(2004, 2005), who showed one actin-poor region at anaphase in the animal pole of surf clam oocytes.
At bulge formation at the animal pole, the surface area of the bulge should increase rapidly.
In Tubifex oocytes, at the animal pole, an actin-bright spot was recognized at anaphase of meiosis II (Shimizu 1990).
2008, Liu 2012) can determine the polar body site, which is not limited to only one restricted site of the oocyte cortex near the animal pole. In starfish oocytes, if the orientation of the meiotic spindle is altered at metaphase, the spindle can attach to a different site (Hamaguchi 2001).
In contrast, oriented microtubule networks were present near the vegetal pole and animal pole by [T.sub.n] = 0.24 and [T.sub.n] = 0.3, respectively.
Near the animal pole, microtubules were oriented more or less along meridian lines and appeared to radiate from a microtubule-organizing center near the male and female pronuclei, which were 38.6 [+ or -] 6.7 [[micro]meter] ([Mathematical Expression Omitted], n = 5) below the surface of the blastodisc at [T.sub.n] [approximately equal to] 0.76 [ILLUSTRATION FOR FIGURE 2D-I OMITTED].
However, the injection of dibromo-BAPTA had profound effects on the microtubule networks near the animal pole, where the radiating pattern of microtubules near the animal pole was disrupted [ILLUSTRATION FOR FIGURE 4C, D OMITTED].
The striking feature of the region near the animal pole was the development of an array of microtubules that radiated from near the pronuclei to approximately 30 [degrees] arc from the animal pole.
Further, because oil droplets move toward the vegetal pole roughly along meridians, we predicted that a network of microtubules, also oriented more or less along meridians, would extend from the animal pole to near the vegetal pole.
The time between injection of dibromo-BAPTA and fixation of the eggs in the present study was sufficient for the buffer to diffuse to both the animal pole and vegetal pole, to dissipate cytosolic [Ca.sup.2+] gradients near the poles, and to inhibit the formation of the blastodisc and the movement of oil droplets toward the vegetal pole (Fluck et al., 1992, 1994).
Specific regions of the egg - animal pole, vegetal pole, equatorial region - were illuminated either en face or en profil.
Using methods described previously (Fluck et al., 1991, 1992, 1994), droplets of fluid were microinjected into the ooplasm between 35 [degrees] and 90 [degrees] arc from the animal pole. Of the 25 eggs used in these experiments, 21 were parthenogenetically activated by the injection needle, and four others were fertilized after injection.
Eggs treated with 1% DMSO formed a blastodisc (volume at [T.sub.n] [approximately equal to] 0.85-1.0 = 15.4 [+ or -] 2.0 nl, [Mathematical Expression Omitted], N = 7 eggs; [ILLUSTRATION FOR FIGURE 1A OMITTED]), displayed cytoplasmic streaming (speed of parcels toward the animal pole = 9.00 [+ or -] 5.52 [[micro]meter] [min.sup.-1], [Mathematical Expression Omitted], N = 7 eggs), and developed normally.
(1993a): (1) oil droplets did not segregate to the vegetal pole but instead floated to the portion of the egg that was uppermost during the experiment - equator [ILLUSTRATION FOR FIGURE 1C OMITTED], animal pole [ILLUSTRATION FOR FIGURE 2C AND D OMITTED], or vegetal pole; (2) a smaller-than-normal blastodisc formed [ILLUSTRATION FOR FIGURE 1C OMITTED]; (3) saltatory motion was absent; and (4) the eggs did not cleave.
For example, of 11 eggs treated with 0.35 [[micro]molar] demecolcine and irradiated en face at the animal pole (2.8 x [10.sup.8] quanta [s.sup.-1] [[[micro]meter].sup.-2]), vegetal pole, or equator, all 11 cleaved and developed an embryonic axis; while of three eggs treated with 3.5 [[micro]molar] demecolcine and irradiated under similar conditions, all three cleaved but none developed an embryonic axis.