Ultrastructure of Meiosis and Centriole Behaviour in Ulva Mutabilis Føyn

1973 ◽  
Vol 13 (1) ◽  
pp. 69-81
Author(s):  
T. BRÅTEN ◽  
Ø. NORDBY
Keyword(s):  
Nuclear Membrane ◽  
Outer Surface ◽  
Central Element ◽  
Synaptinemal Complex ◽  
Cell Divisions ◽  
Prophase I ◽  
Visible Sign

The present work deals with the ultrastructure of the meiotic processes leading to the formation of zoospores. The formation of an exit pore on the outer surface of the sporangium is the first visible sign that the cell will undergo meiosis and not just a somatic division. Prophase I nuclei differ from nuclei in mitotic prophase by having one or several invaginations of the nuclear membrane. Electron-dense lines probably representing the lateral elements of the synaptinemal complex are observed during prophase I. The central element of the complex has, however, never been observed. The fate of the centrioles during meiosis is described in detail. The number of duplications of the centrioles is found to be the same at meiotic and mitotic zooid formation. The number of cell divisions is, however, different in the 2 cases.

Intranuclear membranous inclusions in oocytes of a viviparous teleost (Xiphophorus helleri)

1976 ◽  
Vol 22 (2) ◽  
pp. 325-334
Author(s):  
C. Azevedo
Keyword(s):  
Nuclear Membrane ◽  
Inclusion Bodies ◽  
Intranuclear Inclusions ◽  
Late Prophase ◽  
Xiphophorus Helleri ◽  
Inner Nuclear Membrane ◽  
Prophase I ◽  
Fixed Material ◽  
Metabolic Phenomena

Intranuclear inclusions were observed in oocytes of Xiphophorus helleri during prophase I. In osmium-fixed leptotene nuclei, the inclusions were made up of groups of membrane-limited vesicles or tubules with pale contents, situated near the inner nuclear membrane with which some of them exhibited apparent continuities. In zygotene nuclei, larger vesicles also appeared bounded by two or three membranes and containing tubules apparently invaginated from their walls. In pachytene-dictyate nuclei most vesicular bodies had a wall formed by stratified membranes, or were entirely made up of membranous whorls. In glutaraldehyde-osmium fixed material some of these myeline-like bodies showed a peculiar arrangement, consisting of concentric bands each containing thick inner dense lamellae 2-0-3-0 nm thick and a 5-0 nm outer lamella. It is suggested that these inclusion bodies arise from the inner nuclear membrane of oocytes when cells start to grow intensely during prophase I. The bodies seem to become more complex at late prophase, probably by association of individual vesicles and the occurrence of multiple membrane invaginations, which may be related to active metabolic phenomena taking place at this stage in oocytes.

Further observations on nucleolar tails in amphibian oocytes

1991 ◽  
Vol 99 (3) ◽  
pp. 515-521
Author(s):  
PEDRO LEÓN ◽  
JAMES KEZER ◽  
ERIC SCHABTACH
Keyword(s):  
Electron Microscopy ◽  
Nuclear Envelope ◽  
Nuclear Membrane ◽  
Outer Surface ◽  
Light And Electron Microscopy ◽  
Nuclear Pores ◽  
Core Component ◽  
Amphibian Species ◽  
Attachment Structures ◽  
Convoluted Tubules

Large oocytes from some amphibian species possess beaded or unbeaded intranuclear tails that penetrate the extrachromosomal nucleoli through a distinct pit in their surface and attach to the central core component Here we show, using light and electron microscopy, that tails anchor nucleoli to the nuclear envelope through intricate attachment structures. These structures are composed of interconnected spherical masses containing highly convoluted tubules and associated extratubular proteins, directly directly in contact with the inner nuclear membrane. Fibers emerging from the nuclear pores seemingly hold the attachment complex in place. Beads on the nucleolar tails are formed by the accumulation of proteins on the outer surface of smooth tubules. The function of these intranuclear tubules is unknown

Two well-known mutants of chiasma maintenance function in maize are allelic

Genome ◽  
1998 ◽  
Vol 41 (3) ◽  
pp. 417-421
Author(s):  
Marjorie P Maguire ◽  
Janet Day Jackson
Keyword(s):  
Nuclear Membrane ◽  
Membrane System ◽  
Late Prophase ◽  
Prophase I ◽  
Essentially Normal ◽  
Independent Origin ◽  
Stage Separation ◽  
Bivalent Association ◽  
Diakinesis Stage ◽  
System Breakdown

By a series of traditional crosses, allelism has been tested for two maize recessive mutants of independent origin, dy1 and dsy1, both called desynaptic. These mutants both display loss of chiasmate association during diakinesis (late prophase I) but at differing frequencies. This chiasma loss happens before nucleolar loss and nuclear membrane system breakdown. That crossovers have occurred to establish the chiasmata in the first place has been documented by diakinesis-stage separation of heterozygous heterochromatic regions in univalents formed by bivalent-association breakdown. In the present work, the two mutants have been found to be allelic by the outcome of traditional crosses that produced variant plants which were heterozygous for the two alleles. These plants express a unique phenotype at diakinesis, but are essentially normal at pachytene, metaphase I, anaphase I, and later stages of meiosis.Key words: chiasma, crossover, complementation.

scholarly journals Micromanipulation of prophase I chromosomes from mouse spermatocytes reveals high stiffness and gel-like chromatin organization

2020 ◽  
Author(s):  
Ronald Biggs ◽  
Ning Liu ◽  
Yiheng Peng ◽  
John F. Marko ◽  
Huanyu Qiao
Keyword(s):  
Meiotic Prophase ◽  
Central Element ◽  
Critical Event ◽  
Mitotic Chromosomes ◽  
Large Protein ◽  
Homologous Chromosomes ◽  
Prophase I ◽  
Meiotic Prophase I ◽  
Meiotic Chromosomes ◽  
Genetic Mutants

Meiosis produces four haploid cells after two successive divisions in sexually reproducing organisms. A critical event during meiosis is construction of the synaptonemal complex (SC), a large, protein-based bridge that physically links homologous chromosomes. The SC facilitates meiotic recombination, chromosome compaction, and the eventual separation of homologous chromosomes at metaphase I. We present experiments directly measuring physical properties of captured mammalian meiotic prophase I chromosomes. Mouse meiotic chromosomes are about ten-fold stiffer than somatic mitotic chromosomes, even for genetic mutants lacking SYCP1, the central element of the SC. Meiotic chromosomes dissolve when treated with nucleases, but only weaken when treated with proteases, suggesting that the SC is not rigidly connected, and that meiotic prophase I chromosomes are a gel meshwork of chromatin, similar to mitotic chromosomes. These results are consistent with a liquid- or liquid-crystal SC, but with SC-chromatin stiff enough to mechanically drive crossover interference.

scholarly journals PAIR3, an axis-associated protein, is essential for the recruitment of recombination elements onto meiotic chromosomes in rice

2011 ◽  
Vol 22 (1) ◽  
pp. 12-19 ◽  
Author(s):  
Kejian Wang ◽  
Mo Wang ◽  
Ding Tang ◽  
Yi Shen ◽  
Baoxiang Qin ◽  
...  
Keyword(s):  
Synaptonemal Complex ◽  
Central Element ◽  
Dependent Manner ◽  
Homologous Pairing ◽  
Homologous Chromosomes ◽  
Prophase I ◽  
Meiotic Chromosomes

During meiosis, the paired homologous chromosomes are tightly held together by the synaptonemal complex (SC). This complex consists of two parallel axial/lateral elements (AEs/LEs) and one central element. Here, we observed that PAIR3 localized to the chromosome core during prophase I and associated with both unsynapsed AEs and synapsed LEs. Analyses of the severe pair3 mutant demonstrated that PAIR3 was essential for bouquet formation, homologous pairing and normal recombination, and SC assembly. In addition, we showed that although PAIR3 was not required for the initial recruitment of PAIR2, it was required for the proper association of PAIR2 with chromosomes. Dual immunostaining revealed that PAIR3 highly colocalized with REC8. Moreover, studies using a rec8 mutant indicated that PAIR3 localized to chromosomes in a REC8-dependent manner.

scholarly journals Fine structure of meiotic prophase chromosomes and modified synaptonemal complexes in diploid and triploid Rhoeo spathacea

1979 ◽  
Vol 37 (1) ◽  
pp. 69-84
Author(s):  
Y.J. Lin
Keyword(s):  
Central Region ◽  
Nuclear Membrane ◽  
Central Element ◽  
Diploid Cell ◽  
Crossing Over ◽  
Serial Sections ◽  
Short Segment ◽  
Positive Role ◽  
3 Dimensional ◽  
Terminal Chiasmata

The synaptonemal complex (SC) in the diploid Rhoeo consists of 2 amorphous lateral elements, each about 46.0 nm thick, and one amorphous central element about 30.0 nm thick. The central region is about 115.0 nm wide. SC in the triploid have essentially the same dimensions as those of the diploid; both lateral (46.0 nm) and central (30.0 nm) elements are amorphous, and the central region is about 117.5 nm wide. The coil, observed in both diploid and triploid, is a modified short segment of SC with several twists at the end of a synapsed bivalent that is attached to the nuclear membrane. Serial sections in a diploid cell reveal that a coil extends inwards about 3.5 micron from the nuclear membrane and makes a complete turn at a distance of every 0.5 micron. There is a correlation between the modified ends of SC and terminal chiasmata in Rhoeo. The coils might have a positive role in the process of crossing over, or alternatively might be involved in ring formation by holding chromosome ends together while chiasmata are not involved. SC are present in chromocentres of both diploid and triploid. Chromocentres in diploid and triploid are indistinguishable, and appear to be formed from the aggregation of pericentromeric heterochromatin as a result of translocations which occured close to the centromeres. 3-dimensional hypothetical pachytene configuration of the diploid is presented.

scholarly journals Functions of cyclins and CDKs in mammalian gametogenesis†

2019 ◽  
Vol 101 (3) ◽  
pp. 591-601 ◽  
Author(s):  
Jessica Y Chotiner ◽  
Debra J Wolgemuth ◽  
P Jeremy Wang
Keyword(s):  
Germ Cells ◽  
Cultured Cells ◽  
Early Embryogenesis ◽  
Meiotic Cell ◽  
Cell Cycles ◽  
Genetic Ablation ◽  
Cyclin Dependent Kinases ◽  
Long Period ◽  
Cell Divisions ◽  
Prophase I

Abstract Cyclins and cyclin-dependent kinases (CDKs) are key regulators of the cell cycle. Most of our understanding of their functions has been obtained from studies in single-cell organisms and mitotically proliferating cultured cells. In mammals, there are more than 20 cyclins and 20 CDKs. Although genetic ablation studies in mice have shown that most of these factors are dispensable for viability and fertility, uncovering their functional redundancy, CCNA2, CCNB1, and CDK1 are essential for embryonic development. Cyclin/CDK complexes are known to regulate both mitotic and meiotic cell cycles. While some mechanisms are common to both types of cell divisions, meiosis has unique characteristics and requirements. During meiosis, DNA replication is followed by two successive rounds of cell division. In addition, mammalian germ cells experience a prolonged prophase I in males or a long period of arrest in prophase I in females. Therefore, cyclins and CDKs may have functions in meiosis distinct from their mitotic functions and indeed, meiosis-specific cyclins, CCNA1 and CCNB3, have been identified. Here, we describe recent advances in the field of cyclins and CDKs with a focus on meiosis and early embryogenesis.

scholarly journals Cytoplasmic Membranes and the Nuclear Membrane in the Flagellate Trichonympha

1959 ◽  
Vol 6 (3) ◽  
pp. 369-378 ◽  
Author(s):  
A. V. Grimstone
Keyword(s):  
Electron Microscope ◽  
Steady State ◽  
Golgi Apparatus ◽  
Nuclear Membrane ◽  
Outer Surface ◽  
State System ◽  
The Other ◽  
Cytoplasmic Vesicles ◽  
Cytoplasmic Membranes

The structure of the nuclear and cytoplasmic membranes of Trichonympha, a complex flagellate, has been studied in the electron microscope. The nuclear membrane consists of two 70 A membranes, penetrated by numerous pores. Small (100 A) granules occur on the outer surface, around the rims of the pores. Granule-bearing membranes, only 30 to 40 A thick, form long, ribbon-shaped sacs, with 100 A granules on their outer surface. They apparently form close to the nucleus, from which they probably derive their granules. Smooth membranes occur in the parabasal bodies, which consist of stacks of 70 A membranes, joined at their edges in pairs to form flattened sacs. These can inflate and form cytoplasmic vesicles. A protein fibre is applied laterally to the pile of sacs. New sacs, replacing those lost by inflation, appear to form by a process involving the granular membranes, and there may be a transformation of one into the other. Starving eliminates granular membranes and results in a failure in the formation of new parabasal sacs. Refeeding reverses these effects. A parabasal body is a steady-state system, in which the rates of loss and gain of sacs are normally approximately equal. Parabasal bodies resemble the Golgi apparatus.

scholarly journals Micromanipulation of prophase I chromosomes from mouse spermatocytes reveals high stiffness and gel-like chromatin organization

2020 ◽  
Vol 3 (1) ◽  
Author(s):  
Ronald J. Biggs ◽  
Ning Liu ◽  
Yiheng Peng ◽  
John F. Marko ◽  
Huanyu Qiao
Keyword(s):  
Meiotic Prophase ◽  
Central Element ◽  
Critical Event ◽  
Mitotic Chromosomes ◽  
Large Protein ◽  
Homologous Chromosomes ◽  
Prophase I ◽  
Meiotic Prophase I ◽  
Meiotic Chromosomes ◽  
Genetic Mutants

Abstract Meiosis produces four haploid cells after two successive divisions in sexually reproducing organisms. A critical event during meiosis is construction of the synaptonemal complex (SC), a large, protein-based bridge that physically links homologous chromosomes. The SC facilitates meiotic recombination, chromosome compaction, and the eventual separation of homologous chromosomes at metaphase I. We present experiments directly measuring physical properties of captured mammalian meiotic prophase I chromosomes. Mouse meiotic chromosomes are about ten-fold stiffer than somatic mitotic chromosomes, even for genetic mutants lacking SYCP1, the central element of the SC. Meiotic chromosomes dissolve when treated with nucleases, but only weaken when treated with proteases, suggesting that the SC is not rigidly connected, and that meiotic prophase I chromosomes are a gel meshwork of chromatin, similar to mitotic chromosomes. These results are consistent with a liquid- or liquid-crystal SC, but with SC-chromatin stiff enough to mechanically drive crossover interference.

scholarly journals The Relation between the Axial Complex of Meiotic Prophase Chromosomes and Chromosome Pairing in a Salamander (Plethodon cinereus)

1958 ◽  
Vol 4 (5) ◽  
pp. 633-638 ◽  
Author(s):  
Montrose J. Moses
Keyword(s):  
Electron Microscope ◽  
Meiotic Prophase ◽  
Light And Electron Microscopy ◽  
Central Element ◽  
Primary Spermatocyte ◽  
Plethodon Cinereus ◽  
Axial Complex ◽  
Thin Sections ◽  
Single Chromosome ◽  
Synaptinemal Complex

An investigation of the structure of meiotic chromosomes from primary spermatocytes of two salamanders, Plethodon cinereus and Desmognathus fusca, has been made using correlated light and electron microscopy. Feulgen squashes were compared with stained sections and these related to adjacent thin sections in the electron microscope. A transition from the familiar cytological preparation to the electron image was thus effected. A linear complex consisting of three parallel strands has been observed with the electron microscope, passing along the central axis of primary spermatocyte chromosomes. The complex is similar to that found in comparable chromosomes from at least a dozen animal species. The structure in Plethodon is described in detail. Synapsis has been positively identified as the stage of meiotic prophase at which the complex occurs. Thus the complex is a part of bivalent chromosomes. It has not been seen in other stages or other divisions and is thus thought to be exclusively of synaptic occurrence. The term synaptinemal complex is suggested for the entire structure. By virtue of the material condensed around it, the complex is also seen in the light microscope where it appears as a fine, densely Feulgen-positive central core along the chromosome. The complex is thus closely associated with DNA, if not at least in part, composed of it. In the stages studied, homologous chromosomes are not always completely paired. The lateral elements of the complex separate and follow the single chromosome axes at these points. The central element disappears and thus may be a phenomenon of pairing. It is concluded that the lateral elements of the synaptinemal complex may more correctly be a "core" of the single meiotic prophase chromosome, possibly being concerned with its linear organization.

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