The Mechanism of Cell-Division

1927 ◽  
Vol 5 (2) ◽  
pp. 102-111
Author(s):  
J. GRAY
Keyword(s):  
Cell Division ◽  
Flat Plate ◽  
Average Velocity ◽  
Cleavage Plane ◽  
Direct Action ◽  
Cleavage Furrow ◽  
The Third ◽  
Centre Of Gravity ◽  
Frictional Forces ◽  
Whole Egg

1. The nucleolus in the nucleus of an Echinus oocyte always orientates itself gravitationally on the floor of the nucleus. When the oocyte is disturbed the nucleolus falls through the fluid contents of the nucleus with an average velocity of 0.4 µ per sec. 2. Gravity has no direct action on the direction of the cleavage planes in Echinus eggs, but it orientates the whole egg within the fertilisation membrane. 3. During the first cleavage the mitotic axis can lie in any position in respect to gravity, but if its position deviates appreciably from the horizontal then (as soon as the cell elongates by cleavage) the whole egg moves so as to bring its centre of gravity into equilibrium with gravity and with the frictional forces acting between the egg and the fertilisation membrane. 4. During the second cleavage the mitotic axis must lie in a plane parallel to the first cleavage furrow in conformity with Hertwig's Law. If its position deviates from the horizontal, then the egg orientates itself to gravity. In this way the second division gives rise to four blastomeres resting as a flat plate on the floor of the fertilisation membrane, independently of whatever position was occupied by the mitotic axis. 5. The third cleavage is also in accord with Hertwig's Law and no gravitational disturbances occur. 6. The direction of each cleavage plane is determined by the resultant of three factors: (a) the forces underlying Hertwig's law, (b) gravity, (c) friction between the egg and its fertilisation membrane.

scholarly journals FINE STRUCTURE OF CELL DIVISION IN CHLAMYDOMONAS REINHARDI

1968 ◽  
Vol 38 (2) ◽  
pp. 403-425 ◽  
Author(s):  
Ursula G. Johnson ◽  
Keith R. Porter
Keyword(s):  
Fine Structure ◽  
Electron Microscope ◽  
Cell Division ◽  
Cleavage Plane ◽  
Basal Bodies ◽  
Cleavage Furrow ◽  
Body Formation ◽  
Division Spindle ◽  
Spindle Microtubules ◽  
Mitotic Nucleus

Cell division in log-phase cultures of the unicellular, biflagellate alga, Chlamydomonas reinhardi, has been studied with the electron microscope. The two basal bodies of the cell replicate prior to cytokinesis; stages in basal body formation are presented. At the time of cell division, the original basal bodies detach from the flagella, and the four basal bodies appear to be involved in the orientation of the plane of the cleavage furrow. Four sets of microtubules participate in cell division. Spindle microtubules are involved in a mitosis that is marked by the presence of an intact nuclear envelope. A band of microtubules arcs over the mitotic nucleus, indicating the future cleavage plane. A third set of microtubules appears between the daughter nuclei at telophase, and microtubules comprising the "cleavage apparatus" radiate from the basal bodies and extend along both sides of the cleavage furrow during cytokinesis. Features of cell division in C. reinhardi are discussed and related to cell division in other organisms. It is proposed that microtubules participate in the formation of the cleavage furrow in C. reinhardi.

scholarly journals CHANGES IN PROTOPLASMIC CONSISTENCY AND THEIR RELATION TO CELL DIVISION

1919 ◽  
Vol 2 (1) ◽  
pp. 49-68 ◽  
Author(s):  
Robert Chambers
Keyword(s):  
Cell Division ◽  
Solid State ◽  
Cleavage Plane ◽  
Cleavage Furrow ◽  
Semisolid State ◽  
Fluid State

1. The development of the amphiaster is associated with the formation of two semisolid masses within the more fluid egg substance. 2. The elongation of the egg during cleavage is possibly produced as a consequence of the mutual pressure of these two growing semisolid masses. 3. The division of the egg into two blastomeres consists essentially in a growth, within the egg, of two masses of material at the expense of the surrounding cytoplasm. When all the cytoplasm of the egg is incorporated in these two masses cleavage occurs. 4. After a certain period of time the semisolid masses revert to a more fluid state. In the eggs studied this normally occurs after the cleavage furrow has completed the separation of the two blastomeres. The formation of the furrow, however, may be prevented in various ways, upon which the egg reverts to a single spherical semifluid mass containing two nuclei. 5. An egg mutilated during its semisolid state (amphiaster stage) may or may not revert to a more fluid state. If the more solid state is maintained, the cleavage furrow persists and proceeds till cleavage is completed. If the mutilation causes the egg to revert to the more fluid state the furrow becomes obliterated and a new cleavage plane is subsequently adopted. 6. The nuclei of eggs in the semifluid state are able to alter their positions. In semifluid mutilated eggs the nuclei tend to move to positions which may assure symmetry in aster formation and cleavage.

Relaxations of Contractual Privity and the Need for Third Party Rights in Chinese Contract Law

2018 ◽  
Author(s):  
Chen Lei
Keyword(s):  
Direct Action ◽  
Contract Law ◽  
Third Party ◽  
Chinese Law ◽  
The Third ◽  
Right Of Action ◽  
The Law ◽  
The Third Party ◽  
The Right

This chapter examines the position of third party beneficiaries in Chinese law. Article 64 of the Chinese Contract Law states that where a contract for the benefit of a third party is breached, the debtor is liable to the creditor. The author regards this as leaving unanswered the question of whether the thirdparty has a right of direct action against the debtor. One view regards the third party as having the right to sue for the benefit although this right was ultimately excluded from the law. Another view, supported by the Supreme People’s Court, is that Article 64 does not provide a right of action for a third party and merely prescribes performance in ‘incidental’ third party contracts. The third view is that there is a third party right of action in cases of ‘genuine’ third party contracts but courts are unlikely to recognize a third party action where the contract merely purports to confer a benefit on the third party.

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

Development ◽  
1976 ◽  
Vol 36 (2) ◽  
pp. 321-341
Author(s):  
G. G. Selman ◽  
J. Jacob ◽  
M. M. Perry
Keyword(s):  
Osmium Tetroxide ◽  
Cytochalasin B ◽  
Specific Activity ◽  
High Specific Activity ◽  
Scintillation Counting ◽  
Cleavage Furrow ◽  
Limited Extent ◽  
Normal Medium ◽  
Cleavage Initiation ◽  
Whole Egg

Two to 10 µg/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 activity was prepared and used to study its ability to penetrate the surface of newt eggs during cleavage. Scintillation counting 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 of sectioned eggs whichad been fixed at late cleavage after [3H]CB had flattened the furrow. These showed that CBentered 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.

Nocodazole and cytochalasin D induce tetraploidy in mammalian cells

1984 ◽  
Vol 246 (1) ◽  
pp. C154-C156 ◽  
Author(s):  
G. W. Zieve
Keyword(s):  
Cell Division ◽  
Mammalian Cells ◽  
Cytochalasin D ◽  
Microtubule Assembly ◽  
Reversible Inhibitor ◽  
Cleavage Furrow ◽  
Synchronized Cells ◽  
Cells In Culture ◽  
Wide Range

Nocodazole, a rapidly reversible inhibitor of microtubule assembly is useful for preparing mammalian cells synchronized at all stages of mitosis. When synchronized cells are allowed to progress through mitosis in the presence of cytochalasin D, the cleavage furrow is inhibited and dikaryon cells are formed. These cells become homogeneous populations of stable mononuclear tetraploid cells after the following cell division. This procedure is applicable to a wide range of mammalian cells in culture.

scholarly journals The ultrastructure of cell division in Euglena gracilis

1978 ◽  
Vol 31 (1) ◽  
pp. 25-35
Author(s):  
M.A. Gillott ◽  
R.E. Triemer
Keyword(s):  
Cell Division ◽  
Nuclear Envelope ◽  
Basal Body ◽  
Euglena Gracilis ◽  
Equatorial Region ◽  
Basal Bodies ◽  
Cleavage Furrow ◽  
Free Zone ◽  
Prophase Nucleus

The ultrastructure of mitosis in Euglena gracilis was investigated. At preprophase the nucleus migrates anteriorly and associates with the basal bodies. Flagella and basal bodies replicate at preprophase. Cells retain motility throughout division. The reservoir and the prophase nucleus elongate perpendicular to the incipient cleavage furrow. One basal body pair surrounded by a ribosome-free zone is found at each of the nuclear poles. The spindle forms within the intact nuclear envelope- Polar fenestrae are absent. At metaphase, the endosome is elongated from pole to pole, and chromosomes are loosely arranged in the equatorial region. Distinct, trilayered kinetochores are present. Spindle elongates as chromosomes migrate to the poles forming a dumb-bell shaped nucleus by telophase. Daughter nuclei are formed by constriction of the nuclear envelope. Cytokinesis is accomplished by furrowing. Cell division in Euglena is compared with that of certain other algae.

scholarly journals IFT Proteins Accumulate during Cell Division and Localize to the Cleavage Furrow in Chlamydomonas

PLoS ONE ◽  
2012 ◽  
Vol 7 (2) ◽  
pp. e30729 ◽  
Author(s):  
Christopher R. Wood ◽  
Zhaohui Wang ◽  
Dennis Diener ◽  
James Matt Zones ◽  
Joel Rosenbaum ◽  
...  
Keyword(s):  
Cell Division ◽  
Cleavage Furrow

scholarly journals A RADIOAUTOGRAPHIC STUDY WITH H3-THYMIDINE ON ADRENAL MEDULLA NUCLEI OF RATS INTERMITTENTLY EXPOSED TO COLD

1966 ◽  
Vol 28 (1) ◽  
pp. 9-19 ◽  
Author(s):  
Maria Pia Viola-Magni
Keyword(s):  
Cell Division ◽  
Dna Synthesis ◽  
Adrenal Medulla ◽  
Cold Exposure ◽  
Dna Content ◽  
Room Temperature ◽  
Marked Variation ◽  
Considerable Decrease ◽  
The Third

A considerable decrease (24 to 40%) of DNA content per nucleus previously observed in the adrenal medulla of rats exposed intermittently to cold is followed by restoration to normal and supranormal values. This phenomenon has now been studied by use of H3-thymidine, which was given to normal rats, to rats exposed to cold, and to animals brought to room temperature after cold exposure. In the first two conditions, no significant labeling of nuclei was observed. In the third, labeling took place clearly in the 1st 3 days. The grain counts showed that the early labeled nuclei had more grains than those labeled later, indicating differences in the rate of DNA synthesis. A statistically significant correlation was found, on the same nuclei, between amount of Feulgen dye and number of grains. It is concluded that net synthesis of DNA takes place in the phase of recovery from cold. This fact is not related to cell division, as no mitoses could ever be detected, but rather to the cold-induced loss of DNA. Clear demonstration is thus given of a marked variation in the amount of DNA per nucleus in relation to the functional conditions of adrenal medulla cells.

scholarly journals CLIC4 is a cytokinetic cleavage furrow protein that regulates cortical cytoskeleton stability during cell division

2020 ◽  
Vol 133 (9) ◽  
pp. jcs241117 ◽  
Author(s):  
Eric Peterman ◽  
Mindaugas Valius ◽  
Rytis Prekeris
Keyword(s):  
Cell Division ◽  
Cleavage Furrow ◽  
Cortical Cytoskeleton

Floral development of Aponogeton natans and A. undulatus

1977 ◽  
Vol 55 (9) ◽  
pp. 1106-1120 ◽  
Author(s):  
V. Singh ◽  
R. Sattler
Keyword(s):  
Cell Division ◽  
Developmental Stage ◽  
Floral Development ◽  
Developmental Stages ◽  
Point Of View ◽  
Stages Of Development ◽  
The Third ◽  
Procambial Strand ◽  
Tunica Layer

The primordia of the floral appendages are initiated in an acropetal succession. Members of the same whorl appear nearly simultaneously. The gynoecial whorl and the two staminal whorls are trimerous, whereas the perianth consists only of two anteriolateral tepals. However, the posterior (adaxial) tepal may be present as an extremely reduced buttress whose growth becomes arrested immediately after its inception. If this somewhat questionable tepal rudiment is included we have a perfectly trimerous and tetracyclic flower with alternation of successive whorls. Subtending bracts of the flowers are completely missing in all developmental stages. While the tepal primordia are dorsiventral from their inception, the stamen and pistil (carpel) primordia originate as hemispherical mounds which become dorsiventral in subsequent stages of development. Each pistil (carpel) primordium becomes horseshoe shaped. As the margins grow up and contact they fuse postgenitally. No cross zone is formed. Placentation is submarginal. In A. natans eight ovules are formed and in A. undulatus only two arise; all ovules are bitegmic. The floral apices have a two-layered tunica up to the stage of pistil formation. The inception of all floral appendages (including the ovules) occurs by periclinal cell division in the second tunica layer. The third layer (corpus) may contribute to the formation of the stamens and pistils. Each appendage primordium receives only one procambial strand which begins to differentiate after the inception of the primordium. The questionable rudimentary tepal buttress lacks a procambial strand. Apparently it does not reach the developmental stage at which procambial induction occurs. From the point of view of floral development, the two species of Aponogeton differ drastically from members of the Alismatales studied so far. Among the Helobiae, the Aponogetonaceae appear to be most closely related to the Scheuchzeriaceae and the Juncaginaceae (Triglochinaceae).

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