LOCATION AND ULTRASTRUCTURE OF PRIMORDIAL GERM CELLS (PGCs) IN AMBYSTOMA MEXICANUM

The location and ultrastructure of the primordial germ cells (PGCs) were studied in Ambystoma mexicanum larvae of stages 23 to 47.
PGCs were found in the spaces between the endodermal cell mass and the lateral plate mesoderm at stages 23 to 35. Some of the PGCs at stage 35, and most of them at stages 40 and 42, were located near the Wolffian duct. At stages 46 and 47 all the PGCs were situated in the genital ridges. Cilia, which have hitherto never been reported in PGCs, were occasionally seen in PGCs of Ambystoma from stage 23 till stage 46.
No "germinal plasm" was found in the PGCs prior to stage 40. Specific structures or "nuage material", corresponding to the germinal granules or their derivatives in Xenopus , were first recognized in the vicinity of the nucleus at stage 40. Between stages 40 and 46, the amount of "nuage material" markedly increased. It was finally localized mainly in "intermitochondrial spaces". A possible transfer of material from the nucleus to the cytoplasm or vice versa through nuclear pores was first noticed at stage 40, the material concerned being quite similar in ultrastructure to the "nuage material".     

The fine structure of the endogenous stages of Isospora hemidactyli Carini, 1936 in the Gecko Hemidactylus mabouia from North Brazil

The ultrastructure is described of the meronts, microgamonts and young oocyst stages of Isospora hemidactyli of the gecko Hemidactylus mabouia from Belém, PA, north Brazil. The endogenous stages all develop in the nucleus of the gut epithelial cells. The nucleus remains intact up to the latest stages of the parasite's development, but degenerates by the time the oocyst appears. Merogonic division appears to be asynchronous, and some of the differentiated merozoites contained more than one nucleus. Microgamonts conform in structure with those of other eimeriids. Some of the type 2 wall-forming bodies disintegrate into smaller globules and ground substance of lower density.     

Ultrastructure of the somatic and germ cells of the testes of Dermestes frischii kugelann (Coleoptera : Dermestidae)

To provide a basis for subsequent studies of the effect of X-rays on Dermestes frischii (Coleoptera : Dermestidae), the ultrastructure of the somatic and germ cells of the testes of this species is described. The somatic cells are of 3 types, the apical, cyst wall, and follicle wall cells. The follicle wall consists of a single continuous layer of epithelial cells lying on a basal lamina, which in the germarium is subdivided and contains a discontinuous cell layer. With the exception of the dividing cells, details are given of all the germ cell stages. The pattern of spermatogenesis is generally typical of that observed in other Insecta but several novel observations are reported. In particular, large arc-shaped tubules associated with the nucleus and acrosome in the developing spermatid are reported for the first time and an unusual arrangement in which the axoneme is connected by amorphous strands to the mitochondrial derivatives and plasmalemma is described. The acrosome is very distinctive; the inner cone possesses a ball that fits into a corresponding socket in the nucleus. Details are given of centriole duplication in the primary spermatocyte and the stages leading to the formation of the definitive sperm plasmalemma. Where possible comparisons are made with other Coleoptera.     

Cytologic characteristics of "dark" and "light" cells in the brain amygdaloid complex

This paper reports data on cytological peculiarities of neurons of two main zones of sexual dimorphism in brain amygdala (dorsomedial nucleus and anterior cortical nucleus). The main attention was paid to some characteristics of "dark" and "pale" cells found in the amygdaloid complex for the first time. It is supposed that the dark and pale cells are targets for gonadal steroids, whose cyclic changes in concentration in the blood difined their functional states. Though the ultrastructure of dark and pale cells of the amygdaloid complex is similar to that of neurosecretory cells of hypothalamus, there are necessary electron microscopic and cytochemical evidences.     

Ultrastructure and microtubule organization of isolated generative cells ofAllemanda neriifolia at interphase and prophase

Summary The ultrastructure of isolated generative cells ofAllemanda neriifolia at interphase and prophase was studied. The microtubule organization of the isolated cells was also investigated by immunofluorescence microscopy with a monoclonal anti--tubulin. After the generative cells had been isolated from the growing pollen tubes by osmotic shock, most of the cells were at prophase and only a few were at interphase. The interphase cell is spindle shaped and contains an ellipsoidal nucleus. In addition to the usual organelles, the cytoplasm of the interphase cell contains numerous vesicles (each measuring 40–50 nm in diameter) and two sets of longitudinally oriented microtubule bundles — one in the cortical region and the other near the nucleus. Most of the prophase cells are spherical in shape. Based on the ultrastructure and the pattern of microtubule cytoskeleton organization three types of prophase cells can be recognized. (1) Early prophase cell, which contains the usual organelles, numerous vesicles, and a spherical nucleus with condensed chromosomes. Longitudinally oriented microtubule bundles can no longer be seen present in the early prophase cell. A new type of structure resembling a microtubule aggregate appears in the cytoplasm. (2) Mid prophase cell, which has a spherical nucleus containing chromosomes that appear more condensed than those seen in the early prophase cell. In addition to containing the usual organelles, the cytoplasm of this cell contains numerous apparently randomly oriented microtubules. Few vesicles are seen and microtubule aggregates are no longer present. (3) Late prophase cell, typified by the lack of a nuclear envelope. Consequently, the chromosomes become randomly scattered in the cytoplasm. Microtubules are still present and some become closely associated with the chromosomes. The changes in the ultrastructure and in the pattern of microtubule organization in the interphase and prophase cells are discussed in relation to the method of isolation of the generative cells.     

Implantation of cultured thymic fragments in congenitally athymic (nude) rats

Summary Cultured thymic fragments correspond to the thymic microenvironment depleted of lymphocytes and dendritic cells. When these fragments are implanted under the kidney capsule of congenitally athymic rats, lymphocytes and dendritic cells of host origin enter the graft and induce thymus-dependent immunity in the recipient. This paper describes the ultrastructure of the fragments and the changes that occur during the restoration of normal thymic architecture. At the end of the culture period of 6–9 days and in the early stages after implantation, the grafts consist of keratin-containing epithelial cells of unusual morphology that can be labelled with antibodies raised against the epithelium of the mid/deep cortex and the subcapsule/medulla. Normal thymic architecture develops, including nerves and blood vessels, as lymphocytes populate the environment, and by 4–6 weeks the epithelial cells are the same phenotypically and ultrastructurally as those found in normal rat thymus. However, some areas without lymphocytes still contain the atypical epithelial cells seen before implantation. Large multinucleated giant cells are also present with a few associated epithelial cells of subcapsular/medullary phenotype. In conclusion, the cultured thymic fragments contain a hitherto unknown precursor epithelial cell with an atypical ultrastructure and phenotype that is not seen in normal development.     

Ultrastructure of the Cell of Peucedanum terebinthaceum in Different Stages of Embryogenesis in Suspension Cell Culture

The ultrastructure of the cells from single cell to globular embryo stage in suspension culture were investigated. The amount and morphology of the organelles, especially the plastids spherosomes and protein bodies changed obviously during the embryogenesis. In embryogenetic clump stage there occured in the vacuolated cells direct nucleus division and peripheral cytoplasmic swelling. The vaeuolated cells returned to embryonic state quickly in this way. In this paper the physiological and biological significance of the ultrastructural changes of cells in different stages of somatic embryogenesis are discussed.     

Ultrastructural aspects of Ellipsomyxa mugilis (Myxozoa: Ceratomyxidae) spores and developmental stages in Nereis diversicolor (Polychaeta: Nereidae)

The ultrastructure of the spores and developmental stages of Ellipsomyxa mugilis in Nereis diversicolor were studied by transmission electron microscopy. The ultrastructure features and the developmental stages show many similarities with the general pattern described for other actinospores. However, several new features are definitely worth noting. For example, tetranucleated cells precede the formation of the initial pansporocyst, which preserves the 2 original enveloping cells until the end of sporogony. In the initial stages of sporogony, the future sporoplasm cell acquires the first secondary cell by an engulfment process. In the final stage of sporogony, spores are formed by a sporoplasm with 2 secondary cells and 1 somatic nucleus, and the polar capsule has a polar filament with a helicoidal arrangement possessing 7-8 coils.     

Differentiation of Rat Lens Epithelial Cells in Tissue Culture

The growth and differentiation of rat lens epithelial cells in tissue culture were studied. Cells could be maintained for a number of generations in an undifferentiated state in suspension culture. When cultured as monolayers, they grew and differentiated in a series of six defined stages described here. These stages include morphological changes (elongation, followed by cell "spreading" or formation of cell aggregates), and biochemical changes (appearance of y-crystallin protein as detected by immunofluorescence). The process of differentiation appeared to be accelerated in the vicinity of elongated cells, occurred more rapidly at high cell density, and required frequent changes of medium. This suggests that cell-cell communication, and not medium factors, may be essential for promoting differentiation. The final morphology of the differentiated cells differed, depending on the embryonic age of the rats used as a source of lens epithelial cells. This implies that the programme for differentiation changes as a function of the embryonic age of the lens.     

Differentiation of rat lens epithelial cells in tissue culture. (I) Effects of cell density, medium and embryonic age of initial culture.

The growth and differentiation of rat lens epithelial cells in tissue culture were studied. Cells could be maintained for a number of generations in an undifferentiated state in suspension culture. When cultured as monolayers, they grew and differentiated in a series of six defined stages described here. These stages include morphological changes (elongation, followed by cell "spreading" or formation of cell aggregates), and biochemical changes (appearance of nu-crystallin protein as detected by immunofluorescence). The process of differentiation appeared to be accelerated in the vicinity of elongated cells, occurred more rapidly at high cell density, and required frequent changes of medium. This suggests that cell-cell communication, and not medium factors, may be essential for promoting differentiation. The final morphology of the differentiated cells differed, depending on the embryonic age of the rats used as a source of lens epithelial cells. This implies that the programme for differentiation changes as a function of the embryonic age of the lens.     

The ultrastructure of Blastocystis galli from chickens

The ultrastructure stages of Blastocystis galli were studied in chicken's intestine and in laboratory cultures. There were found morphological structures: surface coat (cell from chickens' intestine showed a very thick surface coat); cell membrane--there were some small electron-opaque deepening "pockets" on the membrane; inner membrane; endoplasmic reticulum with attached ribosomes, which present in the cytoplasm; all cells contained numerous of small vacuoles and large glycogen inclusions in cytoplasm; mitochondria with tubular cristae; nucleus with granules condensed chromatin; central vacuole; Golgi complex was represented by number of plates grouped in a pite; the cyst-like forms were surrounded by multilayered wall.     

ULTRASTRUCTURE AND DEVELOPMENT OF THE INACTIVE STOMATA OF ANABASIS ARTICULATA (FORSK.) MOQ.

The guard cells of Anabasis articulata mature and senesce a short distance from the intercalary meristem in which they form. When the guard cells reach final size, their ultrastructure is similar to that of stomata of other plants. At this stage, they contain clearly definable, numerous mitochondrial profiles, chloroplasts with starch grains and plastoglobuli, active Golgi bodies, a large nucleus that stains deeply for chromatin and large vacuoles. During later stages of development the whole protoplasmic content becomes very dense, with myelin-like figures and crystals appearing in the vacuoles. The cell walls thicken considerably. This is especially true of the tangential walls, where the microfibrils of different lamellae vary in their orientation. It is suggested that as a result of these ultrastructural changes the guard cells lose the ability to move.     

Locus-specific and activity-independent gene repositioning during early tumorigenesis

The mammalian genome is highly organized within the cell nucleus. The nuclear position of many genes and genomic regions changes during physiological processes such as proliferation, differentiation, and disease. It is unclear whether disease-associated positioning changes occur specifically or are part of more global genome reorganization events. Here, we have analyzed the spatial position of a defined set of cancer-associated genes in an established mammary epithelial three-dimensional cell culture model of the early stages of breast cancer. We find that the genome is globally reorganized during normal and tumorigenic epithelial differentiation. Systematic mapping of changes in spatial positioning of cancer-associated genes reveals gene-specific positioning behavior and we identify several genes that are specifically repositioned during tumorigenesis. Alterations of spatial positioning patterns during differentiation and tumorigenesis were unrelated to gene activity. Our results demonstrate the existence of activity-independent genome repositioning events in the early stages of tumor formation.     

Electron microscopy of the thymus in two species of snakes, Crotalus atrox and Lampropeltis getulus

The lymphoid cell population of thymus in the rattlesnake and king snake is similar to that of mammals. Lymphocytes occupy the interstices of an epithelial cell framework. An abudance of tonofilaments and desmosomes occupy the cytoplasm of epithelial cells with light, homogeneous nuclei and prominent nucleoli. Other epithelial cells contain phagocytized material in a dense cytoplasm which surrounds an irregular nucleus with heavily clumped chromatin. Small, granular vesicles are found within some epithelial cells. Myoid cells occur in the medullary area. In mature forms, myofibrils are arranged in a concentric fashion around the nucleus and occupy much of the cytoplasmic volume. The presence of developmental stages of these cells suggests their differentiation within the thymus of the adult animal.     

Ultrastructure of the neurosecretory cells of the anterior commissural nucleus of the hypothalamus in rats

The ultrastructure of neurosecretory cells of the anterior commissural nucleus of rat hypothalamus is similar to that of the supraoptic nucleus and of the "magnocellular" part of the paraventricular nucleus. The only difference is a less expressed granular endoplasmatic reticulum and a smaller diameter of elementary neurosecretory granules (80-150 nm in diameter). Such elementary granules are characteristic of neurosecretory terminals located in the external zone of the median eminence. It is suggested that neurosecretory cells of the anterior commissural nucleus project to this neurohemal region.     

The ultrastructure of imaginal disc cells in primary cultures and during cell aggregation in continuous cell lines

We have examined the ultrastructure of cellular vesicles in primary cultures of wing imaginal disc cells of Drosophila melanogaster. These cells maintain the apico-basal polarity characteristic of epithelial cells. The apical surfaces secrete extracellular material into the lumen of the vesicle from plasma membrane plaques at the tip of microvilli. During the course of one passage, cells from the established cell lines grow to confluence and then aggregate into discrete condensations joined by aligned bridges of cells. Cells in these aggregates are tightly packed, and there appears to be a loss of the epithelial polarity characteristic of the vesicle cells. Elongated cell extensions containing numerous microtubules are found in aggregates, and we suggest that these may be epithelial feet involved in the aggregation process. Virus particles are commonly found both within the nucleus and the cytoplasm of cells in the aggregates.     

Uterine epithelial morphology and progesterone receptors in a mifepristone-treated viviparous lizard Pseudemoia entrecasteauxii (Squamata: Scincidae) during gestation

Structural and functional changes to the uterus associated with maintenance of pregnancy are controlled primarily by steroid hormones such as progesterone. We tested the hypothesis that progesterone regulates uterine structural changes during pregnancy in the viviparous skink, Pseudemoia entrecasteauxii, by treating pregnant females with the progesterone receptor antagonist mifepristone at different stages of pregnancy. Expression and distribution of progesterone receptor was determined using Western blot and immunohistochemistry. During early pregnancy, mifepristone treatment resulted in altered uterine epithelial cell surface morphology and high embryo mortality, but did not affect females at mid and late stages of pregnancy. Females treated with mifepristone in early pregnancy exhibited abnormal uterine epithelial cell morphology such as lateral blebbing and presence of wide gaps between cells indicating loss of intercellular attachment. Chorioallantoic membranes of the embryo were not affected by mifepristone treatment. Two isoforms (55 kDa and 100 kDa) of progesterone receptor were identified using immunoblots and both isoforms were localized to the nucleus of uterine epithelial cells. The 55 kDa isoform was expressed throughout pregnancy, whereas the 100 kDa isoform was expressed during mid and especially late pregnancy. In P. entrecasteauxii, mifepristone may prevent successful embryo attachment in early pregnancy through its effects on uterine epithelial cells but may have little effect on pregnancy once the maternal-embryo structural relationship is established.     

Ultrastructural description of new Rickettsia-like organisms in the commercial abalone Haliotis tuberculata (Gastropoda: Haliotidae) from the NW of Spain

Rickettsia-like organisms (RLOs) were found in the commercially farmed abalone Haliotis tuberculata in the northwestern region of the Atlantic Coast of Spain and are described from light and transmission electron microscopy observations. The RLOs measured approximately 1.6 x 0.9 microm and were found in intracytoplasmic, spherical to ellipsoidal vacuoles (up to 8 microm) in the epithelial cells of the digestive diverticulae. The morphological ultrastructure of these organisms was typically prokaryotic, including a plasmalemma and a thin Gram-negative type cell wall. Several ultrastructural changes were observed in the epithelial cells of the host containing the RLOs. The nuclei became pycnotic and several basophilic dense inclusions appeared in the cytoplasm. In addition, the host cell appeared lysed and was ruptured in advanced stages of infection. It was impossible to ascertain whether the RLOs are responsible for this disease, as a haplosporidian infection was also present. We can only conclude that the presence of RLOs simultaneously with a haplosporidian parasite may contribute to the mortality of the abalone host.     

The ultrastructure of the zoospores of the parasitic dinoflagellate <Emphasis Type="Italic">Ichthyodinium chabelardi</Emphasis> Hollande et J. Cachon, 1952 (Alveolata: Dinoflagellata)

This is the first study on the ultrastructure of the zoospores of Ichthyodinium chabelardi, a parasitoid of the fish egg and early larval stages. The zoospores were characterized by the cell structure specific for dinoflagellates; particularly, cells contained large trichocysts and the “dinokaryon”-type nucleus. An unusual large electron-transparent zone was the only significant difference from the “classical” cell structure in Dinoflagellata. We did not find cell structures for the penetration to the host cell (microtubular basket, conoid, or secretory organelles such as rhoptries). The data on the fine structure of the zoospores of I. chabelardi agree with the results of molecular phylogeny; this allows us argue that excluding this species from Dinoflagellata and assigning it to Protalveolata was a mistake.