Lack of inactivation of a mouse X-linked gene physically separated from the inactivation centre

Development ◽  
1986 ◽  
Vol 97 (1) ◽  
pp. 75-85
Author(s):  
Mary F. Lyon ◽  
J. Zenthon ◽  
E. P. Evans ◽  
M. D. Burtenshaw ◽  
Kathryn A. Wareham ◽  
...  
Keyword(s):  
X Chromosome ◽  
Normal Animal ◽  
Histochemical Staining ◽  
X Inactivation ◽  
Chromosome Break ◽  
Linked Gene ◽  
Short Product ◽  
Chromosome Segments ◽  
Harmful Effects

Previous evidence had shown that, when a mammalian X-chromosome is broken by a translocation, only one of the two X-chromosome segments shows cytological signs of X-inactivation in the form of late replication or Kanda staining. In the two mouse X-autosome translocations T(X;4)37H and T(X;11)38H the X-chromosome break is in the A1–A2 bands; in both, the shorter translocation product fails to exhibit Kanda staining. By in situ hybridization, the locus of ornithine carbamoyltransferase (OCT) was shown to be proximal to the breakpoint (i.e. on the short product) in T37H and distal to the breakpoint in T38H. Histochemical staining for OCT showed that in T38H the locus of OCT undergoes random inactivation, as in a chromosomally normal animal, whereas in T37H the OCT locus remains active in all cells. The interpretation is that, when a segment of X-chromosome is physically separated from the X-inactivation centre, it fails to undergo inactivation. This point is important for the understanding of the mechanism of X-inactivation, since it implies that inactivation is a positive process, brought about by some event that travels along the chromosome. It is also relevant to the interpretation of the harmful effects of X-autosome translocations and the abnormalities seen in individuals carrying such translocations.

scholarly journals Induction of X-chromosome Inactivation by the Histone Demethylase SMCX/KDM5C

2017 ◽  
Author(s):  
Srimonta Gayen ◽  
Emily Maclary ◽  
Yumie Murata-Nakamura ◽  
Christina N. Vallianatos ◽  
Robert S. Porter ◽  
...  
Keyword(s):  
X Chromosome ◽  
Embryonic Stem ◽  
Histone Demethylase ◽  
X Inactivation ◽  
Linked Gene ◽  
Xist Rna ◽  
Evolutionarily Conserved ◽  
Specific Induction ◽  
Female Specific ◽  
Dose Dependent

SUMMARYXY male and XX female mammals equalize X-linked gene expression through the mitotically-stable transcriptional inactivation of an X-chromosome in females. Although most genes are silent on the inactive-X, some escape silencing and are expressed at higher levels in females vs. males. Here, we show that the escapee Smcx/Kdm5c, encoding a histone H3K4me2/3 demethylase, underlies the female-specific induction of X-inactivation. Mouse embryonic epiblast cells and differentiating embryonic stem cells (ESCs) lacking SMCX show reduced expression of Xist RNA, which is required for X-inactivation. Smcx-heterozygous epiblast cells do not silence X-linked genes efficiently, despite robust Xist expression. Overexpression of mouse or human SMCX, but not a catalytically-inactive SMCX or the Y-chromosome homolog SMCY, is sufficient to induce Xist and, separately, to silence X-linked genes in male ESCs. Finally, SMCX dose is inversely correlated with H3K4me2 at X-linked loci. Thus, X-inactivation initiates through the evolutionarily conserved, dose-dependent function of the histone demethylase SMCX.

An X-linked human collagen transgene escapes X inactivation in a subset of cells

Development ◽  
1992 ◽  
Vol 116 (3) ◽  
pp. 687-695
Author(s):  
H. Wu ◽  
R. Fassler ◽  
A. Schnieke ◽  
D. Barker ◽  
K.H. Lee ◽  
...  
Keyword(s):  
In Situ Hybridization ◽  
X Chromosome ◽  
Transgene Expression ◽  
Cultured Cells ◽  
X Inactivation ◽  
Small Subset ◽  
Collagen Gene ◽  
Inactive X Chromosome ◽  
Human Collagen

Transgenic mice carrying one complete copy of the human alpha 1(I) collagen gene on the X chromosome (HucII mice) were used to study the effect of X inactivation on transgene expression. By chromosomal in situ hybridization, the transgene was mapped to the D/E region close to the Xce locus, which is the controlling element. Quantitative RNA analyses indicated that transgene expression in homozygous and heterozygous females was about 125% and 62%, respectively, of the level found in hemizygous males. Also, females with Searle's translocation carrying the transgene on the inactive X chromosome (Xi) expressed about 18% transgene RNA when compared to hemizygous males. These results were consistent with the transgene being subject to but partially escaping from X inactivation. Two lines of evidence indicated that the transgene escaped X inactivation or was reactivated in a small subset of cells rather than being expressed at a lower level from the Xi in all cells, (i) None of nine single cell clones carrying the transgene on the Xi transcribed transgene RNA. In these clones the transgene was highly methylated in contrast to clones carrying the transgene on the Xa. (ii) In situ hybridization to RNA of cultured cells revealed that about 3% of uncloned cells with the transgene on the Xi expressed transgene RNA at a level comparable to that on the Xa. Our results indicate that the autosomal human collagen gene integrated on the mouse X chromosome is susceptible to X inactivation. Inactivation is, however, not complete as a subset of cells carrying the transgene on Xi expresses the transgene at a level comparable to that when carried on Xa.

scholarly journals The lncRNAs at X Chromosome Inactivation Center: Not Just a Matter of Sex Dosage Compensation

2022 ◽  
Vol 23 (2) ◽  
pp. 611
Author(s):  
Chiara Siniscalchi ◽  
Armando Di Palo ◽  
Aniello Russo ◽  
Nicoletta Potenza
Keyword(s):  
X Chromosome ◽  
Dosage Compensation ◽  
Regulatory Networks ◽  
X Chromosome Inactivation ◽  
X Inactivation ◽  
Chromosome Inactivation ◽  
Linked Gene ◽  
Regulatory Circuit ◽  
Rna Targets ◽  
Inactivation Center

Non-coding RNAs (ncRNAs) constitute the majority of the transcriptome, as the result of pervasive transcription of the mammalian genome. Different RNA species, such as lncRNAs, miRNAs, circRNA, mRNAs, engage in regulatory networks based on their reciprocal interactions, often in a competitive manner, in a way denominated “competing endogenous RNA (ceRNA) networks” (“ceRNET”): miRNAs and other ncRNAs modulate each other, since miRNAs can regulate the expression of lncRNAs, which in turn regulate miRNAs, titrating their availability and thus competing with the binding to other RNA targets. The unbalancing of any network component can derail the entire regulatory circuit acting as a driving force for human diseases, thus assigning “new” functions to “old” molecules. This is the case of XIST, the lncRNA characterized in the early 1990s and well known as the essential molecule for X chromosome inactivation in mammalian females, thus preventing an imbalance of X-linked gene expression between females and males. Currently, literature concerning XIST biology is becoming dominated by miRNA associations and they are also gaining prominence for other lncRNAs produced by the X-inactivation center. This review discusses the available literature to explore possible novel functions related to ceRNA activity of lncRNAs produced by the X-inactivation center, beyond their role in dosage compensation, with prospective implications for emerging gender-biased functions and pathological mechanisms.

scholarly journals Histone Macroh2a1.2 Relocates to the Inactive X Chromosome after Initiation and Propagation of X-Inactivation

1999 ◽  
Vol 147 (7) ◽  
pp. 1399-1408 ◽  
Author(s):  
Jacqueline E. Mermoud ◽  
Carl Costanzi ◽  
John R. Pehrson ◽  
Neil Brockdorff
Keyword(s):  
X Chromosome ◽  
Es Cells ◽  
Embryonic Stem ◽  
X Inactivation ◽  
Dense Region ◽  
Rich Domain ◽  
Inactive X Chromosome ◽  
Initiation And Propagation ◽  
Xist Rna

The histone macroH2A1.2 has been implicated in X chromosome inactivation on the basis of its accumulation on the inactive X chromosome (Xi) of adult female mammals. We have established the timing of macroH2A1.2 association with the Xi relative to the onset of X-inactivation in differentiating murine embryonic stem (ES) cells using immuno-RNA fluorescence in situ hybridization (FISH). Before X-inactivation we observe a single macroH2A1.2-dense region in both undifferentiated XX and XY ES cells that does not colocalize with X inactive specific transcript (Xist) RNA, and thus appears not to associate with the X chromosome(s). This pattern persists through early stages of differentiation, up to day 7. Then the frequency of XY cells containing a macroH2A1.2-rich domain declines. In contrast, in XX cells there is a striking relocalization of macroH2A1.2 to the Xi. Relocalization occurs in a highly synchronized wave over a 2-d period, indicating a precisely regulated association. The timing of macroH2A1.2 accumulation on the Xi suggests it is not necessary for the initiation or propagation of random X-inactivation.

scholarly journals Hidden Effects of X Chromosome Introgressions on Spermatogenesis in Drosophila simulans × D. mauritiana Hybrids Unveiled by Interactions Among Minor Genetic Factors

Genetics ◽  
1998 ◽  
Vol 150 (2) ◽  
pp. 745-754 ◽  
Author(s):  
Xulio R Maside ◽  
José P Barral ◽  
Horacio F Naveira
Keyword(s):  
Male Sterility ◽  
X Chromosome ◽  
Seminal Vesicles ◽  
Genetic Dissection ◽  
Research Strategies ◽  
Hybrid Male ◽  
Hybrid Male Sterility ◽  
Epistatic Interactions ◽  
Drosophila Mauritiana ◽  
Chromosome Segments

Abstract One of the most frequent outcomes of interspecific hybridizations in Drosophila is hybrid male sterility. Genetic dissection of this reproductive barrier has revealed that the number of responsible factors is very high and that these factors are frequently engaged in complex epistatic interactions. Traditionally, research strategies have been based on contrasting introgressions of chromosome segments that produce male sterility with those that allow fertility. Few studies have investigated the phenotypes associated with the boundary between fertility and sterility. In this study, we cointrogressed three different X chromosome segments from Drosophila mauritiana into D. simulans. Hybrid males with these three segments are usually fertile, by conventional fertility assays. However, their spermatogenesis shows a significant slowdown, most manifest at lower temperatures. Each of the three introgressed segments retards the arrival of sperm to the seminal vesicles. Other small disturbances in spermatogenesis are evident, which altogether lead to an overall reduction in the amount of motile sperm in their seminal vesicles. These results suggest that a delay in the timing of spermatogenesis, which might be brought about by the cumulative action of many different factors of minor segment, may be the primary cause of hybrid male sterility.

scholarly journals Molecular Characterization of hobo-Mediated Inversions in Drosophila melanogaster

Genetics ◽  
1996 ◽  
Vol 144 (2) ◽  
pp. 647-656
Author(s):  
William B Eggleston ◽  
Nac R Rim ◽  
Johng K Lim
Keyword(s):  
X Chromosome ◽  
Polymerase Chain Reaction Amplification ◽  
Polytene Chromosomes ◽  
Chromosomal Inversions ◽  
Hobo Element ◽  
Reaction Amplification ◽  
Notch Locus ◽  
Polymerase Chain

Abstract The structure of chromosomal inversions mediated by hobo transposable elements in the Uc-1 X chromosome was investigated using cytogenetic and molecular methods. Uc-1 contains a phenotypically silent hobo element inserted in an intron of the Notch locus. Cytological screening identified six independent Notch mutations resulting from chromosomal inversions with one breakpoint at cytological position 3C7, the location of Notch. In situ hybridization to salivary gland polytene chromosomes determined that both ends of each inversion contained hobo and Notch sequences. Southern blot analyses showed that both breakpoints in each inversion had hobo-Notch junction fragments indistinguishable in structure from those present in the Uc-1 X chromosome prior to the rearrangements. Polymerase chain reaction amplification of the 12 hobo-Notch junction fragments in the six inversions, followed by DNA sequence analysis, determined that each was identical to one of the two hobo-Notch junctions present in Uc-1. These results are consistent with a model in which hobo-mediated inversions result from homologous pairing and recombination between a pair of hobo elements in reverse orientation.

C-banding and fluorescence in situ hybridization studies of the wheat–alien hybrid 'Agrotana'

Genome ◽  
1994 ◽  
Vol 37 (3) ◽  
pp. 477-481 ◽  
Author(s):  
Jie Xu ◽  
R. L. Conner ◽  
A. Laroche
Keyword(s):  
In Situ Hybridization ◽  
Fluorescence In Situ Hybridization ◽  
Genomic Dna ◽  
Chromosome Engineering ◽  
C Banding ◽  
Chinese Spring Wheat ◽  
Mother Cells ◽  
Alien Chromatin ◽  
Chromosome Segments

'Agrotana', a wheat-alien hybrid (2n = 56), is a potential source of resistance to common root rot, stem rust, wheat streak mosaic virus, and the wheat curl mite. However, the origin of 'Agrotana', reported to be durum wheat × Agropyron trichophorum (pubescent wheatgrass), is uncertain. The objective of this investigation was to determine the chromosome constitution of 'Agrotana' using C-banding and fluorescence in situ hybridization techniques. The F1 hybrid of 'Agrotana' × 'Chinese Spring' wheat showed 7 I + 21 II in 14.9% of the pollen mother cells, evidence of the presence of the A, B, and D genomes in 'Agrotana'. The hybrid had 16 heavily C-banded chromosomes, namely 4A, and 1-7B of wheat, and a translocation that probably involved wheat chromosomes 2A and 2D. In situ hybridization using biotinylated genomic DNA of Ag. trichophorum cv. Greenleaf blocked with CS DNA failed to identify the alien chromosomes in 'Agrotana', indicating that the alien chromosomes were not likely derived from pubescent wheatgrass. In situ hybridization using labelled wheat genomic DNA blocked with 'Agrotana' DNA revealed that 'Agrotana' had 40 wheat, 14 alien, and 2 (a pair) wheat–alien translocated chromosomes. There was no homology between wheat and the alien chromosomes or chromosome segments involved in the wheat–alien recombinant. Two of the seven pairs of alien chromosomes were homoeologous to each other. The ability to identify alien chromatin in wheat using labelled wheat DNA instead of labelled alien DNA will be particularly useful in chromosome engineering of wheat germplasms having alien chromatin of unknown origin.Key words: wheat–alien hybrid, C-banding, fluorescence in situ hybridization, labelled wheat DNA as probe.

scholarly journals SITE-SPECIFIC INSTABILITY IN DROSOPHILA MELANOGASTER: EVIDENCE FOR TRANSPOSITION OF DESTABILIZING ELEMENT

Genetics ◽  
1982 ◽  
Vol 101 (3-4) ◽  
pp. 461-476
Author(s):  
Todd R Laverty ◽  
J K Lim
Keyword(s):  
Drosophila Melanogaster ◽  
X Chromosome ◽  
Lethal Mutation ◽  
Chromosome Rearrangements ◽  
Chromosome Break ◽  
Secondary Mutation ◽  
X Chromosomes ◽  
Site Specific ◽  
Normal Sequence ◽  
Lethal Mutations

ABSTRACT In this study, we show that at least one lethal mutation at the 3F-4A region of the X chromosome can generate an array of chromosome rearrangements, all with one chromosome break in the 3F-4A region. The mutation at 3F-4A (secondary mutation) was detected in an X chromosome carrying a reverse mutation of an unstable lethal mutation, which was mapped in the 6F1-2 doublet (primary mutation). The primary lethal mutation at 6F1-2 had occurred in an unstable chromosome (Uc) described previously (Lim 1979). Prior to reversion, the 6F1-2 mutation had generated an array of chromosome rearrangements, all having one break in the 6F1-2 doublet (Lim 1979, 1980). In the X chromosomes carrying the 3F-4A secondary lethal mutation the 6F1-2 doublet was normal and stable, as was the 3F-4A region in the X chromosome carrying the primary lethal mutation. The disappearance of the instability having a set of genetic properties at one region (6F1-2) accompanied by its appearance elsewhere in the chromosome (3F-4A) implies that a transposition of the destabilizing element took place. The mutant at 3F-4A and other secondary mutants exhibited all but one (reinversion of an inversion to the normal sequence) of the eight properties of the primary lethal mutations. These observations support the view that a transposable destabilizing element is responsible for the hypermutability observed in the unstable chromosome and its derivaties.

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