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Why do some genes turn on after death?

Why do some genes turn on after death?
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    Imagine you're dead...
    No heartbeat. No brain activity. No breath.
    That seems pretty final.
    But at the cellular level, only part of you is dead--
    some of your cells are still fighting the good fight
    Scientists want to know what is going on
    inside those lingering cells.
    So researchers looked at the activity
    of more than a thousand genes,
    in both zebrafish and mice,
    for up to four days after they died.
    Groups of genes related to immune response,
    inflammation, stress response, and cancer
    were all more active.
    Even more surprising--genes normally only seen
    during development were also suddenly active.
    These genes are tightly locked down by cells
    after the embryo develops and are never expressed
    again -- until, perhaps, the organism dies.
    So why do they revive?
    It might be that some conditions inside the cell
    after death resemble those before birth,
    but they don't know for sure.
    An alternative reason developmental genes
    turn on might lie with changes in
    epigenetic regulatory genes,
    which control gene activity
    by restricting access to the DNA
    The activity of some of those regulators
    was actually shown to increase after death.
    Developmental genes are physically
    tucked away in the genome.
    But if the regulators spin out of control,
    those genes could suddenly become accessible
    and start expressing.
    There isn't really a why question here--
    it doesn't seem likely that there is a purpose
    to these genes turning on.
    That's because genes in a dead organism
    can't be acted on by natural selection.
    There's no evolutionary advantage
    to turning them on after death. Probably.
    If an organism isn't quite dead, there could
    be some advantage to ramping up some genes,
    like those related to stress responses
    and recovery from injury.
    But there's not enough data to know for sure,
    and few other studies have tackled this question.
    One that did looked at human tissue--
    over 9000 samples from 36 different types.
    After death, gene expression in brain and spleen tissue
    was relatively stable.
    But genes in muscle tissue went crazy.
    More than 600 either increased
    or decreased their activity
    And those increases in gene expression
    waxed and waned in a way that suggested biochemical
    machinery was still working.
    What can learn from this?
    Patterns of gene expression
    could be used to estimate time of death,
    something that current forensic techniques
    don't always get right.
    And the experiment that looked at human samples,
    identified the types of tissues that might
    be most helpful to forensics:
    skin and the layer of fat directly beneath.
    And that's not all.
    Patients that get organ transplants
    from dead donors could start receiving better care,
    the more we learn about gene expression after death.
    These changes in gene activity could even help explain
    why some transplant recipients
    are at an increased risk of cancer.
    It's also important for researchers to understand
    gene activity in tissues that can
    only be obtained after death.
    If death alters our genes, scientists need to know
    how that affects the tissues they study.
    And we can't rule out simple curiosity
    as a driving force for this research.
    What our genes get up to after death is a beguiling
    mystery, and one we've only begun to consider.
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