First, activation of the ribonucleoprotein enzyme telomerase, which uses a template sequence embedded within the RNA component of the enzyme to reverse transcribe telomeric sequences directly onto the chromosome termini ( Bryan et al., 1998 Reddel, 2014). Telomere maintenance is achieved by one of two defined mechanisms. However, oncogenic progression necessitates stabilization of the genome to overcome crisis, which is dependent upon activation of a telomere maintenance mechanism (TMM Maciejewski and de Lange, 2017). This process provokes the emergence of cancer cells with tumorigenic advantage. In some rare cases, cells are able to bypass replicative senescence by inactivating tumor suppressor pathways, allowing cells to proceed into crisis, which is characterized by catastrophic telomere shortening and widespread genome instability ( Reddel, 2010). Senescence provides a barrier to unlimited cellular proliferation, thereby fulfilling a potent tumor suppressive role ( Reddel, 2010). The telomere attrition that accompanies cellular proliferation eventually leads to an accumulation of critically short or unprotected telomeres, which signals the onset of replicative senescence ( Hayflick and Moorhead, 1961 Kaul et al., 2012). The negative correlation between telomere length and chronological age is attributed to terminal replication limitations, oxidative damage, and nucleolytic degradation ( Harley et al., 1990 Baird, 2008a). Inter-individual variability is also observed across the human population, superimposed on the well-established age-associated decline in telomere length ( Aubert and Lansdorp, 2008). In normal human somatic cells, telomeres range from 5–15 kb in length ( Pickett et al., 2011), and telomere length variability exists between individual telomeres and between different cell types. Telomeric DNA comprises repetitive sequences of the hexanucleotide TTAGGG n repeat unit, bound in a sequence-specific manner to the protein complex shelterin, and assembled into macromolecular structures called telomere-loops (t-loops Griffith et al., 1999 Blackburn, 2000 Van Ly et al., 2018). Telomeres are specialized nucleoprotein structures at the ends of linear chromosomes that function to protect the chromosome ends, thereby maintaining the stability of the genome. TCA is a simple and versatile technique to measure the distribution of individual telomere lengths in a cell population, offering improved accuracy, and more detailed biological insight for telomere length measurement applications. This not only precludes sampling bias, but also provides the potential for high-throughput applications and clinical development. TCA is amenable to semi-automated image analysis, and can be fully automated using the Genomic Vision molecular combing platform. TCA is performed on isolated DNA, negating the need for cycling cells. TCA was also used to accurately measure telomere length in healthy individuals, and to identify critically short telomeres in patients with telomere biology disorders. We used TCA to measure telomere erosion in primary human fibroblasts, and to detect telomere lengthening in response to activation of telomere maintenance pathways. We have developed the Telomere length Combing Assay (TCA) to measure telomere length on stretched DNA fibers. Multiple methods exist to measure telomere length and telomere content, but a simple and reliable technique to accurately measure individual telomere lengths is currently lacking. ![]() Consequently, telomere length is indicative of the proliferative capacity of a cell. Telomeric DNA is gradually eroded with each round of cell division, resulting in the accumulation of critically short or dysfunctional telomeres that eventually trigger cellular senescence. Telomeres are repetitive regions of DNA bound by specialized proteins at the termini of linear chromosomes that prevent the natural chromosome ends from being recognized as DNA double strand breaks.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |