Environmental and Molecular Mutagenesis - Legacy Tobacco ...

395 1989 EMS Abstracts
THE ROLE OF NUCLEAR MATRIX IN REPAIR Notes
L.H .F. Mullenders', J . Venema', A.•van Hoffen', L. Mayne', A .T . Natarajan' and AA. van Zeeland") Department
of Radiation Genetics and Chemical Mutagenesis, University of Leiden, The Netherlands ; p) Centre of Medical
Research, University of Sussex, U.K .
The organization of the eukaryotic genome into a series of loops anchored to the nuclear matrix bas been
related to functional compartimentalization of the nucleus in order to facilitate processes such as replication and
transcription. We have investigated the role of the nuclear matrix in processing UV-induced damage in human
fibroblasts . Pulse-labelling of normal fibroblasta followed by enzymatic digestion of DNA-nuclear matrix complexes
revealed a time and dose dependent preferential repair of nuclear matrix associated DNA . Pulse-ehase experiments
showed no evidence for compartimentalization of excision repair at the nuclear matrix Le, lesions do not require prior
attachment in order to be repaired . The results favour a model of preferential repair of DNA sequences permanently
associated to the nuclear matrix . Pronounced differences in distribution pattern of repaired sites in DNA-nuclear
matrix complexes were found among normal and UV-sensitive cells exposed to UV-'vradiation . Xeroderma
pigmentosum group C (XP-C) efficiently repaired nuclear matrix associated DNA, but not regions of the genome
further extended into thc DNA loops . In Cockayne's syndrome (CS) cells the reversed situation was found : efficient
repair of loop DNA and inefficient repair of nuclear matrix-associated DNA . These differences in distribution oan
be correlated to efficiencies in repair of UV-damage in transcriptionally active genes . Despite the low overall repair
XP-C cells were found to be as proficient in repair of pyrimidine dimera from the ADA and DHFR gene as normal
fibroblasts. The efficient removal of pyrimidine dimers from active genes was found to be absent in CS cells . The
results suggest the existence of two independent repair pathways directed towards repair of pyrimidine dimers in
either active or inactive DNA .
396
SENTINEL AND OTHER MUTATIONAL EFFECTS IN OFFSPRING OF CANCER SURVIVORS . John J .
Mulvihill, Clinical Epidemiology Branch, National Cancer Institute, Bethesda, MD, USA
To date, no agent has been documented to cause germ cell mutation in human beings,
with the possible exception of radiation causing abnormal meiotic chromosomes in
testes . For studies in humans, mutation epidemiologists prefer the cohort approach,
start ing with an exposed population and looking for mutations that may be expressed
in offspring as variants in health, chromosomes, proteins, or nucleic acids . Currently
patients with cancer are the cohort exposed to the largest doses of potential
mutagens, i .e ., radiotherapy and drugs . In 12 large studies with over 825 p,atients
and 1573 pregnancies, 46 (4%) of 1240 liveborns had a major birth defect, a'rate comparable
to that in the general population . One of these was a classic sentinel phenotype,
i .e ., a new sporadic case of a dominant mendelian syndrome . In collaboration
with 5 U .S . cancer registries, we interviewed a retrospRctive cohort of 2383 patients
diagnosed with cancer under age 20 years, from 1945 thrbugh 1975 . Records were sought
to verify major genetic disease, defined as a cytogenetic or single gene disorder or
1 of 15 isolated birth defects . In 2308 offspring of survivors, 5 had a chromosomal
syndrome, 11 had a single gene disorder, and 62 had at least one major malformation .
Among 4722 offspring of sibling controls, the respective numbers were 7, 12, and 127,
nonsignificant differences . 7% of the parents of the offspring with possibly new
mutations received potentially mutagenic therapy, compared with 12% of parents of
normal children . Since pregnancy in or by cancer survivors is still a rare event,
future efforts to document germ cell mutation may be best studied through international
cooperation coupled with diverse laboratory measures of mutation .
397
MMC INDUCED SCE IN DIVIDING AND NONDIVIDING HUMAN PURIFIED LYMPHOCYTES AND
CHINESE HAMSTER OVARY CELLS . H . Murli, Department of Molecular and Cellular
Services, Hazleton Labs, Kensington, MD .
Repair of MMC induced lesions that result in SCE was studied in purified human
lymphocytes (PHL) and in Chinese hamster ovary cells (CHO) . PHL at 0~ and
confluent cultures of CHO cells were treated with MMC for two hours and held
in G, or confluent for 0, 18, 25, or 48 hours . PHL received PHA and BrdUrd
after the appropriate interval and were recultured for -72 hours . CHO cells
were split after the appropriate interval and recultured for -26 hours with
BrdUrd . SCE frequencies were similar for all the cultures with both cell
types . Thus PHL and CHO cells were incapable of repair of MMC induced SCE
damage under nonreplicating conditions . CHO cells were cultured in log phase
for -14 hours after MMC exposure before Brdurd was added or confluent cultures
exposed to MMC were split after 0 or 24 hours, cultured for 14 hours before
BrdUrd was added and recultured for -25 hours . SCE frequencies were near
control levels for all exposure conditions indicating repair of MMC induced
lesions . PHL were treated with MMC, PHA was added 0 or 24 hours later, and
BrdUrd was added 48 or 72 hours later, respectively . Again SCE frequencies in
all these cultures were near control levels . MMC induced SCE in PHL were
tested under differing exposure conditions to PHA and BrdUrd . These experiments
indicate that MMC induced lesions are repaired only after one round of
DNA replication .
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