ACTION OF COLCEMID IN SEA URCHIN EGGS

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Abstract
The effects of Colcemid, the deacetyl-N-methyl derivative of colchicine, on the eggs of Arbacia punctulata were investigated. Colcemid in concentrations of 2.7 x 10-5 [image] or greater blocks syngamy (the fusion of the pronuclei) in these eggs. Although a tenfold decrease in concentration of Colcemid usually permits the pronuclei to fuse, the subsequent division is blocked. In the sea urchin egg, the duration of presyngamy is about 15 min during which time there is no DNA synthesis. However DNA synthesis is recorded in Colcemid -blocked cells prior to syngamy. Radio-autographs of Colcemid-blocked cells which were immersed into thymidine-3H exhibited silver grains above each of the pronuclei. The action of Col-cemid on Arbacia eggs is reversible. Nevertheless, exposures to 2.7 x 10-5 [image] Colcemid for only 3 min, initiated 5 min. after insemi-nation, caused delays of 70 min. in subsequent division. In general, cells are more sensitive to Colcemid prior to the time when the mitotic spindle is being assembled than at presyngamy stages. The results are discussed in terms of Colcemid action on pronuclear fusion and cell division.