Telomeres and telomerase in basal Metazoa

Abstract

Telomeres are protein-bound tandemly repeated simple DNA sequences placed at the chromosome ends, their role being essential for maintaining genome integrity. Severe telomere damage can trigger potential carcinogenic events such as chromosome fusions, whilst telomere shortening results (at least in mammals) in a protective mechanism known as 'replicative senescence'. In most Metazoa, telomere shortening is avoided by the ribonucleoprotein telomerase. In this brief overview, we focused on the evolutionary conservation of telomeres and telomerase in basal Metazoa (Ctenophora, Porifera, Placozoa, Cnidaria). In all these taxa, telomerase seems to be active and telomeres show the canonical TTAGGG sequence. Presence of telomerase activity and absence of telomere shortening is in accordance with the lack of senescence seen in basal Metazoa, although a clear correspondence between the “demographic senescence” and “replicative senescence” remains to be elucidated. Nonetheless, basal Metazoa can be useful as model organisms in studies on the evolution of telomere biology, Evo-Devo investigations on the control of telomerase activity, the emergence of senescence, as well as telomere-independent effects of telomerase.