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Biomedical subjects

A Ukeshima

Publications and source records attributed to A Ukeshima.

16 recordsLinked to original sources
PubMed1991

A fine morphological study of germ cells in asymmetrically developing right and left ovaries of the chick.

Germ cells of the chick ovary which develop asymmetrically on the right and left sides of the embryo were observed by electron microscopy from 7 to 17 days of incubation. Germ cells showed different patterns in the right and left ovaries, and also differences in the cortex and in the medulla. At 7 to 9 days, germ cells were individually present in both the right and left ovaries. They proliferated from 10 days onward and formed many cell aggregates. In each aggregate, germ cells were joined by intercellular bridges, and their cell cycles were synchronized. Although meiotic features of the germ cells were frequently found in the cortex of the left ovaries at 16 days, some germ cells exhibited these features at earlier days. In the meiotic germ cells, the "Balbiani body," which was composed of a concentration of cell organelles shifted to one pole of the cell, was always seen. The appearance of a meiotic nucleus and Balbiani body was characteristic of germ cells located in the left ovarian cortex, whereas those were never seen in the left medulla and in the right ovary. At 16 and 17 days, some germ cells were released into the lacunae of the medulla of both the right and left ovaries. The meaning of this phenomenon is discussed. Degenerating germ cells were frequently observed in the right ovary, but rarely in the left.

Animals↗
PubMed1991

Scanning and transmission electron microscopic observations of chick primordial germ cells with special reference to the extravasation in their migration course.

Chick primordial germ cells (PGCs) in the final course of their migration were observed by scanning (SEM) and transmission (TEM) electron microscopy, with an emphasis on their extravasation. The profile of the PGCs leaving blood vessels were first revealed under SEM. Chick embryos at stages 16 and 17 (about 2.5 days of incubation) were employed for the present study, since the PGCs emerging out of the vessels in teh gonadal area could be observed in high frequency at this developmental period. PGCs in the vessels showed a round profile, possessing many microvilli, while extravasating PGCs were rather oligovillous except the one side of the cell, where long filopodia extended toward the wall of the vessels. These filopodia seem to adhere to the wall of the vessels prior to emerging out. After extravasation, PGCs moved toward adjacent prospective gonadal epithelium and invaded it by amoeboidism. Following the settling down in the epithelium, PGCs showed rugged surface with few microvilli.

Animals↗
PubMed1990

Bilaterally persistent sciatic arteries.

A very rare developmental anomaly showing bilaterally persistent sciatic arteries was found in a cadaver of 89 year old female. Both right and left sciatic arteries arose from the internal iliac arteries and appeared between the piriformis and superior gemellus muscles at the buttock, being about 10 mm in diameter. Each artery, which accompanied by the companion vein, i.e. sciatic vein, sent the branches to the gluteus maximus and the flexor muscles of thigh. On the other hand, the femoral arteries of both lower limbs were smaller than usual, measuring 4.7 mm in left and 5.2 mm in right. The terminal vessels of those were joined to the sciatic arteries at the popliteal fossa. In addition, the present case also had another developmental anomaly, i.e. superficial brachial artery in the right upper limb.

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PubMed1989

The sites of intra-embryonic haemopoiesis prior to the hepatic haemopoiesis in the chick.

The sites of intra-embryonic haemopoiesis of the chick embryo (stages 15-26) preceding the initiation of hepatic haemopoiesis was investigated by means of serial sections stained with azan liquid. Hitherto undescribed blood islands of large size and clear outline were found in the neck and lateral body fold of the embryo. They consisted of dense aggregations of erythroblasts and thin endothelial cells surrounding them, and could be clearly identified by azan staining. In the neck, the blood islands were located near the branchyal arteries at stages 15-18, while in the lateral fold they were seen mainly at stages 17-19. Examination of serial sections indicated that the blood islands extended in a cephalocaudal direction, assuming a rod shape. The largest blood island was found in the lateral fold, measuring 50 microns in diameter and 900 microns in length. Besides these islands, occasional sites of haemopoiesis were found in the mesonephros, mesentery, dorsal regions of the trunk, head and allantois after stage 18. As the blood islands found in this study alternated their localization sites according to developmental stage, they were considered to be temporary haemopoietic tissues rather than persistent ones.

Animals↗
PubMed1988

Formation of flagella during interphase in secondary spermatocytes from Xenopus laevis in vitro.

In cell culture, single motile flagella, 1 micron in length, were observed to grow from secondary spermatocytes of Xenopus laevis within 2-3 hours after telophase I, at 22 degrees C. About 90% of the secondary spermatocytes formed flagella as observed by phase-contrast microscopy. The flagella grew up to 2-6 microns in length during interphase II, which lasted about 18 hours. The presence of the "9 + 2" microtubular structure of the flagellar axonemes of secondary spermatocytes was confirmed by electron microscopy. When chromosomal condensation began (prophase II), the flagella were resorbed into the cells and, after the second meiotic division, a flagellum was formed again by each of the round spermatids. Thus, there appears to be a close relationship between the meiotic division cycle and the formation of flagella. The possible contribution of Sertoli cells to the formation of flagella in secondary spermatocytes was examined by reducing the number of Sertoli cells to less than ten per culture. Under these conditions, flagella formed in secondary spermatocytes with very high efficiency. It is very likely that secondary spermatocytes form flagella in vivo, since the secondary spermatocytes were observed to have flagella immediately after dissociation of the testes.

Animals↗
PubMed1987

Relationship between genital ridge formation and settlement site of primordial germ cells in chick embryos.

Chick embryos from stage 15 to stage 18, which is the most frequent extravasation period, were investigated by means of serial sections and light microscopy in order to learn the detailed relationship between the settlement sites of the primordial germ cells (PGCs) and the forming genital ridge. PGCs circulating in the vascular system came out of the small vessels in the splanchnopleure posterior to the vitelline artery. This PGC extravasation was limited to an area about 1.2 mm caudal to the vitelline artery. After the extravasation, the PGCs entered the neighboring thickened coelomic epithelium of the splanchnopleure. This thickened epithelium, which had incorporated the PGCs, changed the location toward the future gonadal site with the advance of development. At stage 16, the thickened portion of the epithelium was located in the splanchnopleure; then it moved toward the somatopleure via the coelomic angle; finally, at stage 18, this epithelium occupied the region between coelomic angle and the mesonephros which corresponded to the future genital ridge. This means that the thickened epithelium of the splanchnopleure which initially incorporated the PGCs becomes the superficial epithelium of the genital ridge in more advanced stages. The thickened portion of the epithelium of the splanchnopleure at stage 16 is thought to be the definitive gonadal anlage.

Animals↗
PubMed1976

The origin, migration and morphology of the primordial germ cells in the chick embryo.

Chick primordial germ cells (PGCs) which separated from the "germinal crescent" entoderm in the period from stages 4 to 8 circulated mostly through the developing blood vessels from stage 10 onward and finally migrated into the gonad. The PGCs making their appearance up to this stage were generally spherical in profile, about 14 mum in diameter. Some of the PGCs in contrast, did not enter the blood vessels but remained in the tissue (mesenchyme) of the embryo proper (tissue PGCs) and possessed pseudopodial processes, suggesting their migration by means of amoeboid movements. The circulating PGCs emerged from blood vessels in the vicinity of developing gonads by three days (gonadal PGCs). The principal mechanism responsible for the subsequent migration of gonadal PGCs is assumed to be amoeboid movements as in the case of tissue PGCs. Notable amounts of PAS-positive glycogen were demonstrated in the cytoplasm of PGCs in all stages obsreved. They also contained yolk and lipids intracytoplasmically, the former dissipating in relatively early stages of development. Electron microscopic observation revealed the electron-opaque, "fragmented nucleolus" in the large nucleus (8 mum in diameter), which represented another prominent feature of chick PGCs. PGCs contained a well-developed Golgi complex and endoplasmic reticulum.

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