• Applied Microscopy
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• v.18 no.1
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• pp.77-91
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• 1988

Since the Urechis unicinctus-oocyte grows asynchronously in the body fluid, various oocytes in developmental stages can be prepared from each individual. The oocytes obtained from the coelomic fluid are then classified into five developmental stages according to the fine structural features. The earlier oocytes (${\sim}18{\mu}m$) form cluster and thereafter the oocytes grow singly without a distinct support of somatic cell, such as accessory cell or matrix cell. The yolk granules begin to appear already in the oocyte of cluster stage, however, the typical yolk was observed at the stage IV. Therefore, it was suggested that the yolk deposition is correlated with the coelomic fluid. The mature oocyte measured about $150{\mu}m$ produces the invagination not only on oolemma(indentation) but also on nuclear envelope. After the formation of the indentation, the mature ooytes are stored in storge sacs. The fine structural features were combined in aspect of structural concept of light microscopical observation.

• Proceedings of the Korean Society of Fisheries Technology Conference
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• 2002.05a
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• pp.639-640
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• 2002

• Proceedings of the Malacological Society of Korea Conference
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• 2002.05a
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• pp.25-26
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• 2002

• Applied Microscopy
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• v.30 no.1
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• pp.61-72
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• 2000

Three fertilization envelopes (FE) have been observed after the artificial insemination of U. unicinctus oocytes. The substances of the first fertilization envelope, which is an effective barrier against excessive sperm, come mainly from the surface coat of the oocyte. The secretions of the cortical granules take part in formation of the 2nd fertilization envelope. Histologically, the 3rd fertilization envelope is not amorphous as seen under light microscope, but contains numerous panicles under electron microscope, which would be contributed to harden the envelope by 60 min after the fertilization. With the substantial similarity between the 1st fertilization envelope and the surface coat of the oocyte, and the coincidence of retraction of microvilli and the formation of the 1st fertilization envelope, it is suggested that the microvilli contain the sperm receptors in U. unicinctus. Some granular substances from the distal part of the acrosome diffuse on the surface coat of the oocyte while the acrosomal tubules penetrate into the surface coat. The acrosomal tubules arise from the proximal part of the acrosome and pass through the acrosomal lumen.

• Applied Microscopy
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• v.34 no.1
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• pp.71-81
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• 2004

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.

• Applied Microscopy
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• v.33 no.2
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• pp.105-116
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• 2003

In Vitro fertilization of U. unicinctus eggs observed by immunofluorescence and electron microscopes revealed an overview of the meiotic pattern of the tide animals. The eggs have been fertilized early at germinal vesicle stage, followed by germinal vesicle break down (GVBD), but pre-mitotic aster like structure could not be resolved by the methods employed in this work. The meiotic features, such as rotation-shift movement of spindle fibers, behavior of spermatozoonmonaster in the egg cytoplasm and active spindle fiber of the 1st polar body, have been observed. The antitubulin-FITC fluorescence show the 2nd meiotic apparatus appeared firstly parallel to the tangential line of the oolemma, proceeding the meiosis, its bipolarity is rotated and shifted towards the oolemma. The polar bodysite of the oolemma was not amorphous, but active in a sense of anti-tubulin-FITC reactions during the extrusions of the polar bodies. The immunofluorescence reactions of the spermatozoon centriole appeared at a later stage of the 2nd meiosis. During the time periods, the fertilized spermatozoon resided in the egg cytoplasm. Activating the centrioles, spermatozoon approaches towards the chromosomal materials of the 2nd oocyte. This suggests that spermatozoon centrioles initiate and play a roll to fuse male and female pronuclei.