A STUDY OF THE EFFECTS OF URETHAN ON THE CLEAVAGE OF THE CHAETOPTERUS EGG. I. INHIBITION OF CLEAVAGE

¹ Department of Zoology, University of Pennsylvania, Philadelphia 4, Pa., and the Marine Biological Laboratory, Woods Hole, Mass.

1. Dilute solutions of urethan (about 1%) prevent the division of fertilized Chaetopterus eggs when the eggs are treated beginning 5 minutes after insemination. Relative cytoplasmic viscosity determinations show that the mitotic gelation, which immediately precedes the formation of the mitotic apparatus, does not take place. In concentrations of urethan insufficient to prevent division (less than 0.5%) the mitotic gelation occurs normally. The inhibition is reversible since the eggs reassemble the mitotic apparatus and divide following return to normal sea water. Upon return to sea water the inhibited eggs divide directly into the number of cells present in the controls at that time, thus indicating that metabolic work and chromosome duplication are not affected. During this period there is a rapid and sharp increase in relative cytoplasmic viscosity. Eggs that have begun to form cleavage furrows are not able to complete cytokinesis upon exposure to urethan. The rigidity of the cortex is reduced by inhibitory concentrations of urethan. Cytological preparations reveal that urethan prevents the formation of the mitotic apparatus, and also destroys the organized structure of the mitotic apparatus after it has been formed.

2. Few of the eggs in 1% urethan divide until about four or five hours after fertilization. Untreated eggs at 21°C. divide by 58 minutes after insemination. The addition of small quantities of histamine, histidine, trypsin, chymotrypsin or lipase enables the eggs to divide sooner than four to five hours in the presence of urethan. Calcium, potassium, arginine and protamine were not effective.

3. It has been proposed that the urethan effects observed in this investigation may be reflections of an interaction with the hydrogen bonds that are believed to link together the macromolecular components of the mitotic apparatus.