Incomplete sister chromatid separation is the mechanism of programmed chromosome elimination during early Sciara coprophila embryogenesis

Development ◽  
1996 ◽  
Vol 122 (12) ◽  
pp. 3775-3784 ◽  
Author(s):  
B. de Saint Phalle ◽  
W. Sullivan
Keyword(s):  
X Chromosome ◽  
Sister Chromatid ◽  
Metaphase Plate ◽  
Chromosome Elimination ◽  
Male Meiosis ◽  
X Chromosomes ◽  
Controlling Element ◽  
Sister Chromatid Separation ◽  
The Individual ◽  
In Cis

Sex in Sciara coprophila is determined by maternally supplied factors that control the number of paternal X chromosomes eliminated during the syncytial embryonic divisions. Confocal microscopy and FISH demonstrate that the centromeres of the X chromosomes separate at anaphase and remain functional during the cycle in which the X chromosomes are eliminated. However, a region of the sister chromatids fails to separate and the X chromosomes remain at the metaphase plate. This indicates that failure of sister chromatid separation is the mechanism of chromosome elimination. Elimination of the X chromosomes requires the presence of a previously discovered Controlling Element that acts in cis during male meiosis. Using an X-autosome translocation, we demonstrate that the Controlling Element acts at-a-distance to prevent sister chromatid separation in the arm of an autosome. This indicates that the region in which sister chromatid separation fails is chromosome-independent. Although chromosome elimination occurs in all somatic nuclei and is independent of location of the nuclei within the embryo, the decision to eliminate is made at the level of the individual nucleus. Programmed X chromosome elimination occurs at different cycles in male and female embryos. These observations support a model in which elements on the X chromosome are titrating maternally supplied factors controlling the separation of sister X chromatids.

scholarly journals ERRORS IN THE ELIMINATION OF X CHROMOSOMES IN SCIARA OCELLARIS

Genetics ◽  
1980 ◽  
Vol 94 (3) ◽  
pp. 663-673 ◽  
Author(s):  
Lyria Mori ◽  
A L P Perondini
Keyword(s):  
X Chromosome ◽  
Chromosome Elimination ◽  
Male Meiosis ◽  
Early Embryogenesis ◽  
Maternal Influence ◽  
Recessive Mutation ◽  
X Chromosomes ◽  
Heterozygous Condition ◽  
Selective Elimination

ABSTRACT It was previously assumed that the X-linked recessive mutation, sepia, induced errors in X-chromosome elimination during early embryogenesis of Sciam ocellaris. The results obtained in the present analysis corroborate this assumption and permit a further classification of the type of error this mutation induces. Among 85,244individuals analyzed, three kinds of aberrant flies were identified: mosaics (0.01 %), gynandromorphs (0.42%)and phenotypically exceptional individuals (0.25%).The origin ofthese abnormal flies could be ascribed to errors in selective elimination of X chromosomes that occur in male meiosis or during the early cleavages of the zygote nuclei. This last kind of error could be classified into three types: (a) error in number, (b) error in type, and (c) error in number and type of X chromosome eliminated. Evidence is provided indicating that sepia has no direct effect on the X chromosome; it has a maternal influence and exerts its effect only in the heterozygous condition.

Unorthodox male meiosis in Trichosia pubescens (Sciaridae). Chromosome elimination involves polar organelle degeneration and monocentric spindles in first and second division

1994 ◽  
Vol 107 (1) ◽  
pp. 299-312 ◽  
Author(s):  
H. Fuge
Keyword(s):  
Meiotic Division ◽  
Metaphase Plate ◽  
Chromosome Elimination ◽  
Spindle Pole ◽  
Male Meiosis ◽  
Early Prophase ◽  
Late Prophase ◽  
Section Electron ◽  
The One ◽  
Polar Organelle

Male meiosis in Trichosia pubescens (Sciaridae) was investigated by means of serial section electron microscopy and immunofluorescence light microscopy. From earlier studies of another sciarid fly, Sciara coprophila (Phillips (1967) J. Cell. Biol. 33, 73–92), it is known that the spindle poles in sciarid spermatogonia are characterized by pairs of ‘giant centrioles’, ring-shaped organelles composed of large numbers of singlet microtubules. In the present study spermatocytes in early prophase of Trichosia were found to possess single giant centrioles at opposite sides of the nucleus. The obvious reduction in centriole number from the spermatogonial to the spermatocyte stage is suggested to be the result of a suppression of daughter centriole formation. In late prophase, a large aster is developed around the centriole at one pole. At the opposite pole no comparable aster is formed. Instead, a number of irregular centriolar components appear in this region, a process that is understood to be a degeneration of the polar organelle. The components of the degenerate pole migrate into a cytoplasmic protrusion (‘bud’), which later is also utilized for the elimination of paternal chromosomes. The existence of only one functional polar centre is the reason for the formation of a monopolar monocentric spindle in first meiotic division, which in turn is one of the prerequisites for the elimination of paternal chromosomes. While the set of maternal and L chromosomes orientates and probably moves towards the pole, paternal chromosomes seem to be unable to contact the pole, possibly due to an inactivation of their kinetochores. Retrograde (‘away from the pole’) chromosome motion not involving kinetochores is assumed. Eventually, paternal chromosomes move into the pole-distal bud and are eliminated by casting off, together with the components of the degenerate polar organelle. Chromosome elimination can be delayed until the second meiotic division. The spindle of the second meiotic division is bipolar and monocentric. One spindle pole is marked by the polar centre of first division. The opposite spindle apex is devoid of a polar centre. It is assumed that spindle bipolarity in the second division is induced by the amphi-orientated chromosomes themselves. The maternal and L chromosome set (except the non-disjunctional X chromosome, which is found near the polar centre) congress in a metaphase plate, divide and segregate. Of the two daughter nuclei resulting from the second meiotic division, the one containing the X chromatids is retained as the nucleus of the future spermatozoon. The other nucleus becomes again eliminated within a second cytoplasmic bud.

scholarly journals Localized accumulation of Xist RNA in X chromosome inactivation

Open Biology ◽  
2019 ◽  
Vol 9 (12) ◽  
pp. 190213 ◽  
Author(s):  
Neil Brockdorff
Keyword(s):  
X Chromosome ◽  
X Chromosome Inactivation ◽  
Chromosome Inactivation ◽  
X Chromosomes ◽  
Non Coding Rna ◽  
Xist Rna ◽  
Analogous Manner ◽  
Mammalian Embryos ◽  
Non Coding Rnas ◽  
In Cis

The non-coding RNA Xist regulates the process of X chromosome inactivation, in which one of the two X chromosomes present in cells of early female mammalian embryos is selectively and coordinately shut down. Remarkably Xist RNA functions in cis , affecting only the chromosome from which it is transcribed. This feature is attributable to the unique propensity of Xist RNA to accumulate over the territory of the chromosome on which it is synthesized, contrasting with the majority of RNAs that are rapidly exported out of the cell nucleus. In this review I provide an overview of the progress that has been made towards understanding localized accumulation of Xist RNA, drawing attention to evidence that some other non-coding RNAs probably function in a highly analogous manner. I describe a simple model for localized accumulation of Xist RNA and discuss key unresolved questions that need to be addressed in future studies.

scholarly journals Xist imprinting is promoted by the hemizygous (unpaired) state in the male germ line

2015 ◽  
Vol 112 (47) ◽  
pp. 14415-14422 ◽  
Author(s):  
Sha Sun ◽  
Bernhard Payer ◽  
Satoshi Namekawa ◽  
Jee Young An ◽  
William Press ◽  
...  
Keyword(s):  
X Chromosome ◽  
Germ Line ◽  
Transgenic Animals ◽  
Early Embryo ◽  
Male Meiosis ◽  
Meiotic Pairing ◽  
Male Germ Line ◽  
Specific Expression ◽  
X Chromosomes ◽  
High Level

The long noncoding X-inactivation–specific transcript (Xist gene) is responsible for mammalian X-chromosome dosage compensation between the sexes, the process by which one of the two X chromosomes is inactivated in the female soma. Xist is essential for both the random and imprinted forms of X-chromosome inactivation. In the imprinted form, Xist is paternally marked to be expressed in female embryos. To investigate the mechanism of Xist imprinting, we introduce Xist transgenes (Tg) into the male germ line. Although ectopic high-level Xist expression on autosomes can be compatible with viability, transgenic animals demonstrate reduced fitness, subfertility, defective meiotic pairing, and other germ-cell abnormalities. In the progeny, paternal-specific expression is recapitulated by the 200-kb Xist Tg. However, Xist imprinting occurs efficiently only when it is in an unpaired or unpartnered state during male meiosis. When transmitted from a hemizygous father (+/Tg), the Xist Tg demonstrates paternal-specific expression in the early embryo. When transmitted by a homozygous father (Tg/Tg), the Tg fails to show imprinted expression. Thus, Xist imprinting is directed by sequences within a 200-kb X-linked region, and the hemizygous (unpaired) state of the Xist region promotes its imprinting in the male germ line.

scholarly journals Functional Analysis of the DXPas34Locus, a 3′ Regulator of Xist Expression

1999 ◽  
Vol 19 (12) ◽  
pp. 8513-8525 ◽  
Author(s):  
E. Debrand ◽  
C. Chureau ◽  
D. Arnaud ◽  
P. Avner ◽  
E. Heard
Keyword(s):  
X Chromosome ◽  
Yeast Artificial Chromosome ◽  
Es Cells ◽  
Artificial Chromosome ◽  
Antisense Transcription ◽  
Regulatory Elements ◽  
X Inactivation ◽  
X Chromosomes ◽  
Inactivation Center ◽  
Controlling Element

ABSTRACT X inactivation in female mammals is controlled by a key locus on the X chromosome, the X-inactivation center (Xic). The Xic controls the initiation and propagation of inactivation in cis. It also ensures that the correct number of X chromosomes undergo inactivation (counting) and determines which X chromosome becomes inactivated (choice). The Xist gene maps to the Xic region and is essential for the initiation of X inactivation in cis. Regulatory elements of X inactivation have been proposed to lie 3′ toXist. One such element, lying 15 kb downstream ofXist, is the DXPas34 locus, which was first identified as a result of its hypermethylation on the active X chromosome and the correlation of its methylation level with allelism at the X-controlling element (Xce), a locus known to affect choice. In this study, we have tested the potential function of theDXPas34 locus in Xist regulation and X-inactivation initiation by deleting it in the context of largeXist-containing yeast artificial chromosome transgenes. Deletion of DXPas34 eliminates both Xistexpression and antisense transcription present in this region in undifferentiated ES cells. It also leads to nonrandom inactivation of the deleted transgene upon differentiation. DXPas34 thus appears to be a critical regulator of Xist activity and X inactivation. The expression pattern of DXPas34 during early embryonic development, which we report here, further suggests that it could be implicated in the regulation of imprintedXist expression.

scholarly journals Paternal chromosome elimination and X non-disjunction on asymmetric spindles in Sciara male meiosis

2021 ◽  
Author(s):  
Brigitte de Saint Phalle ◽  
Rudolf Oldenbourg ◽  
Donna F. Kubai ◽  
Edward D. Salmon ◽  
Susan A. Gerbi
Keyword(s):  
Amorphous Material ◽  
Metaphase Plate ◽  
Chromosome Elimination ◽  
Male Meiosis ◽  
Paternal Chromosome ◽  
Bipolar Spindle ◽  
Monopolar Spindle ◽  
A Cell ◽  
Chromosome Imprinting ◽  
Meiosis I

Meiosis in male Sciara is unique with a single centrosome. A monopolar spindle forms in meiosis I, but a bipolar spindle forms in meiosis II. The imprinted paternal chromosomes are eliminated in meiosis I; there is non-disjunction of the X in meiosis II. Despite differences in spindle construction and chromosome behavior, both meiotic divisions are asymmetric, producing a cell and a small bud. Observations of live spermatocytes made with the LC-PolScope, differential interference contrast optics and fluorescence revealed maternal and paternal chromosome sets on the monopolar spindle in meiosis I and formation of an asymmetric monastral bipolar spindle in meiosis II where all chromosomes except the X congress to the metaphase plate. The X remains near the centrosome after meiosis I and stays with it as the spindle forms in meiosis II. Electron microscopy revealed amorphous material between the X and the centrosome. Immunofluorescence with an antibody against the checkpoint protein Mad2 stains the centromeres of the maternal X dyad in late meiosis I and in meiosis II where it fails to congress to the metaphase plate. Mad2 is also present throughout the paternal chromosomes destined for elimination in meiosis I, suggesting a possible role in chromosome imprinting. If Mad2 on the X dyad mediates a spindle checkpoint in meiosis II, it may delay metaphase to facilitate formation of the second half spindle through a non-centrosomal mechanism.

Genetic factors relating to the thyroid with emphasis on complex diseases

2011 ◽  
pp. 371-385
Author(s):  
Francesca Menconi ◽  
Terry F. Davies ◽  
Yaron Tomer
Keyword(s):  
Autoimmune Diseases ◽  
X Chromosome ◽  
Large Fraction ◽  
Somatic Cells ◽  
X Chromosome Inactivation ◽  
Chromosome Inactivation ◽  
Normal Variation ◽  
X Chromosomes ◽  
Embryonic Life ◽  
The Individual

The nucleus of each human cell encodes approximately 30 000 genes. A large fraction of the genes in each individual exist in a form that can vary between individuals. These variable genetic forms are termed polymorphisms, and they account for much of the normal variation in body traits, such as height and hair colour. The genetic information encoded in the DNA is stored on the chromosomes and each somatic cell contains 46 chromosomes (22 autosomes and two sex chromosomes), arranged in 23 pairs, one of each derived from each parent. Since each individual inherits two copies of each chromosome (for autosomes), one from each parent, there are also two copies of each gene. The chromosomal location of a gene is termed the locus of the gene. When the gene in a certain locus exists in two or more forms, these variants of the gene are termed alleles. When an individual’s two alleles at a locus are identical, that individual is said to be homozygous at that locus, and when the two alleles are different, the individual is a heterozygote. Female somatic cells contain two X chromosomes, whereas male somatic cells contain only one X chromosome. Nevertheless, the activity of genes coded for by the X chromosome is no higher in females than in males. This is due to inactivation of most of the genes on one of the two X chromosomes. Thus, in female somatic cells only one X chromosome gene is expressed, and this process of suppression is called X-chromosome inactivation. X-chromosome inactivation occurs early in embryonic life and, thereafter, in each cell either the maternal or paternal chromosome is inactivated. This results in a tissue mosaic of paternally and maternally expressed X-chromosomal alleles, with an average of 1:1 distribution. As a result, a female who is heterozygous for an X-linked gene will show a mosaic-like distribution of cells expressing either one of the two alleles. Recently X-inactivation has been postulated to play a role in autoimmune diseases and may help explain the female preponderance of autoimmune diseases (see below).

Segmental pycnotic reversion of facultative heterochromatin during the second male meiosis in tettigonioid species (Orthoptera)

Genome ◽  
1987 ◽  
Vol 29 (4) ◽  
pp. 570-577 ◽  
Author(s):  
J. Fernández Piqueras ◽  
C. Sentís
Keyword(s):  
X Chromosome ◽  
Male Meiosis ◽  
Silver Impregnation ◽  
Telomeric Region ◽  
Impregnation Method ◽  
Facultative Heterochromatin ◽  
X Chromosomes ◽  
Chromosomal Proteins ◽  
Tandem Fusion ◽  
Facultative Heterochromatinization

The X chromosome invariably exhibits isopycnosis during the most condensed stages of male meiosis after conventional staining procedures in all studied species of Tettigonioidea (Orthoptera). However, differential negative staining of the X chromosome can be achieved during these stages by a silver impregnation method after extraction of chromosomal proteins with 2 × SSC. This differential response to silver may be indicative of a distinctive chromatin organization in the X chromosome with respect to that of the autosomes. Following 2 × SSC – silver impregnation treatment, pycnotic reversion of part of the X chromosome can be observed from the metaphase II stage on in tettigonioids. Pycnotic reversion is initiated from the telomeric region of the X chromosome in the subfamily Ephyppigerinae, while in the subfamily Pycnogastrinae pycnotic reversion occurs at the centromeric region of this chromosome. These two modes of segmental pycnotic reversion may indicate the onset of a reversion of the facultative heterochromatinized state of the X chromosome (euchromatinization) during male meiosis in tettigonioids. An initiation center may be postulated for this process that is located either at the end distal to or proximal to the centromere of the X chromosome. This hypothesis is supported by the observed pycnotic behaviour of neo-X chromosomes in two different neo-XY systems, one involving centric and the other tandem fusion. Facultative heterochromatinization never involves the autosomally derived segments (XR) of the neo-X chromosomes. Occasional failures in the heterochromatinization process of part of the X chromosome, as well as of the neo-X chromosome, in two species suggests that both facultative heterochromatinization and its reversion are two processes that act segmentally. Key words: male meiosis, X chromosome, facultative heterochromatin, segmental euchromatinization.

scholarly journals Advances in understanding chromosome silencing by the long non-coding RNA Xist

2013 ◽  
Vol 368 (1609) ◽  
pp. 20110325 ◽  
Author(s):  
Takashi Sado ◽  
Neil Brockdorff
Keyword(s):  
X Chromosome ◽  
Classical Model ◽  
X Inactivation ◽  
X Chromosomes ◽  
Current State ◽  
Non Coding Rna ◽  
Xist Rna ◽  
To Come ◽  
In Cis ◽  
Long Non Coding Rna

In female mammals, one of the two X chromosomes becomes genetically silenced to compensate for dosage imbalance of X-linked genes between XX females and XY males. X chromosome inactivation (X-inactivation) is a classical model for epigenetic gene regulation in mammals and has been studied for half a century. In the last two decades, efforts have been focused on the X inactive-specific transcript ( Xist ) locus, discovered to be the master regulator of X-inactivation. The Xist gene produces a non-coding RNA that functions as the primary switch for X-inactivation, coating the X chromosome from which it is transcribed in cis . Significant progress has been made towards understanding how Xist is regulated at the onset of X-inactivation, but our understanding of the molecular basis of silencing mediated by Xist RNA has progressed more slowly. A picture has, however, begun to emerge, and new tools and resources hold out the promise of further advances to come. Here, we provide an overview of the current state of our knowledge, what is known about Xist RNA and how it may trigger chromosome silencing.

scholarly journals Evidence of non-random X chromosome activity in the mouse

1972 ◽  
Vol 19 (3) ◽  
pp. 229-240 ◽  
Author(s):  
B. M. Cattanach ◽  
C. E. Williams
Keyword(s):  
X Chromosome ◽  
Female Mouse ◽  
Somatic Cells ◽  
Inbred Strains ◽  
X Inactivation ◽  
Cell Populations ◽  
Alternative States ◽  
X Chromosomes ◽  
Inbred Strains Of Mice ◽  
Controlling Element

SUMMARYX-linked modification of the heterozygous phenotypes of X-linked genes has been detected in the X chromosomes of several inbred strains of mice. The effect is similar to that of the alternative ‘states’ or alleles, of the X chromosome controlling element, Xce, identified in T(1; X)Ct X chromosomes. Tests on two such differing X chromosomes have indicated that the phenotypic modification results either from non-random inactivation of the two X chromosomes or from selection operating on the two cell populations differentiated by X-inactivation. The data provide evidence of non-random X chromosome activity in the somatic cells of the female mouse.

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