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Biotech / Medical : Geron Corp.
GERN 1.535+12.5%1:06 PM EST
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To: maileg who wrote (121)8/16/1997 11:51:00 AM
From: r. peter Dale   of 3578
 
Darci: I cannot completely answer your question. I am not an oncologist nor does my research concern cancer so I'm not familiar with the underlying mechanism of DNA alteration.

I chose my words with intentional 'vagueness'. Lets say you're using the TUNEL assay to measure apoptosis. Simply put, this assay detects a unique characteristic of apoptotic DNA: whereas normal DNA is composed to two strands of nucleic acids that line up end-to-end, apoptotic DNA is not only composed of shorter fragments but its ends are not lined up. In other words, one strand is one (or more) nucleic acids longer than another. This fact allows researchers to identify this abnormal DNA: an enzyme (Terminal Deoxy. Transferase, TdT), which only 'sees' DNA with this type of 'overhang', can attach a 'label' to one of the 'unpaired' nucleic acids. The cell containing this labelled DNA is often designated apoptotic at this stage.

It is essential to know this method to understand my question about cancer: since these oncogenic cells have undergone DNA 'disruption'(by whatever means), isn't there a much greater likelihood that they now contain an elevated number of DNA 'overhangs' that would be detected by the TUNEL assay? A similar argument could be made for another apoptosis assay (gel electrophoresis for DNA fragmentation). These are known as a false positives - a feared phenomena in science that can throw the best minds for a loop.

Please remember that I'm not familiar with the cancer/apoptosis literature so I would welcome subtle comments about my pathetic ignorance.

Best wishes,
Peter
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