title: Unscheduled DNA synthesis induced in mouse spermatids after combined treatment with methyl methanesulfonate and X-rays.
abstract: Unscheduled DNA synthesis (UDS), which is considered to be DNA repair, has been studied in early- to mid-spermatid stages of the mouse after combined treatments with X-rays and methyl methanesulfonate (MMS). UDS in spermatids was detected by giving testicular injections of [methyl-3H]thymidine ([3H]dThd) and making use of the fact that no scheduled DNA synthesis occurs in the germ cells after the last S period in primary spermatocytes. X-rays and MMS are each able to induce UDS in mouse spermatids. However, there was a statistically significant reduction in the amount of UDS observed when X-ray exposures of from 200 to 600 R were given 4 h before an i.p. injection of 75 mg/kg of MMS and concurrent testicular injections of [3H]dThd. This reduction in UDS is more than can be explained by the completion of repair of X-ray-induced DNA lesions. We suggest that the reduction in UDS is the result of an X-ray-produced impairment of a least a part of the repair mechanism involved in correcting MMS-induced DNA lesions. When the time interval between a 600-R X-ray exposure and MMS treatment was between 3 and 20 h (latest time interval s;udied) there was a statistically significant reduction of UDS in the spermatids. No significant decrease in UDS response occurred when the time interval between radiation exposure and MMS treatment was less than approximately 3 h.
mesh_terms: D000818:Animals; D004247:DNA / Q000378:metabolism; D004260:DNA Repair; D004307:Dose-Response Relationship, Radiation; D008297:Male; D008698:Mesylates / Q000494:pharmacology*; D008741:Methyl Methanesulfonate / Q000494:pharmacology*; D051379:Mice; D013087:Spermatids / Q000187:drug effects* / Q000378:metabolism / Q000528:radiation effects*; D013094:Spermatozoa / Q000187:drug effects* / Q000528:radiation effects*; D013997:Time Factors; D014965:X-Rays
chemical_list: D008698:Mesylates; D004247:DNA; D008741:Methyl Methanesulfonate