Cell Proliferation - Visiting Old and Gaining New Perspectives
|From:||"Monson, Frederick C." |
I couldn't help trying to add something of value to the discussion
of cell proliferation. My 'add' follows.
What I have written is not an admonition, or a demonstration of petulance,
or a rank demonstration of raucous pride. It is a demonstration of what one
can glean from a brief historical playback of old knowledge and then a fast
trip on the "Google Express" to finding out where the issues lie today. I
revisited an old reference that has adorned my bookshelf for 30+ years
[Because it was worth keeping!!!].
The point is this! Many folks for many years have simply used one of the
analogs of Thymidine, called Bromodeoxyuridine as accompaniment in the study
of cell cycles in various cell strains and tissues. Many studies that
purport to do population studies avoid the necessity of learning as much as
possible about the biochemistry, and now molecular biology, of the system to
Most people I have met over the years, have not learned to pose questions
very well, and thus, have not learned how to find information that they need
preliminary to beginning an experiment. First of all, 'cell cycle analysis"
itself is based on assumptions that most analyses prove wrong, but this is
an example of assumptions that are applied nonetheless, every time. The
best of these assumptions are: 1) all cells are randomly spread around the
cell cycle, with respect to the time taken for one cell cycle (G1, S, G2 and
M), and 2) all cells in the population are continually involved in the
process. Out of these assumptions come G-zero cells in most natural
populations that are NOT adhering to the assumptions - spiteful things!
If one looks at studies of natural ploidy in normal animal tissues, one
finds that in liver, for example, there are uni- and bi-nucleate cells that
can be demonstrated to contain 2c, 4c, and 8c quantities of DNA. What kinds
of data would an analysis of the cell cycle and population doubling
accumulate, using 3H-TdR (or BrUdR) labeling, and what would those data
reveal about the truth of those issues in normal liver, developing liver,
and regenerating adult liver following the ablation of a single lobe?
Without a coordinated study of the concentration of DNA per cell and per
nucleus, the conclusions would probably not be very conclusive.
What follows is intended to exemplify the uses to which 3H-labeled
nucleotides and their analogs were put when I was learning to do
autoradiography. Following them is the beginning of my search to catch up
which I have shared.
Painter, Jermany, and Rasmussen, 1966, J. Mol. Biol., 17:" 47. Used 3H-TdR
and 3H-BrUdR to estimate the number of replication sites in the genome of
Pujara, C.M., 1964, PhD Thesis, University of Toronto. Mouse L cells
doubling time and cell cycle time was 18hr. After prolonged growth in
BrUdR, at 5ug/ml (300-400hr), population doubling time was measured at 35hr
while the cell cycle time was little changed to 21.5hr.
Measurements of Thymidine nucleotide pools sizes in both tissue cells and
cultured cells from mammals vary from 6 - 250 million molecules/cell, and
concentrations within nuclei are around 12 orders of magnitude greater than
in the whole cell.
The above were taken from:
Cleaver, J.E.(1967), Thymidine Metabolism and Cell Kinetics, North
Holland, Amsterdam, Library of Congress Card No. 67-28014.
Thymidine kinase (thymine 5'-phosphotransferase) has an absolute requirement
for Mg+ and ATP. Cleaver, but also see:
http://www.sangtec.se/products.asp?ID=3 (and refs page)
Also, the following on TdR:
search above for or
Also, the following on BrUdR:
http://www.biology.ucsc.edu/classes/bio126/Barres.pdf (long term)
Behringer Manheim Manual on Cell proliferation and Apoptosis (100+ pages)
The above took me an hour today. In 1965, the same search would, and did,
take weeks. It is the beginning of a necessary catch-up to the literature
in this field. First, to get a handle on recent BrUdR work, and then on the
increased, molecular data on the thymidine salvage pathway.
I start by being interested in everything about a subject. Everything I can
find about similar systems in microbes, invertebrates, vertebrates and
ultimately mammals. Even fungi get some time when I'm searching for a
perspective on an issue.
[Did you know that there is at least one fish in the arctic ocean whose
hemoglobin is NOT housed in a plasma membrane but rather is just suspended
in the plasma? Doesn't THAT raise a question about the fish's kidney
function? And hemoglobin synthesis? And osmoregulation? And oxygen
affinity and binding?
[Did you ever wonder that the liver parenchyma cell performs functions
simultaneously along cellular axes that are at right angles to one another?
This approach is what I learned in graduate school, and it is easy enough
that anyone can do it now.
Among others, I searched:
Hope this exercise has been worth while for those who are interested in the
Frederick C. Monson, PhD
Center for Advanced Scientific Imaging
Schmucker II Science Center
West Chester University
South Church Street and Rosedale
West Chester, Pennsylvania, USA, 19383
CASI URL: http://darwin.wcupa.edu/casi/
WCUPA URL: http://www.wcupa.edu/
Visitors URL: http://www.wcupa.edu/_visitors/
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