Relation of X-ray-induced Thymidine Uptake to Chromosome Reversion at Prophase in Grasshopper Neuroblasts

Summary

Unscheduled DNA synthesis (thymidine uptake) induced by 32 R of x-rays was followed autoradiographically in individual grasshopper neuroblasts. It occurs in those prophase cells that undergo chromosome reversion (chromosomes ‘decondense’, appearing to move backward in the cell-cycle), but not in those that are delayed in the cycle without chromosome reversion or that progress with no delay. The latest point in prophase at which unscheduled DNA synthesis is observed is the initial part of late prophase. Hypotonic culture medium, which by itself causes decondensation of prophase chromosomes but not unscheduled DNA synthesis, enhances both chromosome reversion and unscheduled DNA synthesis when these are induced by radiation.