scholarly journals ELECTRON MICROSCOPIC OBSERVATIONS ON THE SUBMICROSCOPIC MORPHOLOGY OF THE MEIOTIC NUCLEUS AND CHROMOSOMES

1956 ◽  
Vol 2 (6) ◽  
pp. 785-796 ◽  
Author(s):  
E. De Robertis
Keyword(s):  
Meiotic Prophase ◽  
Early Prophase ◽  
Electron Microscopic ◽  
Metaphase Chromosomes ◽  
Late Prophase ◽  
Continuous Transition ◽  
Thin Sections ◽  
Nucleolar Material ◽  
Mean Diameter ◽  
The Mean

Thin sections of the testicular follicles of the grasshopper Laplatacris dispar were studied under the electron microscope. In the primary spermatocytes, during meiotic prophase, three main regions can be recognized within the nucleus: (1) the nucleolus and associated nucleolar material; (2) the interchromosomal regions with the dense particles; and (3) the chromosomes. The nucleolus is generally compact and is surrounded by nucleolar bodies that comprise aggregations of dense round particles 100 to 250 A in diameter. A continuous transition can be observed between these particles and those found isolated or in short chains in the interchromosomal spaces. Particles of similar size (mean diameter of 160 A) can be found associated with the nuclear membrane and in the cytoplasm. The chromosomes show different degrees of condensation in different stages of meiotic prophase. The bulk of the chromosome appears to be made of very fine and irregularly coiled filaments of macromolecular dimensions. Their length cannot be determined because of the thinness of the section but some of them can be followed without interruption for about 1000 to 2000 A. The thickness of the chromosome filaments seems to vary with different stages of prophase and in metaphase. In early prophase, filaments vary between 28 ± 7 A and 84 ± 7 A with a mean of 47 A, in late prophase the mean is about 70 A. In metaphase the filaments vary between 60 and 170 A with a mean of about 100 A. Neither the prophase nor the metaphase chromosomes have a membrane or other inhomogeneities. The finding of a macromolecular filamentous component of chromosomes is discussed in relation to the physicochemical literature on nucleoproteins and nucleic acids and as a result it is suggested that the thinnest chromosome filaments (28 ± 7 A) probably represent single deoxyribonucleoprotein molecules.

scholarly journals Basophilic Lamellar Systems in the Crayfish Spermatocyte

1958 ◽  
Vol 4 (3) ◽  
pp. 267-274 ◽  
Author(s):  
August Ruthmann
Keyword(s):  
Electron Microscopy ◽  
Small Rna ◽  
Meiotic Prophase ◽  
Lamellar Body ◽  
Annulate Lamellae ◽  
Late Prophase ◽  
Lamellar System ◽  
Thin Sections ◽  
Early Spermatid ◽  
Break Up

Histochemical procedures for the demonstration of RNA have shown the presence of intensely basophilic bodies in the cytoplasm of spermatocytes of the crayfish, Cambarus virilis. The staining of thick sections, cut alternately with thin sections for electron microscopy, has permitted identification of the basophilic bodies with two types of lamellar systems. One of these, a set of straight annulate lamellae, is restricted to meiotic prophase. The second type of lamellar systems has been found from late prophase to early spermatid stages. It consists of an ellipsoidal lamellar set which intersects a number of straight lamellae. Within the region of intersection, the ellipsoidal lamellae break up into an array of small tubules of about 150 A diameter. The term tubulate lamellar system was chosen to designate this type of lamellar complex. Small RNA-containing granules could not be detected in annulate lamellar systems. While there are a few granules in the marginal regions of the tubulate lamellar system, their distribution cannot be responsible for the basophilia which is intense within all regions of the lamellar body.

Nucleolus behaviour during the cell cycle of a primitive dinoflagellate eukaryote, Prorocentrum micans Ehr., seen by light microscopy and electron microscopy

1992 ◽  
Vol 102 (3) ◽  
pp. 475-485 ◽  
Author(s):  
MARIE-ODILE SOYER-GOBILLARD ◽  
MARIE-LINE GERAUD
Keyword(s):  
Cell Cycle ◽  
Light Microscopy ◽  
Early Prophase ◽  
Microscopy Observation ◽  
Prorocentrum Micans ◽  
Late Prophase ◽  
Daughter Cells ◽  
Nucleolar Material ◽  
Freeze Fixation ◽  
Higher Eukaryotes

Light-microscopy observation of the dinoflagellate Prorocentrum micans after silver-staining of the argyrophilic proteins of the nucleolar organizing region (Ag-NOR staining) showed the presence of nucleolar material throughout the vegetative cell cycle, and in particular during all the mitotic stages. This contrasts with the case in most higher eukaryotes, in which nucleoli disappear at the end of prophase and are reconstituted in daughter cells during telophase. Electron-microscope (EM) observations after conventional or fast-freeze fixation revealed that during interphase several functional nucleoli with three compartments (NORs, the fibrillogranular and the preribosomal granular compartments) are present in a nucleus in which the envelope is persistent and the chromosomes are always compact. During early prophase, when chromosomes are beginning to split, the nucleoli remain functional, whereas in late prophase they contain only a NOR and the granular component, and the chromosomes are surrounded by many protein masses. In early telophase, the nucleolar material coating the chromosomes migrates along with the chromosomes. Nucleologenesis occurs through the formation of prenucleolar bodies around lateral or telomeric nucleofilaments extruding from the chromosomes. Several chromosomes can contribute to the formation of one nucleolus. The behaviour of these ‘persistent nucleoli’ in a closed-nucleus model such as that of the dinoflagellates is discussed with regard to the higher eukaryotes.

scholarly journals Nexus of frog ventricle.

1977 ◽  
Vol 73 (3) ◽  
pp. 768-781 ◽  
Author(s):  
R W Kensler ◽  
P Brink ◽  
M M Dewey
Keyword(s):  
Rana Pipiens ◽  
Membrane Separation ◽  
Optical Measurements ◽  
Myocardial Cells ◽  
Thin Sections ◽  
Mean Diameter ◽  
The Mean ◽  
Frog Ventricle

Here were demonstrate in Rana pipiens ventricle a nexus with very unusual morphology. This tissue has been reported previously to lack nexuses. The nexus appears in thin sections of ventricle, fixed in aldehyde and OsO4 or permanganate as a series of punctate membrane appositions regularly alternating with regions of membrane separation. The junctional width at membrane appositions, as determined by microdensitometry and optical measurements, is 15-17 nm, and the width of the electron-translucent region between the junctional membranes is 1.8 nm. These values correspond closely to similar measurements of the more typical nexues in frog liver. Along the nexus the mean distance between punctate appositions is 74.5 nm. Freeze-cleave replicas of the nexuses between myocardial cells show particles 10.4 nm in diameter arranged in arrays of up to nine linked circles or partial circles on the PF-face and similar arrays of pits of shallow grooves on the EF-face. The mean diameter of the circles on both membrane fracture faces is 76.7 nm comparsion of the thin-sectioned and freeze-cleaved nexuses demonstrates an excellent correspondence between the spacing of membrane appositions along the junction and the diameters of the freeze-cleaved circles of particles and pits or grooves.

scholarly journals Sister chromatid repair maintains genomic integrity during meiosis in Caenorhabditis elegans

2020 ◽  
Author(s):  
Erik Toraason ◽  
Cordell Clark ◽  
Anna Horacek ◽  
Marissa L. Glover ◽  
Alina Salagean ◽  
...  
Keyword(s):  
Caenorhabditis Elegans ◽  
Sister Chromatid ◽  
Meiotic Prophase ◽  
Genome Integrity ◽  
Early Prophase ◽  
Dna Breaks ◽  
Late Prophase ◽  
Exogenous Dna ◽  
Prophase I ◽  
Meiotic Prophase I

SummaryDuring meiosis, the maintenance of genome integrity is critical for generating viable haploid gametes [1]. In meiotic prophase I, double-strand DNA breaks (DSBs) are induced and a subset of these DSBs are repaired as interhomolog crossovers to ensure proper chromosome segregation. DSBs in excess of the permitted number of crossovers must be repaired by other pathways to ensure genome integrity [2]. To determine if the sister chromatid is engaged for meiotic DSB repair during oogenesis, we developed an assay to detect sister chromatid repair events at a defined DSB site during Caenorhabditis elegans meiosis. Using this assay, we directly demonstrate that the sister chromatid is available as a meiotic repair template for both crossover and noncrossover recombination, with noncrossovers being the predominant recombination outcome. We additionally find that the sister chromatid is the exclusive recombination partner for DSBs during late meiotic prophase I. Analysis of noncrossover conversion tract sequences reveals that DSBs are processed similarly throughout prophase I and recombination intermediates remain central around the DSB site. Further, we demonstrate that the SMC-5/6 complex is required for long conversion tracts in early prophase I and intersister crossovers during late meiotic prophase I; whereas, the XPF-1 nuclease is required only in late prophase to promote sister chromatid repair. In response to exogenous DNA damage at different stages of meiosis, we find that mutants for SMC-5/6 and XPF-1 have differential effects on progeny viability. Overall, we propose that SMC-5/6 both processes recombination intermediates and promotes sister chromatid repair within meiotic prophase I, while XPF-1 is required as an intersister resolvase only in late prophase I.

Memoirs: The Structure of the Somatic Chromosomes of Alstroemeria and Bomarea

1934 ◽  
Vol s2-77 (305) ◽  
pp. 49-75
Author(s):  
FRANK W. JANE
Keyword(s):  
Early Prophase ◽  
Botanic Gardens ◽  
Botanic Garden ◽  
Metaphase Chromosomes ◽  
Birkbeck College ◽  
Late Prophase ◽  
Sister Chromatids ◽  
Spiral Form ◽  
Friendly Criticism ◽  
The University

1. Investigations have been made on the chromatin throughout mitosis in Alstroemeria and Bomarea, and an attempt has been made to interpret the observations. 2. Anaphase chromosomes contain single or double spirals and often chromomeres. The spiral chromonemata are held to arise from the chromomeres. 3. The resting reticulum is formed partly from the remains of the spirals, partly from the telophasic anastomoses between adjacent chromosomes. The chromomeres form the net-knots. 4. The spiral chromosomes seen in early prophase are not regarded as homologous with the anaphase chromonema. It is not certain that all the chromosomes of a nucleus assume the spiral form during prophase. 5. The paired chromatids arise during prophase by the connecting up of adjacent daughter chromomeres into two strips of chromatin. The chromosomes do not split longitudinally at any stage. 6. Connexions between the sister chromatids are regarded as remnants of the chromonema of the previous anaphase. In this respect the interpretation agrees with Martens theory of bilateral repartition. 7. Chromomeres appear in prophase as the chromatids emerge from the spiral stage. They cease to be visible in late prophase as the chromatids thicken and become densely chromatic. 8. Prolonged destaining of the early metaphase chromosomes shows that the chromomeres are still present. Each has divided to form two daughter chromomeres. Between the chromomeres on opposite sides of the chromatid appear connexions, the new chromonema. This investigation was begun at Birkbeck College, University of London, while I was the recipient of a maintenance grant from the Department of Scientific and Industrial Research. My thanks are due to the Trustees of the Dixon Fund for the loan of a suitable microscope; to the Directors of the Eoyal Botanic Gardens, Kew, the Chelsea Physic Garden, and the University Botanic Garden, Cambridge, for material; and especially to Professor Dame Helen Gwynne-Vaughan, under whose direction the work was carried out and who has encouraged me with friendly criticism and advice.

scholarly journals LOCALIZATION OF RIBOSOMAL DNA WITHIN OOCYTES OF THE HOUSE CRICKET, ACHETA DOMESTICUS (ORTHOPTERA: GRYLLIDAE)

1972 ◽  
Vol 55 (2) ◽  
pp. 310-321 ◽  
Author(s):  
Mac Donald Cave
Keyword(s):  
In Situ Hybridization ◽  
Ribosomal Rna ◽  
Ribosomal Dna ◽  
Dna Hybridization ◽  
Meiotic Prophase ◽  
Acheta Domesticus ◽  
Early Prophase ◽  
House Cricket ◽  
Nucleolar Material

A large DNA-containing body is present in addition to the chromosomes in oocytes of the house cricket Acheta domesticus. Large masses of nucleolar material accumulate at the periphery of the DNA body during the diplotene stage of meiotic prophase I. RNA-DNA hybridization analysis demonstrates that the genes which code for 18S and 28S ribosomal RNA are amplified in the ovary. In situ hybridization indicates that the amplified genes are localized within the DNA body of early prophase cells. As the cells proceed through diplotene the DNA which hybridizes with ribosomal RNA is gradually incorporated into the developing nucleolar mass.

scholarly journals Nucleolus disassembly and distribution of segregated nucleolar material in prophase of root-tip meristematic cells in Triticum aestivum L.

2015 ◽  
Vol 67 (2) ◽  
pp. 405-410
Author(s):  
Jianyue Wang ◽  
Feixiong Zhang
Keyword(s):  
Chromatin Condensation ◽  
Triticum Aestivum L ◽  
Wheat Root ◽  
Root Tip ◽  
Early Prophase ◽  
En Bloc ◽  
Late Prophase ◽  
Root Cells ◽  
Transmission Electron ◽  
Nucleolar Material

This paper presents details of the process of nucleolar disassembly, studied by conventional transmission electron microscopy (TEM) in wheat root cells. In early prophase, chromatin condensation and irregular nucleolar morphology are observed, with many small particles appearing around the nucleolus. In middle prophase, the nucleolus radiates outwards; in late prophase, the fine structure of the nucleolus disappears and nucleolar material diffuses away. Using ?en bloc? silver-staining to distinguish between nucleoli and chromatin, we observed that the dispersed nucleolar material aggregates around the chromatin, forming a sheath-like perichromosomal structure that coats the chromosomes in late prophase.

scholarly journals Visualization of early chromosome condensation

2004 ◽  
Vol 166 (6) ◽  
pp. 775-785 ◽  
Author(s):  
Natashe Kireeva ◽  
Margot Lakonishok ◽  
Igor Kireev ◽  
Tatsuya Hirano ◽  
Andrew S. Belmont
Keyword(s):  
Large Scale ◽  
Mitotic Chromosome ◽  
Chromosome Structure ◽  
Early Prophase ◽  
Axial Distribution ◽  
Metaphase Chromosomes ◽  
Topoisomerase Iiα ◽  
Late Prophase ◽  
Chromatin Folding ◽  
Structural Maintenance Of Chromosomes

Current models of mitotic chromosome structure are based largely on the examination of maximally condensed metaphase chromosomes. Here, we test these models by correlating the distribution of two scaffold components with the appearance of prophase chromosome folding intermediates. We confirm an axial distribution of topoisomerase IIα and the condensin subunit, structural maintenance of chromosomes 2 (SMC2), in unextracted metaphase chromosomes, with SMC2 localizing to a 150–200-nm-diameter central core. In contrast to predictions of radial loop/scaffold models, this axial distribution does not appear until late prophase, after formation of uniformly condensed middle prophase chromosomes. Instead, SMC2 associates throughout early and middle prophase chromatids, frequently forming foci over the chromosome exterior. Early prophase condensation occurs through folding of large-scale chromatin fibers into condensed masses. These resolve into linear, 200–300-nm-diameter middle prophase chromatids that double in diameter by late prophase. We propose a unified model of chromosome structure in which hierarchical levels of chromatin folding are stabilized late in mitosis by an axial “glue.”

The Immuno-Electron Microscopic Localization of the Mo-Fe Protein Component of Nitrogenase in Cells of Azotobacter Vinelandii

1973 ◽  
Vol 31 ◽  
pp. 574-575
Author(s):  
J. T. Stasny ◽  
R. C. Burns ◽  
R. W. F. Hardy
Keyword(s):  
Cellular Localization ◽  
Direct Evidence ◽  
Azotobacter Vinelandii ◽  
Intracellular Localization ◽  
Protein Component ◽  
Electron Microscopic ◽  
Thin Sections ◽  
Fe Protein ◽  
Intracytoplasmic Membranes

Structure-functlon studies of biological N2-fixation have correlated the presence of the enzyme nitrogenase with increased numbers of intracytoplasmic membranes in Azotobacter. However no direct evidence has been provided for the internal cellular localization of any nitrogenase. Recent advances concerned with the crystallizatiorTand the electron microscopic characterization of the Mo-Fe protein component of Azotobacter nitrogenase, prompted the use of this purified protein to obtain antibodies (Ab) to be conjugated to electron dense markers for the intracellular localization of the protein by electron microscopy. The present study describes the use of ferritin conjugated to goat antitMo-Fe protein immunoglobulin (IgG) and the observations following its topical application to thin sections of N2-grown Azotobacter.

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