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H W Beams

Publications and source records attributed to H W Beams.

At least 19 recordsLinked to original sources
PubMed1990

Freeze fracture and scanning electron microscope studies on the nuclear envelope and perinuclear cytomembranes (parabasal apparatus) in the protozoan, Lophomonas blattarum.

Phase contrast, scanning electron microscope (SEM), and freeze fracture studies on the parasitic flagellate, Lophomonas blattarum, have demonstrated that the endomembrane system (parabasal apparatus) is highly ordered, restricted in position to a perinuclear zone at the anterior end of the organism, and is supported in this localized cytoplasmic region by overlapping sheets or plates of microtubules, previously called the calyx and axial filament, which may participate in supporting the nucleus-endomembrane system in a restricted region of the cell. Light microscope observations, SEM and freeze fracture data provide support to previous views that the rough- and smooth-surfaced endoplasmic reticulum are interconnected and attached to the outer layer of the nuclear envelope. The continuity of these membrane systems provides an orderly and restricted packing in the perinuclear cytoplasm since other areas of the cell may become filled with yeast. These flagellates are especially adept at phagocytosis of entire yeast. In yeast-laden cells, the flagella-nucleus-parabasal body-calyx-axial filament complex may separate from the remainder of the cell and assume a motile existence for a time. The significance of the described relationships, in addition to providing efficiency in endomembrane localization, may also reflect synthesis of enzymes and proteins by the RER and packaging in the SER, both of which are continuous. Granules characteristic of glycogen are concentrated around the SER which may be involved in glycogen metabolism. Although critical information is lacking, the endomembrane system may also be involved in the synthesis and morphogenesis of lysosomes, and perhaps peroxisomes. Lophomonas thus amplifies a highly ordered spatial relationship between the nuclear envelope and the ER.

Animals↗
PubMed1986

Is the nuclear envelope a 'generator' of membrane? Developmental sequences in cytomembrane elaboration.

Early diplotene oocytes from Necturus maculosus ranging from approximately 0.2 to 0.5 mm in diameter were examined by electron microscopy. In the smallest oocytes of this range, the cytoplasm is largely devoid of membranes, but contains primarily ribosomes and mitochondria. In slightly larger oocytes, smooth-surfaced cytomembranes first appear in the perinuclear cytoplasm. At this time, the outer layer of the germinal vesicle nuclear envelope (GVNE) shows frequent connections with long membranous lamellae that extend for considerable, but variable distances into the juxtanuclear ooplasm. The number of smooth membranous lamellae increases tremendously as the oocytes increase in diameter. In such oocytes as well, frequent continuities are observed between the outer membrane of the GVNE and many of the cytoplasmic membranes. Eventually, as the ooplasm becomes populated with extensive numbers of membranous lamellae, instances of continuity between the membranous lamellae and nuclear envelope now become sparse and eventually non-existent. The frequent connections observed between membranous lamellae and the outer membrane of the GVNE during a circumscribed interval of diplotene strongly implicate the GVNE in the generation of extensive amounts of cytoplasmic membrane. The ooplasm of larger oocytes in the size range indicated contain numerous Golgi complexes and large quantities of annulate lamellae most of which are positioned in the peripheral or subcortical ooplasm, as well as extensive quantities of smooth membranes of the endoplasmic reticulum and lipid droplets.

Animals↗
PubMed1985

The presence and distribution of gap junctions in the oocyte-follicle cell complex of the zebrafish, Brachydanio rerio.

Membranes of teleost female gametes and investing layer of follicle cells characteristically exhibit a prolonged, close spatial relationship. This relationship is manifested, in part, by numerous folds of the plasma membrane of both oocyte and follicle cells that extend through channels called pore canals within a thick, laminated extracellular coat, the vitelline membrane. During oogenesis the folded oocyte processes, or microvilli, increase in number and length, but decrease in width. Follicle cell processes are frequently wider and less numerous than oocyte microvilli, but do not usually touch the unfolded portion of the oocyte surface. Throughout development, distal portions of oocyte microvilli contact either the proximal portion of follicle cell processes or unfolded parts of the follicle cell plasma membrane where many membranous specializations characteristic of gap junctions are present, especially during intermediate and later stages of oogenesis. Freeze-fracture replicas of the oocyte-follicle complexes revealed numerous localized aggregations of discrete intramembranous particles approximately 9-15 nm diameter that are characteristic of gap junctions. Gap junctions were located in the region of contact between the terminals of oocyte microvilli in relation to the different areas of the follicle cell plasma membrane. In ultrathin sections, the apposed plasma membranes of oocyte microvilli and follicle cells, in places, take the form of a seven-layered membrane approximately 18 nm thick which is bisected by a 2 nm gap that appears somewhat electron dense due to uranyl acetate stain. The location of gap junctions in the zebrafish oocyte-follicle is different from the situation in mammals where gap junctions are associated with cumulus cell processes as they make contact with the oocyte. The entire oocyte-follicle cell complex in the zebrafish contains the structural pathways for the transfer of small molecules between these cells.

Age Factors↗
PubMed1984

Relationships between annulate lamellae and filament bundles in oocytes of the zebrafish, Brachydanio rerio.

Bundles of filaments have been observed in the vitellogenic oocyte of the zebrafish, Brachydanio rerio; and these filaments illustrate a close spatial and structural relationship to annulate lamellae. The filaments range from 6-8 nm in diameter, and the annulate lamellae may cap both rounded ends of the bundle as well as extend parallel to the surface of the filament bundles. The ends of the filaments can be observed to exhibit an apparent termination in close relation to pore margins of the annulate lamellae, the membrane of the interpore regions of the annulate lamellae, as well as many nearby polyribosomes. The possible functional significance of this unique relationship is discussed in reference to a recent hypothesis regarding the function of annulate lamellae.

Animals↗
PubMed1984

Intracisternal tubules and intramitochondrial filaments in cells of a snail, Limnaea.

Epithelial and peritubular cells associated with the reproductive tract of the snail, Limnaea stagnalis, contain an extensive system of endoplasmic reticulum that is often dilated with many closely packed intracisternal tubules. The intracisternal tubules are approximately 24-28 nm in diameter and they are often hexagonally packed. They have a two-layered wall, possess fine interconnections, and extend linearly for considerable distances, but angular bends in the tubules also occur. Mitochondria in the peritubular cells contain solid, filamentous structures 9-12 nm in diameter and triangular-shaped structures when sectioned in the mitochondrial matrix.

Animals↗
PubMed1969

Annulate lamellae and "yolk nuclei" in oocytes of the dragonfly, Libellula pulchella.

Annulated membranes in the form of single and short lamellae are present adjacent to and parallel to the nuclear envelope in oogonia and early oocyte (synaptene) stages of the dragonfly, Libellula pulchella. These solitary and short annulate lamellae are usually continuous with long, part rough- and part smooth-surfaced cisternae which extend into more distal areas of the oogonial ooplasm. These particular annulate lamellae then either disappear or decrease in number to be replaced by a much more extensive system of annulate lamellae in the cortical ooplasm of previtellogenic oocytes. The differentiation of extensive stacks of annulate lamellae is consistently observed to be restricted to large cytoplasmic areas of considerable electron density. These cytoplasmic regions consist of material which stains basophilic and contains RNA but differs structurally from the large number of ribosomes which surround the dense masses. The cytoplasmic dense masses, in terms of their formation and staining reactions, are comparable to the "yolk nuclei" or "Balbiani bodies" described in insect oocytes in earlier studies. The results of the present study thus provide evidence that the appearance of cortical ooplasmic stacks of annulate lamellae in the dragonfly oocyte is specifically limited to cytoplasmic areas of high electron density which contain RNA but which do not have a ribosomal morphology.

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