Abstract: The oscillations of chromosomes associated with a single spindle pole in monocentric and bipolar spindles were analysed by time-lapse cinematography in mitosis of primary cultures of lung epithelium from the newt Taricha granulosa. Chromosomes oscillate toward and away from the pole in all stages of mitosis including anaphase. The duration, velocity, and amplitude of such oscillations are the same in all stages of mitosis. The movement away from the pole in monocentric spindle is rapid enough to suggest the existence of a previously unrecognized active component in chromosome movement, presumably resulting from a pushing action of the kinetochore fiber. During prometaphase oscillations, chromosomes may approach the pole even more closely than at the end of anaphase. Together, these observations demonstrate that a monopolar spindle is sufficient to generate the forces for chromosome transport, both toward and away from the pole. The coordination of the aster/centrosome migration in prophase with the development of the kinetochore fibers determines the course of mitosis. After the breaking of the nuclear envelope in normal mitosis, aster/centrosome separation is normally followed by the rapid formation of bipolar chromosomal fibers. There are two aberrant extremes that may result from a failure in coordination between these processes: (a) A monocentric spindle will arise when aster separation does not occur, and (b) an anaphaselike prometaphase will result if the aster/centrosomal complexes are already well-separated and bipolar chromosomal fibers do not form. In the latter case, the two monopolar prometaphase half-spindles migrate apart, each containing a random number of two chromatid (metaphase) monopolar-oriented chromosomes. This random segregation of prometaphase chromosome displays many features of a standard anaphase and may be followed by a false cleavage. The process of polar separation during prometaphase occurs without any visible interzonal structures. Aster/centrosomes and monopolar spindles migrate autonomously by an unknown mechanism. There are, however, firm but transitory connections between the aster center and the kinetochores as demonstrated by the occasional synchrony of centrosome-kinetochore movement. The data suggest that aster motility is important in the progress of both prometaphase and anaphase in normal mitosis.

Abstract: The effects of taxol on mitosis in Haemanthus endosperm were studied. Immuno-gold staining was used to visualize microtubules; observations on microtubule arrangements were correlated with studies in vivo. Mitosis is slowed down, but not arrested, by taxol over a wide range of concentrations. Taxol promotes the formation of abundant new microtubules and lateral association within and between microtubule arrays (spindle fibers). This leads to a pronounced reorganization of the spindle, especially at the polar regions. Chromosome arms may be pushed toward the equator in metaphase. Anaphase chromosomes, with their kinetochores still pointing to the poles, move backward before resuming their poleward migration. During anaphase, the interzone is depleted of microtubules and trailing chromosome arms are stretched and often torn apart by rapidly elongating polar microtubules. Fragments are transported away from the poles, apparently "riding" on the tips of microtubules. This provides evidence of "pushing" by elongating microtubules. The desynchronization of anaphase, often observed as one of the first effects of taxol, indicates that the anchorage of different kinetochore fibers varies. The data draw attention to modifications of spindle structure due to increased microtubule lateral associations and to the role of this process in spindle integrity and chromosome movement.

Abstract: Organization of kinetochore fiber microtubules (MTs) throughout mitosis in the endosperm of Haemanthus katherinae Bak. has been analysed using serial section reconstruction from electron micrographs. Accurate and complete studies have required careful analysis of individual MTs in precisely oriented serial sections through many (45) preselected cells. Kinetochore MTs (kMTs) and non-kinetochore MTs (nkMTs) intermingle within the fiber throughout division, undergoing characteristic, time-dependent, organizational changes. The number of kMTs increases progressively throughout the kinetochore during prometaphase-metaphase. Prometaphase chromosomes which were probably moving toward the pole at the time of fixation have unequally developed kinetochores associated with many nkMTs. The greatest numbers of kMTs (74-109/kinetochore), kinetochore cross-sectional area, and kMT central density all occur at metaphase. Throughout anaphase and telophase there is a decrease in the number of kMTs and, in the kinetochore cross-sectional area, an increased obliquity of kMTs and increased numbers of short MTs near the kinetochore. Delayed kinetochores possess more kMTs than do kinetochores near the poles, but fewer kMTs than chromosomes which have moved equivalent distances in other cells. The frequency of C-shaped proximal MT terminations within kinetochores is highest at early prometaphase and midtelophase, falling to zero at midanaphase. Therefore, in Haemanthus, MTs are probably lost from the periphery of the kinetochore during anaphase in a manner which is related to both time and position of the chromosome along the spindle axis. The complex, time-dependent organization of MTs in the kinetochore region strongly suggests that chromosome movement is accompanied by continual MT rearrangement and/or assembly/disassembly.

Abstract: Rainbow trout gonad cells (RTG-2) were cultured for various lengths of time in the presence of several classes of known mutagenic chemicals and several related compounds that possessed no known mutagenic/carcinogenic activity. During the course of exposure the cells were examined for the presence of abnormalities in the chromosome arrangement of anaphase figures during mitosis. Untreated and solvent-treated (dimethylsulfoxide-treated) cells exhibited a background abnormality rate of 12% with only minor chromosomal defects being observed. This was also true for those cells exposed to naphthol and anthracene, two chemicals with no proven mutagenic or carcinogenic activity. Conversely, significant increases in the frequency of anaphase aberrations were produced in cells treated with N-methyl-N'-nitro-N-nitrosoguanidine, benzo(a)pyrene, 9-aminoacridine and mitomycin-C. These abnormalities were also far more complex and extensive than those observed in the control and nonmutagen-treated cells. Many species of fish have extremely small and numerous chromosomes, making resolution of chromosome defects such as sister chromatid exchange and deletions more difficult than in most mammalian diploid cells, which generally have larger and fewer chromosomes. Examination of cells during anaphase eliminates the need to observe each chromosome separately as well as the need to produce well-spread metaphase chromosomes. Since the sensitivity of anaphase aberrations tomore » known mutagenic/carcinogenic compounds appears to be quite high in trout cells and since hundreds of suitable cells are available for analysis, this may be an appropriate alternative or addition to some of the more standard chromosome macrolesion tests developed in mammalian systems.« less

Abstract: Endopolyploidy, which arises through the duplication of DNA without accompanying nuclear division, occurs in large numbers of lower and higher plants and animals, including the best known, the salivary gland nuclei of Drosophila. Endomitosis is one of the processes leading to endopolyploidy, in which the stages of mitosis (prophase, metaphase, anaphase) take place inside the nuclear membrane and without spindle formation. In mammals, endomitosis has been observed in the trophoblast of the placenta of the mouse, rat and rabbit. This is the first report of endomitosis in a normal human tissue, the trophoblast of first trimester human placenta.

Abstract: Studies using living cells1,2 and experimental manipulation of permeabilized mitotic cells3,4 demonstrate that the movement of anaphase chromosomes consists of two physiologically distinct events: chromosome movement to the spindle poles (anaphase A) and separation of the poles via spindle elongation (anaphase B). Shortening of kinetochore-attached microtubules is associated with anaphase A and rearrangement and lengthening of the polar microtubules, especially those found in the spindle midzone, with anaphase B5,6. It has been suggested that interactions between microtubules, mediated by dynein-like cross-bridges similar to those found in flagella, may be the mechanochemical system responsible for anaphases A and B7,8. Recently Bouchard et al.9 have demonstrated that erythro-9-[3-(2-hydroxynonyl)]adenine (EHNA), a protein carboxyl-methylation inhibitor, is a specific inhibitor of flagellar beat and dynein ATPase activity. I have now investigated the possibility that dynein-like ATPases have a role in anaphase by adding EHNA to permeabilized cell models in conditions compatible with maintenance of anaphases A and B after lysis3,4.I find that EHNA blocks anaphase B but not anaphase A. These results are consistent with the involvement of a dynein-like ATPase in spindle elongation.

Abstract: During micronuclear mitosis of the heterotrichous ciliate Nyctotherus ovalis Leidy rod-shaped composite chromosomes are formed by lateral association of telokinetic chromosomes. The formation of these composite chromosomes seems to be a highly ordered process since only nuclei with either 18 or 24 such chromosomes can be observed, and nuclei with the same chromosome number show a similar length distribution of their chromosomes. Further, these data indicate that we examined two otherwise indistinguishable races. During metaphase the composite chromosomes become arranged in the spindle equator in a holokinetic fashion, their entire poleward surfaces being covered by kinetochore material. These “diffuse” kinetochores have a trilaminar appearance comparable to those of monokinetic chromosomes. Their electron density after employing Bernhard's procedure revealed the same ribonucleoprotein distribution as reported for the localized kinetochores formed during the extranuclear mitosis in other cells. During early anaphase the outer kinetochore layer remains continuous while the individual chromosomes in the composite group show a tendency to separate leaving chromatin-free spaces of about 40 nm diameter. Kinetochore microtubules which are still anchored in the outer kinetochore layer seem to elongate and to extend into the interpolar spindle region predominantly through these “holes” in the chromatin. These observations suggest a like polarity of kinetochore and interpolar microtubules in the polar spindle region while microtubules in the interpolar space seem to interdigitate in an antiparallel fashion. The activity of the kinetochore to act as a microtubule-organizing center (MTOC) seems to be modulated by the chromatin underlying the outer kinetochore layer which may prevent further outgrowth of kinetochore microtubules.

Abstract: Chromosomal aberrations in anaphase cells of first mitosis in roots from artificially aged barley seeds were classified as bridge or fragment types. Single bridge, single fragment, and double bridge types comprised 77% of the chromosomal aberrations, and other types, less than 10% of the total. Combinations of fragments and bridges were very rare. High frequency of bridges was caused by chromosome stickiness, indicating that they were probably chromatid or, more correctly, subchromatid types rather than chromosome types. Chromosomal damage in aged seed may be induced by the irregularity of mitotic cell divisions during early stages of seed germination.

Abstract: In meiosis of haploid rye associations of two or more chromosomes are observed. In order to investigate whether these associations are chiasmate, metaphase I and anaphase I associations were analysed after Giemsa banding. — At anaphase I chromatid exchanges between differently marked chromosome arms were observed, which proved the presence of real chiasmata. The association between banded and unbanded arms shows that the heterochromatic telomeres do not act as secondary pairing sources. Different statistical approaches were used to test randomness of chiasma formation. It appeared to be non-random, which showed that the segments involved were non-randomly located and probably limited in number. The nature of these segments is discussed.

Abstract: Anaphase lagging of autosomes was observed in 6.1±5.4% of the primary spermatocytes in untreated larvae of the crane fly, Nephrotoma suturalis. Lagging was induced by exposure of larvae to 6 ° C and during recovery at 22 ° C from exposure to 0.2, 2, and 6 ° C. The incidence of anaphase lag was maximal at 80 to 90 min of recovery. Induced lagging was observed at that recovery time after exposures of only 2.5 h to 2 or 0.2 ° C, but its incidence increased with longer exposures. As many as 85% of the cells in anaphase contained autosomal laggards after 61 h at 2 ° C and 80 to 90 min of recovery. At 2 ° C, cells reached the prophase-prometaphase transition, but spindles did not appear to form. Those cells proceeded through prometaphase during recovery, reaching mid-anaphase after 80 to 90 min of recovery. Chromosomes that lagged at anaphase during recovery from 2 ° C were observed in living cells to be half-bivalents derived from bivalents that congressed to the metaphase plate. One or both half-bivalents of any bivalent could lag. In some cells, one half-spindle had more half-bivalents than the other. Cells with autosomal laggards often did not cleave, and in uncleaved cells the second division employed spindles having two, three, or four poles. The basis of induced lagging might be a lapse in spindle attachment or motive force application at the start of anaphase or a failure of chromosomes to achieve proper orientation before the onset of anaphase.

Abstract: Mitosis in the protostelidPlanoprotostelium aurantium Olive andStoianovich is characterized by an open, centric spindle. The nuclear envelope breaks down prior to metaphase, begins to reform during late anaphase, and is complete by telophase. Centrioles are present at the poles throughout mitosis and are devoid of rootlet microtubules from metaphase to late anaphase. Chromosomes are small and numerous and are attached to single kinetochore microtubules during metaphase and early anaphase. Chromosome separation takes place by a presumed shortening of the chromosome to pole spindle followed by a lengthening of the interzonal spindle. Mitosis inP. aurantium is similar to that of certain other protostelid amoebae and to myxomycete amoebae, but it is considerably different from that of dictyostelid amoebae. The phylogenetic significance of this is discussed.

Abstract: The meiotic effects of 2, 4-D and 2, 4, 5-T on hexaploid wheat T. aestivum L., tetraploid wheat T. durum Desf. and a diploid related species Ae. ligustica L. The two herbicides increased the percentages of abnormal meiotic cells significantly. The kinds of irregularities observed were lagging chromosomes, single and multiple bridges, fragments and asynchoronization in the disjunction of chromosomes during second anaphase. It was evident that chromosomal stickiness was the cause of most of the aberrations observed. The increase in dose of 2, 4, 5-T caused significant increase in the percentages of meiotic cells with chromosomal aberrations in Ae. ligustica L.

Abstract: Meiosis of T70H/+,Ts(113)70H translocation trisomic male mice has been studied using C-banded preparations of multivalents at the first meiotic division, marker chromosomes at the second meiotic division, and sucrose-spread pachytene spermatocytes for the observation of synaptonemal complexes. During zygotene and pachytene the three marker chromosomes, 131 (long) and 113 (2 x, small) associate with the chromosomes 1 and 13 to form either a Chain of three plus bivalent (CIII+II), a Chain of four plus univalent (CIV+I) or a Chain of five (CV). During pachytene, the 113 univalent of the CIV+I configuration shows association with the sex chromosomes in the sex vesicle while for CV, the unpaired segment of chromosome 1 can do so. — The frequencies of the multivalent configurations during late diplotenemetaphase I were CIII+II, 47.6%, CIV+I, 34.5% and CV, 14.4%. However, among late diplotene-early diakinesis cells, the frequency of CIV+I was 12.9% while in (late) spermatocytes with contracted bivalents it was 45.7%. — The notion that proximity of the interstitital chiasma of chromosome 13 to the centromere affects the chances of non-disjunction for these centromeres within the multivalent (i.e., adjacent 2 segregation) has been strengthened by the observed adjacent 2 frequency of 13.0% in the translocation trisomics compared to the 26.3% found in T70H/+ translocation heterozygotes with more proximal chiasmata. Thus, for reciprocal translocations between acrocentric chromosomes, a proximally located chiasma in an interstitial segment enhances the chance of adjacent 2 segregation. — Other parameters of irregular chromosome behaviour at anaphase I, such as equational separation of chromosome 113 into chromatids and non-disjunction of normal bivalents, were increased in the translocation trisomics when compared with T70H/+ translocation heterozygotes, especially among adjacent 2 segregating cells.

Abstract: Male meiosis was studied in 6 diploid, 3 tetraploid and I pentaploid Rosa species. Chromosome associations at diakinesis and irregularities at anaphase and telophase were scored. Pollen fertility was also determined. The diploids and one tetraploid, R. s. pimpinellifolia showed regular meiosis and high pollen fertility. The tetraploid hybrid species, R. macrantha showed fairly irregular meiosis with only about one third of pollen fertile. Highly irregular meiosis, with 6-7 bivalents and remaining univalents, was observed both in the tetraploid R. glauca and, pentaploid R. canina. Additionally these had a very high frequency of laggards resulting in formation of more than four pollen grains per PMC thereby drastically reducing the pollen fertility.

Abstract: The meiotic behavior of heterozygotes from three different maize pericentric inversion stocks was quantitatively observed at a variety of stages throughout meiosis I and II. With heterozygosity for either of two of these inversions, the usual mode of pairing observed at pachytene involved synapsis of the centromere containing inverted region, and synaptic failure of the centromere region was rarely found. Abnormal chromosome behavior at subsequent meiotic stages was rare in these cases. With heterozygosity for the third inversion, however, homologous synapsis was generally found in the distal regions of the chromosome involved, the inverted region was often non-homologously synapsed, and a substantial frequency of cells apparently showed synaptic failure in the centromere containing inverted region. A substantial frequency of cells at anaphase II in this case contained two lagging monads in the plate region of the spindle. Where cells could be identified as sisters, sister cells showed identical behavior at anaphase II. Findings seem to be most simply explained by the supposition that pachytene synapsis of the centromere region is important to provision for sister centromere association until anaphase II.

Abstract: The present investigation includes the meiotic study of 15 species belonging to the tribe Hibisceae and Ureneae of the family Malvaceae. Of which meiotic study of 7 species has been done for the first time. The meiosis is regular in most of the taxa. Few irregularities like laggards in anaphase and telophase I and II, irregular distribution at anaphase I and non-congressional bivalents, secondary association of bivalents at metaphase I are noticed in a few species. The occurrence of distinct bivalents in majority of the taxa studied, indicate that they represent ancient polyploids.

Abstract: An ultrastructural study was performed on the sex chromosomes (male X1X2X3O) during the spermatogenesis of Tegenaria domestica (Arachnida, Agelenidae). This study was carried out using random and serially cut sections. During pachytene and diplotene the three X chromosomes are longitudinally paired. Each of these consists of a central core of condensed chromatin, surrounded by a field of dense chromatin projections through which the chromosomes are in contact with one another. These projections may be responsible for the recognition and pairing of the sex chromosomes and in some way participate in their non-disjunction during anaphase I. A study of the structure and behaviour of the sex chromosomes during spermatogenesis is also presented. The available information on non-synaptonemal complex-mediated chromosome pairing and a systematization of sex chromosome structure in spiders are discussed.

Abstract: A mitodepressive effect of Tridemorph on the meristematic cells of Allium cepa has been observed. This effect increases with the concentration of the fungicide and the length of treatment, until complete inhibition of cell division occurs under certain conditions. Furthermore, this chemical has been revealed as a strong c-mitotic agent, although there are clear differences between its action and that of colchicine and other c-mitotic drugs. Other important features are the alterations observed in the development of the different mitotic phases depending on the dose employed. A high degree of chromosome contraction has been observed since the cells are in prophase until they reach telophase. Multipolar anaphases and micronuclei, and anomalous chromosome separation and anaphase emigration are other important modifications induced by the treatment on the development of mitosis.

Abstract: An individual of Arcyptera tornosi heterozygous for distal heterochromatic segments affecting M6, S10 and S11 chromosomes has been analyzed during all the meiotic stages in order to establish the pattern of meiotic segregation in anaphase I and II. S-bivalents invariably show an equational separation during anaphase I and the anaphase II separation is non-random, both chromatids with heterochromatic segments often segregating to the same pole. Differences are significant if compared with the expected segregation. Some aspects of this particular chromosome behaviour are briefly discussed.

Abstract: Clean and large dividing cells of cultured lung epithelium of the Japanese newt were used to study physiological and morphological differences that exist between the metaphase and anaphase of mitosis. The response of the mitotic apparatus to pulse treatment with mitotic poisons (10μM of Colcemid or vinblastine) at room temperature was followed with polarization and phase-contrast microscopy.In general, the length and birefringence of the spindles in both metaphase and anaphase gradually decreased on the pulse application of these drugs and finally disappeared. Chromosomes in metaphase in treated cells always maintained their shape and structure for a longer time than did those of the control. Chromosomes in anaphase in treated cells tended to change their structure and formresting nuclei or karyomeres.These results support the belief that the physical properties of chromosomes are altered during the transition from metaphase to anaphase.

Abstract: Spermatogenesis involving an additional chromosome reduplication during zygotene in sporadic males and intersexes of the thelytokous phasmid Carausius morosus Br. has been examined using differential staining of chromatids after 5-bromodeoxycytidine incorporation. After reduplication autobivalents are formed by synapsis between identical sister chromosomes. Chiasmata are only formed after reduplication; they do not occur in constitutive heterochromatin, but can be formed in facultative heterochromatin, dependent on heteropycnosis and sex. Quadrivalents and U-type exchanges occur. In spermatogonia and spermatocytes the number of differentially stained chromosomes varies considerably; sister chromatid exchanges hardly appear. Sex bivalents with differentially stained chromosomes have a lower chiasma frequency than normally stained sex bivalents. Bivalents show reduced staining of all four, two outer, or one inner chromatid. Autobivalents arise in the same way as diplochromosomes; chromatids with the oldest DNA sub-units remain together during reduplication and are thus involved in sister chromosome pairing. The additional reduplication begins 7 days after the premeiotic S-phase, first metaphase after 19 days. Spermatogenesis is abnormal from first anaphase onwards.

Abstract: Autosome-autosome and sex chromosome-autosome constitutional translocations are analyzed in order to determine whether the affected chromosomes have a particular position in the spread metaphase. Except for one t (10;15) and for several t (X;autosome), the rearranged chromosomes and their normal homologues seem to have random positions. In so far as it has been demonstrated that the metaphase chromosome's positions reflect those of the interphase chromosomes, it is concluded that no specific ordering, transmissible cell generation after generation, exists. The position of the chromosomes would be determined after anaphase migration and would remain unchanged until the subsequent metaphase. Therefore, the rearrangements do not impose any particular topological constraints to the involved chromosomes. The only exceptions may concern the sex chromosomes and those carrying nucleolar organizers.

Abstract: Chromosomal aberrations in anaphase cells of first mitosis in roots from artificially aged barley seeds were classified as bridge or fragment types. Single bridge, single fragment, and double bridge types comprised 77% of the chromosomal aberrations, and other types, less than 10% of the total. Combinations of fragments and bridges were very rare. High frequency of bridges was caused by chromosome stickiness, indicating that they were probably chromatid or, more correctly, subchromatid types rather than chromosome types. Chromosomal damage in aged seed may be induced by the irregularity of mitotic cell divisions during early stages of seed germination.