Germ line immortality vs somatic longevity

The germ line (the cell lineage from which reproductive cells are derived) is replicatively immortal — distinct from the soma, where most cells capable of division have a strictly limited replicative capacity, if they’re not entirely postmitotic. Why?

Shawn Ahmed reviews evidence that in the nematode C. elegans, the mechanisms that promote longevity in the soma (sirtuins, as well as players in the IGF-1 signaling axis) are distinct from those that confer immortality on the germ line.

A dichotomy exists between germ and somatic cells in most organisms, such that somatic cell lineages proliferate for a single generation, whereas the germ cell lineage has the capacity to proliferate from one generation to the next, indefinitely. Several theories have been proposed to explain the unlimited replicative life span of germ cells, including the elimination of damaged germ cells by apoptosis or expression of high levels of gene products that prevent aging in somatic cells. These theories were tested in the nematode Caenorhabditis elegans by examining the consequences of eliminating either apoptosis or the daf-16, daf-18 or sir-2.1 genes that promote longevity of postmitotic somatic cells. However, germ cells of strains deficient for these activities displayed an unlimited proliferative capacity. Thus, C. elegans germ cells retain their youthful character via alternative pathways that prevent or eliminate damage that accumulates as a consequence of cell proliferation.

Understanding the proliferative perseverance of the germ line is particularly important when one considers the way in which germ cells violate one of the time-honored justifications for a replicatively limited soma, namely, that an unlimited replicative capacity would place a cell at risk for initiating cancer (see our earlier article on that subject, p16 vs p16: Preventing cancer, limiting self-renewal). Certainly, germ-line derived tumors are not unheard of, but they are rare, even though everyone’s got germ cells — so these lineages serve as an example of replicative immortality that does not confer an unusual risk of carcinogenesis.

Advertisements

4 comments

  1. […] What Can We Learn From Germ Line Cells? Ouroboros looks at that little piece of immortality that resides in all of us: “The germ line (the cell lineage from which reproductive cells are derived) is replicatively immortal – distinct from the soma, where most cells capable of division have a strictly limited replicative capacity, if they’re not entirely postmitotic. Why? … Understanding the proliferative perseverance of the germ line is particularly important when one considers the way in which germ cells violate one of the time-honored justifications for a replicatively limited soma, namely, that an unlimited replicative capacity would place a cell at risk for initiating cancer … Certainly, germ-line derived tumors are not unheard of, but they are rare, even though everyone’s got germ cells – so these lineages serve as an example of replicative immortality that does not confer an unusual risk of carcinogenesis.” Does the key to engineering cancer-free human biochemistry lie somewhere in our germ cells? We will probably know – in detail – the answer to that question within the next twenty years. View the Article Under Discussion: https://ouroboros.wordpress.com/2006/11/17/germ-line-vs-somatic-immortality/ Read More Longevity Meme Commentary: http://www.longevitymeme.org/news/ Published Saturday, November 18, 2006 9:06 AM by Longevity Meme News and Commentary Tags: Aging, Cancer, Germ line cells […]

  2. This is really wicked, I’m always fascinated by the germ/soma dichotomy. It’s very similar to the gene/meme comparison. Progeny/individuality, mortalism/immortalism.

    I dunno, I always get mad at the germ cells because it’s so unfair :p

    I think I will make a character called ‘germ’ who can replicate himself by looking into a mirror (who lasts 1 minute per level of experience) who can go berserker-mode and call it Soma.

  3. I’ve just heard Dr Jonathan Miller talking about death on Radio 4 and the germline-soma dichotomy came up – given the ‘immortality’ of the germ-line replicator in all organisms, can it be seen as the agent of the process of evolution?

  4. Of course you can fit it into evolution! It just so happened that when the first multicellular organisms mutated to be the first sexually reproducing species of the animal kingdom then DNA gave way to the design of immortal life. (sarcasm)

Comments are closed.