THE EFFECT OF X-RAYS ON CLEAVAGE IN ARBACIA EGGS: EVIDENCE OF NUCLEAR CONTROL OF DIVISION RATE

¹ From the Biophysical Laboratory, Memorial Hospital, New York City, and the Marine Biological Laboratory, Woods Hole, Mass.

1. Experiments have been carried out to investigate the influence of X-rays on the division rate of Arbacia eggs.

2. It was found, first, that the time required for the first cleavage was noticably prolonged when the eggs were irradiated before fertilization.

3. Second, it was found that the same effect could be produced by irradiating the sperm before they were allowed to fertilize normal eggs. Thus, an irradiation effect was carried by one gamete into another where the effect became expressed. The non-irradiated gamete was, therefore, caused to behave as though it had been irradiated.

4. Irradiation of both eggs and sperm indicated that the effect obtained was to some extent additive.

5. It was pointed out that only the nucleus and centrosome of the sperm appear to have an important influence on the egg and that the irradiation effect in such a case must have been carried by one or both of these. Reasons were given for believing that the centrosome was not important in this respect, thus indicating that the slowing of cell division observed was due to irradiation effects produced in the nucleus.

6. It appears, therefore, that the nuclei of the cells studied exert at least some control over the rate of cell division, and it is significant that such control is manifested when the damage is produced in a haploid nucleus and the effect is expressed in the presence of a normal haploid nucleus.

7. A method is presented for investigating quantitatively some of the more remote aspects of the radiobiological reactions.