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Biomedical subjects

M M Perry

Publications and source records attributed to M M Perry.

At least 37 records · Page 2Linked to original sources
PubMed1979

The demonstration of very low density lipoprotein in the basal lamina of the granulosa layer in the hen's ovarian follicle.

The isolated basal lamina from the granulosa layer in ovarian follicles of the domestic fowl contains an abundance of spherical particles with a modal cross-sectional diameter of 25-30 nm. The lipid in this basal lamina is predominantly triacylglycerol and its total fatty acid composition resembles that of plasma very low density lipoprotein (VLDL). Immunodiffusion studies and immunoelectrophoresis indicated that this basal lamina contains diffusible antigen identifiable with plasma VLDL. Perfusion with an alkaline buffer displaced the particles from the basal lamina and subsequent perfusion with plasma VLDL in an acidic buffer resulted in the reappearance of particles of similar size and form. Alternatively, when the perfused basal lamina was subsequently perfused with VLDL-free serum, few particulate structures were observed. Measurements of total and VLDL triacylglycerol together with electron microscope studies of the untreated and of the perfused basal lamina provided further evidence for the identification of the majority of particles with plasma VLDL. Other particulate lipoprotein is most probably plasma low density lipoprotein (LDL). These studies demonstrated that this basal lamina is permeable to the circulating VLDL of the laying fowl.

Animals↗
PubMed1979

Yolk transport in the ovarian follicle of the hen (Gallus domesticus): lipoprotein-like particles at the periphery of the oocyte in the rapid growth phase.

Thin sections of the oocyte periphery and surrounding granulosa layer from 1--5 day preovulatory follicles were examined by transmission electron microscopy. With the use of certain procedures in tissue preparation, notably the tannic acid method, numerous particles in the range of 15--40 nm with a mean diameter of 27 nm were observed in both extra- and intracellularly. The particles were abundant in the granulosa basal lamina, in the spaces between the granulosa cells and in the perivitelline space. They appeared to adhere to the oolemma as a continuous double layer which was also observed to line the coated vesicles, 200--350 nm in diameter, invaginating from the oolemma. The layer of particles was not found on the plasma membranes of the granulosa cells, nor were particles present within the cells. In the peripheral cytoplasm of the oocyte the yolk spheres, ranging upwards from 250 nm diameter, were membrane-bound and contained tightly packed particles similar to those on the oolemma. Bodies displaying features intermediate between coated vesicles and yolk spheres suggested that, on entry into the cell, loss of the cytoplasmic coat and obliteration of the vesicular lumen gave rise to nascent yolk spheres which then fused together to form the larger spheres. The extracellular layer, coated vesicles and smaller yolk spheres were absent in oocytes fixed after a 10-min delay. The evidence indicated that 27-nm particles were transferred from the basal lamina to the oocyte surface via the intergranulosa cell channels, incorporated into the cell by adsorptive endocytosis and then transferred to the yolk spheres with little morphological alteration. The identity of the particles with very low density lipoproteins, the major components of the yolk solids, was discussed.

Animals↗
PubMed1978

Electron microscope observations on the ovarian follicle of the domestic fowl during the rapid growth phase.

A survey has been made of the ultrastructural features of the oocyte surface and its enveloping layers, comprising the theca, the granulosa and the perivitelline layer, during the final growth phase of 'yellow yolk' deposition. The following observations suggest that many macromolecular components of the blood plasma have free access from the vasculature to the oolemma: the fenestrated structure of the endothelium of the thecal capillaries, the intercellular spaces containing several erythrocytes in the theca interna, the 20-30 nm particles in the granulosa basal lamina, the wide spaces between the granulosa cells, and the open meshwork of fibres in the perivitelline layer. Numerous coated pits and vesicles, of 0.25-0.35 micron diameter, in the highly convoluted surface layer of the oocyte provide a mechanism for the incorporation of yolk precursors by pinocytosis. Such large coated vesicles and wide spaces between the granulosa cells are lacking in follicles in the preceding growth phase, which is concerned with the deposition of 'white yolk'. Considerable metabolic activity of the granulosa cells is indicated by their prominent Golgi elements, diverse granules, vesicles and villus processes. Cell junctions at the tips of the macrovilli anchor the granulosa to the oocyte. The theca externa, which provides mechanical support for the oocyte and its vascular and nervous elements, consists of sheets of collagen fibrils and fibroblast-like cells. Microfilaments in these cells may contribute to the contractility of the theca. Groups of interstitial cells associated with nerve fibres are present in the theca interna.

Animals↗
PubMed1978

The structure of the germinal disc region of the hen's ovarian follicle during the rapid growth phase.

The structure of the ovarian follicle in the region of the germinal disc, which appears as a white plaque at the surface of the oocyte, was examined by electron microscopy and compared with the non-disc region which overlies the yellow yolk mass of the oocyte in the final growth phase. The main differences concerned the granulosa cell layer and the surface layer of the oocyte. In the disc the granulosa cells were less regularly arranged and the spaces between them varied in width. Their mitotic rate was higher than that in the non-disc region, where cell division was seldom observed at maturity. The perivitelline layer was comparatively poorly developed at the periphery of the germinal vesicle in 15 mm follicles, but eventually attained a uniform thickness throughout the follicle. In the intercellular and perivitelline spaces there were smaller amounts of granular material. Marked differences were observed in the ooxyte surface layer. In 15 mm follicles the surface of the germinal disc was thrown into numerous microvilli and some narrow indentations containing macrovilli from the granulosa cells. Coated vesicles, 120 nm diameter, appeared to be invaginating from the oolemma, whereas 70 nm coated vesicles were present in the deeper cytoplasm. In follicles of more than 25 nm diameter these structural conformations were evident only at the periphery of the disc; for the most part the 120 nm coated vesicles were absent, and over the germinal vesicle microvilli were of rare occurrence. On the other hand, the bulk of the oocyte surface was highly convoluted throughout this period of growth, numerous granulosa cell macrovilli extended into deep pouches associated with 300 nm coated vesicles, and the oolemma possessed a coating of fuzzy material. These observations suggest that there is a restricted passage of yolk precursors to the surface of the germinal disc, and that the inability to transport yellow yolk into the disc is related to differences in the oolemmal surface coat and the population of coated vesicles. The surface modifications, as well as the proliferation of the granulosa cells, are likely to be influenced by the presence of the germinal vesicle.

Animals↗
PubMed1976

The permeability to cytochalasin B of the new unpigmented surface in the first cleavage furrow of the newt's egg.

Two of 10 mug/ml cytochalasin B (CB) caused retraction of the first cleavage furrow in Triturus eggs, a spreading of the unpigmented surface from the furrow region and a flattening of the whole egg. CB appears to act against the contractility of the microfilamentous band at mid-cleavage so as to relax the furrow and also to weaken unpigmented surface to allow the egg to flatten. Uncleaved eggs and the initial formation of the cleavage groove were unaffected by CB. A fully-retracted first cleavage furrow reformed itself on transfer of the egg to normal medium but only at the time of second cleavage. Initiation of second cleavage depended upon there being sufficient of the original pigmented surface on the animal hemisphere. Tritium-labelled CB of high specific activty was prepared and used to study its ability to penetrate the surface of newt eggs during cleavage. Scintillation couting of whole eggs showed that CB was not taken into the newt egg until mid-cleavage (about 17 min after the double stripe stage) when new surface began to spread in the cleavage furrow. Fixation in glutaraldehyde and osmium tetroxide retained radioactivity in the egg, but more CB was retained after fixation in osmium tetroxide alone than after double fixation. Most of the retained radioactivity was in yolk platelets. Autoradiographs were prepared to sectioned eggs which had been fixed at late cleavage after [3H]CB had flattend the furrow. These showed that CB entered the egg through the unpigmented surface which formed in the furrow but it could not enter through the pigmented surface. The impermeability of the pigmented surface explains the observations that CB does not prevent initial furrowing at cleavage. Once inside the egg CB is transported slowly. CB penetrates to a limited extent beneath the pigmented surface from its border with the unpigmented surface in the first cleavage furrow and this seems insufficient in some circumstances to suppress the contractile phase of second cleavage.

Animals↗
PubMed1976

Abnormalities in the differentiation and cellular properties of hyperplastic lens epithelium from strains of chickens selected for high growth rate.

Similar morphological abnormalities of the lens of the eye of two unrelated strains of chicks, both of which had been selected for high growth rate, were found to be associated with epithelial cells showing marked deviations from the normal in cell surface properties, mitotic rate, capacity for differentiation, and in DNA, RNA and protein metabolism. The relationship between these modified properties and the observed morphology is discussed.

Animals↗
PubMed1976

Incorporation of tritiated cytochalasin B into ectodermal explants of the amphibian gastrula.

Ectodermal explants from gastrulae of Triturus alpestris were exposed to tritiated cytochalasin B (5 and 10 mug/ml) for 1/2-2 1/2 h. The flat explants failed to heal into compact spheres and the component cells gradually rounded up. Radioactivity in the fixed and sectioned material was analysed by light and electron microscopic autoradiography. Silver grains were found predominantly over the yolk platelets, but were also scattered over other cellular components. Areas containing pigment granules or the feltwork material, present in the apices of dissociating cells of the superficial layer, exhibited higher activity than areas containing mitochondria or cytoplasmic matrix. Lipid droplets and nuclei showed comparatively little activity. The results are discussed in relation to previous findings on the uptake of tritiated cytochalasin D by cell fractions.

Animals↗
PubMed1975

Microfilaments in the external surface layer of the early amphibian embryo.

A comparison was made by transmission electron microscopy of the microfilaments in the surface layers of the early embryos of Triturus alpestris and Xenopus laevis at stages of development up to neurulation. Actin-like filaments which bound heavy meromyosin (HMM) were found in cell extracts of all stages, but were comparatively rare in the newly fertilized egg. Ten nm microfilaments were present throughout development in Xenopus, and from the mid-neurula stage in Triturus. Both kinds of microfilament were located in the circumferences of superficial ectoderm cells at the level of the apical junctions, the 10 nm microfilaments in association with desmosomes which began to develop before gastrulation in Xenopus. The accumulations of microfilaments in the apical constrictions, which form in ectoderm cells of Triturus early gastrulae when dissociated in a calcium-free medium, suggest that they are contractile elements. In the absence of such accumulations in the cell apices, the reverse curling exhibited by Xenopus ectodermal explants is attributed rather to a separation of the cells' lateral borders. Cytochalasin B (5 mug/ml) caused ectodermal explants from the early gastrulae of both species to disaggregate. With the rupture of the apical junctions there was a disorganization of the associated microfilamentous layer.

Actins↗