Influence of Oxygen, Helium, and Metabolic Inhibition on X-ray Induced Dominant Lethality in Stage 7 and Stage 14 Oocytes of Drosophila Melanogaster.

D O S E fractionation, centrifugation, or metabolic inhibition studies of X-ray induced dominant lethality (PARKER 1959) or detachment of attached-X chromosomes (PARKER 1959; PARKER and HAMMOND 1958) in Stage 7 and Stage 14 primary oocytes (KING, RUBINSON, and SMITH 1956) of Drosophila melanogaster have demonstrated that a significant amount of the X-radiation damage can be repaired within 15 minutes in Stage 7 oocytes. No repair was noted in similar studies of Stage 14 oocytes, during the approximately 24 hours between irradiation and fertilization. For this stage, repair may be associated with fertilization (PARKER 1959). There is also a large difference in the relative radiosensitivity of the two types of cells. The LD,, for Stage 7 oocytes is approximately 3000r, for Stage 14 oocytes, 300r. The high sensitivity and “one-hit” survival curve of Stage 14 as contrasted with the low sensitivity and “multi-hit’’ curve for Stage 7 oocytes has been attributed to the difference in repair (PARKER 1959, 1963; PARKER and HAMMOND 1958; ABRAHAMSON 1961). Primary breaks in the two types of cells may restitute in the original configurations, rejoin illegitimately with an independently produced break, or perhaps may not be repaired. The first event leads to no observable effect, the second to a multi-hit dose response, while the third is a one-hit event. PARKER (1963) argues that rapid repair of damage in Stage 7 oocytes brings about primarily the first two events, while anaphase I, which may intervene between breakage and repair in Stage 14 cells, results in breaks spatially separated at the time of repair in Stage 14 oocytes so that the third event is predominant. ABRAHAMSON (1959) studied the effect of various oxygen tensions on X-ray damage in oocytes of D. melmogmter. He reported that anoxia between fractionated X-ray doses caused an increase in rearrangements in Stage 7 cells over that observed when air was present between the irradiations. Further, giving nitrogen for one hour to Stage 7 oocytes immediately after irradiation caused an increased rearrangement frequency. SOBELS (1961) found that cyanide, a metabolic inhibitor, given after irradiation of D. melanogaster males caused an increase in translocation frequencies in spermatids over that observed when no posttreatment was given.