C. elegans survivors without telomerase.

In most eukaryotic organisms with a linear genome, the telomerase complex is essential for telomere maintenance and, thus, for genomic integrity. Proper telomerase function in stem and germ cell populations counteracts replication-dependent telomere shortening. On the other hand, repression of telomerase expression in most somatic tissues limits the proliferative potential of these cells through the induction of a permanent cell cycle arrest termed senescence upon critical telomere erosion. Thus, senescence, induced by telomere shortening and subsequent DNA damage signaling, is an essential tumor suppressive mechanism, emphasized by the fact that repression of telomerase is lost in about 90% of cancers, endowing them with unlimited proliferative potential. In 10% of cancers telomeres are maintained using the recombination-based alternative mechanism of telomere lengthening (ALT). To date, ALT and ALT-like mechanisms have only been described in the context of individual cells such as cancer cells and yeast. Now, several "survivor" strains of the nematode Caenorhabditis elegans have been generated that can propagate despite mutations of the telomerase gene. These nematode strains represent the first multi-cellular organism with canonical telomerase that can survive in the absence of a functional telomerase pathway.