scholarly journals The concept of the prophase of meiosis

Hereditas ◽  
2009 ◽  
Vol 86 (2) ◽  
pp. 205-210 ◽  
Author(s):  
I. KLÁŠTERSKÁ
Keyword(s):  
Prophase Of Meiosis

scholarly journals Mps1 promotes poleward chromosome movements in meiotic pro-metaphase

2020 ◽  
Author(s):  
Régis E Meyer ◽  
Aaron R Tipton ◽  
Gary J Gorbsky ◽  
Dean S Dawson
Keyword(s):  
Chromosome Pair ◽  
Single Unit ◽  
Spindle Pole ◽  
Microtubule Depolymerization ◽  
Data Support ◽  
Chromosome Movements ◽  
Meiosis I ◽  
Prophase Of Meiosis

ABSTRACTIn prophase of meiosis I, homologous partner chromosomes pair and become connected by crossovers. Chiasmata, the connections formed between the partners enable the chromosome pair, called a bivalent, to attach as a single unit to the spindle. When the meiosis I spindle forms in prometaphase, most bivalents are associated with a single spindle pole and go through a series of oscillations on the spindle, attaching to and detaching from microtubules until the partners of the bivalent are bi-oriented, that is, attached to microtubules from opposite sides of the spindle, and prepared to be segregated at anaphase I. The conserved, kinetochore-associated kinase, Mps1, is essential for the bivalents to be pulled by microtubules across the spindle in prometaphase. Here we show that MPS1 is not required for kinetochores to attach microtubules but instead is necessary to trigger the migration of microtubule-attached kinetochores towards the poles. Our data support the model that Mps1 triggers depolymerization of microtubule ends once they attach to kinetochores in prometaphase. Thus, Mps1 acts at the kinetochore to co-ordinate the successful attachment of a microtubule and the triggering of microtubule depolymerization to move the chromosome.

scholarly journals Differential Uptake of Tritiated Thymidine into Hetero- and Euchromatin in Melanoplus and Secale

1959 ◽  
Vol 6 (3) ◽  
pp. 457-466 ◽  
Author(s):  
A. Lima-de-Faria
Keyword(s):  
Sex Chromosome ◽  
Unit Area ◽  
Tritiated Thymidine ◽  
Early Prophase ◽  
Chromosome Counts ◽  
Heterochromatic Block ◽  
Melanoplus Differentialis ◽  
Photometric Measurements ◽  
Silver Grains ◽  
Prophase Of Meiosis

Grasshoppers of the species Melanoplus differentialis were injected with tritium-labelled thymidine. At intervals thereafter autoradiographic stripping film was applied over Feulgen squashes and sections. In this species during early prophase of meiosis the sex chromosome forms a heterochromatic block large enough to be resolved in tritium autoradiographs. A study of the squash preparations reveals that the sex chromosome is synthesizing DNA at a different period of time from the euchromatic autosomes. Since there is a developmental sequence of spermatocyte cysts along the testicular tubes it is possible from the sections to show that the heterochromatin synthesizes DNA later than does the euchromatin. To find out whether the results obtained in Melanoplus were characteristic of heterochromatin in general, young seedlings of rye were grown in a tritiated thymidine solution and Feulgen squashes were made as for Melanoplus. In rye leaf nuclei there is a large block of heterochromatin constituted by the proximal regions of the chromosomes and a euchromatic one formed by the median and distal regions of the same chromosomes. Here also the heterochromatin synthesizes DNA at a different period of time from the euchromatin. It is concluded that in rye the asynchrony of synthesis occurs within each chromosome. Counts of silver grains over the two types of chromatin in nuclei of Melanoplus and Secale disclosed that the number of grains per unit area was two to three times higher over the heterochromatin. To check the DNA content, Feulgen photometric measurements were made of Melanoplus nuclei at the same stage. The Feulgen and grain counts agree in showing that the heterochromatin contains two to three times more DNA per unit area than the euchromatin.

scholarly journals Tet1 regulates epigenetic remodeling of the pericentromeric heterochromatin and chromocenter organization in DNA hypomethylated cells

PLoS Genetics ◽  
2021 ◽  
Vol 17 (6) ◽  
pp. e1009646
Author(s):  
Yota Hagihara ◽  
Satoshi Asada ◽  
Takahiro Maeda ◽  
Toru Nakano ◽  
Shinpei Yamaguchi
Keyword(s):  
Molecular Mechanisms ◽  
Critical Role ◽  
Pericentromeric Heterochromatin ◽  
Dna Hypomethylation ◽  
Cellular Events ◽  
Epigenetic Remodeling ◽  
Core Components ◽  
Liquid Liquid Phase Separation ◽  
Prophase Of Meiosis

Pericentromeric heterochromatin (PCH), the constitutive heterochromatin of pericentromeric regions, plays crucial roles in various cellular events, such as cell division and DNA replication. PCH forms chromocenters in the interphase nucleus, and chromocenters cluster at the prophase of meiosis. Chromocenter clustering has been reported to be critical for the appropriate progression of meiosis. However, the molecular mechanisms underlying chromocenter clustering remain elusive. In this study, we found that global DNA hypomethylation, 5hmC enrichment in PCH, and chromocenter clustering of Dnmt1-KO ESCs were similar to those of the female meiotic germ cells. Tet1 is essential for the deposition of 5hmC and facultative histone marks of H3K27me3 and H2AK119ub at PCH, as well as chromocenter clustering. RING1B, one of the core components of PRC1, is recruited to PCH by TET1, and PRC1 plays a critical role in chromocenter clustering. In addition, the rearrangement of the chromocenter under DNA hypomethylated condition was mediated by liquid-liquid phase separation. Thus, we demonstrated a novel role of Tet1 in chromocenter rearrangement in DNA hypomethylated cells.

scholarly journals The external mechanics of the chromosomes III-Meiosis in triploids

1936 ◽  
Vol 121 (823) ◽  
pp. 290-300 ◽  
Keyword(s):  
Sexual Reproduction ◽  
Chromosome Pairing ◽  
Natural Experiment ◽  
Diploid Species ◽  
Homologous Chromosomes ◽  
Normal Series ◽  
Mitosis And Meiosis ◽  
Meiosis I ◽  
Prophase Of Meiosis ◽  
The Way

Triploid organisms have three homologous chromosomes of each kind instead of the two of diploids. The regular mechanism of heredity fails in these circumstances. The triploid is incapable of breeding true by sexual reproduction. But the way in which it carries out the process of chromosome pairing and segregation is of great significance. The processes take place in normal series, but the relationships they establish are abnormal. A triploid thus provides a natural experiment, with the diploid of its own species as a control for one variable, and with triploids of different species as controls for others. In Tulipa and Hyacinthus I have made use of this experiment for inducing the principles of the external mechanics of chromosomes during the prophase of meiosis. I have inferred from them the relationships between the forces working in mitosis and meiosis. The triploid forms of various Fritillaria species make it possible to test the principles of metaphase mechanics induced from observations on structural hybrids and other polyploids (Darlington, 1932, b , and 1933, c ) as well as from the exceptional behaviour in the diploid species of Fritillaria already discussed.

Sexual reproduction of white spruce (Picea glauca)

1979 ◽  
Vol 57 (2) ◽  
pp. 152-169 ◽  
Author(s):  
John N. Owens ◽  
Marje Molder
Keyword(s):  
Picea Glauca ◽  
Early Embryo ◽  
Bud Dormancy ◽  
Embryo Abortion ◽  
Lower Elevation ◽  
High Incidence ◽  
Cone Development ◽  
Mother Cells ◽  
Vegetative Bud ◽  
Prophase Of Meiosis

Reproductive buds broke dormancy at the same time as vegetative buds. Pollen mother cells entered prophase of meiosis immediately after dormancy and five-celled, winged pollen was mature about 6 weeks later. Megasporogenesis occurred 3 weeks after microsporogenesis and the female gametophyte was mature in about 6 weeks. Pollination occurred over about 1 week in late May or early June and fertilization occurred about 3 weeks after pollination. One to four archegonia developed. A comparable number of 16-celled proembryos usually developed within 1 week after fertilization and cotyledons began to develop about 1 month after fertilization. Simple polyembryony occurred in most ovules but cleavage polyembryony was not observed. Embryos were fully developed in late August and seeds were mature and shed in September.The small number of archegonia often present, the high incidence of self-pollination, which may have been the cause of the high frequency of early embryo abortion, and the failure of basal and distal ovules to become pollinated were major causes of empty seed.The phenology of reproductive development varied with the site and the elevation but varied little at one site in successive years. Differences were greatest early in the growing season, but by the time of fertilization, higher elevation trees which began development much later had nearly caught up with lower elevation trees and seeds from all sites were mature and shed at about the same time.Reproductive bud dormancy like vegetative bud dormancy was broken in response to photo-period rather than temperature; however, subsequent cone development was greatly affected by temperature.

scholarly journals asunder Is a Critical Regulator of Dynein–Dynactin Localization during Drosophila Spermatogenesis

2009 ◽  
Vol 20 (11) ◽  
pp. 2709-2721 ◽  
Author(s):  
Michael A. Anderson ◽  
Jeanne N. Jodoin ◽  
Ethan Lee ◽  
Karen G. Hales ◽  
Thomas S. Hays ◽  
...  
Keyword(s):  
Chromosome Segregation ◽  
Meiotic Spindle ◽  
Nuclear Surface ◽  
Drastic Reduction ◽  
Cell Cycles ◽  
M Phase ◽  
Microtubule Motor ◽  
Phase Entry ◽  
Prophase Of Meiosis ◽  
Drosophila Mutant

Spermatogenesis uses mitotic and meiotic cell cycles coordinated with growth and differentiation programs to generate functional sperm. Our analysis of a Drosophila mutant has revealed that asunder (asun), which encodes a conserved protein, is an essential regulator of spermatogenesis. asun spermatocytes arrest during prophase of meiosis I. Strikingly, arrested spermatocytes contain free centrosomes that fail to stably associate with the nucleus. Spermatocytes that overcome arrest exhibit severe defects in meiotic spindle assembly, chromosome segregation, and cytokinesis. Furthermore, the centriole-derived basal body is detached from the nucleus in asun postmeiotic spermatids, resulting in abnormalities later in spermatogenesis. We find that asun spermatocytes and spermatids exhibit drastic reduction of perinuclear dynein–dynactin, a microtubule motor complex. We propose a model in which asun coordinates spermatogenesis by promoting dynein–dynactin recruitment to the nuclear surface, a poorly understood process required for nucleus–centrosome coupling at M phase entry and fidelity of meiotic divisions.

scholarly journals Loss of CEP70 function affects acrosome biogenesis and flagella formation during spermiogenesis

2021 ◽  
Vol 12 (5) ◽  
Author(s):  
Qiang Liu ◽  
Qianying Guo ◽  
Wei Guo ◽  
Shi Song ◽  
Nan Wang ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Mutation Screening ◽  
Sem Analysis ◽  
Specific Mechanism ◽  
Heterozygous Site ◽  
Transmission Electron ◽  
Tandem Mass Tag ◽  
Deformation Stages ◽  
Human Spermatogenesis ◽  
Prophase Of Meiosis

AbstractThe spermatogenesis process is complex and delicate, and any error in a step may cause spermatogenesis arrest and even male infertility. According to our previous transcriptomic data, CEP70 is highly expressed throughout various stages of human spermatogenesis, especially during the meiosis and deformation stages. CEP70 is present in sperm tails and that it exists in centrosomes as revealed by human centrosome proteomics. However, the specific mechanism of this protein in spermatogenesis is still unknown. In this study, we found a heterozygous site of the same mutation on CEP70 through mutation screening of patients with clinical azoospermia. To further verify, we deleted CEP70 in mice and found that it caused abnormal spermatogenesis, leading to male sterility. We found that the knockout of CEP70 did not affect the prophase of meiosis I, but led to male germ-cell apoptosis and abnormal spermiogenesis. By transmission electron microscopy (TEM) and scanning electron microscopy (SEM) analysis, we found that the deletion of CEP70 resulted in the abnormal formation of flagella and acrosomes during spermiogenesis. Tandem mass tag (TMT)-labeled quantitative proteomic analysis revealed that the absence of CEP70 led to a significant decrease in the proteins associated with the formation of the flagella, head, and acrosome of sperm, and the microtubule cytoskeleton. Taken together, our results show that CEP70 is essential for acrosome biogenesis and flagella formation during spermiogenesis.

An Electron Microscopy Study of the Glycocalyx of Isolated Germinal Cells of the Rat

1975 ◽  
Vol 33 ◽  
pp. 596-597
Author(s):  
P. Hernández-Jáuregui ◽  
R. Trejo-Bayona ◽  
G. Delhumeau-Ongay
Keyword(s):  
Electron Microscopy ◽  
Mechanical Treatment ◽  
Plant Cells ◽  
Microscopy Study ◽  
Electron Microscopy Study ◽  
Surface Coat ◽  
Isolated Cells ◽  
Specific Permeability ◽  
Germinal Cells ◽  
Prophase Of Meiosis

The surface coat or glycocalyx of animal and plant cells plays an important role in cell properties such as antigenicity, specific permeability, and ATP ase activity. In the spermatozoa the glycocalyx may be of great importance in capacitation and fertilization phenomena. The glycocalyx is rich in fucose, mannose, galactose and sialic acid. These components are diminished during cell division. During spermatogenesis in mammals, spermatocytes represent a long prophase of meiosis. The purpose of this work was to demostrate the possible variations in the amount of glycocalyx in isolated germinal cells during spermatogenesis differentiation.Rat testes from 10, 23, and 38 days old, were finely scissored, in presence of Eagle essential medium, (mechanical treatment) Another similar group of isolated cells was treated with colagenase. (chemical treatment). Once separation of cells was completed, samples were treated for cytochemical electron microscopy using Alcian blue-lanthanum nitrate as previously described.

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