

Half a Billion Years of Suicide - rpm4321
http://phenomena.nationalgeographic.com/2014/06/09/half-a-billion-years-of-suicide/

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quotient
Very interesting. This is just speculation on my part --- but perhaps a reason
why the fruit fly and the nematode worm only have one TNF is precisely because
they are small organisms that frequently come into contact with other
organisms. If they had dozens of TNFs, then it would be much easier for their
apoptosis processes to be triggered by external influences, which could prove
debilitating.

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DaniFong
Doesn't explain the differential population in coral and humans; the simpler
organisms have shorter lifespans, it should matter less if they're susceptible
to an external influence.

More likely there are so many receptors because the type and mechanism of cell
death is important for the programming of complexity in organisms and
macroorganisms.

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stevenquistad
Re Quotient: The cool thing about these TNF receptors is that not all of them
lead to apoptosis. In humans for a TNF receptor to move towards apoptosis it
requires a "Death Domain." In corals only 11 of the 40 TNF receptors have
these death domains so the other 29 TNF receptors are likely involved in a
variety of other cellular process besides apoptosis

Re DaniFong: "simpler" organisms do not always have shorter lifespans. For
example many clams/molluscs can live to be hundreds of years old. In fact, the
oldest mollusc is estimated to be over 400 years old!

Re: Why so many TNF receptors in coral there are variety of possibilites:

In terms of the biological reasons for so many TNF-receptors in coral there
are a couple possibilities

1) Genome duplication events can occur during evolution leading to expansion
of gene families. This appears to be the case in the Zebra fish model organism
Danio rerio, they have 33 TNF receptors which seem to have appeared through
genomic duplication. I did not specefically look for genome duplication events
in the coral genome, but is an interesting direction for future research.

2) Microbial-host interactions- corals harbor a diverse assemblage of
bacteria, viruses, fungi, and algae which changes in response to coral health.
TNF receptors may be involved in managing these complex interactions. Of the
40 TNFR in coral, only 11 have a "Death Domain". We hypothesize that these
death domain TNFR are involved with directly guiding a cell towards apotosis
which leaves 29 other receptors that may be involved with other cellular
processes

3) Coral resilience to environmental stress- Recent work by Steve Palumni
showed that TNF-receptors are involved with resilance to heat stress. They
placed naturally heat resistant coral into cold water and found that
expression levels of specefic TNF receptors were maintained in the heat-
resistant coral but not the heat-sensitive coral. This suggests a genetic
component to heat stress via TN-receptors.

If anybody has any questions about my paper, evolution, or coral in general
please do not hesitate to ask me on Twitter @StevenQuistad

Thanks for your interest in my work!

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terminado
What about convergent evolution?

[https://en.wikipedia.org/wiki/List_of_examples_of_convergent...](https://en.wikipedia.org/wiki/List_of_examples_of_convergent_evolution#In_proteins.2C_enzymes_and_biochemical_pathways)

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tritium
From paragraph #10:

    
    
      Could corals and humans have evolved our TNF 
      families independently? It’s unlikely, given 
      how compatible the two proteins are.
    

But no further detail is given.

