LOCATION AND BEHAVIOR OF DORSAL DETERMINANTS DURING FIRST CELL-CYCLE IN XENOPUS EGGS

In Xenopus eggs, removal of small volumes of cytoplasm along with the surface (2-10% of the entire egg volume) causes very severe dorsal red uction (average DAI=1.4) when made at a site ventrally 30 degrees off the vegetal pole at 20% time of first cell cycle (0.2 NT). The greates t dorsal reduction (average DAI=1.1) occurs when removal is done at th e vegetal pole at 0.3 NT, and intermediate reductions (average DAI=2.2 -2.6) when done at sites dorsally, dorsolaterally or laterally 30 degr ees off the vegetal pole at 0.4 NT. Removal at sites dorsally, dorsola terally or laterally 60 degrees off the vegetal pole provokes slight d orsal reduction (average DAI=3.5-3.9) when made at 0.4-0.5 NT. Removal at all sites after 0.4 NT causes a steady decrease in the extent of d orsal reduction. By contrast, removal of larger volumes of dorsal cyto plasm (16-50% of the entire egg volume) causes a steady increase in th e extent of dorsal reduction during first cell cycle with its maximum effect at 1.0 NT (average DAI=3.1). The surgery for the cytoplasmic re moval does not affect cortical rotation. We conclude from these result s that dorsal determinants are concentrated first in a small region ve ntrally 30 degrees off the vegetal pole by 0.2 NT, then move toward th e vegetal pole during the period 0.2-0.3 NT and disperse to a broad re gion spanning over both the presumptive dorsal and ventral, but mainly the dorsal, hemispheres during the period 0.3-0.8 NT.