From: Derek Gatherer (d.gatherer@vir.gla.ac.uk)
Date: Mon 21 Nov 2005 - 08:51:35 GMT
What I'd like to ask Dr Hill is, when he splits the unexposed
culture, do the cells to be exposed to the agent go into the same
flask as the previous exposure was carried out in? Or is the
exposure culture set up in a clean flask each time?
At 19:57 18/11/2005, you wrote:
>Dr. Hill has responded to my query regarding possible contamination in the
>experiments he conducted which demonstrate entanglement among physically
>separated cell cultures. Alas, he didn't directly address my question but
>simply argued that contamination could not have occurred. Here's my
>question:
>
>I've gotten into a discussion with a UK researcher named Derek Gatherer.
>Not surprisingly, Dr. Gatherer, a molecular biologist, is skeptical of your
>findings. He claims that the cells not exposed to the toxin must have been
>contaminated by cells that were exposed. When I asked him why he would
>assume contamination, he responded that the countless researchers who have
>performed experiments on cell cultures would have noticed if resistance to
>compounds transferred from one flask to another. I asked him how he would
>know whether or not one culture is influencing a physically separated
>culture unless he directly tested for it. He responded that he has tested
>for it, that "setting up a negative control flask is a standard part of the
>procedure."
>
>Not being a scientist, I don't know how to respond to this point. Is
>setting up a negative control flask adequate for revealing whether or not
>one culture is influencing a physically separated culture?
>***
>
>And Dr. Hill's response:
>
>Either Dr. Gatherer did not read my articles or was unable
>(or not willing) to understand. I cannot imagine how he could see any
>possibility of contamination. Our so-called serial assays started
>with cells which at the beginning were unable to generate a resistant
>phenotype against, e. g., a toxic drug, a high temperature, a shortage of
>essential nutrients etc. Mutants we expected to produce against these
>harmful agents to our best knowledge not yet existed. Thus no way to
>imagine contamination. Each serial assay was carried out as follows. A
>starting population of established mammalian cells was split into two
>samples. A large sample was assayed for resistance against a harmful agent
>and a small one was subcultured into a non-harmful medium. The cells in the
>large sample all died whereas those in the small one proliferated. Three to
>four days later the growing cells should be passaged. Again at the passage,
>the cell population was split into a large sample for resistance assay and
>a small one for proliferation. And again the cells in the large sample all
>died and those in the small one proliferated. The same happened through
>many passages, thus showing that no resistant mutants were so far present.
>Not yet. These occurred at later passage levels as could be detected in
>resistance assays now containing colonies of resistant cells. The finding
>of mutants could not be interpreted by accidental contamination because
>nowhere was the source of ready-made mutants. Hence we concluded that
>mutations from sensitivity to resistance took place in growing cells. The
>most salient feature was that these cells never encountered the harmful
>agent but their close relatives did. Taken together, the findings showed
>that serial testing of resistance against a harmful agent gave rise to
>adaptive mutations in closely related cells growing a separate cultures and
>never exposed to the harmful agent of this kind.
>
>It is important to keep in mind that there was a considerable lapse of time
>from the starting point of serial assays to the occurrence of first
>mutants. Therefore, I am unable to understand how Dr. Gatherer imagine any
>even remote possibility of contamination. Perhaps the best way would be to
>you ask Dr. Gatherer for more detail or better a drawing.
>
>People used to imagine that a growing cell culture may contain spontaneous
>mutants of any kind. Our experiments show that it is not true. This
>understandably renders the proponents of neo-Darwinian doctrine unhappy.
>
>I hope my comments may be helpful to you.
>Yours sincerely, Dr. Miroslav Hill
>
>P. S. One more comment. Our experiments usually lasted each for several
>months and required a well trained staff. Therefore, I think there would be
>not easy to run similar experiments just in a routine laboratory not
>specialized enough to handle large amounts of long-term cell cultures. In
>this context, I remember the case of our transfection experiments with Rous
>sarcoma virus DNA which the Temin's laboratory tried to repeat without
>success during nearly three years. Howard Temin visited our lab to ask
>details, saying "you should have some magic". Then he learned the "magic"
>and in 1974 presented his own "magic" transfections in Cold Spring Harbor.
>***
>
>The original article, printed in Scripta Medica, is located here:
>
>http://med.muni.cz/biomedjournal/pdf/2000/04/211-222.pdf
>
>ted
>
>
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This was distributed via the memetics list associated with the
Journal of Memetics - Evolutionary Models of Information Transmission
For information about the journal and the list (e.g. unsubscribing)
see: http://www.cpm.mmu.ac.uk/jom-emit
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