In a message dated 5/1/00 9:54:53 PM Pacific Daylight Time,
> <CurtAdams@aol.com> Wrote:
> >Mice cells can go forever in culture;
> I assume you mean cancerous mouse cells, the same is true of humans cells.
I was referring to explanted normal cells. Normal mice
explants almost always transform (more or less become
cancerous) after grown in culture for a while. Human
cells never transform in culture. The transforming
mutations, statistically, must happen; apparently human
cellular self-screening is nearly flawless in culture.
(I.e., cells with pre-cancerous mutations kill themselves)
It's obviously not *that* good in vivo, although it's
obviously very good. One hypothesis is that human cancer
arises when cell are subject to certain strong growth
signals, which overide the suicide genes, permitting
>> human cells always have a finite lifespan.
>That was true until about a year ago when the Geron corporation found a way
>non cancerous human cells could be immortalized by lengthening their
I was thinking of explants, not engineered cells.
>>I think you may get more divisions prior to transformation, but that's
>>not a telomerase issues; it just means longer-lived species have better
>Or it could mean telomerase issues have something to do with cancer control.
I do find the "standard explanation" for the benefit of our limiting telomeres
compelling; an absolute and fairly short limit to cell replication means
there's just not enough generations for mutations of small effect to add up
to a cancerous cell. If the surveilance systems can catch most of the
big mutation (probably a fairly limited set; knock out gene A, constituitively
activate B, etc.) then cancer becomes nearly impossible. There has to
be some benefit to turning off telomerase, or it'd just be on everywhere.
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