scholarly journals Meiosis in Sciara coprophila: structure of the spindle and chromosome behavior during the first meiotic division.

1982 ◽  
Vol 93 (3) ◽  
pp. 655-669 ◽  
Author(s):  
D F Kubai
Keyword(s):  
Chromosome Segregation ◽  
Chromosome Movement ◽  
Serial Sections ◽  
Chromosome Behavior ◽  
Monopolar Spindle ◽  
Prophase Nucleus ◽  
Fungus Gnat ◽  
Spindle Microtubules ◽  
Conical Radiation ◽  
Meiosis I

Light microscope descriptions of meiosis I in males of the fungus gnat Sciara coprophila suggested the presence of a monopolar spindle in which maternal and limited chromosomes move poleward while paternal chromosomes "back away" from the pole. The ultrastructural analysis reported here, based upon serial sections of cells in different stages of meiosis I, shows that the spindle is indeed monopolar with a distinctive differentiation, the polar complex, at one pole. This complex is the focus of a conical radiation of spindle microtubules. Kinetochores of paternal chromosomes face the complex and microtubules associated with these kinetochores run toward the complex. No kinetochore microtubules were discovered on maternal or limited chromosomes. When the position of paternal, maternal, and limited chromosomes is compared at various stages, it is found that limited chromosomes always remain near the polar complex, paternal chromosomes remain far from it and only maternal chromosomes move closer to the pole. Apparently, chromosome segregation does not depend on paternal chromosomes "backing away" from the pole, and the required movement of maternal chromosomes take place in the absence of kinetochore microtubules. In the prophase nucleus, limited and maternal chromosomes are already spatially separate from paternal chromosomes before the spindle forms. Thus, the monopolar spindle functions only to increase the distance between already segregated sets of chromosomes. An extensive system of microtubule-associated membranes outlines the spindle; the possibility that maternal chromosome movement is somehow related to the presence of this membrane is discussed.

Role of microtubules and microtubule organizing centers on meiotic chromosome elimination in Sciara ocellaris

1997 ◽  
Vol 110 (6) ◽  
pp. 721-730 ◽  
Author(s):  
M.R. Esteban ◽  
M.C. Campos ◽  
A.L. Perondini ◽  
C. Goday
Keyword(s):  
Meiotic Chromosome ◽  
Chromosome Elimination ◽  
Male Meiosis ◽  
Meiotic Spindle ◽  
Monopolar Spindle ◽  
Meiotic Spindles ◽  
Cytoplasmic Microtubules ◽  
Spindle Microtubules ◽  
Meiosis I

Spindle formation and chromosome elimination during male meiosis in Sciara ocellaris (Diptera, Sciaridae) has been studied by immunofluorescence techniques. During meiosis I a monopolar spindle is formed from a single polar complex (centrosome-like structure). This single centrosomal structure persists during meiosis II and is responsible for the non-disjunction of the maternal X chromatids. During meiosis I and II non-spindle microtubules are assembled in the cytoplasmic bud regions of the spermatocytes. The chromosomes undergoing elimination during both meiotic divisions are segregated to the bud region where they associate with bundles of microtubules. The presence and distribution of centrosomal antigens in S. ocellaris meiotic spindles and bud regions has been investigated using different antibodies. gamma-Tubulin and centrin are present in the bud as well as in the single polar complex of first meiotic spindle. The results suggest that spermatocyte bud regions contain microtubule-organizing centres (MTOCs) that nucleate cytoplasmic microtubules that are involved in capturing chromosomes in the bud regions. The distribution of actin and myosin in the spermatocytes during meiosis is also reported.

scholarly journals Cohesins Determine the Attachment Manner of Kinetochores to Spindle Microtubules at Meiosis I in Fission Yeast

2003 ◽  
Vol 23 (11) ◽  
pp. 3965-3973 ◽  
Author(s):  
Shihori Yokobayashi ◽  
Masayuki Yamamoto ◽  
Yoshinori Watanabe
Keyword(s):  
Fission Yeast ◽  
Chromosome Segregation ◽  
Sister Chromatid ◽  
Specific Requirement ◽  
Spindle Poles ◽  
Chromatid Cohesion ◽  
Spindle Microtubules ◽  
Yeast Meiosis ◽  
Meiosis I ◽  
Random Division

ABSTRACT During mitosis, sister kinetochores attach to microtubules that extend to opposite spindle poles (bipolar attachment) and pull the chromatids apart at anaphase (equational segregation). A multisubunit complex called cohesin, including Rad21/Scc1, plays a crucial role in sister chromatid cohesion and equational segregation at mitosis. Meiosis I differs from mitosis in having a reductional pattern of chromosome segregation, in which sister kinetochores are attached to the same spindle (monopolar attachment). During meiosis, Rad21/Scc1 is largely replaced by its meiotic counterpart, Rec8. If Rec8 is inactivated in fission yeast, meiosis I is shifted from reductional to equational division. However, the reason rec8Δ cells undergo equational rather than random division has not been clarified; therefore, it has been unclear whether equational segregation is due to a loss of cohesin in general or to a loss of a specific requirement for Rec8. We report here that the equational segregation at meiosis I depends on substitutive Rad21, which relocates to the centromeres if Rec8 is absent. Moreover, we demonstrate that even if sufficient amounts of Rad21 are transferred to the centromeres at meiosis I, thereby establishing cohesion at the centromeres, rec8Δ cells never recover monopolar attachment but instead secure bipolar attachment. Thus, Rec8 and Rad21 define monopolar and bipolar attachment, respectively, at meiosis I. We conclude that cohesin is a crucial determinant of the attachment manner of kinetochores to the spindle microtubules at meiosis I in fission yeast.

scholarly journals The functions and consequences of force at kinetochores

2013 ◽  
Vol 200 (5) ◽  
pp. 557-565 ◽  
Author(s):  
Florencia Rago ◽  
Iain M. Cheeseman
Keyword(s):  
Recent Work ◽  
Chromosome Segregation ◽  
Chromosome Movement ◽  
Classical Studies ◽  
Spindle Microtubules

Chromosome segregation requires the generation of force at the kinetochore—the multiprotein structure that facilitates attachment of chromosomes to spindle microtubules. This force is required both to move chromosomes and to signal the formation of proper bioriented attachments. To understand the role of force in these processes, it is critical to define how force is generated at kinetochores, the contributions of this force to chromosome movement, and how the kinetochore is structured and organized to withstand and respond to force. Classical studies and recent work provide a framework to dissect the mechanisms, functions, and consequences of force at kinetochores.

scholarly journals Nonrandom chromosome arrangements in germ line nuclei of Sciara coprophila males: the basis for nonrandom chromosome segregation on the meiosis I spindle.

1987 ◽  
Vol 105 (6) ◽  
pp. 2433-2446 ◽  
Author(s):  
D F Kubai
Keyword(s):  
Chromosome Segregation ◽  
Direct Evidence ◽  
Germ Line ◽  
Chromosome Translocation ◽  
Chromosome Behavior ◽  
Direct Role ◽  
Nonrandom Distribution ◽  
Chromosome Arrangements ◽  
Meiotic Spindles ◽  
Meiosis I

Meiosis I in males of the Dipteran Sciara coprophila results in the nonrandom distribution of maternally and paternally derived chromosome sets to the two division products. Based on an earlier study (Kubai, D.F. 1982. J. Cell Biol. 93:655-669), I suggested that the meiosis I spindle does not play a direct role in the nonrandom sorting of chromosomes but that, instead, haploid sets are already separated in prophase nuclei well before the onset of spindle formation. Here I report more direct evidence that this hypothesis is true; this evidence was gained from ultrastructural reconstruction analyses of the arrangement of chromosomes in germ line nuclei (prophase nuclei in spermatogonia and spermatocytes) of males heterozygous for an X-autosome chromosome translocation. Because of this translocation, the maternal and paternal chromosome sets are distinguishable, so it is possible to demonstrate that (a) the two haploid chromosome sets occupy distinct maternal and paternal nuclear compartments and that (b) nuclei are oriented so that the two haploid chromosome sets have consistent relationships to a well-defined cellular axis. The consequences of such nonrandom aspects of nuclear structure for chromosome behavior on premeiotic and meiotic spindles are discussed.

scholarly journals Bipolar spindle attachments affect redistributions of ZW10, a Drosophila centromere/kinetochore component required for accurate chromosome segregation.

1996 ◽  
Vol 134 (5) ◽  
pp. 1127-1140 ◽  
Author(s):  
B C Williams ◽  
M Gatti ◽  
M L Goldberg
Keyword(s):  
Chromosome Segregation ◽  
Male Meiosis ◽  
Chromosome Behavior ◽  
Bipolar Spindle ◽  
Chromosome Missegregation ◽  
Spindle Poles ◽  
Anaphase Onset ◽  
Sister Chromatids ◽  
Chromosome Separation ◽  
Meiosis I

Previous efforts have shown that mutations in the Drosophila ZW10 gene cause massive chromosome missegregation during mitotic divisions in several tissues. Here we demonstrate that mutations in ZW10 also disrupt chromosome behavior in male meiosis I and meiosis II, indicating that ZW10 function is common to both equational and reductional divisions. Divisions are apparently normal before anaphase onset, but ZW10 mutants exhibit lagging chromosomes and irregular chromosome segregation at anaphase. Chromosome missegregation during meiosis I of these mutants is not caused by precocious separation of sister chromatids, but rather the nondisjunction of homologs. ZW10 is first visible during prometaphase, where it localizes to the kinetochores of the bivalent chromosomes (during meiosis I) or to the sister kinetochores of dyads (during meiosis II). During metaphase of both divisions, ZW10 appears to move from the kinetochores and to spread toward the poles along what appear to be kinetochore microtubules. Redistributions of ZW10 at metaphase require bipolar attachments of individual chromosomes or paired bivalents to the spindle. At the onset of anaphase I or anaphase II, ZW10 rapidly relocalizes to the kinetochore regions of the separating chromosomes. In other mutant backgrounds in which chromosomes lag during anaphase, the presence or absence of ZW10 at a particular kinetochore predicts whether or not the chromosome moves appropriately to the spindle poles. We propose that ZW10 acts as part of, or immediately downstream of, a tension-sensing mechanism that regulates chromosome separation or movement at anaphase onset.

scholarly journals Kinetochore-independent chromosome segregation driven by lateral microtubule bundles

eLife ◽  
2015 ◽  
Vol 4 ◽  
Author(s):  
Christina C Muscat ◽  
Keila M Torre-Santiago ◽  
Michael V Tran ◽  
James A Powers ◽  
Sarah M Wignall
Keyword(s):  
Cell Division ◽  
Chromosome Segregation ◽  
Protein Complex ◽  
Chromosome Movement ◽  
Chromosome Dynamics ◽  
Anaphase Onset ◽  
Independent Segregation ◽  
Main Driver ◽  
Chromosome Associations ◽  
Spindle Microtubules

During cell division, chromosomes attach to spindle microtubules at sites called kinetochores, and force generated at the kinetochore-microtubule interface is the main driver of chromosome movement. Surprisingly, kinetochores are not required for chromosome segregation on acentrosomal spindles in Caenorhabditis elegans oocytes, but the mechanism driving chromosomes apart in their absence is not understood. In this study, we show that lateral microtubule–chromosome associations established during prometaphase remain intact during anaphase to facilitate separation, defining a novel form of kinetochore-independent segregation. Chromosome dynamics during congression and segregation are controlled by opposing forces; plus-end directed forces are mediated by a protein complex that forms a ring around the chromosome center and dynein on chromosome arms provides a minus-end force. At anaphase onset, ring removal shifts the balance between these forces, triggering poleward movement along lateral microtubule bundles. This represents an elegant strategy for controlling chromosomal movements during cell division distinct from the canonical kinetochore-driven mechanism.

Unorthodox Mitosis in Trichonympha Agilis: Kinetochore Differentiation and Chromosome Movement

1973 ◽  
Vol 13 (2) ◽  
pp. 511-552
Author(s):  
DONNA F. KUBAI
Keyword(s):  
Nuclear Envelope ◽  
Direct Contact ◽  
Direct Interaction ◽  
Stage Iv ◽  
Spindle Pole ◽  
Stage Ii ◽  
Nuclear Surface ◽  
Chromosome Movement ◽  
Serial Sections ◽  
Spindle Microtubules

Changes in rostral structures and the nuclear events which occur in dividing cells of Trichonympha agilis (obtained from experimentally refaunated termites) were studied by means of electron microscopy of serial sections. It is possible to characterize 5 stages of division: Stage I. During this earliest recognizable division stage, the bilaterally symmetrical hemirostra have begun to separate and spindle microtubules appear in the intervening space. As in interphase, the kinetochore regions of chromosomes are distinguishable as fibrillar masses underlying the intact nuclear envelope; and, in individual sections, they are often seen to occur in pairs. These pairs are taken to be sister kinetochores. Stage II. The extranuclear spindle has become established between the posterior ends of well separated hemirostral tubes. Elaboration of daughter rostral structures begins and will continue through the subsequent stages of division. Kinetochores differentiate, becoming bipartite structures consisting of a fibrillar element underlain by a dense disk. The fibrillar kinetochore element is associated with the still-intact nuclear envelope which lies between kinetochores and cytoplasmic spindle microtubules. Reconstruction from serial sections shows all kinetochores to be disposed in pairs which are distributed randomly over the nuclear surface. Stage III. The fibrillar elements of kinetochores are enclosed in evaginations of the nuclear envelope, while the disk elements have come to lie in the plane of the nuclear surface. Kinetochores remain separated from the extranuclear spindle microtubules by the intact nuclear envelope. The distribution of kinetochores has changed relative to that seen in stage II: kinetochores no longer appear to be paired, and they are confined to that hemisphere of the nuclear surface closest to the spindle. Stage IV. The nuclear envelope opens at the sites of kinetochores, leaving the dense disk kinetochore element inserted in pore-like discontinuities of the nuclear envelope and the fibrillar element in the cytoplasm. Direct interaction between fibrillar kinetochore element and extranuclear spindle microtubules is, however, not yet established. Stage V. The cytoplasmically situated fibrillar elements of ‘inserted’ kinetochores are now in direct contact with spindle microtubules. As seen in reconstructions of the nucleus from serial sections, kinetochores have become segregated in 2 groups on the nuclear surface, one near each spindle pole. It is during this stage that final elaboration of rostral structures takes place. On the basis of the observed changes in kinetochore distribution which occur between stages II and III while the intact nuclear envelope prevents any direct interaction between intra-nuclear kinetochores and extranuclear spindle microtubules, it is suggested that kinetochore-membrane interaction is involved in early chromosome movement in Trichonympha agilis. Only during stage V, when direct contact between kinetochores and spindle microtubules is established, may the microtubules assume their usual role in chromosome movement.

scholarly journals Spindle microtubules and their mechanical associations after micromanipulation in anaphase.

1982 ◽  
Vol 95 (1) ◽  
pp. 91-104 ◽  
Author(s):  
R B Nicklas ◽  
D F Kubai ◽  
T S Hays
Keyword(s):  
Electron Microscopy ◽  
Three Dimensional ◽  
Chromosome Movement ◽  
Serial Sections ◽  
Microtubule Bundle ◽  
Uncertain Significance ◽  
Glutaraldehyde Solution ◽  
Spindle Microtubules

Micromanipulation of living grasshopper spermatocytes in anaphase has been combined with electron microscopy to reveal otherwise obscure features of spindle organization. A chromosome is pushed laterally outside the spindle and stretched, and the cell is fixed with a novel, agar-treated glutaraldehyde solution. Two- and three-dimensional reconstructions from serial sections of seven cells show that kinetochore microtubules of the manipulated chromosome are shifted outside the confusing thicket of spindle microtubules and mechanical associations among microtubules are revealed by bent or shifted microtubules. These are the chief results: (a) The disposition of microtubules invariably is consistent with a skeletal role for spindle microtubules. (b) The kinetochore microtubule bundle is composed of short and long microtubules, with weak but recognizable mechanical associations among them. Some kinetochore microtubules are more tightly linked to one other microtubule within the bundle. (c) Microtubules of the kinetochore microtubule bundle are firmly connected to other spindle microtubules only near the pole, although some nonkinetochore microtubules of uncertain significance enter the bundle nearer to the kinetochore. (d) The kinetochore microtubules of adjacent chromosomes are mechanically linked, which provides an explanation for interdependent chromosome movement in "hinge anaphases." In the region of the spindle open to analysis after chromosome micromanipulation, microtubules may be linked mechanically by embedment in a gel, rather than by dynein or other specific, cross-bridging molecules.

Confocal analysis of chromosome behavior in wheat × maize zygotes

Genome ◽  
2004 ◽  
Vol 47 (1) ◽  
pp. 199-205 ◽  
Author(s):  
Keiichi Mochida ◽  
Hisashi Tsujimoto ◽  
Tetsuo Sasakuma
Keyword(s):  
Metaphase Plate ◽  
Chromosome Elimination ◽  
Chromosome Movement ◽  
Hybridization Method ◽  
Chromosome Behavior ◽  
Whole Mount ◽  
Hybrid Embryo ◽  
Spindle Microtubules ◽  
Spindle Structure

Herein, we profile the first embryonic mitosis in a hybrid of wheat and maize by using a whole-mount genomic in situ hybridization method and immunofluorescence staining with a tubulin-specific antibody. We have successfully captured the dynamics of each set of parental chromosomes in the first zygotic division of the hybrid embryo 24-28 h after crossing. During the first zygotic metaphase, although both sets of parental chromosomes congressed into the equatorial plate of the zygote, the maize chromosomes tended to lag in comparison with the wheat chromosomes. During anaphase, each parental chromosome separated into its sister chromosomes; however, some of the maize chromosomes lagged around the metaphase plate as segregants. The maize sister chromosomes that did move toward the pole showed delayed and asymmetric movement as compared with the wheat ones. Immunological staining of tubulin revealed a bipolar spindle structure in the first zygotic metaphase. The kinetochores of the maize chromosomes that lagged around the metaphase plate did not attach to the spindle microtubules. These results suggest that factors on the kinetochores of maize chromosomes that are required to control chromosome movement are deficient in the zygotic cell cycle.Key words: whole-mount, GISH, chromosome elimination, hybrid embryogenesis.

scholarly journals Nonrandom chromosome segregation in Neocurtilla (Gryllotalpa) hexadactyla: an ultrastructural study.

1981 ◽  
Vol 88 (2) ◽  
pp. 281-293 ◽  
Author(s):  
D F Kubai ◽  
D Wise
Keyword(s):  
Chromosome Segregation ◽  
Spatial Relationship ◽  
Lateral Position ◽  
Serial Sections ◽  
Mole Cricket ◽  
Y Chromosomes ◽  
Dense Substance ◽  
Kinetochore Region ◽  
Small Bundle ◽  
Meiosis I

During meiosis I in males of the mole cricket Neocurtilla (Gryllotalpa) hexadactyla, the univalent X1 chromosome and the heteromorphic X2Y chromosome pair segregate nonrandomly; the X1 and X2 chromosomes move to the same pole in anaphase. By means of ultrastructural analysis of serial sections of cells in several stages of meiosis I, metaphase of meiosis II, and mitosis, we found that the kinetochore region of two of the three nonrandomly segregating chromosomes differ from autosomal kinetochores only during meiosis I. The distinction is most pronounced at metaphase I when massive aggregates of electron-dense substance mark the kinetochores of X1 and Y chromosomes. The lateral position of the kinetochores of X1 and Y chromosomes and the association of these chromosomes with microtubules running toward both poles are also characteristic of meiosis I and further distinguish X1 and Y from the autosomes. Nonrandomly segregating chromosomes are typically positioned within the spindle so that the kinetochoric sides of the X2Y pair and the X1 chromosome are both turned toward the same interpolar spindle axis. This spatial relationship may be a result of a linkage of X1 and Y chromosomes lying in opposite half spindles via a small bundle of microtubules that runs between their unusual kinetochores. Thus, nonrandom segregation in Neocurtilla hexadactyla involves a unique modification at the kinetochores of particular chromosomes, which presumably affects the manner in which these chromosomes are integrated within the spindle.

Sign in / Sign up

Export Citation Format

Share Document