[The demonstration of heritable lethal mutations in the progeny of x-ray-irradiated CHO cells by micronucleus count in clone cells].
OBJECTIVE
Low doses of ionizing radiation reduce the growth rates of clones following irradiation of the progenitor cells. Such reductions of clone growth have been proven by means of measurements of clone size distributions. The medians of such distributions can be used to quantify the radiation damage. Prolongations of generation times and cell death as result of heritable lethal mutations have been discussed as causes for the reduction of clone growth.


METHODS
The cell number of a clone of hypotetraploid CHO-cells was compared to the frequency of micronucleated binucleated cells in the same clone using the cytokinesis-block-micronucleus method. The dose dependent reduction of clone sizes is measured by the difference of the medians (after log transformation) of the clone size distributions.


RESULTS
At cytochalasin-B concentrations of 1 microgram/ml and after an incubation time of 16 h a yield of binucleated cells of about 50% was obtained. Median clone size differences as a measure of clonal radiation damage increased linearly with incubation times of 76, 100, 124, and 240 h following irradiation with 3, 5, 7, and 12 Gy. The frequency of binucleated clone cells with micronuclei strongly increased with decreasing clone size by a factor up to 20 following irradiation with 3, 5, and 7 Gy. The frequency of micronucleated binucleated clone cells was found to be independent of incubation time after irradiation.


CONCLUSIONS
Radiation induced clone size reductions result from cell losses caused by intraclonal expression of micronuclei which have its origin in heritable lethal mutations. Measurements of clone size distributions can be done automatically. They can serve as predictive test for determination of median cell loss rates of surviving cell clones.
Hagemann
G
G
Bereich Experimentelle Radiologie, Medizinische Hochschule Hannover.
Kreczik
A
A
Treichel
M
M
D000818:Animals; D016466:CHO Cells; D002460:Cell Line; D002470:Cell Survival / Q000528:radiation effects; D002999:Clone Cells / Q000528:radiation effects / Q000648:ultrastructure; D006224:Cricetinae; D003412:Cricetulus; D004307:Dose-Response Relationship, Radiation; D005260:Female; D005804:Genes, Lethal / Q000528:radiation effects*; D015162:Micronucleus Tests; D009154:Mutation; D013997:Time Factors
Nachweis vererbbarer Letalmutationen in Nachkommen röntgenbestrahlter CHO-Zellen durch Mikrokernzählung in Klonzellen.