scholarly journals The asymmetry of female meiosis reduces the frequency of inheritance of unpaired chromosomes

eLife ◽  
2015 ◽  
Vol 4 ◽  
Author(s):  
Daniel B Cortes ◽  
Karen L McNally ◽  
Paul E Mains ◽  
Francis J McNally
Keyword(s):  
Caenorhabditis Elegans ◽  
X Chromosome ◽  
High Frequency ◽  
Germ Line ◽  
Extra Chromosome ◽  
Polar Body ◽  
Contractile Ring ◽  
Female Meiosis ◽  
Random Segregation ◽  
The Asymmetry

Trisomy, the presence of a third copy of one chromosome, is deleterious and results in inviable or defective progeny if passed through the germ line. Random segregation of an extra chromosome is predicted to result in a high frequency of trisomic offspring from a trisomic parent. Caenorhabditis elegans with trisomy of the X chromosome, however, have far fewer trisomic offspring than expected. We found that the extra X chromosome was preferentially eliminated during anaphase I of female meiosis. We utilized a mutant with a specific defect in pairing of the X chromosome as a model to investigate the apparent bias against univalent inheritance. First, univalents lagged during anaphase I and their movement was biased toward the cortex and future polar body. Second, late-lagging univalents were frequently captured by the ingressing polar body contractile ring. The asymmetry of female meiosis can thus partially correct pre-existing trisomy.

Major sex-determining genes and the control of sexual dimorphism in Caenorhabditis elegans

Genome ◽  
1989 ◽  
Vol 31 (2) ◽  
pp. 625-637 ◽  
Author(s):  
Jonathan Hodgkin ◽  
Andrew D. Chisholm ◽  
Michael M. Shen
Keyword(s):  
Caenorhabditis Elegans ◽  
Sex Determination ◽  
X Chromosome ◽  
Germ Line ◽  
Cell Lineage ◽  
Regulatory Genes ◽  
Nematode Caenorhabditis Elegans ◽  
X Chromosomes ◽  
The Many ◽  
Lineage Analysis

Sex determination in Caenorhabditis elegans involves a cascade of major regulatory genes connecting the primary sex determining signal, X chromosome dosage, to key switch genes, which in turn direct development along either male or female pathways. Animals with one X chromosome (XO) are male, while animals with two X chromosomes (XX) are hermaphrodite: hermaphrodite development occurs because the action of the regulatory genes is modified in the germ line so that both sperm and oocytes are made inside a completely female soma. The regulatory genes are being examined by both genetic and molecular means. We discuss how these major genes, in particular the last switch gene in the cascade, tra-1, might regulate the many different sex-specific events that occur during the development of the hermaphrodite and of the male.Key words: nematode, Caenorhabditis elegans, sex determination, sexual differentiation, cell lineage analysis.

Distributive pairing in the grasshopper Chorthippus binotatus

Genome ◽  
1991 ◽  
Vol 34 (1) ◽  
pp. 139-143 ◽  
Author(s):  
M. D. Lopez-Leon ◽  
J. Cabrero ◽  
J. P. M. Camacho
Keyword(s):  
X Chromosome ◽  
High Frequency ◽  
Germ Line ◽  
Somatic Cells ◽  
Male Meiosis ◽  
Almost All ◽  
In Cells ◽  
Metaphase I

Six males of the grasshopper Chorthippus binotatus were mosaic for the presence of extra (E) chromosomes in the germ line, but lacked them in the somatic cells of gastric caeca. E chromosomes were very similar to the X chromosome in size and meiotic properties (heteropycnosis and autopairing). X and E chromosomes associated frequently at diplotene, but the associations never persisted until metaphase I, which indicated that they were not chiasmate. When one E was present, X and E univalents segregated preferentially to opposite poles. In cells with two E, they formed a bivalent in almost all cells, and decreased the frequency of X–E associations by 20%. These cells showed a high frequency of nondisjunction between the two E chromosomes, such that they segregated independently despite the high persistence of their association at metaphase I. These results are interpreted and discussed in the light of the distributive pairing model.Key words: distributive pairing, X chromosome, E chromosome, Chorthippus, male meiosis.

The synaptonemal complexes of Caenorhabditis elegans: pachytene karyotype analysis of hermaphrodites from the recessive him-5 and him-7 mutants

1986 ◽  
Vol 82 (1) ◽  
pp. 119-127
Author(s):  
P. Goldstein
Keyword(s):  
Caenorhabditis Elegans ◽  
X Chromosome ◽  
High Frequency ◽  
Karyotype Analysis ◽  
Nuclear Morphology ◽  
Group V ◽  
Haploid Chromosome Number ◽  
High Incidence ◽  
Physical Position ◽  
Pachytene Karyotype

The him-5 and him-7 mutants (high incidence of males) of Caenorhabditis elegans both showed increased rates of X chromosome non-disjunction (16% and 3%, respectively) but him-7 also had a high frequency of autosomal non-disjunction (34%). Synaptonemal complex (SC) karyotype analysis revealed a haploid chromosome number of six in each strain. Alterations in him-7 nuclear morphology were observed but there were no aberrations in SC structure that could account for the increased frequency of autosomal non-disjunction. However, the frequency of X-chromosome non-disjunction occurred at predicted rates on the basis of the number of disjunction regulator regions (DRRs) present on the SCs. The observation that the levels of X-chromosome non-disjunction were not influenced by the increase in the frequency of autosomal non-disjunction supports the notion that the X chromosome is subject to separate controls during meiosis. The him-7 mutant is nested within the rad-4 map region on linkage group V, however, SC analysis did not reveal the physical position on the chromosome because of synaptic adjustment.

scholarly journals Flamenco, a gene controlling the gypsy retrovirus of Drosophila melanogaster.

Genetics ◽  
1995 ◽  
Vol 139 (2) ◽  
pp. 697-711 ◽  
Author(s):  
N Prud'homme ◽  
M Gans ◽  
M Masson ◽  
C Terzian ◽  
A Bucheton
Keyword(s):  
Drosophila Melanogaster ◽  
X Chromosome ◽  
Maternal Effect ◽  
High Frequency ◽  
Mutant Allele ◽  
Null Allele ◽  
Germ Line ◽  
Endogenous Retrovirus ◽  
Host Gene ◽  
Dominant Mutation

Abstract Gypsy is an endogenous retrovirus of Drosophila melanogaster. It is stable and does not transpose with detectable frequencies in most Drosophila strains. However, we have characterized unstable strains, known as MG, in which it transposes at high frequency. These stocks contain more copies of gypsy than usual stocks. Transposition results in mutations in several genes such as ovo and cut. They are stable and are due to gypsy insertions. Integrations into the ovoD1 female sterile-dominant mutation result in a null allele of the gene and occurrence of fertile females. This phenomenon, known as the ovoD1 reversion assay, can be used to quantitate gypsy activity. We have shown that the properties of MG strains result from mutation of a host gene that we called flamenco (flam). It has a strict maternal effect on gypsy mobilization: transposition occurs at high frequency only in the germ line of the progeny of females homozygous for mutations of the gene. It is located at position 65.9 (20A1-3) on the X chromosome. The mutant allele present in MG strains is essentially recessive. Flamenco seems to control the infective properties of gypsy.

scholarly journals X Chromosome Crossover Formation and Genome Stability in Caenorhabditis elegans Are Independently Regulated by xnd-1

2016 ◽  
Vol 6 (12) ◽  
pp. 3913-3925 ◽  
Author(s):  
T Brooke McClendon ◽  
Rana Mainpal ◽  
Francis R G Amrit ◽  
Michael W Krause ◽  
Arjumand Ghazi ◽  
...  
Keyword(s):  
Dna Repair ◽  
Caenorhabditis Elegans ◽  
X Chromosome ◽  
Chromatin Structure ◽  
Transcriptional Activation ◽  
Genome Stability ◽  
Germ Line ◽  
Genome Instability ◽  
Ectopic Expression ◽  
Genome Integrity

Abstract The germ line efficiently combats numerous genotoxic insults to ensure the high fidelity propagation of unaltered genomic information across generations. Yet, germ cells in most metazoans also intentionally create double-strand breaks (DSBs) to promote DNA exchange between parental chromosomes, a process known as crossing over. Homologous recombination is employed in the repair of both genotoxic lesions and programmed DSBs, and many of the core DNA repair proteins function in both processes. In addition, DNA repair efficiency and crossover (CO) distribution are both influenced by local and global differences in chromatin structure, yet the interplay between chromatin structure, genome integrity, and meiotic fidelity is still poorly understood. We have used the xnd-1 mutant of Caenorhabditis elegans to explore the relationship between genome integrity and crossover formation. Known for its role in ensuring X chromosome CO formation and germ line development, we show that xnd-1 also regulates genome stability. xnd-1 mutants exhibited a mortal germ line, high embryonic lethality, high incidence of males, and sensitivity to ionizing radiation. We discovered that a hypomorphic allele of mys-1 suppressed these genome instability phenotypes of xnd-1, but did not suppress the CO defects, suggesting it serves as a separation-of-function allele. mys-1 encodes a histone acetyltransferase, whose homolog Tip60 acetylates H2AK5, a histone mark associated with transcriptional activation that is increased in xnd-1 mutant germ lines, raising the possibility that thresholds of H2AK5ac may differentially influence distinct germ line repair events. We also show that xnd-1 regulated him-5 transcriptionally, independently of mys-1, and that ectopic expression of him-5 suppressed the CO defects of xnd-1. Our work provides xnd-1 as a model in which to study the link between chromatin factors, gene expression, and genome stability.

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.

Nonrandom Segregation of the Mouse Univalent X Chromosome: Evidence of Spindle-Mediated Meiotic Drive

Genetics ◽  
2000 ◽  
Vol 156 (2) ◽  
pp. 775-783 ◽  
Author(s):  
Renée LeMaire-Adkins ◽  
Patricia A Hunt
Keyword(s):  
X Chromosome ◽  
Chromosome Abnormality ◽  
Three Dimensional ◽  
Fundamental Principle ◽  
Mendelian Inheritance ◽  
Segregation Behavior ◽  
Chromosome Transmission ◽  
Distortion Effect ◽  
Random Segregation ◽  
Transmission Distortion

Abstract A fundamental principle of Mendelian inheritance is random segregation of alleles to progeny; however, examples of distorted transmission either of specific alleles or of whole chromosomes have been described in a variety of species. In humans and mice, a distortion in chromosome transmission is often associated with a chromosome abnormality. One such example is the fertile XO female mouse. A transmission distortion effect that results in an excess of XX over XO daughters among the progeny of XO females has been recognized for nearly four decades. Utilizing contemporary methodology that combines immunofluorescence, FISH, and three-dimensional confocal microscopy, we have readdressed the meiotic segregation behavior of the single X chromosome in oocytes from XO females produced on two different inbred backgrounds. Our studies demonstrate that segregation of the univalent X chromosome at the first meiotic division is nonrandom, with preferential retention of the X chromosome in the oocyte in ∼60% of cells. We propose that this deviation from Mendelian expectations is facilitated by a spindle-mediated mechanism. This mechanism, which appears to be a general feature of the female meiotic process, has implications for the frequency of nondisjunction in our species.

scholarly journals glp-3 Is Required for Mitosis and Meiosis in the Caenorhabditis elegans Germ Line

Genetics ◽  
1997 ◽  
Vol 145 (1) ◽  
pp. 111-121 ◽  
Author(s):  
Lisa C Kadyk ◽  
Eric J Lambie ◽  
Judith Kimble
Keyword(s):  
Caenorhabditis Elegans ◽  
Germ Cells ◽  
Germ Line ◽  
Stem Cell Population ◽  
Phenotypic Characterization ◽  
Loss Of Function ◽  
Dapi Staining ◽  
Cell Cycles ◽  
C Elegans ◽  
Mitosis And Meiosis

The germ line is the only tissue in Caenorhabditis elegans in which a stem cell population continues to divide mitotically throughout life; hence the cell cycles of the germ line and the soma are regulated differently. Here we report the genetic and phenotypic characterization of the glp-3 gene. In animals homozygous for each of five recessive loss-of-function alleles, germ cells in both hermaphrodites and males fail to progress through mitosis and meiosis, but somatic cells appear to divide normally. Germ cells in animals grown at 15° appear by DAPI staining to be uniformly arrested at the G2/M transition with <20 germ cells per gonad on average, suggesting a checkpoint-mediated arrest. In contrast, germ cells in mutant animals grown at 25° frequently proliferate slowly during adulthood, eventually forming small germ lines with several hundred germ cells. Nevertheless, cells in these small germ lines never undergo meiosis. Double mutant analysis with mutations in other genes affecting germ cell proliferation supports the idea that glp-3 may encode a gene product that is required for the mitotic and meiotic cell cycles in the C. elegans germ line.

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