Anaphase Movement Of Chromosomes Research Articles

Genetically identical parthenogenetic mouse embryos produced by inhibition of the first meiotic cleavage with cytochalasin D

The microfilament inhibitor cytochalasin D inhibits extrusion of the first polar body when present during the first meiotic division of mouse oocytes; however, it does not interfere with anaphase movement of chromosomes, and thus induces the formation of tetraploid oocytes. After the separation of chromosomes in anaphase, two spindles start to assemble. However, they merge rapidly and a single meiotic spindle forms. During the transition between metaphase I and metaphase II, in the presence of cytochalasin D, a drop in histone kinase activity takes place demonstrating a transitional decrease in the activity of the maturation promoting factor. These oocytes can be activated parthenogenetically a few hours after washing out the inhibitor. After completion of the second meiotic division and extrusion of a polar body, they contain a diploid number of chromosomes. They are genetically identical to each other and to their mother. Such eggs develop to the blastocyst stage and can implant in the uteri of foster mothers. Most of these fetuses die before the 9th day of gestation, as do diploid control fetuses treated with cytochalasin D during the second meiotic division. The heterozygous state of the experimental embryos obtained after activation of eggs recovered from heterozygous females and treated with cytochalasin D during the first meiotic division was confirmed using a glucose-phosphate isomerase assay. This technique allows the production of genetic clones of parthenogenetic embryos by simple means.

The anaphase movement of chromosomes in Tradescantia reflexa and Spirogyra.

The movement of chromosomes in anaphase was studied in staminal hair cells of Tradescantia reflexa and in algal cells of Spirogyra. Nuclei at various stages of anaphase were photographed, and the movement of chromosomes was measured in enlarged photographs. The anaphase movement of chromosomes in Tradescantia reflexa mostly involved the approach of chromosomes towards the spindle pole, while in Spirogyra the movement of chromosomes was induced by the separation of poles.

Polewards chromosome movement driven by microtubule depolymerization in vitro.

We constructed complexes between isolated chromosomes and microtubules made from purified tubulin to study the movement of chromosomes towards the 'minus' end of microtubules in vitro, a process analogous to the movement of chromosomes towards the pole of the spindle at anaphase of mitosis. Our results show that the energy for this movement is derived solely from microtubule depolymerization, and indicate that anaphase movement of chromosomes is both powered and regulated by microtubule depolymerization at the kinetochore.

Effect of inhibition of the catalytic activity of cyclic AMP-dependent protein kinase on mitosis in PtK1 cells.

Evidence has suggested that cyclic AMP, acting through activation of the type II cyclic AMP-dependent protein kinase, may play a role in the regulation of interphase and mitotic microtubules. In order to examine the potential role of the type II cAMP-dependent kinase during mitosis, dividing PtK1 cells were microinjected with two specific inhibitors of the catalytic activity of the type II kinase. These inhibitors were a specific protein inhibitor of cAMP-dependent protein kinase (PKI) and an affinity-purified polyclonal antiserum (anti-C) directed against the catalytic subunit of the kinase. Both have been shown previously to inhibit kinase activity in vitro. Microinjection of PKI during early- to mid-prophase significantly delayed the progression of the cells through mitosis, with the greatest delay occurring in metaphase. PKI injected during prometaphase also delayed progression through mitosis but to a lesser extent. Microinjection of anti-C during early- to mid-prophase also caused a significant delay in the completion of mitosis, with many cells becoming "hung up" in prometaphase. Anti-C injected during prometaphase had little effect on subsequent progression through mitosis. Microinjection of either anti-C or PKI during metaphase had no discernible effect. No effect on anaphase movement of chromosomes was observed with any treatment. These results provide further evidence that cAMP-dependent phosphorylation may be involved in the regulation of mitosis, although whether it acts directly through regulation of mitotic spindle microtubules is unclear.

Mitosis in Tilia americana endosperm.

The endosperm cells of the American basswood Tilia americana are favorable experimental material for investigating the birefringence of living plant spindles and anaphase movement of chromosomes. The behavior of the chromosomes in anaphase and the formation of the phragmoplast are unique. The numerous (3 n equals 123), small chromosomes move in precise, parallel rows until midanaphase when they bow away from the poles. Such a pattern of anaphase chromosome distribution has been described once before, but was ascribed to fusion of the chromosomes. The bowing of chromosome rows in Tilia is explainable quantitatively by the constant poleward velocity of the chromosomes during anaphase. Peripheral chromosomes are moving both relative to the spindle axis and laterally closer to the axis, whereas chromosomes lying on the spindle axis possess no lateral component in their motion, and thus at uniform velocity progress more rapidly than peripheral chromosomes relative to the spindle axis. The chromosomes are moved poleward initially by pole-to-pole elongation of the spindle, then moved farther apart by shortening of the kinetochore fibers. In contrast to other plant cells where the phragmoplast forms in telophase, the phragmoplast in Tilia endosperm is formed before midanaphase and the cell during midanaphase, while the chromosomes are still in poleward transit.

A quantitative study on anaphase movement of chromosomes in living grasshopper spermatocytes.

The present investigation has been undertaken to obtain data for the analysis of the chromosome movement at anaphase and the formation of a cleavage furrow. The study is based on simultaneous measurements of the spindle and cell diameters as well as of the chromosome separation in living spermatocyte divisions of the grasshoppers, Podisma sapporense and Acrydium japonicum.

Ryanodine and contractile phenomena in the mitotic spindle

Spontaneous contraction of mouse heart muscle in tissue culture is stopped by ryanodine at 1–2 mg/ml. These concentrations also block mitosis. In the dividing Echinarachnius egg, anaphase movement of chromosomes is retarded and incomplete in ryanodine at 6–8 mg/ml, although some of the eggs complete 2 or 3 cleavages. Increasing the length of exposure prior to cleavage does not alter the character of response and only slightly increases the severity. These phenomena are consistent with an inhibition of traction fiber contraction by ryanodine, but are insufficient to demonstrate the existence of such a contractile phenomenon.

THE ANAPHASE MOVEMENT OF CHROMOSOMES IN THE SPERMATOCYTES OF THE GRASSHOPPER

The movement of chromosomes and the changes in spindle size have been recorded in living spermatocytes of the grasshopper during the meiotic divisions. Anaphase movement consists of two separate processes which are related to the action of distinct cellular organelles: (1) The shortening of chromosomal fibers moves the chromosomes to the poles. (2) The elongation of the spindle further separates the daughter plates. The two processes act simultaneously in the grasshopper. With chloralhydrate, spindle elongation can be inhibited without affecting the action of the chromosomal fibers. This demonstrates the independence of these two factors.The effect of temperature on chromosome movement is shown by measurements at 17°, 23° and 30° C. Between 17° and 23° there is a greater increase in velocity of chromosome movement than from 23°-30° C. Temperatures above 32° C. inhibit mitosis through the destruction of the spindle.Abnormal spindle elongation is found whenever chromosomes stick at anaphase. The spindle, unable to elongate in its long axis, expands laterally into a disc-shaped body which later forms one or several finger-like processes, pushing out the cell membrane. These lateral elongations usually give rise to one or more cleavage furrows, pinching off one or, rarely, more anuclear buds. This demonstrates clearly the relationship between spindle elongation, cell elongation, and cleavage furrow.The role of the mitotic organelles in the anaphase movement of chromosomes is discussed. Indispensable for a regular anaphase are the kinetochores on the chromosomes, the chromosomal fibers, and the spindle body. No evidence was found for a specialized region in the spindle acting as "Stemmkörper." The spindle is uniform in structure and elongates uniformly.Distinct recognition of the structures involved in anaphase movement, and a quantitative description of their function, forms a basis for experimental analysis of their composition as well as their mode of action.

On the Anaphase Movement of Chromosomes

On the Anaphase Movement of Chromosomes

MONOCENTRIC MITOSIS WITH SEGREGATION OF CHROMOSOMES IN SCIARA AND ITS BEARING ON THE MECHANISM OF MITOSIS

The present paper supplements previous studies on the monocentric first spermatocyte division in Sciara and considers the findings in relation to the general problem of the mechanism of mitosis. Contrary to generally accepted principles of mitosis, an accurate segregation of chromosomes is effected in a unipolar field during the mitosis in question. The segregation is highly selective in that paternal chromosomes react in opposite fashion from their maternal homologs and pass away from the pole instead of toward it. These chromosomes which "retreat" from the poles exhibit characteristics which are believed (1) to demonstrate the functional reality of the so-called "spindle fibers," which in this case retard the movement of the chromosomes, and (2) to suggest that the opposing force or activity responsible for the movement of the chromosomes is due to an activity of the chromosomes themselves. The hypothesis of "autonomous" movement on the part of the chromosomes is suggested particularly by two lines of evidence: (1). Each retreating chromosome in its movement directly away from the pole acts independently of the others and may move along any radial line within the theoretical cone delimited by imaginary extension of the half spindle. Its path appears to be determined entirely by its original position with respect to the pole. (2). Each retreating chromosome appears to move in a small mass of protoplasm derived from the original half spindle, and to maintain its position at the apex of this mass during the movement. On account of the opposing activity represented by the so-called "spindle fiber," it seems improbable that the chromosome could retain this apical position if it were not itself responsible for the movement. The suggestion is made that the anaphase movement of chromosomes may be primarily due to such activity of the chromosomes themselves and that this activity serves to bring about movement by producing localized alterations in the viscosity of the adjacent protoplasm. II Experimental evidence is reviewed which shows that the retreating chromosomes are alive and therefore theoretically capable of functioning as postulated during the movements in question. This evidence also bears on the interrelations between sex and chromosome behavior to be considered subsequently.