. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. Figure 1. Unfertilized eggs stained with DAPI. Three eggs in the upper row are binucleates. One egg in the lower left is trinucleate. Two eggs (central and right in the lower row) are mononucleates. Scale bar = 100 ^m. center of the egg. No difference was detected between the time course of a single nucleus and that of each of partial nuclei. According to Hamaguchi and Hiramoto (1986) two partial pronuclei fuse and then fuse with the sperm nucleus. Fused zygote nuclei formed a spindle (Fig. 3), and the time of the first clea
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. Figure 1. Unfertilized eggs stained with DAPI. Three eggs in the upper row are binucleates. One egg in the lower left is trinucleate. Two eggs (central and right in the lower row) are mononucleates. Scale bar = 100 ^m. center of the egg. No difference was detected between the time course of a single nucleus and that of each of partial nuclei. According to Hamaguchi and Hiramoto (1986) two partial pronuclei fuse and then fuse with the sperm nucleus. Fused zygote nuclei formed a spindle (Fig. 3), and the time of the first cleavage was normal. Thus, partial nuclei can only be detected during a short interval of de- velopment, and they leave no noticeable trace of their occurrence. Von Ledebur-Villeger (1972) and Mar (1980) found that the central migration of female nuclei still occurs, even in parthenogenetically activated sea urchin eggs without sperm asters. We confirmed this in Clypeaster. Figure 3. Fusion of partial pronuclei. Numerals are times in mm after fertilization. The two pronuclei fused at 17 min. Sperm aster is not clear in this series of pictures. The picture taken at 36 min shows the nuclear envelope starting to break down. At 42 min, polarization-optical observation reveals the anaphase spindle. 26°C. Scale bar = 25 >im. eggs activated by treatment with 10 Mg/ml Ca-ionophore (A 23187) for 2 min (Fig. 5), although the migration started later and was slower (Fig. 6) than that observed for normally fertilized eggs (also noticed by Mar, 1980). In any event, partial nuclei in activated eggs behaved sim- ilarly to single nuclei. Microtubule inhibitors suppress the migration of nuclei towards syngamy (Zimmerman and Zimmerman, 1967; Schatten and Schatten, 1981; Hamaguchi and Hiramoto 1986). Movement of Clypeaster nuclei was stopped by treating eggs with 1 mAl colchicine in seawater 5 min after activation. The movement of partial nuclei was sim- ilarly suppressed, and they remained separa
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
