Hydra: Immortal
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Senescence, a deteriorative process that increases the probability of death of an organism with increasing chronological age, has been found in all metazoans where careful studies have been carried out. There has been much controversy, however, about the potential immortality of hydra, a solitary freshwater member of the phylum Cnidaria, one of the earliest diverging metazoan groups. Researchers have suggested that hydra is capable of escaping aging by constantly renewing the tissues of its body. But no data have been published to support this assertion. To test for the presence or absence of aging in hydra, mortality and reproductive rates for three hydra cohorts have been analyzed for a period of four years. The results provide no evidence for aging in hydra: mortality rates have remained extremely low and there are no apparent signs of decline in reproductive rates. Hydra may have indeed escaped senescence and may be potentially immortal.
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My dissertation work included a study of aging in Hydra addressing the controversy regarding the immortality of this creature. I have continued this work at UC Irvine. Individual hydra have been kept alive for almost four years now. Only a few animals have died during this period and there has been no apparent decline in budding rates. This suggests that hydra seems to escape aging, a process known to affect all other metazoans.
This work has lead to an interest in investigating the presence of telomerase in hydra. Telomeres are nucleoprotein complexes at the end of chromosomes which protect chromosomes from degradation and fusion. Unless they are maintained, telomeres shorten with multiple cell divisions. Shortening of chromosomes might be responsible for "replicative aging", i.e., the finite proliferative capacity of somatic cells. Germline cells of most eukaryotes maintain their chromosomal ends by the action of telomerase, a ribonucleoprotein enzyme. Somatic cells appear to lack mechanisms to prevent the shortening of telomeres; perhaps an evolved trait to limit the proliferative potential of somatic cells in multicellular organisms. The epithelial cells of hydra, however, have retained their proliferative capacity. This results in the constant renewal of hydra's body and might explain hydra's immortality. The mechanism for preserving telomere integrity in the somatic cells of hydra is not known. I plan to investigate the presence of telomerases in the somatic cells of hydra in the future. This work could include cnidarians that undergo aging, e.g. several colonial hydroids, to investigate whether or not the evolution of aging is related to the loss of telomerase activity in somatic cells.
http://www.biology.p...inez/aging.html
