25 = : best ry of itrate ld be collumn rate. lange total t be Rect etettnne n ex- te rticu- 4, Edgington, D. N. and Lucas, H. F., Jr. Radiological Physics Division, Argonne National Laboratory, unpublished data. 5. Yamagata, N. U. 8. Atomic Energy Commission Report NP-15366 (1965). «4. Wester, P. O., Brune, D. and Samsahl, K. Jat. J. Appi. Radiation Isotepes 16, 59 (1964}. 7. Smales, A. A. and Salmon, L. Analyst 80, 37 (1955). gy. Amphlett, C. B., McDonald, L. A., Burges, J. 5., and Maynard, J. C. J. Inorg. Nuel. Chem, 10, 69 (1959). 9, Krtil, J. J. Inorg. Nucl. Chem. 19, 298 (1961). 10, Krtil, J. and Kourim, V. J. Inorg. Nucl. Chem, 12, (1960). 11. Ibid, p. 370. 367 12. Yamagata, N., Iswashimia, K., and Tajima, E. J. Radiat. Res. (Tokyo) 4, 30 (1962). 13. Prout, W. E., Russell, FE. R., and Groh, H. J. J. Inorg. Nuel. Chem. 27, 473 (1965). 14. Langford, J. C. U. S. Atomic Energy Commission Report HW-49668 (1967). 15. Gorenc, B. and Kosta, L. 7. Anal. Chem, 223, 410 (1966). 16. Mohanrao, G. J. and Folsom, T. R. Analyst 88, 105 (1963). 17. Kourim, V., Rais, J., and Million, B. J. Inorg, Nucl. Chem. 26, 1111 (1964). 18. Schuly, W. W. and McKenzie, T. R. U.S. Atomie Energy Commission Report TID-7517 (1955). 19. Watari, K., Imai, K., and Izawa, M. J. Nuel. Sez. Technol. 4, 190 (1967). r ad- uted. sium diffiiepaimns ilues the lons, | sea lum cenidioe is vity 1 to rly, bidthe 21es. : be ited ore, yid; of nns wa20lof me pasle-~ RECOVERY AND MODIFICATION OF RADIATION-INDUCED DIVISION DELAY IN DEVELOPING SEA URCHIN EGGS* Patricia Failla Treatment of fertilized sea urchin eggs with a number of agents that prolong the normal cell division cycle permits recovery during the prolongation period from division delay caused by previous irradiation of one or both gametes. Treatment with several of these agents has also been shown to modify the subsequent response of fertilized eggs to radiation. Some implications of the results in the elucidation of the recovery process are discussed. Virtually all dividing cells exposed to sufficient doses of ionizing radiation exhibit division delay. Developing sea urchin eggs are an excellent material in which to study this effect for a number of reasons. First, a remarkable natural synchrony of the initial divisions greatly facilitates experimental procedures. Second, since this material has long been a favorite of embryologists and molecular biologists, extensive morphological and biochemical information is readily available. Third, the eggs are rugged and can tolerate treatments that mammalian cells cannot. Finally, there is the opportunity to compare the reactions of irradiation of almost pure nuclear material (sperm), nucleus and cytoplasm (eggs) or a developing diploid system (fertilized eggs or zygotes). The criterion of radiation damage under consideration, therefore, is the delay in the time of first division of fertilized sea urchin eggs after one or both gametes have beenir- radiated. The magnitude of this radiation-induced cleavage delay, however, can be altered both before and after fertilization. It is this aspect that will be emphasized. ure Ops 44, Henshaw” 2) showed over 30 years ago that the division delay resulting from the irradiation of un* Presented in part at the Fifty-fourth Scientific Assembly and Annual Meeting of the Radiological Society of North America, Chicago, Illinois, December 1-6, 1968. fertilized eggs could be reduced by increasingthe in- terval between irradiation and fertilization. Post- ponementof fertilization of normal eggs with irradiated sperm, however, had no such effect. This suggested that some cytoplasmic constituent was involved in this type of recovery. More recently, a postfertilization recovery from division delay has been demonstrated in both irradiated eggs and sperm.) During the study of this recovery process modification of radiation-induced division delay itself has been achieved. The postfertilization recovery process involves a prolongation of the first division cycle by various chemical or physical means during which the radiation effect. on either egg, sperm or zygote diminishes. The experimental protocol is outlined schematically in Figure 20. On lines 2 and 4 the sperm is depicted as irradiated, resulting in radiation-induced division delays of D and D’, respectively. On lines 3 and 4 a chemical or physical agent is applied to the fertilized egg inducing a prolongation of the division cycle which serves as a recovery period. If D’ is less than D, recovery is said to have occurred during the time R. By using agents which are known to interfere with specific cellular activities, the influence of this interference or inhibition on the recovery process can be investigated and the process itself better character- ized. While studyimg the mfluence of various agents on the recovery process, it was decided to ascertain which portion of the cell cycle was being prolonged. That, is, although the agents are applied for various intervals soon after fertilization, they may produce a delay in a later portion of the cell cycle. This is the case with radiation: no matter when the gametes or fertilized eggs are irradiated, the radiation-induced