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D Mazia

Publications and source records attributed to D Mazia.

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

Fine structure of the mitotic cycle of unfertilized sea urchin eggs activated by ammoniacal sea water.

Unfertilized sea urchin eggs enter a mitotic chromosome cycle after treatment with sea water containing ammonia. Centrioles cannot be found but microtubules are formed in the later stages of the cycle. The microtubules are displayed in an astral arrangement centered on clusters of osmiophilic bodies. In early stages, distinct kinetochores on the condensed chromosomes show no attachments to microtubules. Later, a few microtubules may be attached to the kinetochores. The chromosomes and microtubules are contained in a "clear zone", a large compact accumulation of membranes which displaces yolk particles and mitochondria, but not ribosomes, from that region of the cell. No bipolar spindle is formed.

Ammonia↗
PubMed1977

The phosphorylation of thymidine and the synthesis of histones in ammonia-treated eggs and egg fragments of the sea urchin.

Unfertilized sea urchin eggs may be preloaded with workable amounts of 3H-thymidine. After fertilizing the eggs or treating the eggs with ammonia, the preloaded thymidine is incorporated into DNA in amounts that are proportional to the number of chromosomes that are replicated. The phosphorylation of the internal thymidine is turned on by fertilization and ammonia treatment, but 3H-TTP does not accumulate because it is immediately used for nuclear DNA synthesis. Accumulation of 3H-TTP occurs only in ammonia-treated enucleate fragments in which no nuclear DNA synthesis can occur. Along with the phosphorylation of thymidine, the synthesis of histones occurs in ammonia-treated enucleate egg fragments.

Ammonia↗
PubMed1976

The surface events of fertilization: the movements of the spermatozoon through the sea urchin egg surface and the roles of the surface layers.

The sea urchin egg surface at fertilization has been examined with the scanning electron microscope to reveal the movements of the spermatozoon from the exterior, through the surface layers, and into the egg cytoplasm. The layers that the spermatozoon encounter have been studied to determine their physical and chemical natures and their role in early development. By studying the outside of whole eggs and the inner face of surfaces isolated shortly after fertilization, it has been possible to compile data on the movements of the spermatozoon through the egg surface. The spermatozoon initially contacts the egg with the elongated acrosomal process. The vitelline sheet, the outermost layer of the egg, separates slightly next to the attached spermatozoon. As membrane fusion between the gametes occurs, the plasma membrane from the egg engulfs the spermhead, the cortical granules start to discharge their contents, and a spreading surface deformation, concommitant with a distortion of the fibrous cortex, is initiated. A cluster of elongate microville surround the perpendicularly fusing spermatozoon. These microvilli interidigitate as the spermatozoon is forced to lie upon the egg surface between the plasma membrane and the matrix of cortical fibers. The spermatozoon then rotates additionally to enter the egg cytoplasm with the posterior end first; it has rotated 180 degrees through the cell surface. Finally, it detaches into the egg cytoplasm, leaving a scar in the cortex through which it penetrated. The egg cortex, previously unobserved by electron microscopy, is revealed to be composed of 50-200 nm fibers. At fertilization they are uniformly organized but during later development this order is lost. The cortex is from 0.2-0.5 micronm thick and is a contractile structure. The role of the outer surface in releasing the cell from the metabolic constraints of the unfertilized egg is shown, and the apparent differences in the mobilities of the membranes derived from the sperm and from the egg are demonstrated. The relation of these layers to the movements of the spermatozoon, to the activation of the egg, to the block to polyspermy, and to each other are discussed.

Acrosome↗
PubMed1975

Turning on of activities in unfertilized sea urchin eggs: correlation with changes of the surface.

Unfertilized sea urchin eggs exposed to low concentrations of ammonia enter into a number of activities which normally appear after fertilization. It is shown that the effects are attributable to ammonia, rather than to NH4+ ions of elevated pH. The same effects are obtained by exposure to isotonic urea and to glycerol at very low ionic strengths. All treatments which produce these changes (such as the turning on of chromosome replication and condensation in unfertilized eggs) also bring about changes of the outer cell surface which are visible in the scanning electron microscope. The most striking indicator is the elongation of the microvilli which cover the surface of the unfertilized egg. The changes of the surface are interpreted as the dissociation of a component from the outer surface layer. This component is not the "vitelline" sheet as defined morphologically or by the ability of the egg to form a fertilization membrane upon insemination. It is proposed further that this component is a peripheral component of the plasma membrane, whose removal modifies the membrane functionally and leads to the derepression of various processes within the egg.

Ammonia↗
PubMed1975

Visualization of actin fibers associated with the cell membrane in amoebae of Dictyostelium discoideum.

Amoebae of Dictyostelium discoideum were attached to a surface coated with polylysine, and the upper portion of the cells was sheared off with a stream of buffer. Scanning and transmission electron microscopy showed that the cytoplasmic surface of the exposed membrane was covered with fibers consisting of actin-containing filaments. The actin was identified by its solubility properties and its ability to interact with muscle myosin.

Actins↗
PubMed1975

Adhesion of cells to surfaces coated with polylysine. Applications to electron microscopy.

Cells of many kinds adhere firmly to glass or plastic surfaces which have been pretreated with polylysine. The attachment takes place as soon as the cells make contact with the surfaces, and the flattening of the cells against the surfaces is quite rapid. Cells which do not normally adhere to solid surfaces, such as sea urchin eggs, attach as well as cells which normally do so, such as amebas or mammalian cells in culture. The adhesion is interpreted simply as the interaction between the polyanionic cell surfaces and the polycationic layer of adsorbed polylysine. The attachment of cells to the polylysine-treated surfaces can be exploited for a variety of experimental manipulations. In the preparation of samples for scanning or transmission electron microscopy, the living material may first be attached to a polylysine-coated plate or grid, subjected to some experimental treatment (fertilization of an egg, for example), then transferred rapidly to fixative and further passed through processing for observation; each step involves only the transfer of the plate or grid from one container to the next. The cells are not detached. The adhesion of the cell may be so firm that the body of the cell may be sheared away, leaving attached a patch of cell surface, face up, for observation of its inner aspect. For example, one may observe secretory vesicles on the inner face of the surface (3) or may study the association of filaments with the inner surface (Fig. 1). Subcellular structures may attach to the polylysine-coated surfaces. So far, we have found this to be the case for nuclei isolated from sea urchin embryos and for the microtubules of flagella, which are well displayed after the membrane has been disrupted by Triton X-100 (Fig. 2).

Animals↗
PubMed1975

Microtubules and filaments in ciliate contractility.

The basis for cell body contractility in heterotrich ciliates resides in the interaction of two discrete contractile fiber systems, the myonemes and km fibers. The motive force for rapid cell contraction in these ciliates has been associated with a calcium-induced change in the macromolecular conformation of the contractile filaments of the myonemes. In Stentor coeruleus, changes in the contractile state of the myonemes are reflected in a reversible calcium-dependent transformation of thin, oriented filaments to shorter tubular forms. Dimensional changes in the km fibers in Stentor coeruleus are generated by the relative sliding of the component parallel microtubule arrays. Changes in the morphology of cross-bridges extending between the sliding components suggest that these structures function in the process of cell extension either in developing the sliding forces required for active displacement of adjacent microtubule ribbons or regulating the extent to which sliding occurs.

Adenosine Triphosphate↗
PubMed1974

Chromosome cycles turned on in unfertilized sea urchin eggs exposed to NH4OH.

In unfertilized sea urchin eggs treated with NH(4)OH-sea water, the chromosomes condense after a first round of DNA synthesis and go through a chromosome cycle. The chromosomes split visibly, but sister chromosomes are not further separated. They regress into an interphase nucleus. These cycles repeat, producing eggs with large numbers of chromosomes. No mitotic apparatus is seen and the eggs do not divide. There is some microscopic evidence of limited chromosome movement, interpreted as centrifugal movement of the condensed chromosomes before they split and a centripetal movement as the split chromosomes decondense to reconstitute the nucleus. The eggs so treated with NH(4)OH are considered to be unfertilized eggs and can be fertilized later. Such later fertilization permits the introduction of paternal nuclei after the maternal nuclei have progressed some way toward the above-described chromosome condensation. The paternal chromosomes condense prematurely at the time when the maternal chromosomes condense. At the same time, premature with respect to the time of fertilization, mitotic apparatus form.

Animals↗
PubMed1974

The cell cycle.

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Animals↗