Abstract:
Purpose: There has historically been no tissue-model of
radiation-induced mitotic cell death, the most common form of cell dea
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Purpose: There has historically been no tissue-model of
radiation-induced mitotic cell death, the most common form of cell death
post-irradiation, limiting our ability to understand radioresistance at the
molecular level. We have created the
first and only in vivo tissue-model of mitotic cell death using the nematode C.
elegans. Our phenotype in this system
is seen in the hermaphrodite vulva, a tissue whose development is primarily due
to the EGFR/Ras/MAPK signaling pathway, a pathway commonly associated with
radioresistance. We have used this
system to determine which components of these signaling pathways and others are
necessary for protection from mitotic cell death. Materials and Methods: Radiation is performed on synchronized
worms using a Cs 137 irradiator (Mark 1 Model 68). Radiation sensitivity or
resistance is easily measured by scoring post-irradiation vulval abnormalities
using Nomarksi optics at 60x magnification.
We have confirmed that the cell death in this system is mitotic by using
lineage analysis, light microscopy and fluorescent microscopy. We have studied the radiosensitivity of worm
strains with loss-of-function (lof) and gain-of-function (gof) mutations in the
EGFR-signaling pathway. We have also
studied the radiosensivitity of worm strains with lof mutations in cell cycle
checkpoint genes and worm strains with lof mutations in DNA damage repair
proteins. Strains used in this study
were obtained from the C.elegans Genetics center (CGC). Results: While the
EGFR-signaling pathway lof mutant strains that we studied have no abnormalities
in normal vulva development, with exposure to radiation they were all
radiosensitive as compared to wild-type worms.
We also found that worm strains with lof mutations in cell cycle
checkpoint genes were sensitive to radiation, and a subset of worm strains with
lof mutations in DNA damage repair proteins were radiosensitive. In contrast, we found that several mutant
worm strains that were gof for the EGFR/Ras/MAPK pathway were radioresistant as
compared to wild-type worms.
Conclusion: We have shown that EGFR-signaling pathway and
components of the DNA damage response pathway are necessary for protection from
mitotic cell death in an in vivo tissue-model.
We have also shown that overexpression of the EGFR pathway protects
against mitotic cell death and leads to radioresistance. We plan to try and order the events of the
radiation response at the molecular level, by creating crosses between gof and
lof worm strains and determining their radiosensitivity phenotype.
Weidhaas MD, PhD, J,
An in Vivo Model of Mitotic Cell Death and the Ras/MAPK Pathway. Radiological Society of North America 2003 Scientific Assembly and Annual Meeting, November 30 - December 5, 2003 ,Chicago IL.
http://archive.rsna.org/2003/3230001.html
