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Telomere length and canis familiaris study can begin with a study of the genus Canis. Canis familiaris is a part of genus Canis, which is thought to be descended from the common wolf, has been habituated by man since ancient times and occurs in several breeds. There is significant disparity in life history among the diverse dog breeds, such as differences in endurance. Normally, smaller dog breeds tend to live longer and may age slower, however, some have argued that this might be because of artificial selection for high growth-rates. In addition, dogs are considered ole when they attain 12 years, but a few can live even more than 20 years.
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What are Telemeres?
Telomeres are explicit nucleoprotein structures that are present at the end of eukaryotic chromosomes. Their structures are well conserved across species and possess a huge number of tandem repeats of short G-rich sequences plus associated proteins. In case of vertebrates, the telomere repeat sequence is TTAGGG.
Though the structure of the telomeric repeat sequences are highly conserved, the number of repeats within the telomeric regions varies extensively. For example, canine telomeres possess 10 - 23 kbp as compared to the larger 10 -- 60 kbp present in mice. Besides interspecies variation, telomere lengths have been seen to differ broadly within similar species. This kind of variation may be linked with the age of the individuals concerned. One of the studies has shown a reduction in the standard length of human fibroblast telomeres with growing age. In addition, difference in telomere length may also be linked within the cell lines taken from a single unit and even among the chromosomes of a single cell.
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The Function of the Telomerase Enzyme
The telomerase enzyme plays a significant role in cellular propagation and tumorigenesis as well. Telonerase is an RNA directed DNA polymerase, which is composed mainly of and RNA subunit (TR) plus a catalytic-protein component (TERT). The protein component, TERT acts as a reverse transcriptase and catalyzes the addition of telomeric repeats onto the ends of chromosomes using the RNA subunit as a template.
Although both RNA and catalytic subunits are vital for telomerase activity, the TERT component of telomerase is considered to be the key determinant for enzyme activity as expression of TERT is chiefly restricted to cells with telomerase activity. The telomerase catalytic subunit from Canis familiaris, dogTERT consists of 1123-aa residues and possesses all the signature motif of the TERT family members. Sequence comparison of dogTERT with mammalian TERT proteins showed that dogTERT shows the utmost level of sequence resemblance to the human TERT protein, supporting the dog as a model system for telomerase-based studies. In addition, TERT mRNA expression is thought to be associated with telomerase activity in canine-cultured cells, quite similar to TERT expression in human cells.
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In regards to telomere length and canis familiaris, research studies have reported Telomerase activity in various canine tumors and dogTERT. With every DNA replication, telomeres get shorten because of the failure of DNA polymerase to replicate the ends of linear chromosomes. As a consequence, telomere attrition takes place and triggers cell growth arrest plus cellular senescence. However, cancer cells have developed the mechanism to get rid of telomere shortening, thus bypassing senescence and allowing persistence of proliferation. Well, the enzyme that is associated with this process by elongating sequence is a ribonucleoprotein complex, called as telomerase. In general, the telomerase activity is down regulated in somatic cells, and it is up regulated in actively dividing cells including malignant cells – a truth that suggest the role of telomerase in tumorigenesis.
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(Web): Isolation and expression of the reverse transcriptase component of the Canis familiaris telomerase -- http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6T39-4CJCXXB-3&_user=10&_coverDate=07/07/2004&_rdoc=1&_fmt=high&_orig=search&_sort=d&_docanchor=&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=394f95d03dfd1f8cbb2474f3f762d28c
(Web): Telomerase Reverse Transcriptase (TERT) Expression in Canine Mammary Tissues: A Specific Marker for Malignancy? -- http://ar.iiarjournals.org/content/29/1/319.full