The inhibition of pronuclear movements by dibromo-BAPTA is consistent with the explanation that the buffer disrupts the organization of microtubules near the animal pole.
The suggestion that the medaka egg has two independent microtubule networks is consistent with the situation in X, laevis, in which two independent networks of microtubules are present during the first cell cycle: one is near the animal pole and is associated with the pronuclei, while the other is the parallel array of microtubules near the vegetal pole (Elinson and Rowning, 1988; Houliston and Elinson, 1991; Elinson and Palacek, 1993; Sardet et al.
The movements of droplets within the irradiated regions were very similar to those in control (not treated with demecolcine) eggs; that, is roughly along meridian lines and away from the animal pole [ILLUSTRATION FOR FIGURE 3 OMITTED].
Droplets of mineral oil were injected into five eggs, which were oriented with their animal pole uppermost.
We injected vegetable oil into 11 eggs and oriented them with their animal pole uppermost.
In other words, endogenous droplets, moving toward the vegetal pole, passed by the droplets of injected fluid, which were either stationary or moving toward the animal pole.
The inhibition suggests that the formation of the blastodisc in the medaka egg is the result of the streaming of ooplasm to the animal pole and that microfilaments are involved in this streaming.
2+] present at the animal pole throughout the period of segregation (Fluck et al.
Specifically, in demecolcine-treated eggs oriented with their animal pole uppermost, oil droplets collected at the animal pole even as ooplasm was also streaming in that direction.
Moreover, the failure of injected droplets of several other fluids - fluorinated aliphatic compounds, silicone fluid, mineral oil, and vegetable oil - consistently to move away from the animal pole and toward the vegetal pole during segregation is inconsistent with the hypothesis.