scholarly journals Condensins promote chromosome individualization and segregation during mitosis, meiosis, and amitosis in Tetrahymena thermophila

2018 ◽  
Vol 29 (4) ◽  
pp. 466-478 ◽  
Author(s):  
Rachel Howard-Till ◽  
Josef Loidl
Keyword(s):  
Tetrahymena Thermophila ◽  
Nuclear Organization ◽  
Chromosome Condensation ◽  
Meiotic Metaphase ◽  
Somatic Nucleus ◽  
Homologous Chromosomes ◽  
Multiple Copies ◽  
The Common ◽  
Somatic Pairing ◽  
Mitosis And Meiosis

Condensin is a protein complex with diverse functions in chromatin packaging and chromosome condensation and segregation. We studied condensin in the evolutionarily distant protist model Tetrahymena, which features noncanonical nuclear organization and divisions. In Tetrahymena, the germline and soma are partitioned into two different nuclei within a single cell. Consistent with their functional specializations in sexual reproduction and gene expression, condensins of the germline nucleus and the polyploid somatic nucleus are composed of different subunits. Mitosis and meiosis of the germline nucleus and amitotic division of the somatic nucleus are all dependent on condensins. In condensin-depleted cells, a chromosome condensation defect was most striking at meiotic metaphase, when Tetrahymena chromosomes are normally most densely packaged. Live imaging of meiotic divisions in condensin-depleted cells showed repeated nuclear stretching and contraction as the chromosomes failed to separate. Condensin depletion also fundamentally altered chromosome arrangement in the polyploid somatic nucleus: multiple copies of homologous chromosomes tended to cluster, consistent with a previous model of condensin suppressing default somatic pairing. We propose that failure to form discrete chromosome territories is the common cause of the defects observed in the absence of condensins.

scholarly journals Klp2 and Ase1 synergize to maintain meiotic spindle stability during metaphase I

2020 ◽  
Author(s):  
Fan Zheng ◽  
Fenfen Dong ◽  
Shuo Yu ◽  
Tianpeng Li ◽  
Yanze Jian ◽  
...  
Keyword(s):  
Molecular Mechanisms ◽  
Yeast Cells ◽  
Meiotic Spindle ◽  
Homologous Chromosomes ◽  
Spindle Dynamics ◽  
Live Cell Microscopy ◽  
Spindle Stability ◽  
Cell Microscopy ◽  
Mitosis And Meiosis ◽  
Meiosis I

ABSTRACTThe spindle apparatus segregates bi-oriented sister chromatids during mitosis but mono-oriented homologous chromosomes during meiosis I. It has remained unclear if similar molecular mechanisms operate to regulate spindle dynamics during mitosis and meiosis I. Here, we employed live-cell microscopy to compare the spindle dynamics of mitosis and meiosis I in fission yeast cells and demonstrated that the conserved kinesin-14 motor Klp2 plays a specific role in maintaining metaphase spindle length during meiosis I, but not during mitosis. Moreover, the maintenance of metaphase spindle stability during meiosis I requires the synergism between Klp2 and the conserved microtubule crosslinker Ase1 as the absence of both proteins causes exacerbated defects in metaphase spindle stability. The synergism is not necessary for regulating mitotic spindle dynamics. Hence, our work reveals a new molecular mechanism underlying meiotic spindle dynamics and provides insights into understanding differential regulation of meiotic and mitotic events.

Gene amplification in Tetrahymena thermophila: formation of extrachromosomal palindromic genes coding for rRNA

1985 ◽  
Vol 5 (6) ◽  
pp. 1260-1267
Author(s):  
M C Yao ◽  
S G Zhu ◽  
C H Yao
Keyword(s):  
Tetrahymena Thermophila ◽  
Telomeric Sequence ◽  
Inverted Repeats ◽  
Simple Explanation ◽  
Chromosomal Breakage ◽  
Site Specific ◽  
Dna Elimination ◽  
Multiple Copies ◽  
Chromosomal Copy ◽  
Nucleotide Repeats

Tetrahymena thermophila contains in the macronucleus multiple copies of extrachromosomal palindromic genes coding for rRNA (rDNA) which are generated from a single chromosomal copy during development. In this study we isolated the chromosomal copy of rDNA and determined the structure and developmental fate of the sequence surrounding its 5' junction. The result indicates that specific chromosomal breakage occurs at or near the 5' junction of rDNA during development. The breakage event is associated with DNA elimination and telomeric sequence addition. Similar results were also found previously for the 3' junction of this gene. These results could explain how the extrachromosomal rDNA is first generated. Near both junctions of the chromosomal rDNA, a pair of 20-nucleotide repeats was found. These sequences might serve as signals for site-specific breakage. In addition, we found a pair of perfect inverted repeats at the 5' junction of this gene. The repeats are 42 nucleotides long and are separated by 28 nucleotides. The existence of this structure provides a simple explanation for the formation of the palindromic rDNA.

scholarly journals Chromosome condensation in mitosis and meiosis of rye (Secale cereale L.)

2004 ◽  
Vol 105 (1) ◽  
pp. 134-144 ◽  
Author(s):  
J.F. Zoller ◽  
R.G. Herrmann ◽  
G. Wanner
Keyword(s):  
Secale Cereale ◽  
Chromosome Condensation ◽  
Mitosis And Meiosis

scholarly journals Gene amplification in Tetrahymena thermophila: formation of extrachromosomal palindromic genes coding for rRNA.

1985 ◽  
Vol 5 (6) ◽  
pp. 1260-1267 ◽  
Author(s):  
M C Yao ◽  
S G Zhu ◽  
C H Yao
Keyword(s):  
Tetrahymena Thermophila ◽  
Telomeric Sequence ◽  
Inverted Repeats ◽  
Simple Explanation ◽  
Chromosomal Breakage ◽  
Site Specific ◽  
Dna Elimination ◽  
Multiple Copies ◽  
Chromosomal Copy ◽  
Nucleotide Repeats

Tetrahymena thermophila contains in the macronucleus multiple copies of extrachromosomal palindromic genes coding for rRNA (rDNA) which are generated from a single chromosomal copy during development. In this study we isolated the chromosomal copy of rDNA and determined the structure and developmental fate of the sequence surrounding its 5' junction. The result indicates that specific chromosomal breakage occurs at or near the 5' junction of rDNA during development. The breakage event is associated with DNA elimination and telomeric sequence addition. Similar results were also found previously for the 3' junction of this gene. These results could explain how the extrachromosomal rDNA is first generated. Near both junctions of the chromosomal rDNA, a pair of 20-nucleotide repeats was found. These sequences might serve as signals for site-specific breakage. In addition, we found a pair of perfect inverted repeats at the 5' junction of this gene. The repeats are 42 nucleotides long and are separated by 28 nucleotides. The existence of this structure provides a simple explanation for the formation of the palindromic rDNA.

scholarly journals akirin is required for diakinesis bivalent structure and synaptonemal complex disassembly at meiotic prophase I

2013 ◽  
Vol 24 (7) ◽  
pp. 1053-1067 ◽  
Author(s):  
Amy M. Clemons ◽  
Heather M. Brockway ◽  
Yizhi Yin ◽  
Bhavatharini Kasinathan ◽  
Yaron S. Butterfield ◽  
...  
Keyword(s):  
Synaptonemal Complex ◽  
Meiotic Prophase ◽  
Chromosome Condensation ◽  
Late Prophase ◽  
Homologous Chromosomes ◽  
Prophase I ◽  
Meiotic Prophase I ◽  
Evolutionarily Conserved ◽  
Key Events

During meiosis, evolutionarily conserved mechanisms regulate chromosome remodeling, leading to the formation of a tight bivalent structure. This bivalent, a linked pair of homologous chromosomes, is essential for proper chromosome segregation in meiosis. The formation of a tight bivalent involves chromosome condensation and restructuring around the crossover. The synaptonemal complex (SC), which mediates homologous chromosome association before crossover formation, disassembles concurrently with increased condensation during bivalent remodeling. Both chromosome condensation and SC disassembly are likely critical steps in acquiring functional bivalent structure. The mechanisms controlling SC disassembly, however, remain unclear. Here we identify akir-1 as a gene involved in key events of meiotic prophase I in Caenorhabditis elegans. AKIR-1 is a protein conserved among metazoans that lacks any previously known function in meiosis. We show that akir-1 mutants exhibit severe meiotic defects in late prophase I, including improper disassembly of the SC and aberrant chromosome condensation, independently of the condensin complexes. These late-prophase defects then lead to aberrant reconfiguring of the bivalent. The meiotic divisions are delayed in akir-1 mutants and are accompanied by lagging chromosomes. Our analysis therefore provides evidence for an important role of proper SC disassembly in configuring a functional bivalent structure.

POLARIZATION AND PROGRESSION IN PAIRING: II. PREMEIOTIC ORIENTATION AND THE INITIATION OF PAIRING

1942 ◽  
Vol 20d (8) ◽  
pp. 221-229 ◽  
Author(s):  
Stanley G. Smith
Keyword(s):  
Homologous Chromosomes ◽  
Sister Chromatids ◽  
Somatic Pairing ◽  
The One

Homologous chromosomes in the Diptera associate side by side in pairs at each and every anaphase (somatic pairing) and reappear in the following prophases relationally coiled. In plants and animals other than Diptera the homologues at anaphase (with one exception) show no such specific attraction: at prophase the relational coiling of homologues is here supplanted by a relational coiling of sister chromatids. The one exception arises at the anaphase of the last premeiotic division—homologues become associated in pairs and reappear in the following prophase relationally coiled.In the Diptera the chromosomes are single at each and every anaphase: in other animals and plants the chromosomes are double at all anaphases except that of the last premeiotic division. Hence at this latter division the attraction in pairs between chromatids is replaced by an attraction between pairs of homologues.

Accurate processing and amplification of cloned germ line copies of ribosomal DNA injected into developing nuclei of Tetrahymena thermophila

1989 ◽  
Vol 9 (3) ◽  
pp. 1092-1099
Author(s):  
M C Yao ◽  
C H Yao
Keyword(s):  
Developmental Stages ◽  
Transformation Efficiency ◽  
Tetrahymena Thermophila ◽  
Germ Line ◽  
Rrna Genes ◽  
Somatic Nucleus ◽  
Dna Breakage ◽  
Cis Acting ◽  
Palindromic Structure ◽  
Rdna Amplification

The ciliate Tetrahymena thermophila contains a chromosomally integrated copy of the rRNA genes (rDNA) in its germinal (micronuclear) genome. These genes are excised from the chromosome through a process involving site-specific DNA breakage, become linear palindromic molecules with added telomeres, and are greatly amplified during development of the somatic nucleus (macronucleus). In this study, we cloned a 15-kilobase segment of the germ line DNA containing these genes and injected it into developing macronuclei of T. thermophila. Up to 11% of injected cells were transformed to the paromomycin-resistant phenotype specified by the injected DNA. Transformation efficiency was dependent on the developmental stages of the injected cells and the integrity of the injected DNA but not the DNA concentration or conformation. The injected DNA was apparently processed and amplified correctly to produce rDNA molecules with the expected linear palindromic structure which carried the appropriate physical markers. Thus, the 15-kilobase DNA contained all cis-acting sequences sufficient for the DNA-processing events leading to rDNA amplification in T. thermophila.

Reproducible and variable genomic rearrangements occur in the developing somatic nucleus of the ciliate Tetrahymena thermophila

1985 ◽  
Vol 5 (8) ◽  
pp. 2039-2050
Author(s):  
E A Howard ◽  
E H Blackburn
Keyword(s):  
Repetitive Dna ◽  
Dna Sequences ◽  
High Frequency ◽  
Tetrahymena Thermophila ◽  
Genomic Rearrangements ◽  
Repetitive Dna Sequences ◽  
Whole Genome ◽  
Specific Sequence ◽  
Somatic Nucleus ◽  
Variant Cell

We analyzed the extent, reproducibility, and developmental control of genomic rearrangements in the somatic macronucleus of the ciliate Tetrahymena thermophila. To exclude differences caused by genetic polymorphisms, we constructed whole-genome homozygotes, and we compared the homozygous progeny derived from single macronuclear differentiation events. This strategy enabled us to identify a novel form of variable rearrangement and to confirm previous findings that rearranged sequences occur at a high frequency in the Tetrahymena genome. Rearrangements studied here were deletions of both unique and interchromosomally dispersed repetitive DNA sequences involving DNA rejoining of internal, nontelomeric regions of macronuclear DNAs. We showed that although rearrangements of some sequence classes are reproducible among independently developed macronuclei, other specific sequence classes are variably rearranged in macronuclear development. The variable somatic genomes so produced may be the source of phenotypically variant cell lines.

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.

scholarly journals A comparative genomics study of neuropeptide genes in the cnidarian subclasses Hexacorallia and Ceriantharia

BMC Genomics ◽  
2020 ◽  
Vol 21 (1) ◽  
Author(s):  
Thomas L. Koch ◽  
Cornelis J. P. Grimmelikhuijzen
Keyword(s):  
Signal Sequence ◽  
Consensus Sequence ◽  
Amide Group ◽  
Nematostella Vectensis ◽  
Current Analysis ◽  
Terminal Sequence ◽  
Animal Phyla ◽  
Multiple Copies ◽  
The Common ◽  
Laboratory Models

Abstract Background Nervous systems originated before the split of Proto- and Deuterostomia, more than 600 million years ago. Four animal phyla (Cnidaria, Placozoa, Ctenophora, Porifera) diverged before this split and studying these phyla could give us important information on the evolution of the nervous system. Here, we have annotated the neuropeptide preprohormone genes of twenty species belonging to the subclass Hexacorallia or Ceriantharia (Anthozoa: Cnidaria), using thirty-seven publicly accessible genome or transcriptome databases. Studying hexacorals is important, because they are versatile laboratory models for development (e.g., Nematostella vectensis) and symbiosis (e.g., Exaiptasia diaphana) and also are prominent reef-builders. Results We found that each hexacoral or ceriantharian species contains five to ten neuropeptide preprohormone genes. Many of these preprohormones contain multiple copies of immature neuropeptides, which can be up to 50 copies of identical or similar neuropeptide sequences. We also discovered preprohormones that only contained one neuropeptide sequence positioned directly after the signal sequence. Examples of them are neuropeptides that terminate with the sequence RWamide (the Antho-RWamides). Most neuropeptide sequences are N-terminally protected by pyroglutamyl (pQ) or one or more prolyl residues, while they are C-terminally protected by an amide group. Previously, we isolated and sequenced small neuropeptides from hexacorals that were N-terminally protected by an unusual L-3-phenyllactyl group. In our current analysis, we found that these N-phenyllactyl-peptides are derived from N-phenylalanyl-peptides located directly after the signal sequence of the preprohormone. The N-phenyllactyl- peptides appear to be confined to the hexacorallian order Actiniaria and do not occur in other cnidarians. On the other hand, (1) the neuropeptide Antho-RFamide (pQGRFamide); (2) peptides with the C-terminal sequence GLWamide; and (3) tetrapeptides with the X1PRX2amide consensus sequence (most frequently GPRGamide) are ubiquitous in Hexacorallia. Conclusions We found GRFamide, GLWamide, and X1PRX2amide peptides in all tested Hexacorallia. Previously, we discovered these three neuropeptide classes also in Cubozoa, Scyphozoa, and Staurozoa, indicating that these neuropeptides originated in the common cnidarian ancestor and are evolutionarily ancient. In addition to these ubiquitous neuropeptides, other neuropeptides appear to be confined to specific cnidarian orders or subclasses.

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