Vitelline Membrane :: ultrastructure
Tissue Cell. 2011 Aug ;43 (4):230-7 21550621
Sugadaira Montane Research Center, University of Tsukuba, Sugadaira Kogen, Ueda, Nagano 386-2204, Japan. firstname.lastname@example.org
The structural features of eggs of Zorotypus caudelli Karny are described in detail. The egg is elliptic with long and short diameters of 0.6 and 0.3 mm respectively, and creamy white. The egg shows a honeycomb pattern on its surface, without any specialized structures for hatching such as an operculum or a hatching line. The fringe formed by a fibrillar substance secreted after the completion of the chorion encircles the lateral surface. The egg layer is composed of an exochorion, an endochorion, and a vitelline envelope. The exochorion and endochorion are electron-dense and homogeneous in structure. The exochorion shows a perforation of numerous branching aeropyles. The exo- and endochorion are connected by numerous small columnar structures derived from the latter. The vitelline envelope is very thin and more electron-dense than the chorion. A pair of micropyles is present at the equator on the dorsal side of the egg. Originating at the micropyle, the micropylar canal runs through the chorion obliquely. The structural features of the eggs of Zoraptera were compared with those of other polyneopteran and paraneopteran orders.
Most cited papers:
Release of ovoperoxidase from sea urchin eggs hardens the fertilization membrane with tyrosine crosslinks.
One feature of fertilization is the alteration of the vitelline layer, by components released from the egg, to produce an elevated, covalently crosslinked, hard, insoluble, fertilization membrane. The following evidence indicates that crosslinking and hardening are caused by the production of diand trityrosyl residues, by oxidation of protein-bound tyrosyl residues in the presence of a peroxidase. Hardening of the fertilization membrane, as evidenced by its loss of solubility in 50 mM dithiothreitol, is inhibited by compounds known to inhibit many peroxidases. A peroxidase, here called the ovoperoxidase, is released from eggs at fertilization. This enzyme is inhibited by the same compounds that inhibit hardening and at similar concentrations. Inhibitors of the ovoperoxidase and the hardening reaction include KCN, 3-amino-1,2,4-triazole, NaN(3), phenylhydrazine, K(4)Fe(CN)(6), sodium sulfite, and glycine ethyl ester. In addition, tyramine and N-acetyltyrosine both inhibit hardening, but O-methyltyrosine does not. Dityrosyl and trityrosyl residues are found in acid hydrolysates of isolated, hardened fertilization membranes. These residues have been identified by cellulose phosphate column chromatography, thin-layer chromatography, and amino acid analysis. The amino acid data have been used to estimate that there is one dityrosine crosslink per 55,000 daltons of protein. We suggest that, by catalyzing the crosslinking of tyrosyl residues, the ovoperoxidase leads to the production of a hard fertilization membrane that blocks the entry of additional sperm. Because peroxidases are spermicidal, a secondary function of the enzyme could be to kill sperm in the vicinity of the fertilized egg.
The clinical and pathologic features of 71 endodermal sinus tumors of the ovary were studied in an effort to delineate the histogenesis and biologic behavior of this neoplasm and to evaluate the efficacy of different forms of treatment. Alpha-fetoprotein (AFP) was identified in hyaline droplets, cell cytoplasm, and intercellular spaces of all 15 tumors examined by an immunoperoxidase technique; this supports the view that the neoplasm simulates yolk sac endoderm. There were only nine survivors among 65 patients on whom follow-up information was available; the actuarial survival was 13% at 3 years. Of the neoplasms that recurred, 93% did so within 1 year, and of those patients who died, 93% did so within 2 years. The size and stage of the tumor had prognostic significance, but the patient's age, the mitotic activity, and histologic pattern did not. Although 71% of the patients had Stage I tumors at the time of diagnosis, subclinical metastasis was present in 84% of Stage I patients. Triple chemotherapy (vincristine, actinomycin D, and cyclophosphamide (VAC)) employed after unilateral salpingo-oophorectomy in four patients with Stage I tumors resultivors among 12 Stage I patients treated with combined surgery and radiation. The finding of AFP in all tumors in which this was evaluated suggests that serum radioimmunoassay might be useful to monitor response to therapy.
The eggshell of Drosophila melanogaster. I. Fine structure of the layers and regions of the wild-type eggshell.
The fine structure of the several layers and regional specializations in the Drosophila melanogaster eggshell has been studied by a combination of shell isolation procedures and ultrastructural techniques (conventional TEM, whole-mount TEM, SEM, HVEM, freeze-fracture electron microscopy utilizing rotary replication, shadow casting, optical diffraction and stereo imaging). The main shell consists of 5 layers: the vitelline membrane (300 nm thick), the wax layer, the innermost chorionic layer (40-50 nm), the endochorion (500-700 nm), and the exochorion (300-500 nm). The vitelline membrane consists of irregularly organized particles. The wax layer appears to contain multilayered hydrophobic plates which split tangenitally upon freeze fracturing. The innermost chorionic layer is composed of a crystalling lattice. The endochorion is made of a thin (40 nm) fenestrated floor composed of 40-nm fibres and an outer solid (200 nm) roof covered with a network of 40-nm strands. Intermittently spaced pillar connect these 2 parts. Similarities in the substructure of the floor, pillars and roof suggest that they may be composed of similar or identical structural elements. The specialized regions of the shell are the 2 respiratory appendages, the operculum area and the posterior pole. The appendages exhibit 2 sharply distinct surfaces, a dorsal side with isolated 1.5-micrometer plaques and a ventral side with strands of 40-50 nm connected in a network with openings of 70-80 nm. The operculum area, which includes the micropoyle and the collar, is distinguished by 3 unique types of cell imprints. The posterior pole contains 2 distinctive populations of cell imprints: the central area has very thin intercellular ridges and a thin, perforated, endochorionic roof, while the peripheral area contains mixed, thick and thin, intercellular ridges and serves as a transition zone to the main shell pattern. The pillars in the central area of the posterior pole have a distinct arrangement, forming one peripheral circle within each cell imprint. An analysis utilizing structural and developmental criteria indicates that as many as ten different populations of follicular epithelial cells may be involved in the construction of the various regions of the Drosophila eggshell.
Quantitative studies of pinocytosis. I. Kinetics of uptake of (125I)polyvinylpyrrolidone by rat yolk sac cultured in vitro.
A method is described for the in vitro culture of 17.5-day rat visceral yolk sac. Tissue survival was good as judged by light and electron microscopy. The rate of pinocytic uptake of 125I-labeled polyvinylpyrrolidone by the tissue was constant both within and between experiments. Within the concentration range 0.15-24 mug/ml, the 125I-labeled polyvinylpyrrolidone neither stimulated nor inhibited pinocytosis. The system offers many advantages in the quantitative study of the physical basis of pinocytosis.
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.
Oogenesis in Xenopus laevis (Daudin). V. Relationships between developing oocytes and their investing follicular tissues.
Department of Biochemistry and Biophysics, University of California, Davis 95616.
The extracellular matrix (ECM) surrounding the anuran egg is composed of jelly coat layers, an envelope, and the perivitelline space, which separates the envelope from the egg plasma membrane. Both the jelly coat layers and egg envelopes are required for fertilization in anurans. This paper reviews the current understanding of the structure-function relations of the ECM, with emphasis on the egg envelope. The fibrous egg envelope exists in four related forms. The envelope forms differ in their ultrastructures, macromolecular compositions, and cellular functions. After the oocyte is released from the ovary, conversion of one envelope form to another is brought about by factors secreted by the oviduct prior to fertilization and by factors released from the egg in the sperm-triggered cortical reaction. An additional extracellular matrix structure, located in the perivitelline space, has recently been identified in Xenopus laevis, as well as a previously undescribed reorganization of envelope fibers occurring at fertilization. The molecular changes in the ECM glycoproteins (limited proteolysis, lectin-ligand binding, and conformational changes) and the oviductal and egg macromolecules responsible for the conversion of envelope forms are discussed. New experimental evidence that supports the lectin-ligand hypothesis for the formation of the fertilization layer is presented. It is proposed that the molecular changes in the ECM are responsible for the ultrastructural alterations of the ECM and for modifications of the fertilization and developmental functions of the anuran egg ECM.
The vitelline layer of the sea urchin egg and its modification during fertilization. A freeze-fracture study using quick-freezing and deep-etching.
Eggs of the sea urchin Strongylocentrotus purpuratus were quick-frozen, freeze fractured, and deep-etched to reveal the detailed structure of the vitelline layer (VL), an extracellular coat. The VL consisted of a network of fibers lying in sheet raised 20 nm off the plasma membrane and connected to it by a series of short processes. Sperm attached to the fibers of this sheet and upon fertilization the VL rose off the egg surface to form the fertilization envelope (FE). By 1 min postinsemination (p.i.), the FE had become augmented by a new set of smaller fibrils, and the original fibers of the VL appeared to be undergoing degradation. The FE exhibited casts of microvilli the VL had once covered. These were rounded at 1 min p.i., but by 2 min they had become angular and coated with an orderly array of repeating macromolecular units. In areas between casts, the coating process was slower; incomplete rows of units were seen at 5 min p.i. and complete rows at 10 min. Deep-etching of FE isolated from eggs by homogenization and differential centrifugation showed that both top and bottom surfaces were coated. The coat pattern was made up of 17.5-nm wide rows of parallelogram-like units that repeated every 12.2 nm along the row axis. Units in adjacent rows were in register to produce a secondary axis 76 degrees from the row axis. The results of this and previous studies suggest that the coating process plays a major role in "hardening" the FE to produce a tough barrier that protects the early embryo from chemical and mechanical injury.