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> Telomeres are short segments of DNA which cap the ends of every chromosome, acting as 'buffers' against wear and tear. They shorten with every cell division,

> Telomeres are short segments of DNA which cap the ends of every chromosome, acting as 'buffers' against wear and tear. They shorten with every cell division, eventually getting too short to protect the chromosome, causing the cell to malfunction and the body to age. Can anyone explain what happens to telomere length when a new human is born? Presumably the telomere length is reset? Is there a beneficial reason for telomeres shortening with time?

8note 11y ago
> Is there a beneficial reason for telomeres shortening with time? So that people die instead of reproducing when they're old
- nanofortnight 11y ago
  It is also the final defense against unrestrained cell divison; a natural protection against diseases such as cancer.
- estefan 11y ago
  There were cultures where the oldest men in the tribe got exclusivity over the teenage girls to reproduce with. Also, since men can reproduce in old age, that sounds questionable to me.
- dsjoerg 11y ago
  So that people die when they're no longer reproductively viable / relevant, rather than using up valuable resources. Wouldn't telomere shortening have some selection-pressure advantage?
maxander 11y ago
Indeed, in gametes (sperm and egg cells) the cells use enzymes that rebuild telomeres. Telomeres "shorten" when DNA is copied for cell replication; the benefit of this is that it means telomeres quickly whittle down to nothing, and kill the resulting cells, when a rogue cell line has started replicating an unnecessary number of times- e.g., in cancer.
- seanwilson 11y ago
  > Indeed, in gametes (sperm and egg cells) the cells use enzymes that rebuild telomeres. Is it practical to harness this somehow to extend life then?
  - brianwawok 11y ago
    If someone had the secret to eternal life would they break it on hacker news?
  - estefan 11y ago
    Some scientists consider ageing to be a disease. They're trying to rebuild telomere length to keep us young, so this sounds like a step towards that goal.
  - maxander 11y ago
    That's probably exactly what the article was talking about- though its very short on details, aside from that the treatment was a form of "gene therapy." But my guess would be that the therapy involved the addition of a gene for this very enzyme (telomerase) in a form that it would become active in adult somatic cells. Of course whether this would actually meaningfully extend life is uncertain- aging is complicated.
- lambertsimnel 11y ago
  I assume that this is far from unique to humans, but not quite universal. I wonder whether the "immortal jellyfish" turritopsis dohrnii has some telomere rebuilding mechanism for all cells that provide its age-defying abilities. I also wonder whether there is a second advantage to telomere depletion; reducing the instances of organisms from different generations carrying the same genes competing for resources. After all, we're here for the benefit of our genes, not the other way round.
  - toufka 11y ago
    We do know that smaller (shorter lived) mammals at least have significantly shorter telomeres than humans. Here's a paper comparing max life span (MLS) against body temperature, body mass, and telomere length. [1] [1] http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3680702/figure/F1/ http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3680702/figure/F...
estefan 11y ago
I'm no biologist, but as I recall newborns have long DNA strands. As it says, each time cells split the strands shorten a bit eventually leading to age related illnesses. AFAIK there are no benefits to telomere length shortening with time. As I understand it, after we've reproduced and raised children - which we generally do before age-related illnesses kick in - we only have limited evolutionary value and no longer face stringent selection pressures. So it's probably that there were few opportunities for evolution to correct age related illnesses, or few survival-of-the-fittest opportunities (since we've already reproduced by the time they occur). However, this theory ignores the ability for grandparents to look after children. I suppose it's only minor enough for us to have evolved to live to ~80 but doesn't require youthful health any more.
astazangasta 11y ago
Telomeres shorten because we have linear chromosomes and it is physically impossible to replicate them without losing a bit off the ends (because in order to extend strand 1, you need to template off strand 2, so the end of strand 2 can't be copied). The telomere is a solution to this problem; you just pad the ends of your chromosomes with useless repetitive sequence so if you do lose a bit while replicating it doesn't matter. Any anti tumor properties of this system are an ancillary benefit.
- seanwilson 11y ago
  > Telomeres shorten because we have linear chromosomes and it is physically impossible to replicate them without losing a bit off the ends If that were true though wouldn't successive newborns have shorter and shorter telomeres?
  - astazangasta 11y ago
    No, there is a specialized enzyme called telomerase which is responsible for lengthening telomeres. It is active in germline cells and most stem cells, allowing those cells to safely and indefinitely replicate. The enzyme is basically a piece of RNA template that you can slap onto the ragged end of the chromosome and hold in place to allow extension.
reasonattlm 11y ago
Early in the process of embryonic development all sorts of radical restoration of damage takes place, things that couldn't happen in an adult organism without severe disruption. Telomere lengthening via telomerase is just one of them. E.g.: http://phys.org/news/2011-09-body.html http://phys.org/news/2011-09-body.html Early embyros have a lot in common with negligibly senescent lower species like hydra in that they are in a state of always-on regeneration. Repair everything, all the time. That state of being was lost somewhere along the way to organisms that have complex nervous systems made up of long-lived cells and structures that have to record state. An adult human couldn't operate like a hydra and live. The setup for most species is that adults have small groups of stem cells with telomerase and unlimited self-renewal, but the bulk of tissue is made up of somatic cells without telomerase, or with much less telomerase activity, that have a limited number of divisions before self-destruction or clearance by the immune system. Stem cells produce in a small number of new somatic cells as needed, and are the only tiny set of cells with the unlimited replication privilege. Telomere length is a part of the countdown mechanism that limits divisions in somatic cells - see the Hayflick Limit - because of the end replication problem in that a little of the length is lost with each cell division. This situation is shaped by the existence of cancer. The whole arrangement looks very much like something that came into being to fend off cancer, with ever more checks and balances arising to prevent uncontrolled replication, while still incorporating the mechanisms needed for embryonic growth and later regeneration.

8note 11y ago

> Is there a beneficial reason for telomeres shortening with time? So that people die instead of reproducing when they're old

nanofortnight 11y ago
It is also the final defense against unrestrained cell divison; a natural protection against diseases such as cancer.
estefan 11y ago
There were cultures where the oldest men in the tribe got exclusivity over the teenage girls to reproduce with. Also, since men can reproduce in old age, that sounds questionable to me.
dsjoerg 11y ago
So that people die when they're no longer reproductively viable / relevant, rather than using up valuable resources. Wouldn't telomere shortening have some selection-pressure advantage?

maxander 11y ago

Indeed, in gametes (sperm and egg cells) the cells use enzymes that rebuild telomeres. Telomeres "shorten" when DNA is copied for cell replication; the benefit of this is that it means telomeres quickly whittle down to nothing, and kill the resulting cells, when a rogue cell line has started replicating an unnecessary number of times- e.g., in cancer.

seanwilson 11y ago
> Indeed, in gametes (sperm and egg cells) the cells use enzymes that rebuild telomeres. Is it practical to harness this somehow to extend life then?
- brianwawok 11y ago
  If someone had the secret to eternal life would they break it on hacker news?
- estefan 11y ago
  Some scientists consider ageing to be a disease. They're trying to rebuild telomere length to keep us young, so this sounds like a step towards that goal.
- maxander 11y ago
  That's probably exactly what the article was talking about- though its very short on details, aside from that the treatment was a form of "gene therapy." But my guess would be that the therapy involved the addition of a gene for this very enzyme (telomerase) in a form that it would become active in adult somatic cells. Of course whether this would actually meaningfully extend life is uncertain- aging is complicated.
lambertsimnel 11y ago
I assume that this is far from unique to humans, but not quite universal. I wonder whether the "immortal jellyfish" turritopsis dohrnii has some telomere rebuilding mechanism for all cells that provide its age-defying abilities. I also wonder whether there is a second advantage to telomere depletion; reducing the instances of organisms from different generations carrying the same genes competing for resources. After all, we're here for the benefit of our genes, not the other way round.
- toufka 11y ago
  We do know that smaller (shorter lived) mammals at least have significantly shorter telomeres than humans. Here's a paper comparing max life span (MLS) against body temperature, body mass, and telomere length. [1] [1] http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3680702/figure/F1/ http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3680702/figure/F...

estefan 11y ago

I'm no biologist, but as I recall newborns have long DNA strands. As it says, each time cells split the strands shorten a bit eventually leading to age related illnesses. AFAIK there are no benefits to telomere length shortening with time. As I understand it, after we've reproduced and raised children - which we generally do before age-related illnesses kick in - we only have limited evolutionary value and no longer face stringent selection pressures. So it's probably that there were few opportunities for evolution to correct age related illnesses, or few survival-of-the-fittest opportunities (since we've already reproduced by the time they occur). However, this theory ignores the ability for grandparents to look after children. I suppose it's only minor enough for us to have evolved to live to ~80 but doesn't require youthful health any more.

astazangasta 11y ago

Telomeres shorten because we have linear chromosomes and it is physically impossible to replicate them without losing a bit off the ends (because in order to extend strand 1, you need to template off strand 2, so the end of strand 2 can't be copied). The telomere is a solution to this problem; you just pad the ends of your chromosomes with useless repetitive sequence so if you do lose a bit while replicating it doesn't matter. Any anti tumor properties of this system are an ancillary benefit.

seanwilson 11y ago
> Telomeres shorten because we have linear chromosomes and it is physically impossible to replicate them without losing a bit off the ends If that were true though wouldn't successive newborns have shorter and shorter telomeres?
- astazangasta 11y ago
  No, there is a specialized enzyme called telomerase which is responsible for lengthening telomeres. It is active in germline cells and most stem cells, allowing those cells to safely and indefinitely replicate. The enzyme is basically a piece of RNA template that you can slap onto the ragged end of the chromosome and hold in place to allow extension.

reasonattlm 11y ago

Early in the process of embryonic development all sorts of radical restoration of damage takes place, things that couldn't happen in an adult organism without severe disruption. Telomere lengthening via telomerase is just one of them. E.g.: http://phys.org/news/2011-09-body.html http://phys.org/news/2011-09-body.html Early embyros have a lot in common with negligibly senescent lower species like hydra in that they are in a state of always-on regeneration. Repair everything, all the time. That state of being was lost somewhere along the way to organisms that have complex nervous systems made up of long-lived cells and structures that have to record state. An adult human couldn't operate like a hydra and live. The setup for most species is that adults have small groups of stem cells with telomerase and unlimited self-renewal, but the bulk of tissue is made up of somatic cells without telomerase, or with much less telomerase activity, that have a limited number of divisions before self-destruction or clearance by the immune system. Stem cells produce in a small number of new somatic cells as needed, and are the only tiny set of cells with the unlimited replication privilege. Telomere length is a part of the countdown mechanism that limits divisions in somatic cells - see the Hayflick Limit - because of the end replication problem in that a little of the length is lost with each cell division. This situation is shaped by the existence of cancer. The whole arrangement looks very much like something that came into being to fend off cancer, with ever more checks and balances arising to prevent uncontrolled replication, while still incorporating the mechanisms needed for embryonic growth and later regeneration.