Memoirs: The Spermatogenesis of Lepidosiren Paradoxa

The different generations of cells composing the germinal epithelium, resemble those often described in other forms, especially in the Amphibia. Very little arrangement of the different generations in different parts of the testis could be observed. The somatic number of chromosomes is thirty-eight. One pair of these is conspicuously larger than the rest. The reduced number of chromosomes in the bouquet stage appears to be arrived at by a parallel conjugation in the early prophase according to von Winiwarter's scheme. In strepsinema, which synchronises with the onset of synizesis, the conjugants separate except at their ends, to form very long-drawn-out rings. During synizesis and diakinesis the rings break into their constituents, and the somatic number of univalent chromosomes is again obtained, the "homologous" chromosomes being often widely separated from each other. During diakinesis each univalent becomes divided by a transverse constriction, which probably corresponds with the apices of the V's of the pre-meiotic chromosomes, and also with the transverse division of the Copepod type of tetrad, which cannot therefore be taken as indicating the point of junction of two chromosomes united end to end, As in Copepods, the transverse constriction is not the division plane in either mitosis, but disappears during anaphase II. After the dissolution of the nuclear membrane "homologous" chromosomes are seen to approach each other, and join together a second time to form the rings or modifications of them found in metaphase I. The first maturation division separates entire "homologous" chromosomes. There is no resting stage between the two divisions. In the second division the chromosomes divide longitudinally, forming "tetrads," etc., very like those of metaphase I. A resting or semi-resting stage may be intercalated into the spermatocyte diakinesis. In this condition the chromosomes, in the somatic number, are distributed round the periphery of the nucleus just under the nuclear membrane. In advanced stages they lose their regular shapes and become connected by numerous anastomoses. In one testis several spermatocytes in this stage have taken on all the characters of oocytes. The spermatogonial prophases are of a very simple nature, and show no sign of anything comparable to the stage of zygonerna. In the spermatogonial and also in the somatic nuclei the chromosomes are arranged in a definite plan, the smaller and larger ones being grouped together. Within the main groups there is also evidence of a tendency for chromosomes of equal size to be next to each other.

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Telomeres act autonomously in maize to organize the meiotic bouquet from a semipolarized chromosome orientation

The Journal of Cell Biology ◽

10.1083/jcb.200110126 ◽

2002 ◽

Vol 157 (2) ◽

pp. 231-242 ◽

Cited By ~ 39

Author(s):

Peter M. Carlton ◽

W. Zacheus Cande

Keyword(s):

Large Scale ◽

Nuclear Periphery ◽

Small Region ◽

Homologous Chromosomes ◽

Cis Acting ◽

Chromosome Architecture ◽

Meiotic Chromosomes ◽

Ring Chromosomes ◽

Bouquet Stage ◽

Chromosome Regions

During meiosis, chromosomes undergo large-scale reorganization to allow pairing between homologues, which is necessary for recombination and segregation. In many organisms, pairing of homologous chromosomes is accompanied, and possibly facilitated, by the bouquet, the clustering of telomeres in a small region of the nuclear periphery. Taking advantage of the cytological accessibility of meiosis in maize, we have characterized the organization of centromeres and telomeres throughout meiotic prophase. Our results demonstrate that meiotic centromeres are polarized prior to the bouquet stage, but that this polarization does not contribute to bouquet formation. By examining telocentric and ring chromosomes, we have tested the cis-acting requirements for participation in the bouquet. We find that: (a) the healed ends of broken chromosomes, which contain telomere repeats, can enter the bouquet; (b) ring chromosomes enter the bouquet, indicating that terminal position on a chromosome is not necessary for telomere sequences to localize to the bouquet; and (c) beginning at zygotene, the behavior of telomeres is dominant over any centromere-mediated chromosome behavior. The results of this study indicate that specific chromosome regions are acted upon to determine the organization of meiotic chromosomes, enabling the bouquet to form despite large-scale changes in chromosome architecture.

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Staining plant cells with silver. II. Chromosome cores

Genome ◽

10.1139/g91-138 ◽

1991 ◽

Vol 34 (6) ◽

pp. 900-908 ◽

Cited By ~ 23

Author(s):

Stephen M. Stack

Keyword(s):

Silver Staining ◽

Plant Cells ◽

Lilium Longiflorum ◽

Early Prophase ◽

Metaphase Chromosomes ◽

Homologous Chromosomes ◽

Meiotic Chromosomes ◽

Plant Chromosomes ◽

Sister Chromatids ◽

A New Technique

A new technique called salt-nylon silver staining has been used to stain cores in the chromosomes of Lilium longiflorum. Cores are visible in both mitotic and meiotic chromosomes. In C-metaphase chromosomes, a thin core is coiled to form a thick core in each chromatid. In early prophase I of meiosis, silver-stained axial cores and synaptonemal complexes show no indication of coiling before their disappearance in early diplotene. In diakinesis, pairs of thin cores reappear in large major coils. These cores can be seen to cross over between homologous chromosomes. By metaphase I, thin cores coil to form thick cores, which themselves spiral in major coils. The most striking appearance of the cores occurs during anaphase I, when homologous chromosomes separate and sister chromatids swing apart to display thick cores in major coils. During meiosis II cores are in minor coils embedded in elongate chromosomes that show relic major coiling. These observations indicate that plant chromosomes have silver-stainable cores that are comparable with cores that have been reported in the chromosomes of mammals and grasshoppers.Key words: chromosome cores, silver staining, mitosis, meiosis, plants.

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A mammalian KASH domain protein coupling meiotic chromosomes to the cytoskeleton

The Journal of Cell Biology ◽

10.1083/jcb.201304004 ◽

2013 ◽

Vol 202 (7) ◽

pp. 1023-1039 ◽

Cited By ~ 112

Author(s):

Henning F. Horn ◽

Dae In Kim ◽

Graham D. Wright ◽

Esther Sook Miin Wong ◽

Colin L. Stewart ◽

...

Keyword(s):

Nuclear Membrane ◽

Cytoplasmic Dynein ◽

Futile Cycle ◽

Homologous Chromosomes ◽

Meiotic Progression ◽

Meiotic Chromosomes ◽

Attachment Sites ◽

Domain Protein ◽

Inner Nuclear Membrane Protein ◽

Chromosome Movements

Chromosome pairing is an essential meiotic event that ensures faithful haploidization and recombination of the genome. Pairing of homologous chromosomes is facilitated by telomere-led chromosome movements and formation of a meiotic bouquet, where telomeres cluster to one pole of the nucleus. In metazoans, telomere clustering is dynein and microtubule dependent and requires Sun1, an inner nuclear membrane protein. Here we provide a functional analysis of KASH5, a mammalian dynein-binding protein of the outer nuclear membrane that forms a meiotic complex with Sun1. This protein is related to zebrafish futile cycle (Fue), a nuclear envelope (NE) constituent required for pronuclear migration. Mice deficient in this Fue homologue are infertile. Males display meiotic arrest in which pairing of homologous chromosomes fails. These findings demonstrate that telomere attachment to the NE is insufficient to promote pairing and that telomere attachment sites must be coupled to cytoplasmic dynein and the microtubule system to ensure meiotic progression.

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Molecular organization of mammalian meiotic chromosome axis revealed by expansion STORM microscopy

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1902440116 ◽

2019 ◽

Vol 116 (37) ◽

pp. 18423-18428 ◽

Cited By ~ 20

Author(s):

Huizhong Xu ◽

Zhisong Tong ◽

Qing Ye ◽

Tengqian Sun ◽

Zhenmin Hong ◽

...

Keyword(s):

Meiotic Chromosome ◽

Molecular Organization ◽

Homologous Chromosomes ◽

Meiotic Chromosomes ◽

C Terminus ◽

Stochastic Optical Reconstruction Microscopy ◽

Optical Reconstruction ◽

20 Nm ◽

Chromosome Axis

During prophase I of meiosis, chromosomes become organized as loop arrays around the proteinaceous chromosome axis. As homologous chromosomes physically pair and recombine, the chromosome axis is integrated into the tripartite synaptonemal complex (SC) as this structure’s lateral elements (LEs). While the components of the mammalian chromosome axis/LE—including meiosis-specific cohesin complexes, the axial element proteins SYCP3 and SYCP2, and the HORMA domain proteins HORMAD1 and HORMAD2—are known, the molecular organization of these components within the axis is poorly understood. Here, using expansion microscopy coupled with 2-color stochastic optical reconstruction microscopy (STORM) imaging (ExSTORM), we address these issues in mouse spermatocytes at a resolution of 10 to 20 nm. Our data show that SYCP3 and the SYCP2 C terminus, which are known to form filaments in vitro, form a compact core around which cohesin complexes, HORMADs, and the N terminus of SYCP2 are arrayed. Overall, our study provides a detailed structural view of the meiotic chromosome axis, a key organizational and regulatory component of meiotic chromosomes.

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A molecular model for the role of SYCP3 in meiotic chromosome organisation

eLife ◽

10.7554/elife.02963 ◽

2014 ◽

Vol 3 ◽

Cited By ~ 62

Author(s):

Johanna Liinamaria Syrjänen ◽

Luca Pellegrini ◽

Owen Richard Davies

Keyword(s):

Molecular Model ◽

Meiotic Chromosome ◽

Lateral Element ◽

Homologous Chromosomes ◽

Meiotic Chromosomes ◽

Double Stranded Dna ◽

Evolutionarily Conserved ◽

20 Nm ◽

Chromosome Organisation

The synaptonemal complex (SC) is an evolutionarily-conserved protein assembly that holds together homologous chromosomes during prophase of the first meiotic division. Whilst essential for meiosis and fertility, the molecular structure of the SC has proved resistant to elucidation. The SC protein SYCP3 has a crucial but poorly understood role in establishing the architecture of the meiotic chromosome. Here we show that human SYCP3 forms a highly-elongated helical tetramer of 20 nm length. N-terminal sequences extending from each end of the rod-like structure bind double-stranded DNA, enabling SYCP3 to link distant sites along the sister chromatid. We further find that SYCP3 self-assembles into regular filamentous structures that resemble the known morphology of the SC lateral element. Together, our data form the basis for a model in which SYCP3 binding and assembly on meiotic chromosomes leads to their organisation into compact structures compatible with recombination and crossover formation.

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One-dimensional spatial patterning along mitotic chromosomes: A mechanical basis for macroscopic morphogenesis

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.2013709117 ◽

2020 ◽

Vol 117 (43) ◽

pp. 26749-26755

Author(s):

Lingluo Chu ◽

Zhangyi Liang ◽

Maria V. Mukhina ◽

Jay K. Fisher ◽

John W. Hutchinson ◽

...

Keyword(s):

Spatial Patterning ◽

Geometric Form ◽

Mitotic Chromosomes ◽

Homologous Chromosomes ◽

One Dimensional ◽

Meiotic Chromosomes ◽

Planar Arrays ◽

Mechanical Basis ◽

Continuous Presence ◽

Morphological Patterns

Spatial patterns are ubiquitous in both physical and biological systems. We have recently discovered that mitotic chromosomes sequentially acquire two interesting morphological patterns along their structural axes [L. Chu et al., Mol. Cell, 10.1016/j.molcel.2020.07.002 (2020)]. First, axes of closely conjoined sister chromosomes acquire regular undulations comprising nearly planar arrays of sequential half-helices of similar size and alternating handedness, accompanied by periodic kinks. This pattern, which persists through all later stages, provides a case of the geometric form known as a “perversion.” Next, as sister chromosomes become distinct parallel units, their individual axes become linked by bridges, which are themselves miniature axes. These bridges are dramatically evenly spaced. Together, these effects comprise a unique instance of spatial patterning in a subcellular biological system. We present evidence that axis undulations and bridge arrays arise by a single continuous mechanically promoted progression, driven by stress within the chromosome axes. We further suggest that, after sister individualization, this same stress also promotes chromosome compaction by rendering the axes susceptible to the requisite molecular remodeling. Thus, by this scenario, the continuous presence of mechanical stress within the chromosome axes could potentially underlie the entire morphogenetic chromosomal program. Direct analogies with meiotic chromosomes suggest that the same effects could underlie interactions between homologous chromosomes as required for gametogenesis. Possible mechanical bases for generation of axis stress and resultant deformations are discussed. Together, these findings provide a perspective on the macroscopic changes of organized chromosomes.

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Mammalian Protein SCP1 Forms Synaptonemal Complex-like Structures in the Absence of Meiotic Chromosomes

Molecular Biology of the Cell ◽

10.1091/mbc.e04-09-0771 ◽

2005 ◽

Vol 16 (1) ◽

pp. 212-217 ◽

Cited By ~ 65

Author(s):

Rupert Öllinger ◽

Manfred Alsheimer ◽

Ricardo Benavente

Keyword(s):

Chromosome Segregation ◽

Meiotic Prophase ◽

Experimental Conditions ◽

Homologous Chromosomes ◽

Meiotic Chromosomes ◽

Heterologous System ◽

Primary Determinant ◽

Specific Proteins ◽

Mammalian Protein

Synaptonemal complexes (SCs) are evolutionary conserved, meiosis-specific structures that play a central role in synapsis of homologous chromosomes, chiasmata distribution, and chromosome segregation. However, it is still for the most part unclear how SCs do assemble during meiotic prophase. Major components of mammalian SCs are the meiosis-specific proteins SCP1, 2, and 3. To investigate the role of SCP1 in SC assembly, we expressed SCP1 in a heterologous system, i.e., in COS-7 cells that normally do not express SC proteins. Notably, under these experimental conditions SCP1 is able to form structures that closely resemble SCs (i.e., polycomplexes). Moreover, we show that mutations that modify the length of the central α-helical domain of SCP1 influence the width of polycomplexes. Finally, we demonstrate that deletions of the nonhelical N- or C-termini both affect polycomplex assembly, although in a different manner. We conclude that SCP1 is a primary determinant of SC assembly that plays a key role in synapsis of homologous chromosomes.

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Rod-Shaped Bivalents indicate new assemblage among Anatolian Water Frog Populations

Amphibia-Reptilia ◽

10.1163/156853806776052083 ◽

2006 ◽

Vol 27 (1) ◽

pp. 47-53 ◽

Cited By ~ 1

Author(s):

Beria Falakali Mutaf ◽

Nurşen Alpagut Keskin

Keyword(s):

Rana Ridibunda ◽

Lake District ◽

Separate Species ◽

Water Frog ◽

The North ◽

Meiotic Chromosomes ◽

Water Frogs ◽

Metaphase I

AbstractThe general features of the mitotic and meiotic chromosomes analysed in 91 frogs belonging to nine water frog populations distributed in Southwest Anatolia. The differences found in mitotic and meiotic chromosomes revealed the existence of two groups among the populations: the first "Aegean Group" includes those from Izmir, Bulca, Pazarağaç, and the second – "Lake District Group" from Eber, Akşehir, Gelendost, Eğirdir, Gölcük, and Beyşehir populations. The major distinction appeared in the number of the rod-shaped bivalents in metaphase I, with only one in the "Aegean Group" compared to one or two in the "Lake District Group". This result indicates a new assemblage among Anatolian water frogs and strengthens the suggestion that the "Lake District Group" that have one or two rod shaped bivalents in metaphase I due to the inclusion of hybrid lineages containing both parental genomes. It is clear that at least two separate species are present in Anatolia; one of them is possibly Rana ridibunda from the north and the second is closer to the Balkan species Rana epeirotica and Rana shqiperica.

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Varietal variation and chromosome behaviour during meiosis in Solanum tuberosum

Heredity ◽

10.1038/s41437-020-0328-6 ◽

2020 ◽

Vol 125 (4) ◽

pp. 212-226 ◽

Cited By ~ 3

Author(s):

Anushree Choudhary ◽

Liam Wright ◽

Olga Ponce ◽

Jing Chen ◽

Ankush Prashar ◽

...

Keyword(s):

Solanum Tuberosum ◽

Meiotic Chromosome ◽

In Situ Hybridisation ◽

Fluorescence In Situ Hybridisation ◽

Form Complex ◽

Meiotic Chromosomes ◽

Varietal Variation ◽

Reference Map ◽

Allelic Segregation ◽

Metaphase I

Abstract Naturally occurring autopolyploid species, such as the autotetraploid potato Solanum tuberosum, face a variety of challenges during meiosis. These include proper pairing, recombination and correct segregation of multiple homologous chromosomes, which can form complex multivalent configurations at metaphase I, and in turn alter allelic segregation ratios through double reduction. Here, we present a reference map of meiotic stages in diploid and tetraploid S. tuberosum using fluorescence in situ hybridisation (FISH) to differentiate individual meiotic chromosomes 1 and 2. A diploid-like behaviour at metaphase I involving bivalent configurations was predominant in all three tetraploid varieties. The crossover frequency per bivalent was significantly reduced in the tetraploids compared with a diploid variety, which likely indicates meiotic adaptation to the autotetraploid state. Nevertheless, bivalents were accompanied by a substantial frequency of multivalents, which varied by variety and by chromosome (7–48%). We identified possible sites of synaptic partner switching, leading to multivalent formation, and found potential defects in the polymerisation and/or maintenance of the synaptonemal complex in tetraploids. These findings demonstrate the rise of S. tuberosum as a model for autotetraploid meiotic recombination research and highlight constraints on meiotic chromosome configurations and chiasma frequencies as an important feature of an evolved autotetraploid meiosis.

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Cytogenetics of decaploid Agropyron elongatum (Elytrigia elongata) (2n = 70). I. Frequency of decavalent formation

Genome ◽

10.1139/g90-122 ◽

1990 ◽

Vol 33 (6) ◽

pp. 811-817 ◽

Cited By ~ 23

Author(s):

Mikio Muramatsu

Keyword(s):

High Frequency ◽

Chromosome Association ◽

Agropyron Elongatum ◽

Homologous Chromosomes ◽

Ring Shape ◽

Meiotic Configuration ◽

Multivalent Formation ◽

A Cell ◽

Chromosome Associations ◽

Metaphase I

The multivalents that appeared in the decaploid strain of Agropyron elongatum (2n = 10x = 70), a relative of wheat, ranged from trivalent to decavalent. Few univalents occurred. The metaphase I chromosome association in 12 cells where all configurations could clearly be identified averaged 0.42 ring X + 0.17 chain X + 0.42 ring VIII + 0.17 branched VIII + 0.25 chain VIII + 0.17 chain VII + 1.17 ring VI + 0.33 branched VI + 0.5 chain VI + 1.67 ring IV + 0.42 branched IV + 0.58 chain IV + 0.08 branched III + 0.17 chain III + 12.58 ring II + 3.75 open II + 0.25 I. The occurrence of decavalents, up to two in one cell, and of a cell with five multivalents, each of which involved more than five chromosomes, and many multivalents of ring shape indicated that the strain is autodecaploid.The chromosome associations of each cell can be interpreted as seven groups of 10 homologous chromosomes. The high frequency of bivalents indicated a tendency toward reduced multivalent formation, for which an explanation is suggested.Key words: Agropyron elongatum, meiotic configuration, decaploid, multivalent.

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