Editing Hydra (genus) (section)

==Non-senescence==
Daniel Martinez claimed in a 1998 article in ''Experimental Gerontology'' that ''Hydra'' are [[Biological immortality|biologically immortal]].<ref>{{cite journal | vauthors = Martínez DE | title = Mortality patterns suggest lack of senescence in hydra | journal = Experimental Gerontology | volume = 33 | issue = 3 | pages = 217–25 | date = May 1998 | pmid = 9615920 | doi = 10.1016/S0531-5565(97)00113-7 | s2cid = 2009972 }}</ref> This publication has been widely cited as evidence that ''Hydra'' do not [[senescence|senesce]] (do not age), and that they are proof of the existence of non-senescing organisms generally. In 2010, [[Preston Estep]] published (also in ''Experimental Gerontology'') a letter to the editor arguing that the Martinez data refutes the hypothesis that ''Hydra'' do not senesce.<ref>{{cite journal | vauthors = Estep PW | title = Declining asexual reproduction is suggestive of senescence in hydra: comment on Martinez, D., "Mortality patterns suggest lack of senescence in hydra." Exp Gerontol 33, 217–25 | journal = Experimental Gerontology | volume = 45 | issue = 9 | pages = 645–6 | date = September 2010 | pmid = 20398746 | doi = 10.1016/j.exger.2010.03.017 | s2cid = 35408542 }}</ref>

The controversial unlimited lifespan of ''Hydra'' has attracted much attention from scientists. Research today appears to confirm Martinez' study.<ref name="B–K">{{cite journal | vauthors = Boehm AM, Khalturin K, Anton-Erxleben F, Hemmrich G, Klostermeier UC, Lopez-Quintero JA, Oberg HH, Puchert M, Rosenstiel P, Wittlieb J, Bosch TC | title = FoxO is a critical regulator of stem cell maintenance in immortal Hydra | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 109 | issue = 48 | pages = 19697–702 | date = November 2012 | pmid = 23150562 | pmc = 3511741 | doi = 10.1073/pnas.1209714109 | bibcode = 2012PNAS..10919697B | doi-access = free }}</ref> ''Hydra'' stem cells have a capacity for indefinite self-renewal. The [[transcription factor]] "[[FOX proteins|forkhead box O]]" (FoxO) has been identified as a critical driver of the continuous self-renewal of ''Hydra''.<ref name="B–K" /> In experiments, a drastically reduced population growth resulted from FoxO [[down-regulation]].<ref name="B–K" />

In bilaterally symmetrical organisms ([[Bilateria]]), the transcription factor FoxO affects stress response, lifespan, and increase in stem cells. If this transcription factor is knocked down in bilaterian model organisms, such as [[Drosophila melanogaster|fruit flies]] and [[nematode]]s, their lifespan is significantly decreased. In experiments on ''[[Hydra vulgaris|H. vulgaris]]'' (a radially symmetrical member of phylum [[Cnidaria]]), when FoxO levels were decreased, there was a negative effect on many key features of the ''Hydra'', but no death was observed, thus it is believed other factors may contribute to the apparent lack of aging in these creatures.<ref name=":2" />