X-Ray-Induced Incorporation of Tritiated Thymidine into Deoxyribonucleic Acid of Grasshopper Neuroblast Chromosomes

Abstract

This study was to determine whether irradiated neuroblasts that are delayed, stopped, or reverted mitotically incorporate tritiated thymidine (H3T) during cell stages not usually associated with normal DNA synthesis. Hanging-drop cultures of embryonic grasshopper (Chortophaga viridifasciata) tissue were exposed to H3T, then to either 32 or 250 r. Prophase cells (at least 35 min. past the end of normal DNA synthesis) were identified in living preparations and also in fixed and stained preparations of the same tissue. Four more or less distinct mitotic responses of irradiated (32r) prophase neuroblasts can be distinguished nondelay, delay, stoppage, and reversion; The greatest number of types of response is seen in cells which were irradiated in late prophase, whereas the least variety of responses occurs after treatment of very early pro-phases; Prophase neuroblasts which are delayed, stopped, or reverted mitotically in response to 32r of X-rays incorporate H3T; Nondelayed, nonreverted cells show no incorporation of H3T.