Chromosomal fusion and meiotic behaviour in Delena cancerides (Araneae: Sparassidae). I. Chromosome pairing and X-chromosome segregation

Genome ◽  
1991 ◽  
Vol 34 (4) ◽  
pp. 561-566 ◽  
Author(s):  
D. M. Rowell
Keyword(s):  
Synaptonemal Complex ◽  
Chromosome Segregation ◽  
X Chromosome ◽  
Chromosome Pairing ◽  
X Chromosomes ◽  
Translocation Heterozygote ◽  
Complex Translocation ◽  
Monobrachial Homology ◽  
Pairing Initiation ◽  
Surface Spreading

Surface spreading of meiotic material in Delena cancerides indicates that pairing initiation among metacentric chromosomes with monobrachial homology differs from that of telocentric forms and free metacentric bivalents and results in a star-shaped structure at pachytene. Distance cosegregation of the three X chromosomes in ancestral, telocentric forms is prefaced by a centric association early in prophase I. This centric association of the X chromosomes is conserved in metacentric races despite the presence of an X-autosome fusion.Key words: synaptonemal complex, translocation heterozygote, X chromosome, spider.

scholarly journals Condensin DC spreads linearly and bidirectionally from recruitment sites to create loop-anchored TADs in C. elegans

2021 ◽  
Author(s):  
David Sebastian Jimenez ◽  
Jun Kim ◽  
Bhavana Ragipani ◽  
Bo Zhang ◽  
Lena Annika Street ◽  
...  
Keyword(s):  
Chromosome Segregation ◽  
X Chromosome ◽  
Molecular Motors ◽  
Sequence Motif ◽  
X Chromosomes ◽  
C Elegans ◽  
Eukaryotic Chromosome ◽  
Multiple Copies

AbstractCondensins are molecular motors that compact DNA for chromosome segregation and gene regulation. In vitro experiments have begun to elucidate the mechanics of condensin function but how condensin loading and translocation along DNA controls eukaryotic chromosome structure in vivo remains poorly understood. To address this question, we took advantage of a specialized condensin, which organizes the 3D conformation of X chromosomes to mediate dosage compensation (DC) in C. elegans. Condensin DC is recruited and spreads from a small number of recruitment elements on the X chromosome (rex). We found that ectopic insertion of rex sites on an autosome leads to bidirectional spreading of the complex over hundreds of kilobases. On the X chromosome, strong rex sites contain multiple copies of a 12-bp sequence motif and act as TAD borders. Inserting a strong rex and ectopically recruiting the complex on the X chromosome or an autosome creates a loop-anchored TAD. Unlike the CTCF system, which controls TAD formation by cohesin, direction of the 12-bp motif does not control the specificity of loops. In an X;V fusion chromosome, condensin DC linearly spreads into V and increases 3D DNA contacts, but fails to form TADs in the absence of rex sites. Finally, we provide in vivo evidence for the loop extrusion hypothesis by targeting multiple dCas9-Suntag complexes to an X chromosome repeat region. Consistent with linear translocation along DNA, condensin DC accumulates at the block site. Together, our results support a model whereby strong rex sites act as insulation elements through recruitment and bidirectional spreading of condensin DC molecules and form loop-anchored TADs.

Ultrastructural analysis of the X1X2X3O sex chromosome system during the spermatogenesis of Tegenaria domestica (Arachnida)

1982 ◽  
Vol 58 (1) ◽  
pp. 411-422
Author(s):  
R. Benavente ◽  
R. Wettstein ◽  
M. Papa
Keyword(s):  
Synaptonemal Complex ◽  
Chromosome Pairing ◽  
Sex Chromosomes ◽  
Ultrastructural Study ◽  
Chromosome Structure ◽  
Sex Chromosome ◽  
X Chromosomes ◽  
Sex Chromosome System ◽  
Available Information ◽  
Dense Chromatin

An ultrastructural study was performed on the sex chromosomes (male X1X2X3O) during the spermatogenesis of Tegenaria domestica (Arachnida, Agelenidae). This study was carried out using random and serially cut sections. During pachytene and diplotene the three X chromosomes are longitudinally paired. Each of these consists of a central core of condensed chromatin, surrounded by a field of dense chromatin projections through which the chromosomes are in contact with one another. These projections may be responsible for the recognition and pairing of the sex chromosomes and in some way participate in their non-disjunction during anaphase I. A study of the structure and behaviour of the sex chromosomes during spermatogenesis is also presented. The available information on non-synaptonemal complex-mediated chromosome pairing and a systematization of sex chromosome structure in spiders are discussed.

scholarly journals Lack of detectable genetic recombination on the X chromosome during the parthenogenetic production of female and male aphids

2002 ◽  
Vol 79 (3) ◽  
pp. 203-209 ◽  
Author(s):  
DINAH F. HALES ◽  
ALEX C. C. WILSON ◽  
MATHEW A. SLOANE ◽  
JEAN-CHRISTOPHE SIMON ◽  
JEAN-FRANÇOIS LEGALLIC ◽  
...  
Keyword(s):  
X Chromosome ◽  
Chromosome Pairing ◽  
Reproductive Strategies ◽  
Genetic Recombination ◽  
Full Range ◽  
Nucleolar Organizer ◽  
Male Production ◽  
Cyclical Parthenogenesis ◽  
X Chromosomes ◽  
Polymorphic Microsatellite

We used polymorphic microsatellite markers to look for recombination during parthenogenetic oogenesis between the X chromosomes of aphids of the tribe Macrosiphini. We examined the X chromosome because it comprises ∼25% of the genome and previous cytological observations of chromosome pairing and nucleolar organizer (NOR) heteromorphism suggest recombination, although the same is not true for autosomes. A total of 564 parthenogenetic females of Myzus clones with three distinct reproductive modes (cyclical parthenogenesis, obligate parthenogenesis and obligate parthenogenesis with male production) were genotyped at three informative X-linked loci. Also, parthenogenetically produced males from clones encompassing the full range of male-producing reproductive strategies were genotyped. These included 391 Myzus persicae males that were genotyped at three X-linked loci and 538 males from Sitobion clones that were genotyped at five informative X-linked loci. Our results show no departure from clonality in parthenogenetic generations of aphids of the tribe Macrosiphini: no recombinant genotypes were observed in parthenogenetically produced males or females.

Dependence on genie balance for synaptonemal complex formation in Drosophila melanogaster

Genome ◽  
1988 ◽  
Vol 30 (2) ◽  
pp. 258-264 ◽  
Author(s):  
T. M. Grishayeva ◽  
Y. F. Bogdanov
Keyword(s):  
Drosophila Melanogaster ◽  
Synaptonemal Complex ◽  
X Chromosome ◽  
Central Element ◽  
Sharp Decrease ◽  
Electron Microscopic Examination ◽  
Electron Microscopic ◽  
X Chromosomes ◽  
Ovary Cells ◽  
Synaptonemal Complexes

Electron microscopic examination of gonads of Drosophila melanogaster with different genotypes, including a metafemale 3X;2A and an intersex XXY;3A, have revealed that the formation of synaptonemal complexes is controlled by the genie balance, i.e., the ratio of X chromosomes to autosomes. The Y chromosome is not involved in the genetic control of the formation of precursors of the central element of synaptonemal complexes in males, nor does it disturb their formation in [Formula: see text] females. Hyperploidy for sections 1 – 3A and 18A – 20 of the X chromosome does not lead to the appearance of synaptonemal complexes in males and does not interfere with their formation in females. Females hyperploid for extensive regions of the X chromosome (sections 1 – 11A, 11A – 20, and 8C – 20) are fertile and show apparently normal formation of synaptonemal complexes. Hyperploidy for sections 8C – 11A of the X results in a sharp decrease in the viability of females, in abnormal differentiation of ovary cells, and in the lack of synaptonemal complexes. These data suggest a possible important role for the sections 8C – 11A in the genic balance controlling the formation of synaptonemal complexes in D. melanogaster. The lack of synaptonemal complexes in hypoploid females may be the result of abnormal cell differentiation in gonads.Key words: Drosophila melanogaster, synaptonemal complex, sex chromosomes, genic balance.

The effect of colchicine on meiosis in the Rhoeo discolor stabile complex translocation heterozygote

Genome ◽  
1992 ◽  
Vol 35 (4) ◽  
pp. 611-613 ◽  
Author(s):  
R. C. Verma ◽  
P. Vyas ◽  
S. N. Raina
Keyword(s):  
Chromosome Pairing ◽  
Translocation Heterozygote ◽  
Complex Translocation ◽  
Complete Chain ◽  
Chain Complexes ◽  
Metaphase I

Rhoeo discolor (2n = 12) was used to study the effect of colchicine on chromosome pairing during meiosis. Pachytene pairing appeared unaffected, but only 17.5% of the PMCs formed a ring of 12 chromosomes at metaphase I of meiosis. While 27.5% of cells had a complete chain of 12, 49.0% had chain configurations of varying (2–11) number of chromosomes and 6.0% had complete univalence. Adjacent orientation was found in the majority of cells with chain complexes of 2–11 chromosomes. The result was highly disturbed anaphase I where 58.4% PMCs were abnormal. It is concluded that the presence of aberrant cells at metaphase I is either due to colchicine-induced ineffectiveness of pairing at the very small pairing regions or failure of chiasma formation.Key words: colchicine, meiosis, Rhoeo discolor, translocation heterozygote, univalents, alternate/adjacent orientation.

scholarly journals Recombination between small X chromosome duplications and the X chromosome in Caenorhabditis elegans.

Genetics ◽  
1989 ◽  
Vol 121 (4) ◽  
pp. 723-737
Author(s):  
R K Herman ◽  
C K Kari
Keyword(s):  
Caenorhabditis Elegans ◽  
X Chromosome ◽  
Chromosome Pairing ◽  
Meiotic Chromosome ◽  
Wild Type ◽  
X Chromosomes ◽  
Meiotic Chromosome Pairing ◽  
Small X ◽  
The One ◽  
The Right

Abstract Twelve new X chromosome duplications were identified and characterized. Eight are translocated to autosomal sites near four different telomeres, and four are free. Ten include unc-1(+), which in wild type is near the left end of the X chromosome, and two of these, mnDp72(X;IV) and mnDp73(X;f), extend rightward past dpy-3. Both mnDp72 and mnDp73 recombined with the one X chromosome in males in the unc-1-dpy-3 interval at a frequency 15- to 30-fold higher than was observed for X-X recombination in hermaphrodites in the same interval. Recombinant duplications and recombinant X chromosomes were both recovered. Recombination with the X chromosome in the unc-1-dpy-3 interval was also detected for five other unc-1(+) duplications, even though their right breakpoints lie within the interval. In hermaphrodites, mnDp72 and mnDp73 promoted meiotic X nondisjunction and recombined with an X chromosome in the unc-1-dpy-3 interval at frequencies comparable to that found for X-X recombination; mnDp72(X;IV) also promoted trisomy for chromosome IV. A mutation in him-8 IV was identified that severely reduced recombination between the two X chromosomes in hermaphrodites and between mnDp73 and the X chromosome in males. Recombination between the X chromosome and duplications of either the right end of the X or a region near but not including the left end was rare. We suggest that the X chromosome has one or more elements near its left end that promote meiotic chromosome pairing.

Synaptonemal complex spreading in Allium. II. Tetraploid A. vineale

1986 ◽  
Vol 28 (5) ◽  
pp. 754-761 ◽  
Author(s):  
Josef Loidl
Keyword(s):  
Nuclear Envelope ◽  
Synaptonemal Complex ◽  
Chromosome Pairing ◽  
Long Distance ◽  
Homologous Alignment ◽  
Pairing Initiation

In tetraploid Allium vineale four homologous axes are closely aligned in unsynapsed regions at early zygotene. This alignment is brought about by intercalary and terminal associations. The intercalary association sites are possibly targets of forces for long distance attraction of homologues and potential pairing initiation sites. The terminal associations are mediated by dense spherules and result possibly from the attachment of the telomeres to the nuclear envelope. In pachytene the alignment is abolished and the four axes are synapsed two by two, resulting in bivalents or, owing to partner switches in the synapsed axes, in quadrivalents. From the number of partner switches per configuration the number of pairing initiation sites is estimated. Homologous alignment and synapsis are discussed, comparing them with the conditions in a triploid species, which were described in a previous paper.Key words: Allium vineale, synaptonemal complex, polyploids, chromosome pairing, meiosis.

scholarly journals Crossover Distribution and High Interference for Both the X Chromosome and an Autosome During Oogenesis and Spermatogenesis in Caenorhabditis elegans

Genetics ◽  
2002 ◽  
Vol 162 (3) ◽  
pp. 1169-1177 ◽  
Author(s):  
Philip M Meneely ◽  
Anna F Farago ◽  
Tate M Kauffman
Keyword(s):  
Caenorhabditis Elegans ◽  
Chromosome Segregation ◽  
X Chromosome ◽  
Normal Chromosome ◽  
Relative Distribution ◽  
X Chromosomes ◽  
Double Crossover ◽  
Sequence Tagged Site ◽  
Very High ◽  
Double Crossovers

Abstract Regulation of both the number and the location of crossovers during meiosis is important for normal chromosome segregation. We used sequence-tagged site polymorphisms to examine the distribution of all crossovers on the X chromosome during oogenesis and on one autosome during both oogenesis and spermatogenesis in Caenorhabditis elegans. The X chromosome has essentially one crossover during oogenesis, with only three possible double crossover exceptions among 220 recombinant X chromosomes. All three had one of the two crossovers in the same chromosomal interval, suggesting that crossovers in that interval do not cause interference. No other interval was associated with double crossovers. Very high interference was also found on an autosome during oogenesis, implying that each chromosome has only one crossover during oogenesis. During spermatogenesis, recombination on this autosome was reduced by ∼30% compared to oogenesis, but the relative distribution of the residual crossovers was only slightly different. In contrast to previous results with other autosomes, no double crossover chromosomes were observed. Despite an increased frequency of nonrecombinant chromosomes, segregation of a nonrecombinant autosome during spermatogenesis appears to occur normally. This indicates that an achiasmate segregation system helps to ensure faithful disjunction of autosomes during spermatogenesis.

scholarly journals Bisection of the X chromosome disrupts the initiation of chromosome silencing during meiosis in Caenorhabditis elegans

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Yisrael Rappaport ◽  
Hanna Achache ◽  
Roni Falk ◽  
Omer Murik ◽  
Oren Ram ◽  
...  
Keyword(s):  
Caenorhabditis Elegans ◽  
Rna Polymerase Ii ◽  
X Chromosome ◽  
Sex Chromosomes ◽  
Sex Chromosome ◽  
Transcription Analysis ◽  
X Chromosomes ◽  
Unique Character ◽  
Active Transcription ◽  
Heterogametic Sex

AbstractDuring meiosis, gene expression is silenced in aberrantly unsynapsed chromatin and in heterogametic sex chromosomes. Initiation of sex chromosome silencing is disrupted in meiocytes with sex chromosome-autosome translocations. To determine whether this is due to aberrant synapsis or loss of continuity of sex chromosomes, we engineered Caenorhabditis elegans nematodes with non-translocated, bisected X chromosomes. In early meiocytes of mutant males and hermaphrodites, X segments are enriched with euchromatin assembly markers and active RNA polymerase II staining, indicating active transcription. Analysis of RNA-seq data showed that genes from the X chromosome are upregulated in gonads of mutant worms. Contrary to previous models, which predicted that any unsynapsed chromatin is silenced during meiosis, our data indicate that unsynapsed X segments are transcribed. Therefore, our results suggest that sex chromosome chromatin has a unique character that facilitates its meiotic expression when its continuity is lost, regardless of whether or not it is synapsed.

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