for the maintenance of telomere length in the human male germline. We have previously described extensive allelic variation in somatic cell telomere length that is set in the zygote, the ultimate source of which may be the germline. This implies that despite telomerase activity, substantial telomere length variation can be generated and tolerated in the germline; in order to investigate this further, we have examined the nature of telomere length variation in the human male germline. Here, we describe an analysis of both genome-wide telomere length and single molecule analysis of specific chromosome ends in human sperm. We observed individual specific differences in genome-wide telomere length. This variation may result from genetic differences within the components that determine the telomere length setting of each individual. Superimposed on the genome wide telomere length setting was a stochastic component of variation that generates germ-cells containing severely truncated telomeres. If not re-lengthened during early embryogenesis, such telomeres may limit the replicative capacity of cells derived from the zygote and have the potential to create fusagenic chromosomes, unbalanced translocations and terminal micro-deletions. These data may have implications for the genetic determination of ageing, genetic disease and fertility.

Age Factors↗
PubMed2005

New developments in telomere length analysis.

Telomeres provide an essential 'capping' function, which prevents the natural end of a chromosome from being recognised as a simple dsDNA break. The biology of human telomeres is inextricably linked with both cancer and ageing. As such there is considerable interest in determining the length of these essential and dynamic structures. Here I review, from the standpoint of ageing research in humans, the current situation with regards to technologies available to determine telomere length in human cells and tissues.

Base Sequence↗
PubMed2005

Prevention of accelerated cell aging in Werner syndrome using a p38 mitogen-activated protein kinase inhibitor.

We investigated the role of p38 mitogen-activated protein kinase (MAPK) signalling in the accelerated aging of Werner Syndrome (WS) fibroblasts by use of SB203580, a cytokine-suppressive anti-inflammatory drug that targets p38 activity. SB203580 treatment reverts the aged morphology of young WS fibroblasts to that seen in young normal fibroblasts. In addition, SB203580 increases the life span and growth rate of WS fibroblasts to within the normal range. In young WS cells, p38 is activated coincident with an up-regulation of p21(WAF1), and a reduction in the levels of both activated p38 and p21(WAF1) are seen following treatment with SB203580. As these effects are not seen in young normal cells, our data suggest that the abbreviated replicative life span of WS cells is due to a stress-induced, p38-mediated growth arrest that is independent of telomere erosion. With some p38 inhibitors already in clinical trials, our data suggest a potential route to drug intervention in a premature aging syndrome.

Actins↗
PubMed2004

Strain-specific telomere length revealed by single telomere length analysis in Caenorhabditis elegans.

Terminal restriction fragment analysis is the only method currently available for measuring telomere length in Caenorhabditis elegans. Its limitations include low sensitivity and interference by the presence of interstitial telomeric sequences in the C.elegans genome. Here we report the adaptation of single telomere length analysis (STELA) to measure the length of telomeric repeats on the left arm of chromosome V in C.elegans. This highly sensitive PCR-based method allows telomere length measurement from as few as a single worm. The application of STELA to eight wild-type C.elegans strains revealed considerable strain-specific differences in telomere length. Within individual strains, short outlying telomeres were observed that were clearly distinct from the bulk telomere length distributions, suggesting that processes other than end-replication losses and telomerase-mediated lengthening may generate telomere length heterogeneity in C.elegans. The utility of this method was further demonstrated by the characterization of telomere shortening in mrt-2 mutants. We conclude that STELA appears to be a valuable tool for studying telomere biology in C.elegans.

Animals↗
PubMed2004

Normal telomere erosion rates at the single cell level in Werner syndrome fibroblast cells.

The aim of this study was to investigate whether the accelerated replicative senescence seen in Werner syndrome (WS) fibroblasts is due to accelerated telomere loss per cell division. Using single telomere length analysis (STELA) we show that the mean rate of telomere shortening in WS bulk cultures ranges between that of normal fibroblasts [99 bp/population doubling (PD)] and four times that of normal (355 bp/PD). The telomere erosion rate in the fastest eroding strain slows in the later stages of culture to that observed in normal fibroblasts, and appears to be correlated with a reduction in the heterogeneity of the telomere-length distributions. Telomere erosion rates in clones of WS cells are much reduced compared with bulk cultures, as are the variances of the telomere-length distributions. The overall lack of length heterogeneity and the normal erosion rates of the clonal populations are consistent with simple end-replication losses as the major contributor to telomere erosion in WS cells. We propose that telomere dynamics at the single cell level in WS fibroblasts are not significantly different from those in normal fibroblasts, and suggest that the accelerated replicative decline seen in WS fibroblasts does not result from accelerated telomere erosion.

Cells, Cultured↗
PubMed2004

The extent and significance of telomere loss with age.

By imposing a limit on the proliferative life span of some human cell types, telomere loss and the subsequent onset of replicative senescence have been proposed to contribute to age-related disease. Although there is a large body of in vitro data to reveal the mechanisms by which telomere erosion triggers senescence, technical limitations have hampered our ability to understand the full extent of telomere erosion in vivo. Thus far, we have evidence of age-related telomere loss; however, the lack of resolution of existing technologies does not allow us to determine if telomere erosion is extensive enough to trigger replicative senescence in vivo. This coupled with the considerable interindividual heterogeneity, and the overlap in telomere lengths between young and elder individuals, render any correlation weak and the significance unclear. However, recent technical developments, including adaptations of quantitative telomere fluorescence, in situ hybridization (Q-FISH), and the PCR-based single telomere length analysis (STELA), have increased the resolution of telomere length analysis. These technologies promise to provide the evidence required to address the full extent and significance of telomere loss in the human aging process. Here, we review published data on the dynamics of telomere erosion with age in the human body.

Aging↗
PubMed2003

Extensive allelic variation and ultrashort telomeres in senescent human cells.

By imposing a limit on the proliferative lifespan of most somatic cells, telomere erosion represents an innate mechanism for tumor suppression and may contribute to age-related disease. A detailed understanding of the pathways that link shortened telomeres to replicative senescence has been severely hindered by the inability of current methods to analyze telomere dynamics in detail. Here we describe single telomere length analysis (STELA), a PCR-based approach that accurately measures the full spectrum of telomere lengths from individual chromosomes. STELA analysis of human XpYp telomeres in fibroblasts identifies several features of telomere biology. We observe bimodal distributions of telomeres in normal fibroblasts; these distributions result from inter-allelic differences of up to 6.5 kb, indicating that unexpectedly large-scale differences in zygotic telomere length are maintained throughout development. Most telomeres shorten in a gradual fashion consistent with simple losses through end replication, and the rates of erosion are independent of allele size. Superimposed on this are occasional, more substantial changes in length, which may be the consequence of additional mutational mechanisms. Notably, some alleles show almost complete loss of TTAGGG repeats at senescence.

Alleles↗