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Biomedical subjects

A Ukeshima

Publications and source records attributed to A Ukeshima.

At least 19 recordsLinked to original sources
PubMed1996

Germ cell death in the degenerating right ovary of the chick embryo.

The right ovary of chick embryos is known to degenerate during embryogenesis, while the left one advanced its normal growth. The present study demonstrates germ cell death in the degenerating right ovary. In the process of germ cell death, chromatin condensation, reduction of cell size, and formation of apoptotic bodies were observed. The cell organelles were almost normal in the early stages of the process. Fragments of broken germ cells were phagocytosed by neighboring cells or macrophages. From these observations, it may be assumed that germ cell death in the right ovary of chicks is related to apoptosis. In the normal left ovary, similar cell death was only observed in the germ cells in the medulla, but not in the cortex. Therefore, germ cell death seems to be a phenomenon common to the medullae of both the right and left ovaries.

Animals↗
PubMed1995

Surface morphology of quail ovaries in late embryonic stages.

Embryonic quail ovaries were examined with a scanning electron microscope. The same as in many bird species, the quail ovary degenerated on the right side, and normal development occurred only on the left side. The surface of the developing left ovary had a rough appearance. The epithelial cell surface was extremely swollen with many globular protrusions, and the cell borders were lined by ridge-like protrusions. On the other hand, the degenerating right ovarian surface was rather smooth in appearance. Each cell surface had a few short microvilli. Several stomata were found near the border between the ovary and mesonephros in the posterior region of the right ovary. The size and number of stomata were variable, but tended to increase in the later stages. These findings were compared with those in the chick ovary, and a discussion is included.

Animals↗
PubMed1994

Abandonment of germ cells in the embryonic chick ovary: TEM and SEM studies.

BACKGROUND: Embryonic chick ovary forms medulla and cortex successively in early developmental stages. Unlike the cortex, which is a functioning tissue in the adult, the medulla regresses as development advances. Although germ cells are included in these respective regions, their behavior within these regions is different. This study focuses on the fate of germ cells in the medulla of both ovaries. METHODS: Germ cells found in the medulla of the developing chick ovary from 7 to 19 days of incubation were observed by TEM and SEM. RESULTS: From 10 days of incubation onward, medullary germ cells in both right and left ovaries were often released into medullary lacunae. During the releasing process, germ cells were covered by thin cytoplasm of epithelial cells of the lacunae. After release, however, they were freed from the thin coat of epithelial cells. Abandoned germ cells were seen in the lacunae as solitary cells or as a mass composed of several cells. In the right ovary, germ cells released into the lacunae were subsequently found at the holes of the ovarian surface, which were continuous with the medullary lacunae. Moreover, germ cell death was often found in late stages in the medullary tissues of both right and left ovaries. CONCLUSIONS: The present study clarifies the fact that chick germ cells of the medulla of both right and left ovaries are either discarded by a process of programmed cell death and/or released into medullary lacunae with increasing embryo age.

Animals↗
PubMed1993

Ultrastructural characteristics of primordial germ cells in the quail embryo.

An avian species, the quail has become a desirable animal model in experimental embryology and reproductive biology. To understand the ultrastructural characteristics of primordial germ cells (PGC) of this species, we studied PGC in the Japanese quail (Coturnix coturnix japonica) embryo at various developmental stages from their appearance in the germinal crescent through migration to settlement in the gonadal ridges by means of electron microscopy. The results were compared with those of another well-known avian species, the chick. Several ultrastructural characteristics of quail PGC not described previously in chick PGC were observed as follows: 1) No glycogen particles were detected in the cytoplasm at any stage examined. 2) Electron-dense and membrane-bounded granules were found in the PGC cytoplasm during the sexually indifferent gonadal stages. 3) Quail PGC were characterized by a prominent nucleolus associated with condensed chromatin (heterochromatin), and the developmental changes of the nucleus were noted; the nucleolus initially appeared as a compact mass at the germinal crescent stage and became dispersed at later stages during the colonization of the gonadal ridges. These findings suggest several physiological and functional differences in the cell cycle between these two avian species. This is the first report describing detailed ultrastructural characteristics of PGC in the quail embryo.

Animals↗
PubMed1993

The sites and expansion of intra-embryonic blood islands in the early chick embryo.

The intraembryonic blood islands preceding the hepatic haemopoiesis, were examined in embryos from stage 17 to 19 by light microscopy, and their three-dimentional expansion was demonstrated. These blood islands were located in the mesenchyme of the lateral fold, mesentery, allantois and ventral aorta, commonly showing large scale. Except the lateral fold, however, those were just temporary sites. Particularly large islands were necessarily found in the mesenchyme of the lateral fold at the stages examined. They were present bilaterally and exhibited cephalocaudally long, rod-like structures with variable sizes. The largest island measured over 2,600 microns in length.

Animals↗
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.

Aged↗
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↗
PubMed1986

Surface morphology of the human yolk sac: endoderm and mesothelium.

The yolk sac of human embryos from the 5th to 7th week of gestation was first revealed under the scanning electron microscope (SEM) with complementary observations under the transmission electron microscope (TEM). The inner and outer surfaces of the human yolk sac basically showed profiles similar to those of other mammalian yolk sacs reported by previous workers. The free surface of the endodermal cell measured 10-15 microns in diameter and was only slightly swollen in its earlier stages, possessing microvilli of 100-600 nm in length. On the other hand, the outer surface of mesothelial cells was swollen, but much smaller in size (8-10 microns). The mesothelial microvilli were much longer than those of the endoderm, measuring about 1.5 micron in length. On the endodermal surface, ruffles and various sizes of holes with short microvilli were occasionally found. The latter became larger with development, and seemed to be continuous with the endodermal tubules.

Endoderm↗
PubMed1982

Microscopic studies on chick thrombocytes in early development.

Thrombocytes of early chick embryos were observed in blood smear and whole embryo preparations stained with PAS. In the blood smear preparations, thrombocytes usually had one large glycogen mass in the cytoplasm until 3 days of incubation, and it became progressively smaller with the advance of embryonal development. While, the application of PAS to whole embryo preparations was shown to be a very useful method for observation of the blood cells in embryos at early stages when their blood could not be collected. Thrombocytes were clearly identified in situ in the embryo by PAS staining even in very early stages when no blood circulation occurred. At stage 12, distribution of the thrombocytes coincided with that of blood islands, but was limited within the area opaca. Mitotic figures of the thrombocytes were frequently found in and near the blood islands. This suggests that blood islands are the proliferation sites of the thrombocytes in early chick embryos.

Animals↗