Ultrastructure of cell division in Cladophora. Pregametangial cell division in the haploid generation of Cladophora flexuosa

1976 ◽  
Vol 54 (13) ◽  
pp. 1546-1560 ◽  
Author(s):  
J. L. Scott ◽  
K. W. Bullock
Keyword(s):  
Life History ◽  
Electron Microscope ◽  
Cell Division ◽  
Nuclear Envelope ◽  
Double Membrane ◽  
Cell Divisions ◽  
Gamete Formation ◽  
Reproductive Differentiation ◽  
Different Types ◽  
Vacuolar System

Cell division preceding gamete formation in the haploid generation of Cladophora flexuosa was studied with the electron microscope. Numerous, asynchronous mitotic nuclear divisions are concurrent with the progressive cleavage of the cytoplasm by invaginations of a central and peripheral vacuolar system. The spindle is enclosed by the nuclear envelope during all stages of mitosis and is associated with polar centriole pairs. The cytokinetic process is not associated with microtubules and is basically similar to that observed in other macroscopic, multinucleate green algae. Unusual mitochondria, characterized by specialized double-membrane-enclosed, presumptive DNA regions, were found during the later stages of reproductive differentiation. It is emphasized that the different types of cell divisions which can occur in plants possessing a haplodiplontic type of life history should all be thoroughly examined before the establishment of a particular mitotic sequence for any given species.

scholarly journals SOME OBSERVATIONS ON THE NUCLEAR ENVELOPE

1960 ◽  
Vol 8 (1) ◽  
pp. 233-245 ◽  
Author(s):  
W. Gordon Whaley ◽  
Hilton H. Mollenhauer ◽  
James H. Leech
Keyword(s):  
Electron Microscope ◽  
Nuclear Envelope ◽  
Epoxy Resin ◽  
Membrane Structure ◽  
Root Meristem ◽  
Double Membrane ◽  
Nuclear Membranes ◽  
Cytoplasmic Surface ◽  
Different Types ◽  
The Status

In maize root meristem cells, fixed in KMnO4, embedded in epoxy resin, ultrathin sectioned, and studied with an electron microscope, the nuclear envelope is demonstrated to be a double membrane structure. In the nuclear envelope there are: pores of the sort reported in many species of animals and plants; different types of openings associated with extensions of both nuclear membranes into the cytoplasm; and also, often, large discontinuities. The nuclear envelope is a component of the general vesicular reticulum. The reticula of neighboring cells including the nuclear envelopes make up, at certain stages at least, a "systemic" structure. The status of the nuclear envelope as a component of the general cellular reticulum is recognized to change during differentiation. The existence of several types of discontinuities in the nuclear envelope and the extent of nuclear-cytoplasmic surface relationships indicated suggests alteration in concepts of transport and exchanges between nucleus and cytoplasm.

The growth of supernumerary legs in the cockroach

Development ◽  
1986 ◽  
Vol 92 (1) ◽  
pp. 115-131
Author(s):  
Paul R. Truby
Keyword(s):  
Wound Healing ◽  
Cell Division ◽  
Rapid Rate ◽  
Large Area ◽  
Anteroposterior Axis ◽  
Cell Divisions ◽  
Leucophaea Maderae ◽  
Different Types ◽  
Local Cell

When the anteroposterior axis of a cockroach leg is reversed at a graft by exchanging a left leg for a right leg at the mid-tibia level, regeneration occurs in the region of the graft/host junction. This results in the formation of a pair of lateral supernumerary legs. In these experiments the patterns of cell division which take place during supernumerary leg formation were observed in sections of regenerating legs of the cockroach Leucophaea maderae. Early patterns of cell division resemble those seen in control grafts in which no axial reversal had been carried out during grafting. These cell divisions are associated with the process of wound healing. Later, a large area of the epidermis proximal to the graft/host junction becomes activated and shows a rapid rate of cell division. This area forms two outgrowths which grow by cell division throughout their epidermis to form the epidermis of the supernumerary legs. The results are more consistent with the view that the formation of supernumerary legs involves dedifferentiation of the epidermis in the region of the graft/host junction to form a blastema, rather than being due to local cell division at the point of maximum pattern discontinuity. This conclusion is used to offer an explanation for the range of different types of outcome of left-right grafts that has been observed.

Unequal cleavage in leech embryos: zygotic transcription is required for correct spindle orientation in subset of early blastomeres

Development ◽  
1996 ◽  
Vol 122 (2) ◽  
pp. 599-606
Author(s):  
S.T. Bissen ◽  
C.M. Smith
Keyword(s):  
Cell Division ◽  
Early Period ◽  
Spindle Orientation ◽  
Mitotic Spindles ◽  
Maternal Control ◽  
Transcription Analysis ◽  
Cell Divisions ◽  
Zygotic Transcription ◽  
Different Types ◽  
Alpha Amanitin

Leech embryos undergo invariant sequences of equal and unequal cell divisions to give rise to identifiable progeny cells. While many of the early cleavages are under maternal control, the divisions of a subset of early blastomeres (the large cells of the D' lineage) are perturbed after the inhibition of zygotic transcription. Analysis of the different types of cells produced in embryos injected with the transcriptional inhibitor, alpha-amanitin, revealed that the symmetry of cell division is perturbed in these large D'-derived cells during this early period of development. These cells, which would normally undergo a series of equal and unequal cleavages, always undergo equal cleavages after the inhibition of zygotic transcription. It appears that zygotically transcribed gene product(s) are required in the large cells of the D' lineage to orient the mitotic spindles properly for these unequal cell cleavages.

The Ultrastructure of the Nuclear Events of Binary Fission in Paramecium bursaria and the Effects of Colchicine on Cell Division

1974 ◽  
Vol 32 ◽  
pp. 276-277
Author(s):  
L. M. Lewis
Keyword(s):  
Cell Division ◽  
Nuclear Envelope ◽  
Condensed Chromatin ◽  
Binary Fission ◽  
Paramecium Bursaria ◽  
Nuclear Events ◽  
Division Axis

The effects of colchicine on extranuclear microtubules associated with the macronucleus of Paramecium bursaria were studied to determine the possible role that these microtubules play in controlling the shape of the macronucleus. In the course of this study, the ultrastructure of the nuclear events of binary fission in control cells was also studied.During interphase in control cells, the micronucleus contains randomly distributed clumps of condensed chromatin and microtubular fragments. Throughout mitosis the nuclear envelope remains intact. During micronuclear prophase, cup-shaped microfilamentous structures appear that are filled with condensing chromatin. Microtubules are also present and are parallel to the division axis.

Stimulated Virus Production in Vinblastine and Cytochalasin-Induced Multinucleate Cells

1970 ◽  
Vol 28 ◽  
pp. 186-187
Author(s):  
Krishan Awtar
Keyword(s):  
Cell Division ◽  
Normal Cell ◽  
Virus Production ◽  
Multinucleate Cells ◽  
Daughter Cells ◽  
Cell Divisions ◽  
Nuclear Membranes ◽  
Division 2 ◽  
Vinblastine Sulfate

Exposure of cells to low sublethal but mitosis-arresting doses of vinblastine sulfate (Velban) results in the initial arrest of cells in mitosis followed by their subsequent return to an “interphase“-like stage. A large number of these cells reform their nuclear membranes and form large multimicronucleated cells, some containing as many as 25 or more micronuclei (1). Formation of large multinucleate cells is also caused by cytochalasin, by causing the fusion of daughter cells at the end of an otherwise .normal cell division (2). By the repetition of this process through subsequent cell divisions, large cells with 6 or more nuclei are formed.

Ultrastructure of Plant Leaf Tissue Infected with Mite-Borne Viral-Like Pathogens

1970 ◽  
Vol 28 ◽  
pp. 178-179 ◽  
Author(s):  
O. E. Bradfute ◽  
R. E. Whitmoyer ◽  
L. R. Nault
Keyword(s):  
Triticum Aestivum ◽  
Zea Mays ◽  
Electron Microscope ◽  
Hordeum Vulgare ◽  
Microscope Study ◽  
Electron Microscope Study ◽  
Leaf Tissue ◽  
Leaf Ultrastructure ◽  
Double Membrane ◽  
Aceria Tulipae

A pathogen transmitted by the eriophyid mite, Aceria tulipae, infects a number of Gramineae producing symptoms similar to wheat spot mosaic virus (1). An electron microscope study of leaf ultrastructure from systemically infected Zea mays, Hordeum vulgare, and Triticum aestivum showed the presence of ovoid, double membrane bodies (0.1 - 0.2 microns) in the cytoplasm of parenchyma, phloem and epidermis cells (Fig. 1 ).

scholarly journals Haploid induction by a maize cenh3 null mutant

2021 ◽  
Vol 7 (4) ◽  
pp. eabe2299 ◽  
Author(s):  
Na Wang ◽  
Jonathan I. Gent ◽  
R. Kelly Dawe
Keyword(s):  
Histone H3 ◽  
Null Mutation ◽  
Null Mutant ◽  
Wild Type ◽  
Haploid Induction ◽  
Cell Divisions ◽  
Gamete Formation ◽  
Simplified Method ◽  
Single Cross ◽  
Subsequent Loss

The production of haploids is an important first step in creating many new plant varieties. One approach used in Arabidopsis involves crossing plants expressing different forms of centromeric histone H3 (CENP-A/CENH3) and subsequent loss of genome with weaker centromeres. However, the method has been ineffective in crop plants. Here, we describe a greatly simplified method based on crossing maize lines that are heterozygous for a cenh3 null mutation. Crossing +/cenh3 to wild-type plants in both directions yielded haploid progeny. Genome elimination was determined by the cenh3 genotype of the gametophyte, suggesting that centromere failure is caused by CENH3 dilution during the postmeiotic cell divisions that precede gamete formation. The cenh3 haploid inducer works as a vigorous hybrid and can be transferred to other lines in a single cross, making it versatile for a variety of applications.

scholarly journals The nucleoporin Nup205/NPP-3 is lost near centrosomes at mitotic onset and can modulate the timing of this process in Caenorhabditis elegans embryos

2012 ◽  
Vol 23 (16) ◽  
pp. 3111-3121 ◽  
Author(s):  
Virginie Hachet ◽  
Coralie Busso ◽  
Mika Toya ◽  
Asako Sugimoto ◽  
Peter Askjaer ◽  
...  
Keyword(s):  
Cell Division ◽  
Rna Interference ◽  
Caenorhabditis Elegans ◽  
Nuclear Envelope ◽  
Aurora A Kinase ◽  
Aurora A ◽  
Time And Space ◽  
Local Loss ◽  
Necessary And Sufficient

Regulation of mitosis in time and space is critical for proper cell division. We conducted an RNA interference–based modifier screen to identify novel regulators of mitosis in Caenorhabditis elegans embryos. Of particular interest, this screen revealed that the Nup205 nucleoporin NPP-3 can negatively modulate the timing of mitotic onset. Furthermore, we discovered that NPP-3 and nucleoporins that are associated with it are lost from the nuclear envelope (NE) in the vicinity of centrosomes at the onset of mitosis. We demonstrate that centrosomes are both necessary and sufficient for NPP-3 local loss, which also requires the activity of the Aurora-A kinase AIR-1. Our findings taken together support a model in which centrosomes and AIR-1 promote timely onset of mitosis by locally removing NPP-3 and associated nucleoporins from the NE.

scholarly journals The Role of Non-Coding RNAs in the Regulation of the Proto-Oncogene MYC in Different Types of Cancer

Biomedicines ◽  
2021 ◽  
Vol 9 (8) ◽  
pp. 921
Author(s):  
Ekaterina Mikhailovna Stasevich ◽  
Matvey Mikhailovich Murashko ◽  
Lyudmila Sergeevna Zinevich ◽  
Denis Eriksonovich Demin ◽  
Anton Markovich Schwartz
Keyword(s):  
Malignant Tumors ◽  
Current Data ◽  
Cellular Processes ◽  
Cell Divisions ◽  
Specific Tumor ◽  
Different Types ◽  
Myc Gene ◽  
Non Coding Rnas ◽  
Tumor Types

Alterations in the expression level of the MYC gene are often found in the cells of various malignant tumors. Overexpressed MYC has been shown to stimulate the main processes of oncogenesis: uncontrolled growth, unlimited cell divisions, avoidance of apoptosis and immune response, changes in cellular metabolism, genomic instability, metastasis, and angiogenesis. Thus, controlling the expression of MYC is considered as an approach for targeted cancer treatment. Since c-Myc is also a crucial regulator of many cellular processes in healthy cells, it is necessary to find ways for selective regulation of MYC expression in tumor cells. Many recent studies have demonstrated that non-coding RNAs play an important role in the regulation of the transcription and translation of this gene and some RNAs directly interact with the c-Myc protein, affecting its stability. In this review, we summarize current data on the regulation of MYC by various non-coding RNAs that can potentially be targeted in specific tumor types.

discordia mutations specifically misorient asymmetric cell divisions during development of the maize leaf epidermis

Development ◽  
1999 ◽  
Vol 126 (20) ◽  
pp. 4623-4633 ◽  
Author(s):  
K. Gallagher ◽  
L.G. Smith
Keyword(s):  
Cell Division ◽  
Preprophase Band ◽  
Cytochalasin D ◽  
Leaf Epidermis ◽  
Asymmetric Cell Divisions ◽  
Maize Leaf ◽  
Cell Divisions ◽  
Cytoskeletal Structure ◽  
Dividing Cells ◽  
Preprophase Bands

In plant cells, cytokinesis depends on a cytoskeletal structure called a phragmoplast, which directs the formation of a new cell wall between daughter nuclei after mitosis. The orientation of cell division depends on guidance of the phragmoplast during cytokinesis to a cortical site marked throughout prophase by another cytoskeletal structure called a preprophase band. Asymmetrically dividing cells become polarized and form asymmetric preprophase bands prior to mitosis; phragmoplasts are subsequently guided to these asymmetric cortical sites to form daughter cells of different shapes and/or sizes. Here we describe two new recessive mutations, discordia1 (dcd1) and discordia2 (dcd2), which disrupt the spatial regulation of cytokinesis during asymmetric cell divisions. Both mutations disrupt four classes of asymmetric cell divisions during the development of the maize leaf epidermis, without affecting the symmetric divisions through which most epidermal cells arise. The effects of dcd mutations on asymmetric cell division can be mimicked by cytochalasin D treatment, and divisions affected by dcd1 are hypersensitive to the effects of cytochalasin D. Analysis of actin and microtubule organization in these mutants showed no effect of either mutation on cell polarity, or on formation and localization of preprophase bands and spindles. In mutant cells, phragmoplasts in asymmetrically dividing cells are structurally normal and are initiated in the correct location, but often fail to move to the position formerly occupied by the preprophase band. We propose that dcd mutations disrupt an actin-dependent process necessary for the guidance of phragmoplasts during cytokinesis in asymmetrically dividing cells.

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