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4, Edgington, D. N. and Lucas, H. F., Jr. Radiological Physics
Division, Argonne National Laboratory, unpublished
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11. Ibid, p. 370.
367
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Res. (Tokyo) 4, 30 (1962).
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Nuel. Chem. 27, 473 (1965).
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HW-49668 (1967).
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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
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4, 190 (1967).
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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