. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 266 Y. K. MARUYAMA. \ K Figure 2. Dissociation of spindle organization-centers from the nucleus in oocytes compressed before GV migration (at K) mm of maturation). The oocytes were successively observed (A-J and K-L illustrate different oocytes). A: 23 min. The arrow-head points to the pole. B. C: 33 min. The GV has broken down. The distance between the GV and the pole is 72 ^m. A pair of asters (indicated by arrows: also in D) at the pole (top), and the clear spot (bottom) at the antipole, are seen. D: 48 min. E: 58 min. Th
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 266 Y. K. MARUYAMA. \ K Figure 2. Dissociation of spindle organization-centers from the nucleus in oocytes compressed before GV migration (at K) mm of maturation). The oocytes were successively observed (A-J and K-L illustrate different oocytes). A: 23 min. The arrow-head points to the pole. B. C: 33 min. The GV has broken down. The distance between the GV and the pole is 72 ^m. A pair of asters (indicated by arrows: also in D) at the pole (top), and the clear spot (bottom) at the antipole, are seen. D: 48 min. E: 58 min. The arrow points to the chromosomes. F: 63 min. G: 73 min. H: S3 mm. I: 88 min. J: 98 min. K: Another oocyte at 40 mm. A pair of asters are some distance from the nucleoplasmic area. L: The same oocyte as K. observed under a polarizing microscope. The pair of asters show a spindle-like figure. A birefringent body (bottom-right) is the clear spot. Bars: 50 ^m (in A for A-B. in C for C-J. and in K for K-L). Temperature: 24-2VC. Results Meiolic events in intact oocytes In prophase-arrested oocytes, the GV was located cen- trally or slightly off-center toward the pole (Fig. 1 A). The GV began to migrate toward the pole 11 -15 min after the start of maturation (27-29°C), and finally became asso- ciated with the pole (Figs. 1 B. C). Follicle cells surrounding each oocyte were detached during the migration. The GV broke down at about 20 min (Fig. ID), and the disap- pearance of its membrane left a transparent nucleoplasmic area adjacent to the pole. Chromosomes and two small birefringent asters appeared there, and a spindle with two astral foci formed (Fig. 1H). Chromosomes were aligned to form a metaphase plate (Fig. 1 E). The newly formed meiotic spindle was oriented obliquely or vertically with regard to the main axis of the oocyte, denned by the pole (Fig. 1H). Through its rotation at 30-40 min (Fig. II). the spindle was "attached" to the pole with one end (Fig. U). With
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
