scholarly journals THE MITOTIC APPARATUS

1962 ◽  
Vol 15 (2) ◽  
pp. 279-287 ◽  
Author(s):  
R. E. Kane
Keyword(s):  
Fine Structure ◽  
Granular Material ◽  
Sea Urchin ◽  
Osmium Tetroxide ◽  
Mitotic Apparatus ◽  
Isolation Medium ◽  
Sea Urchin Egg ◽  
Dividing Cells

The fine structure of the mitotic apparatus isolated from the sea urchin egg has been investigated. The isolation was accomplished by lysis of metaphase eggs in a 1 M solution of hexanediol, buffered at pH 6. The fine structure of the isolated apparatus was studied after fixation with osmium tetroxide directly in the isolation medium. The spindle is composed of fine fibrils, approximately 20 mµ in diameter, which appear tubular. Similar fibrils, radially oriented, are found in the aster. If the isolated mitotic apparatus is exposed to water at pH 6 before fixation, the structure is considerably modified. The most pronounced effects are an increase in the number of large membrane-bounded vesicles and in the amount of free granular material present. The conditions necessary for the fixation of the mitotic apparatus in dividing cells are discussed in the light of these observations on the isolated unit.

Surface Characters of Dividing Cells

1958 ◽  
Vol 35 (2) ◽  
pp. 396-399
Author(s):  
SHOZO ISHIZAKA
Keyword(s):  
Sea Urchin ◽  
Optical Section ◽  
Camera Lucida ◽  
Centre Of Gravity ◽  
Whole Process ◽  
Spindle Axis ◽  
Sea Urchin Egg ◽  
Dividing Cells

1. The surface movements during division have been studied by marking the naked surface of the sea-urchin egg with charcoal particles. 2. The contours of the largest optical section, the positions of the particles thereon and the positions of the astral centres are recorded in a series of camera lucida drawings. 3. The drawings are then superimposed, the centre of gravity and spindle axis being used for reference. 4. It is thereby shown that there are two surface rings which remain in the same positions throughout the whole process of division. 5. It is concluded that these rings indicate regions where stresses remain balanced during division.

scholarly journals A Quantitative Description of Protoplasmic Movement During Cleavage in the Sea-Urchin Egg

1958 ◽  
Vol 35 (2) ◽  
pp. 407-424
Author(s):  
Y. HIRAMOTO
Keyword(s):  
Cell Division ◽  
Sea Urchin ◽  
Quantitative Description ◽  
Motive Force ◽  
Mitotic Apparatus ◽  
Band Theory ◽  
Cytoplasmic Granules ◽  
Carbon Particles ◽  
Sea Urchin Egg ◽  
Protoplasmic Movement

1. Protoplasmic movements during cleavage in the eggs of the heart-urchin Clypeaster japonicus have been followed by tracing the movements of cytoplasmic granules and of carbon particles adhering to the surface. 2. These movements are quantitatively described in normal eggs and in eggs whose mitotic apparatus has been destroyed by colchicine. 3. The results obtained are qualitatively similar to those obtained by Spek and by Dan and his collaborators. 4. Endoplasmic movement and changes in the length and shape of the astral rays are readily explained by the contracting-ring (band) theory. 5. The location of the motive force of cell division is discussed.

Surface Characters of Dividing Cells

1966 ◽  
Vol 44 (2) ◽  
pp. 225-232
Author(s):  
SHOZO ISHIZAKA
Keyword(s):  
Sea Urchin ◽  
Surface Stress ◽  
Radius Of Curvature ◽  
Surface Movement ◽  
Daughter Cells ◽  
Sea Urchin Egg ◽  
Area Increase ◽  
Dividing Cells ◽  
Division Process ◽  
Surface Area Increase

1. Surface movement of the dividing spermatocyte of the grasshopper, Acrida lata, was followed by a marking method. 2. Throughout the division process of the spermatocytes, incipient daughter cells maintain spherical contours. 3. By direct observation of markers and calculation using the condition given in item 2, the following points are established. (a) As in the sea-urchin egg, there are a pair of circular zones on a grasshopper spermatocyte surface which retain their respective radii unchanged while the cell undergoes a division. (b) In the grasshopper spermatocyte, unlike the sea-urchin egg, the surfaces of these circular zones do change their positions and move towards the poles during division. (c) As a spherical cell goes through a constricted form to become two daughter cells, not only is the radius of curvature of the surface everywhere uniform (item 2), but both axial length and surface area increase uniformly everywhere except in the region of the furrow. 4. From the findings of item 3 it is inferred that the prevailing surface stress is uniform and isotropic, like surface tension, and that the force causing division must be derived from some other parts of the cell such as the furrow cortex or the endoplasm. 5. Basically, the nature of the surface of sea-urchin eggs is similar to that of the spermatocyte. That the circular zones of the former are stationary while those of the latter move steadily during cleavage is tentatively explained in terms of the speed of advance of the furrow in relation to the relaxation time of the cortex.

Spindle birefringence of isolated mitotic apparatus analysed by treatments with cold, pressure, and diluted isolation medium

1976 ◽  
Vol 20 (2) ◽  
pp. 329-339
Author(s):  
A. Forer ◽  
A.M. Zimmerman
Keyword(s):  
Electron Microscopy ◽  
Sea Urchin ◽  
Half Life ◽  
Cold Treatment ◽  
Pressure Treatment ◽  
Mitotic Apparatus ◽  
Isolation Medium ◽  
Spindle Structure ◽  
Cold Pressure

Mitotic apparatus (MA) were isolated from sea-urchin zygotes using glycerol-dimethyl-sulphoxide. Cold treatment had no effect on MA birefringence when MA were in isolation medium, but caused a 10–15% reduction of MA birefringence when MA were in quarter-strength isolation medium. Pressure treatment also caused a reduction in MA birefringence, but the cold and pressure treatments were not additive, suggesting that both treatments affected the same MA component. MA were not stable in quarter-strength isolation medium, and birefringence gradually decayed, with a half-life of about 40 h. Electron microscopy after cold treatment, or after decay of 55% of the MA birefringence showed abundant, normal-looking microtubules, suggesting that alterations in non-microtubule components cause the reductions in birefringence. Addition of EGTA eliminates the effect of cold treatment, suggesting that Ca2+ has a role in maintenance of spindle structure. We discuss possible reasons why isolated MA do not respond to cold treatment like MA in vivo.

scholarly journals SOME STRUCTURAL AND FUNCTIONAL ASPECTS OF THE MITOTIC APPARATUS IN SEA URCHIN EMBRYOS

1962 ◽  
Vol 14 (3) ◽  
pp. 475-487 ◽  
Author(s):  
Patricia Harris
Keyword(s):  
Sea Urchin ◽  
Salt Concentration ◽  
Sea Water ◽  
Divalent Cations ◽  
Cell Stage ◽  
Mitotic Apparatus ◽  
Central Spindle ◽  
Sea Urchin Embryos ◽  
Cilia Formation ◽  
Dividing Cells

The mitotic figures in dividing cells of sea urchin embryos, from first division to the onset of cilia formation, were studied with regard to the filament system and its relation to kinetochores, chromosomes, and poles, as well as to fixation conditions which would best preserve these structures. With regard to fixation, variations in the salt concentration and pH of the fixative indicated that an extraction effect on the chromosomes noted in earlier work was probably due to a combination of neutral pH and salt concentration equivalent to sea water. The presence of the 15 mµ filaments depended on the presence of either of two stabilizing conditions: pH 6.1 or presence of the salts of sea water, presumably the divalent cations of Ca and Mg. Kinetochores and centrioles were unaffected by the fixative variations. The 15 mµ filaments, reported earlier in the central spindle, are also found in great numbers in the asters of early cleavage divisions. However, with successive divisions and reduction in cell size, the aster disappears at about the 32 to 64 cell stage, and the 15 mµ filaments are entirely associated with the central spindle. This disappearance of the aster suggests that it may be, in fact, merely a specialization of large cells for cytokinesis.

scholarly journals ELECTRON MICROSCOPE STUDY OF MITOSIS IN SEA URCHIN BLASTOMERES

1961 ◽  
Vol 11 (2) ◽  
pp. 419-431 ◽  
Author(s):  
Patricia Harris
Keyword(s):  
Endoplasmic Reticulum ◽  
Fine Structure ◽  
Sea Urchin ◽  
Electron Microscope Study ◽  
Osmium Tetroxide ◽  
Mitotic Cycle ◽  
Sea Water ◽  
Strongylocentrotus Purpuratus ◽  
Double Membrane ◽  
Late Anaphase

The fine structure of cells at different stages of the mitotic cycle was studied in the blastomeres of 6-hour-old embryos of the sea urchin Strongylocentrotus purpuratus. The material was fixed in 1 per cent osmium tetroxide in sea water, buffered with veronal-acetate to pH 7.5, embedded in Araldite, and sectioned with glass knives. The aster, as it forms around the centriole, has the appearance of the endoplastic reticulum, with elements oriented radially from the centrosphere to the periphery of the cell. Anaphase structures described include the kinetochores, with bundles of fine filaments extending toward the centrioles, as well as continuous filaments passing between the chromosomes. Two cylindrical centrioles composed of parallel rods are present in each of the anaphase asters. At late anaphase, elements of the endoplasmic reticulum condense on the surface of the chromosomes to form a double membrane which already at this stage possesses pores or annuli. At telophase bundles of continuous filaments can be seen in the interzonal region. These filaments, as well as those associated with the chromosomes, have a diameter of approximately 15 mµ, and appear physically different from the astral structure.

Spindle birefringence of isolated mitotic apparatus analysed by pressure treatment

1976 ◽  
Vol 20 (2) ◽  
pp. 309-327
Author(s):  
A. Forer ◽  
A.M. Zimmerman
Keyword(s):  
Electron Microscopy ◽  
Sea Urchin ◽  
Dimethyl Sulphoxide ◽  
Pressure Treatment ◽  
Mitotic Apparatus ◽  
Isolation Medium ◽  
Hexylene Glycol ◽  
X 24 ◽  
Induced Changes

Sea-urchin zygote mitotic apparatus (MA) isolated in a glycerol/dimethylsulphoxide medium were treated with pressure. Pressure treatment had no effect on spindle birefringence when MA were in full-strength isolation medium. After placing MA in quarter-strength isolation medium, pressures of 4-0 X 10(3)-1-8 X 10(4) lbf in.-2 (2 X 76 X 10(4)-I X 24 X 10(5) k N m-2) for 15 min caused reduction of birefringence which occurred in 2 steps: firstly 20–30% of the birefringence was lost, and then, at higher pressures, the rest of the birefringence was lost. Electron microscopy suggested that pressure-induced changes were in non-microtubule material. Pressure treatment had no effect on MA isolated with hexylene glycol when the MA were pressurized in hexylene glycol; but pressure treatment did cause loss of birefringence when MA isolated in hexylene glycol were transferred immediately into glycerol/dimethylsulphoxide medium and were subsequently treated with pressure (after dilution into quarter-strength glycerol/dimethyl-sulphoxide). We discuss the differences in response between isolated MA and in vivo MA, and we discuss the possibility that 2 components contribute to MA birefringence.

A Ca-activated ATPase in the mitotic apparatus of the sea urchin egg (isolated by a new method)

1972 ◽  
Vol 70 (2) ◽  
pp. 325-332 ◽  
Author(s):  
D. Mazia ◽  
Chr. Petzelt ◽  
R.O. Williams ◽  
I. Meza
Keyword(s):  
Sea Urchin ◽  
New Method ◽  
Mitotic Apparatus ◽  
Sea Urchin Egg
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