Maize meiotic spindles assemble around chromatin and do not require paired chromosomes

1998 ◽  
Vol 111 (23) ◽  
pp. 3507-3515 ◽  
Author(s):  
A. Chan ◽  
W.Z. Cande
Keyword(s):  
Nuclear Envelope ◽  
Higher Plants ◽  
Metaphase Plate ◽  
Meiotic Spindle ◽  
Wild Type ◽  
Homologous Chromosomes ◽  
Nuclear Envelope Breakdown ◽  
Meiotic Spindles ◽  
Meiotic Mutations ◽  
Bipolar Spindles

To understand how the meiotic spindle is formed and maintained in higher plants, we studied the organization of microtubule arrays in wild-type maize meiocytes and three maize meiotic mutants, desynaptic1 (dsy1), desynaptic2 (dsy2), and absence of first division (afd). All three meiotic mutations have abnormal chromosome pairing and produce univalents by diakinesis. Using these three mutants, we investigated how the absence of paired homologous chromosomes affects the assembly and maintenance of the meiotic spindle. Before nuclear envelope breakdown, in wild-type meiocytes, there were no bipolar microtubule arrays. Instead, these structures formed after nuclear envelope breakdown and were associated with the chromosomes. The presence of univalent chromosomes in dsy1, dsy2, and afd meiocytes and of unpaired sister chromatids in the afd meiocytes did not affect the formation of bipolar spindles. However, alignment of chromosomes on the metaphase plate and subsequent anaphase chromosome segregation were perturbed. We propose a model for spindle formation in maize meiocytes in which microtubules initially appear around the chromosomes during prometaphase and then the microtubules self-organize. However, this process does not require paired kinetochores to establish spindle bipolarity.

scholarly journals The cdc25 homologue twine is required for only some aspects of the entry into meiosis in Drosophila

1993 ◽  
Vol 106 (4) ◽  
pp. 1035-1044 ◽  
Author(s):  
H. White-Cooper ◽  
L. Alphey ◽  
D.M. Glover
Keyword(s):  
Nuclear Envelope ◽  
Chromosome Condensation ◽  
Wild Type ◽  
Spindle Formation ◽  
Nuclear Envelope Breakdown ◽  
Spindle Poles ◽  
Meiotic Spindles ◽  
Metaphase I

The twineHB5 mutation prevents spindle formation during the entry into meiosis in Drosophila males, but chromosome condensation and nuclear envelope breakdown both still occur. This suggests the possibility that this particular cdc25 homologue is required to activate a p34cdc2 kinase required for only some of the events of this G2-M transition. In contrast, meiotic spindles do form in twineHB5 females, although these appear abnormal. However, the female meiotic divisions do not arrest at metaphase I as in wild type, but continue repeatedly, leading to gross non-disjunction. Small chromatin masses, corresponding in size to the fourth chromosomes, often segregate properly to the spindle poles. These can persist into the embryos derived from twineHB5 females, where they appear to participate in mitotic divisions on thin spindles. In addition, these embryos contain a small number of large chromatin masses that are not associated with spindles.

Changes in the metaphase transit times and the pattern of sister chromatid separation in stamen hair cells of Tradescantia after treatment with protein phosphatase inhibitors

1992 ◽  
Vol 102 (4) ◽  
pp. 691-715 ◽  
Author(s):  
S.M. Wolniak ◽  
P.M. Larsen
Keyword(s):  
Nuclear Envelope ◽  
Transit Time ◽  
Okadaic Acid ◽  
Hair Cells ◽  
Protein Phosphatase ◽  
Metaphase Plate ◽  
Spindle Pole ◽  
Phosphatase Inhibitors ◽  
Nuclear Envelope Breakdown ◽  
Transit Times

Stamen hair cells from the spiderwort plant, Tradescantia virginiana, exhibit remarkably predictable metaphase transit times, making them uniquely suitable for temporal studies on mitotic regulation. In this study, we describe two kinds of experiments that test whether protein phosphatase activity is a necessary prerequisite for entry into anaphase in living, mitotic cells. We treated cells at specific points during prophase, prometaphase and metaphase with the broad-spectrum protein phosphatase inhibitor, alpha-naphthyl phosphate (administered by microinjection), or with the naturally occurring, potent phosphatase inhibitors okadaic acid, microcystin-LR or microcystin-RR (administered by perfusion), and we have observed changes in the metaphase transit time that are primarily dependent on the time of initial exposure to the inhibitor. Maximal extensions of the metaphase transit time result from alpha-naphthyl phosphate microinjections initiated in mid-metaphase, 10–20 min after nuclear envelope breakdown. Perfusions with okadaic acid started during a specific interval in mid-metaphase, 15–20 min after nuclear envelope breakdown, resulted in a statistically significant extension of the metaphase transit time. Perfusions with either microcystin-LR or microcystin-RR initiated 15–26 min after nuclear envelope breakdown extended the metaphase transit times significantly. Treatments of cells with okadaic acid or with either of the microcystins initiated outside this mid-metaphase interval either were without effect or, alternatively, resulted in a significant shortening of the metaphase transit time. In addition to their effects on the timing of anaphase onset, treatments with these protein phosphatase inhibitors also resulted in a remarkable change in the way in which these cells enter anaphase. Sister chromatid separation in stamen hair cells typically requires only 5 seconds, but after treatment with any of these inhibitors some, but not all, of the chromatids split apart at anaphase onset. Those that split begin to migrate toward the spindle pole regions, while those that fail to split remain at the metaphase plate. Later, more of the paired chromatids split apart and begin moving toward the spindle pole regions. Those that fail to separate remain at the metaphase plate. This process can be repeated several times before all of the chromatids have separated. Thus, entry into anaphase becomes extremely asynchronous, and as much as 30 min can transpire between the centromeric separation of the first and last chromosomes. Some of the chromosomes complete their anaphase movements before others have even split apart at the metaphase plate. Asynchronous separation did not result in a permanent segregation anomaly.(ABSTRACT TRUNCATED AT 400 WORDS)

scholarly journals Kinesin-1 mediates translocation of the meiotic spindle to the oocyte cortex through KCA-1, a novel cargo adapter

2005 ◽  
Vol 169 (3) ◽  
pp. 447-457 ◽  
Author(s):  
Hsin-ya Yang ◽  
Paul E. Mains ◽  
Francis J. McNally
Keyword(s):  
Meiotic Spindle ◽  
Cell Cortex ◽  
Anaphase Promoting Complex ◽  
Wild Type ◽  
Kinesin Light Chain ◽  
Polar Bodies ◽  
Meiotic Spindles ◽  
Redundant Mechanism ◽  
Meiosis I ◽  
Egg Cortex

In animals, female meiotic spindles are attached to the egg cortex in a perpendicular orientation at anaphase to allow the selective disposal of three haploid chromosome sets into polar bodies. We have identified a complex of interacting Caenorhabditis elegans proteins that are involved in the earliest step in asymmetric positioning of anastral meiotic spindles, translocation to the cortex. This complex is composed of the kinesin-1 heavy chain orthologue, UNC-116, the kinesin light chain orthologues, KLC-1 and -2, and a novel cargo adaptor, KCA-1. Depletion of any of these subunits by RNA interference resulted in meiosis I metaphase spindles that remained stationary at a position several micrometers from the cell cortex during the time when wild-type spindles translocated to the cortex. After this prolonged stationary period, unc-116(RNAi) spindles moved to the cortex through a partially redundant mechanism that is dependent on the anaphase-promoting complex. This study thus reveals two sequential mechanisms for translocating anastral spindles to the oocyte cortex.

scholarly journals Chromosome–nuclear envelope tethering – a process that orchestrates homologue pairing during plant meiosis?

2020 ◽  
Vol 133 (15) ◽  
pp. jcs243667
Author(s):  
Adél Sepsi ◽  
Trude Schwarzacher
Keyword(s):  
Nuclear Envelope ◽  
Chromosome Segregation ◽  
Higher Plants ◽  
Nuclear Periphery ◽  
Genetic Material ◽  
Strand Break ◽  
Genome Integrity ◽  
Homologous Chromosomes ◽  
Prophase I ◽  
Plant Meiosis

ABSTRACTDuring prophase I of meiosis, homologous chromosomes pair, synapse and exchange their genetic material through reciprocal homologous recombination, a phenomenon essential for faithful chromosome segregation. Partial sequence identity between non-homologous and heterologous chromosomes can also lead to recombination (ectopic recombination), a highly deleterious process that rapidly compromises genome integrity. To avoid ectopic exchange, homology recognition must be extended from the narrow position of a crossover-competent double-strand break to the entire chromosome. Here, we review advances on chromosome behaviour during meiotic prophase I in higher plants, by integrating centromere- and telomere dynamics driven by cytoskeletal motor proteins, into the processes of homologue pairing, synapsis and recombination. Centromere–centromere associations and the gathering of telomeres at the onset of meiosis at opposite nuclear poles create a spatially organised and restricted nuclear state in which homologous DNA interactions are favoured but ectopic interactions also occur. The release and dispersion of centromeres from the nuclear periphery increases the motility of chromosome arms, allowing meiosis-specific movements that disrupt ectopic interactions. Subsequent expansion of interstitial synapsis from numerous homologous interactions further corrects ectopic interactions. Movement and organisation of chromosomes, thus, evolved to facilitate the pairing process, and can be modulated by distinct stages of chromatin associations at the nuclear envelope and their collective release.

scholarly journals Katanin maintains meiotic metaphase chromosome alignment and spindle structure in vivo and has multiple effects on microtubules in vitro

2014 ◽  
Vol 25 (7) ◽  
pp. 1037-1049 ◽  
Author(s):  
Karen McNally ◽  
Evan Berg ◽  
Daniel B. Cortes ◽  
Veronica Hernandez ◽  
Paul E. Mains ◽  
...  
Keyword(s):  
Point Mutations ◽  
Metaphase Plate ◽  
Meiotic Spindle ◽  
Loss Of Function ◽  
Microtubule Organization ◽  
Bipolar Structure ◽  
Microtubule Severing ◽  
Meiotic Spindles

Assembly of Caenorhabditis elegans female meiotic spindles requires both MEI-1 and MEI-2 subunits of the microtubule-severing ATPase katanin. Strong loss-of-function mutants assemble apolar intersecting microtubule arrays, whereas weaker mutants assemble bipolar meiotic spindles that are longer than wild type. To determine whether katanin is also required for spindle maintenance, we monitored metaphase I spindles after a fast-acting mei-1(ts) mutant was shifted to a nonpermissive temperature. Within 4 min of temperature shift, bivalents moved off the metaphase plate, and microtubule bundles within the spindle lengthened and developed a high degree of curvature. Spindles eventually lost bipolar structure. Immunofluorescence of embryos fixed at increasing temperature indicated that MEI-1 was lost from spindle microtubules before loss of ASPM-1, indicating that MEI-1 and ASPM-1 act independently at spindle poles. We quantified the microtubule-severing activity of purified MEI-1/MEI-2 complexes corresponding to six different point mutations and found a linear relationship between microtubule disassembly rate and meiotic spindle length. Previous work showed that katanin is required for severing at points where two microtubules intersect in vivo. We show that purified MEI-1/MEI-2 complexes preferentially sever at intersections between two microtubules and directly bundle microtubules in vitro. These activities could promote parallel/antiparallel microtubule organization in meiotic spindles.

F-actin is required for spindle anchoring and rotation in Xenopus oocytes: a re-examination of the effects of cytochalasin B on oocyte maturation

Zygote ◽  
1995 ◽  
Vol 3 (1) ◽  
pp. 17-26 ◽  
Author(s):  
David Lynn Gard ◽  
Byeong-Jik Cha ◽  
Amy Diane Roeder
Keyword(s):  
Cytochalasin B ◽  
Meiotic Spindle ◽  
The Novel ◽  
Actin Assembly ◽  
Cortical Actin ◽  
Rhodamine Phalloidin ◽  
Confocal Immunofluorescence Microscopy ◽  
Confocal Immunofluorescence ◽  
Meiotic Spindles ◽  
Bipolar Spindles

SummaryWe used confocal immunofluorescence microscopy to examine spindle migration, morphology and orientation during the maturation of Xenopus oocytes, in the presence or absence of cytochalasin B (CB), an inhibitor of actin assembly. Treatment with CB during maturation (10–50 μg/ml beginning 0–3h prior to addition of progesterone) disrupted the normal organisation of the novel MTOC and transient microtubule array (MTOC-TMA complex) that serves as the immediate precursor of the first meiotic spindle, suggesting that F-actin plays an important role in the assembly or maintenance of this complex. However, CB treatment did not block translocation of the MTOC-TMA complex to the oocyte cortex, suggesting that MTOC-TMA translocation is not dependent on an actin-based mechanism. Bipolar spindles were observed in CB-treated oocytes fixed during both M1 and M2. However, rotation of the M1 and M2 spindles into an orientation orthogonal to the oocyte surface was inhibited by CB. Rhodamine-phalloidin revealed a concentration of F-actin at the site of M1 spindle attachment, further suggesting that cortical actin is required for anchoring and rotation of the meiotic spindles. Finally, the incidence of M1 monasters was significantly increased in CB-treated oocytes, suggesting that interactions between the nascent M1 spindle and cortex are dependent on F-actin.

scholarly journals Localization of the mei-1 gene product of Caenorhaditis elegans, a meiotic-specific spindle component.

1994 ◽  
Vol 126 (1) ◽  
pp. 199-209 ◽  
Author(s):  
S Clark-Maguire ◽  
P E Mains
Keyword(s):  
Regulatory Network ◽  
Meiotic Spindle ◽  
Loss Of Function ◽  
Wild Type ◽  
Female Meiosis ◽  
Gain Of Function ◽  
Spindle Poles ◽  
Meiotic Spindles ◽  
Female Germline ◽  
Meiosis I

Genetic evidence suggests that the product of the mei-1 gene of Caenorhabditis elegans is specifically required for meiosis in the female germline. Loss-of-function mei-1 mutations block meiotic spindle formation while a gain-of-function allele instead results in spindle defects during the early mitotic cleavages. In this report, we use immunocytochemistry to examine the localization of the mei-1 product in wild-type and mutant embryos. During metaphase of meiosis I in wild-type embryos, mei-1 protein was found throughout the spindle but was more concentrated toward the poles. At telophase I, mei-1 product colocalized with the chromatin at the spindle poles. The pattern was repeated during meiosis II but no mei-1 product was visible during the subsequent mitotic cleavages. The mei-1 gain-of-function allele resulted in ectopic mei-1 staining in the centers of the microtubule-organizing centers during interphase and in the spindles during the early cleavages. This aberrant localization is probably responsible for the poorly formed and misoriented cleavage spindles characteristic of the mutation. We also examined the localization of mei-1(+) product in the presence of mutations of genes that genetically interact with mei-1 alleles. mei-2 is apparently required to localize mei-1 product to the spindle during meiosis while mel-26 acts as a postmeiotic inhibitor. We conclude that mei-1 encodes a novel spindle component, one that is specialized for the acentriolar meiotic spindles unique to female meiosis. The genes mei-2 and mel-26 are part of a regulatory network that confines mei-1 activity to meiosis.

scholarly journals Temporal and spatial coordination of chromosome movement, spindle formation, and nuclear envelope breakdown during prometaphase in Drosophila melanogaster embryos.

1990 ◽  
Vol 111 (6) ◽  
pp. 2815-2828 ◽  
Author(s):  
Y Hiraoka ◽  
D A Agard ◽  
J W Sedat
Keyword(s):  
Drosophila Melanogaster ◽  
Nuclear Envelope ◽  
Temporal Dynamics ◽  
Three Dimensional ◽  
Metaphase Plate ◽  
Time Lapse ◽  
Three Dimensions ◽  
Nuclear Envelope Breakdown ◽  
High Resolution Analysis ◽  
Nuclear Structures

The spatial and temporal dynamics of diploid chromosome organization, microtubule arrangement, and the state of the nuclear envelope have been analyzed in syncytial blastoderm embryos of Drosophila melanogaster during the transition from prophase to metaphase, by three-dimensional optical sectioning microscopy. Time-lapse, three-dimensional data recorded in living embryos revealed that congression of chromosomes (the process whereby chromosomes move to form the metaphase plate) at prometaphase occurs as a wave, starting at the top of the nucleus near the embryo surface and proceeding through the nucleus to the bottom. The time-lapse analysis was augmented by a high-resolution analysis of fixed embryos where it was possible to unambiguously trace the three-dimensional paths of individual chromosomes. In prophase, the centromeres were found to be clustered at the top of the nucleus while the telomeres were situated at the bottom of the nucleus or towards the embryo interior. This polarized centromere-telomere orientation, perpendicular to the embryo surface, was preserved during the process of prometaphase chromosome congression. Correspondingly, breakdown of the nuclear envelope started at the top of the nucleus with the mitotic spindle being formed at the positions of the partial breakdown of the nuclear envelope. Our observation provide an example in which nuclear structures are spatially organized and their functions are locally and coordinately controlled in three dimensions.

scholarly journals Identification of Novel Drosophila Meiotic Genes Recovered in a P-Element Screen

Genetics ◽  
1999 ◽  
Vol 152 (2) ◽  
pp. 529-542 ◽  
Author(s):  
Jeff J Sekelsky ◽  
Kim S McKim ◽  
Lisa Messina ◽  
Rachael L French ◽  
Wendy D Hurley ◽  
...  
Keyword(s):  
Genetic Background ◽  
Meiotic Chromosome ◽  
Structure And Function ◽  
P Element ◽  
Meiotic Spindle ◽  
High Fidelity ◽  
Crossing Over ◽  
Wild Type ◽  
Homologous Chromosomes ◽  
And Function

Abstract The segregation of homologous chromosomes from one another is the essence of meiosis. In many organisms, accurate segregation is ensured by the formation of chiasmata resulting from crossing over. Drosophila melanogaster females use this type of recombination-based system, but they also have mechanisms for segregating achiasmate chromosomes with high fidelity. We describe a P-element mutagenesis and screen in a sensitized genetic background to detect mutations that impair meiotic chromosome pairing, recombination, or segregation. Our screen identified two new recombination-deficient mutations: mei-P22, which fully eliminates meiotic recombination, and mei-P26, which decreases meiotic exchange by 70% in a polar fashion. We also recovered an unusual allele of the ncd gene, whose wild-type product is required for proper structure and function of the meiotic spindle. However, the screen yielded primarily mutants specifically defective in the segregation of achiasmate chromosomes. Although most of these are alleles of previously undescribed genes, five were in the known genes αTubulin67C, CycE, push, and Trl. The five mutations in known genes produce novel phenotypes for those genes.

scholarly journals The Kinesinlike Protein Subito Contributes to Central Spindle Assembly and Organization of the Meiotic Spindle in Drosophila Oocytes

2005 ◽  
Vol 16 (10) ◽  
pp. 4684-4694 ◽  
Author(s):  
J. K. Jang ◽  
T. Rahman ◽  
K. S. McKim
Keyword(s):  
Meiotic Spindle ◽  
Spindle Formation ◽  
Present Evidence ◽  
Homologous Chromosomes ◽  
Central Spindle ◽  
Bipolar Spindle ◽  
Passenger Proteins ◽  
Bipolar Spindles ◽  
Meiosis I

In the oocytes of many species, bipolar spindles form in the absence of centrosomes. Drosophila melanogaster oocyte chromosomes have a major role in nucleating microtubules, which precedes the bundling and assembly of these microtubules into a bipolar spindle. Here we present evidence that a region similar to the anaphase central spindle functions to organize acentrosomal spindles. Subito mutants are characterized by the formation of tripolar or monopolar spindles and nondisjunction of homologous chromosomes at meiosis I. Subito encodes a kinesinlike protein and associates with the meiotic central spindle, consistent with its classification in the Kinesin 6/MKLP1 family. This class of proteins is known to be required for cytokinesis, but our results suggest a new function in spindle formation. The meiotic central spindle appears during prometaphase and includes passenger complex proteins such as AurB and Incenp. Unlike mitotic cells, the passenger proteins do not associate with centromeres before anaphase. In the absence of Subito, central spindle formation is defective and AurB and Incenp fail to properly localize. We propose that Subito is required for establishing and/or maintaining the central spindle in Drosophila oocytes, and this substitutes for the role of centrosomes in organizing the bipolar spindle.

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