IntroductionTelomeres in their telomere structure when compared to

IntroductionTelomeres are structures located at the end of chromosome arms possessing a repetitive (TTAGGG) DNA-protein complex, with its length maintained by telomerase activity. Telomeres form closed chromatin loops or t-loops that arise from the invasion of a 3′ overhang on the G rich strand of the telomere into the double-stranded region of the TTAGGG tract (Griffith et al., 1999; Nikitina and Woodcock, 2004; Wei and Price, 2004). Telomere-associated proteins such as shelterin proteins defend the telomeres from deoxyribonucleic acid (DNA) damage response pathways which triggers senescence. The study of telomeres is critical as it aids in the research of cancer (oncogenesis) and aging (senescence) in humans. As when the telomeres shorten, they are no longer capable of cellular division but are still metabolically active, and this causes tumors to generate (tumorigenesis). This specific study on telomere maintenance, mechanism and function has been carried on mouse telomeres to a detailed degree, but there are fundamental differences in their telomere structure when compared to human’s (Swanberg et al., 2010). This makes the mouse a less optimal candidate of comparison when studying human telomeres. Chickens on the other hand have a similar set of chromosomes and genetic characteristics compared to humans such as Telomerase Reverse Transcriptase (TERT) and they possess a highly conserved telomere genome with distinctive features, enhancing its suitability for the study. Also, the cell and genetic lines of the chicken exhibit unique variations in distribution and heterogeneity of telomeric arrays as well as diversity in telomerase activity profiles and expression of telomerase components, these distinctive features makes the chicken a suitable organism in the study of telomere maintenance, mechanism, functions and dysfunctions. The aging process of the chicken is also similar to that of humans, thus allowing a more accurate comparison. Henceforth, the objective of this article is to discuss how chicken telomeres are used in the study of aging (senescence) in humans. Some methods used in the study are: Fluorescence In-Situ Hybridisation and Southern Blot.Experimental SystemThe reason why this particular study is so crucial is attributed to the link between telomeres, telomerase and aging. Telomeres shorten in length with each cellular division the cell undergoes and the issue with that is that excessive shortening of the telomeres results in dysfunctional telomeres. These dysfunctional telomeres then elicits DNA damage responses, triggering senescence or aging on a cellular level. Through this process, chromosomal instability is induced, contributing to genomic instability which could lead to oncogenesis or cancer, cells with oncogenic mutations bypass aging and goes on to develop cancer in the individual. However, with telomerase activity maintaining telomere length, as telomerase activity decreases with age, an increase in division-dependent telomere shortening can be observed. This phenomenon increases the possibility of excessive telomere shortening which could potentially expedite aging and increase the potential for development of oncogenesis. Due to the fact that chickens possess a distinctive telomere genome, research would be facilitated and it would be easier to study their telomeres. The methods used to observe telomere biology are :Fluorescence In-Situ Hybridisation which is a type of hybridization that uses a fluorescent labeled complementary DNA or RNA probe to localize specific DNA or RNA sequences in tissues or cells. A fluorescent probe sequence which is complementary to the target sequence or a modified copy of the target sequence that can be mae fluorescent later in the procedure is prepared. Denaturation of the target and probe sequence is done with heat or chemicals to break off existing hydrogen bonds between the DNA double helix structure, allowing new hydrogen bonds to form between the probe and target sequences, hybridising the sequences in a complementary manner identical to how the original DNA helix structure is. The site of hybridisation is then ready for viewing under the electron microscope. This method allows research to be focused on specific cells, a crucial step in facilitating the understanding of the organization, regulation and function of genes. This allows different gene sequences to be hybridised at the same time, enabling easier comparison of the sequences, enabling the classification of avian telomeric arrays to be published. Southern Blot is a molecular technique typically used to identify specific DNA sequences in a sample. The procedure begins with cleaving the DNA into smaller fragments with the aid of restriction enzymes to ensure clear data (DNA Restriction). The DNA fragments are run through agarose gel in different wells, with the gel separating the fragments by size and charge, if the fragments were to be larger than 15kb, the gel may be treated with acid for depurination, further fragmenting into smaller fragments (Gel Electrophoresis). The results of Gel Electrophoresis is passed onto positively charged nitrocellulose or nylon membrane by applying even pressure throughout on the membrane, allowing buffer transfer by capillary action with ionic interactions binding the negatively charged DNA to the positively charged membrane (Blotting). Membrane is then baked at 80? for 2 hours (nitrocellulose or nylon) or exposed to ultraviolet radiation (nylon) to permanently attach the transferred DNA. A nucleic acid probe with a gene sequence complementary to the target gene sequence is labelled with radioactivity, fluorescent dyes or enzymes for detection when exposed to the appropriate substrate (Probe Labeling). Reduction of non-specific binding of the probe is done with deionised formamide and detergents such as SDS while salmon or herring sperm DNA is used to block the membrane surface and target DNA, ensuring specificity in the probe to DNA binding. Excess, non-hybridised probe is washed out from the membrane using low stringency buffer washes such as SSC, SSPE after hybridisation is complete. High stringency buffer washes are also utilised to remove traces of partially hybridised probe molecules leaving behind only the fully hybridised molecules for study. (Hybridisation and Washing) Method of detection is dependent on the way the probe is labelled, for example, radiographic probes can be identified with an X-Ray or phosphorimaging instruments while enzyme labelled ones typically undergo incubation with an chemiluminescent substance before undergoing an X-Ray.Experiments and resultsConclusionIn conclusion, the chicken telomere has a wide variety of comparable aspects that can be utilized to study telomeres in general, making it a very suitable animal to be used as a basis for telomere studies. Chickens and avians in general have been preferred over laboratory rats and mice due to their longer lifespan, easy attainability as well as a thorough characterization with respect to their basic physiology (Holmes et al., 1995). In laboratory rats and mice, they do not express age-related or division-dependent telomere shortening, while birds do (Swanberg et al. 2010). With these qualities and with the chicken’s unique telomere genome, the chicken has become a flexible organism to study, including telomere biology. In the recent years and many years to come, the chicken will be a suitable organism for researching telomeres and telomerase research. Suggested future studies can be conducted on the reconstitution of chicken telomerase by addition of exogenous cTERT or cTR. Reconstitution of the telomerase leads to the lengthening of telomeres, potentially delaying the aging process of the telomere and in turn, reducing the possibility of oncogenesis. Through this study, chicken telomere biology can be compared to the human telomere biology on a deeper level, and be applied accordingly in the biotechnology industry.SignificanceThis article has successfully shown that there are other alternative animals that can be used in the study of comparative biology of telomeres and telomerase, with the article showing how chicken telomeres is a more suitable candidate for this area of study than mouse telomeres, which has been commonly used for this purpose. This article could also spark off more research into finding other animal models which could potentially be a better candidate for developmental biology research.