인공수정에 의한 Urechis unicinctus 난자의 난할형식 = Cleavage Pattern of Urechis unicinctus Eggs in Vitro Fertilization

다국어 초록 (Multilingual Abstract)

When U. unicinctus mature oocytes were fertilized in vitro, germinal vesicle breakdown (GVBD) and meioses occurred and the zygotes entered cleavage stage. A modified pattern of spiral cleavages, suggestively based on behavior of mitotic spindles, have been observed in this work. The first and second cleavages were meridional and the third was equatorial, and then followed by repetitions of meridional-equatorial cleavage. The cleavage of the isolecithal egg were equal and holoblastic and its patterns were spiral. The anti-${\alpha}-,-{\beta}$- tubulin reactions and confocal microscopy revealed mitotic apparates tilted obliquely at each mitosis causing oblique displacements of the blastomeres. Despite isolecithal distribution of yolk, this observations implicated that tilting of mitotic apparates induced spiral cleavage and the displacements of blastomeres. However, these features would not be the typical spiral cleavage, but represented a modified pattern of known Spiralian s in the sense of the equal cleavage. During the first cleavage, heart-shaped eggs have been produced. Electron microscopies exhibited the first cleavage furrow extended with its membranous structure deeply into the cytoplasm. Contractile ring has not been observed.

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