The Chicken as a Paradigm for Aging Research

Organisms frequently used in aging studies include yeast, Drosophila, C. elegans, and M. musculus, the laboratory mouse. With all of these well-characterized models available, particularly a mammalian vertebrate as well-studied as the lab mouse, why use an avian model? The advantages of using a vertebrate are obvious, and the mouse would at first glance appear to be a better choice than the chicken except for shortcomings of the mouse vis-a-vis the study of aging and oncogenesis. For example, mice have a very short lifespan. In contrast, maximum life expectancies of many species of birds approach the human life expectancy (Forsyth et al., 2002; Austad, 1997). Lifespan is significant, as cellular and genetic mechanisms governing cell proliferation are likely conserved in longer-lived species.

In addition to the issue of lifespan, laboratory mouse somatic cells retain telomerase activity and do not appear to display division-dependent telomere shortening (Prowse and Greider, 1995; Forsyth et al., 2002; Kim et al., 2002). Mouse models of telomere shortening have been developed, but it takes several generations in the telomerase knockout mouse (TR-/TR-) to achieve a phenotype that demonstrates division-dependent telo-mere shortening (Cheong et al., 2003). In contrast, human and chicken somatic cells lack telomerase, with down-regulation of telomerase occurring early in development. Division-dependent telomere shortening is established in chicken chromosomes (in vivo and in vitro) and human chromosomes. In human, mouse and chicken, highly proliferative tissues such as embryonic cells and intestine as well as transformed cells exhibit telomerase activity

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