Showing papers on "X chromosome published in 1996"
TL;DR: Evidence for gene targeting of Xist, the proposed candidate for the X inactivation centre, is provided, and its absolute requirement in the process of X chromosome inactivation is provided.
Abstract: The Xist gene has been proposed as a candidate for the X inactivation centre, the master regulatory switch locus that controls X chromosome inactivation So far this hypothesis has been supported solely by indirect evidence Here we describe gene targeting of Xist, and provide evidence for its absolute requirement in the process of X chromosome inactivation
1,219 citations
TL;DR: The results suggest that G4.5 is the genetic locus responsible for the Barth syndrome, and introduces stop codons in the open reading frame interrupting translation of most of the putative proteins.
Abstract: Barth syndrome is a severe inherited disorder, often fatal in childhood, characterized by cardiac and skeletal myopathy, short stature and neutropenia. The disease has been mapped to a very gene-rich region in distal portion of Xq28. We now report the identification of unique mutations in one of the genes in this region, termed G4.5, expressed at high level in cardiac and skeletal muscle. Different mRNAs can be produced by alternative splicing of the primary G4.5 transcript, encoding novel proteins that differ at the N terminus and in the central region. The mutations introduce stop codons in the open reading frame interrupting translation of most of the putative proteins (which we term 'tafazzins'). Our results suggest that G4.5 is the genetic locus responsible for the Barth syndrome.
686 citations
TL;DR: It is demonstrated that Sox-3, as well as Sox-1 and Sox-2, are expressed in the urogenital ridge and that their protein products are able to bind the same DNA sequence motif as Sry in vitro, but with different affinities, suggesting an evolutionary link between the genes.
Abstract: The Sox gene family consists of a large number of embryonically expressed genes related via the possession of a 79-amino-acid DNA-binding domain known as the HMG box Partial clones for the first three Sox genes (al-a3) were isolated by homology to the HMG box of the testis-determining gene Sry and are now termed Sox-1, Sox-2 and Sox-3, Sox-3 is highly conserved amongst mammalian species and is located on the X chromosome This has led to the proposal that Sry evolved from Sox-3 We present the cloning and sequencing of Sox-1, Sox-2 and Sox-3 from the mouse and show that Sox-3 is most closely relate to Sry We also confirm that mouse Sox-3 is located on the X chromosome between Hprt and Dmd Analysis of the distribution of Sox-3 RNA shows that its main site of expression is in the developing central nervous system, suggesting a role for Sox-3 in neural development Moreover, we demonstrate that Sox-3, as well as Sox-1 and Sox-2, are expressed in the urogenital ridge and that their protein products are able to bind the same DNA sequence motif as Sry in vitro, but with different affinities These observations prompt discussion of an evolutionary link between the genes and support the model that Sry has evolved from Sox-3 However our findings imply that if this is true, then Sry has undergone concomitant changes resulting in loss of CNS expression and altered DNA-binding properties
504 citations
TL;DR: Sequence analysis indicates that the Y–chromosomal DAZ cluster arose during primate evolution by transposing the autosomal gene to the Y, amplifying and pruning exons within the transposed gene and amplifying the modified gene.
Abstract: It is widely believed that most or all Y–chromosomal genes were once shared with the X chromosome. The DAZ gene is a candidate for the human Y–chromosomal Azoospermia Factor (AZF). We report multiple copies of DAZ (>99% identical in DNA sequence) clustered in the AZF region and a functional DAZ homologue (DAZH) on human chromosome 3. The entire gene family appears to be expressed in germ cells. Sequence analysis indicates that the Y–chromosomal DAZ cluster arose during primate evolution by (i) transposing the autosomal gene to the Y, (ii) amplifying and pruning exons within the transposed gene and (iii) amplifying the modified gene. These results challenge prevailing views of sex chromosome evolution, suggesting that acquisition of autosomal fertility genes is an important process in Y chromosome evolution.
448 citations
TL;DR: It is concluded that Xist-mediated X chromosome inactivation can occur in the absence ofDNA methylation, arguing that DNA methylation may be required to repress Xist expression for the maintenance of a transcriptionally active Xa.
Abstract: Xist and other X-linked gene expression was examined by fluorescence in situ hybridization in cells of wild type and DNA methyltranferase (Dnmt) mutant embryos and embryonic stem (ES) cells to determine whether demethylation-induced Xist expression leads to inappropriate X chromosome inactivation. In undifferentiated ES cells low-level Xist expression was detected from the single active X chromosome (Xa) in male cells and on both Xa's in female cells. Upon differentiation Xist expression was detected only in female cells, in which Xist RNA colocalized with the entire inactive X chromosome (Xi). Differentiated Dnmt mutant ES cells or cells of mutant postgastrulation embryos showed aberrant patterns of Xist expression: Xist transcripts colocalized with the single X chromosome in male cells and with both X chromosomes in female cells. X-linked gene expression was not detected from chromosomes coated with Xist RNA. These results suggest that ectopic Xist expression, induced by DNA hypomethylation, may lead to the inactivation of X-linked genes. We conclude that Xist-mediated X chromosome inactivation can occur in the absence of DNA methylation, arguing that DNA methylation may be required to repress Xist expression for the maintenance of a transcriptionally active Xa. In differentiated Dnmt mutant ES cells the activation of Xist expression correlated with a dramatic increase in apoptotic bodies, suggesting that Xist-mediated X chromosome inactivation may result in cell death and contribute to the embryonic lethality of the Dnmt mutation.
386 citations
TL;DR: It is argued that the Xic is contained within 450 kb and that these sequences are sufficient for chromosome counting, choosing, and initiation of X inactivation.
331 citations
TL;DR: A linkage stud in twelve bipolar families, carrying out a single family genome search employing 193 markers indicate linkage on chromosome 4p where the marke D4S394 generated a two-point lod score under a dominant model of inheritance.
Abstract: The main clinical feature of bipolar affective disorder is a change of mood to depression or elation. Unipolar disorder, also termed major depressive disorder, describes the occurrence of depression alone without episodes of elevated mood. Little is understood about the underlying causes of these common and severe illnesses which have estimated lifetime prevalences in the region of 0.8% for bipolar and 6% for unipolar disorder. Strong support for a genetic aetiology is found in the familial nature of the condition, the increased concordance of monozygotic over dizygotic twins and adoption studies showing increased rates of illness in children of affected parents. However, linkage studies have met with mixed success. An initial report of linkage on the short arm of chromosome 11 (ref. 4) was revised and remains unreplicated. Reports proposing cosegregation of genes found on the X chromosome with bipolar illness have not been supported by others. More recently bipolar disorder has been reported to be linked with markers on chromosomes 18, 21, 16 and a region on the X chromosome different from those previously suggested. We have carried out a linkage study in twelve bipolar families. In a single family a genome search employing 193 markers indicated linkage on chromosome 4p where the marker D4S394 generated a two-point lod score of 4.1 under a dominant model of inheritance. Three point analyses with neighbouring markers gave a maximum lod score of 4.8. Eleven other bipolar families were typed using D4S394 and in all families combined there was evidence of linkage with heterogeneity with a maximum two-point lod score of 4.1 (theta = 0, alpha = 0.35).
273 citations
TL;DR: It is shown that an underacetylated X chromosome appears only after 4 days of differentiation, and only in female cells, and that selective deacetylation of H4 on specific genes would not be detected by the microscopical approach, suggesting that it is an intrinsic part of the X-inactivation process.
260 citations
TL;DR: A large gene (FMR2) transcribed distally from the CpG island at FRAXE, and down-regulated by repeat expansion and methylation is identified, which is novel, expressed in adult brain and placenta, and shows similarity with another human protein, MLLT2, expressed from a gene at chromosome 4q21 involved in translocations found in acute lymphoblastic leukaemia cells.
Abstract: Five folate-sensitive fragile sites have been identi-fied at the molecular level to date1–8. Each is characterized by an expanded and methylated trinucleotide repeat of CGG (CCG). Of the three X chromosome sites, FRAXA, FRAXE and FRAXF, the former two are associated with mental retar-dation in their expanded forms. FRAXA expansion results in fragile X syndrome due to down regula-tion of expression of the FMR1 gene, which carries the hypermutable CGG repeat in the 5′ untranslated portion of its first exon9,10. Mild mental retardation without ponsistent physical findings has been found associated with expanded CCG repeats at FRAXE11–13. We have identified a large gene (FMR2) transcribed distally from the CpG island at FRAXE, and down-regulated by repeat expansion and methylation. The gene is novel, expressed in adult brain and placenta, and shows similarity with another human protein, MLLT2, expressed from a gene at chromosome 4q21 involved in translocations found in acute lymphoblastic leukaemia (ALL) cells14,15. Identifi-cation of this gene will facilitate further studies to determine the role of its product in FRAXE associated mental deficiency.
252 citations
TL;DR: A genetic map based on microsatellite polymorphisms for the African human malaria vector, Anopheles gambiae, is presented, an integrated tool for cytogenetic, genetic, and molecular analysis.
Abstract: We present a genetic map based on microsatellite polymorphisms for the African human malaria vector, Anopheles gambiae. Polymorphisms in laboratory strains were detected for 89% of the tested microsatellite markers. Genotyping was performed for individual mosquitoes from 13 backcross families that included 679 progeny. Three linkage groups were identified, corresponding to the three chromosomes. We added 22 new markers to the existing X chromosome map, for a total of 46 microsatellite markers spanning a distance of 48.9 cM. The second chromosome has 57 and the third 28 microsatellite markers spanning a distance of 72.4 and 93.7 cM, respectively. The overall average distance between markers is 1.6 cM (or 1.1, 1.2, and 3.2 cM for the X, second, and third chromosomes, respectively). In addition to the 131 microsatellite markers, the current map also includes a biochemical selectable marker, Dieldrin resistance (Dl), on the second chromosome and five visible markers, pink-eye (p) and white (w) on the X, collarless (c) and lunate (lu) on the second, and red-eye (r) on the third. The cytogenetic locations on the nurse cell polytene chromosomes have been determined for 47 markers, making this map an integrated tool for cytogenetic, genetic, and molecular analysis.
208 citations
Journal Article•
TL;DR: The chromosomal basis of sex determination results in an inequality of gene copy number and content between males and females, but in humans the potential imbalance of gene expression from the two X chromosomes in females is resolved by inactivating one X in all the somatic tissues.
Abstract: The chromosomal basis of sex determination (i.e., XX in females, XY in males) results in an inequality of gene copy number and content between males and females. In humans (and other mammals) the potential imbalance of gene expression from the two X chromosomes in females is resolved by inactivating one X in all the somatic tissues. Beginning in the late blastocyst stage of embryonic development, one of the two X chromosomes is globally down-regulated in each somatic cell, resulting in expression from only one allele at the vast majority of X-encoded loci. While the paternal X is selectively inactive in the extraembryonic tissues (vide infra), in the embryo proper the process of X inactivation is random between the maternal and paternal X chromosomes. The result is that most females have mosaic expression of maternal and paternal alleles of X chromosome loci. The mean contribution from each chromosome is 50%, but because the process is generally random, a normal female may vary considerably from the mean. 67 refs., 1 fig.
TL;DR: The (X;1)(p11;q21) translocation is a recurrent chromosomal abnormality in a subset of human papillary renal cell carcinomas, and is sometimes the sole cytogenetic abnormality present.
Abstract: The (X;1)(p11;q21) translocation is a recurrent chromosomal abnormality in a subset of human papillary renal cell carcinomas, and is sometimes the sole cytogenetic abnormality present. Via positional cloning, we were able to identify the genes involved. The translocation results in a fusion of the transcription factor TFE3 gene on the X chromosome to a novel gene, designated PRCC, on chromosome 1. Through this fusion, reciprocal translocation products are formed, which are both expressed in papillary renal cell carcinomas. PRCC is ubiquitously expressed in normal adult and fetal tissues and encodes a putative protein of 491 aa with a relatively high content of prolines. No relevant homologies with known sequences at either the DNA or the protein level were found.
TL;DR: A dosage compensation complex was identified in the nematode Caenorhabditis elegans that reduces transcript levels from the two X chromosomes in hermaphrodites.
Abstract: In nematodes, flies, and mammals, dosage compensation equalizes X-chromosome gene expression between the sexes through chromosome-wide regulatory mechanisms that function in one sex to adjust the levels of X-linked transcripts. Here, a dosage compensation complex was identified in the nematode Caenorhabditis elegans that reduces transcript levels from the two X chromosomes in hermaphrodites. This complex contains at least four proteins, including products of the dosage compensation genes dpy-26 and dpy-27. Specific localization of the complex to the hermaphrodite X chromosomes is conferred by XX-specific regulatory genes that coordinately control both sex determination and dosage compensation.
Journal Article•
TL;DR: Examination of nonmalignant breast epithelium from two reduction mammaplasties and a mastectomy found that entire lobules and large ducts of normal breast tissue have the same X chromosome inactivated, suggesting that they are derived from the same stem cell.
Abstract: Tissue clonality can be assessed in females by analyzing the methylation status of polymorphic DNA markers on X-linked genes because extensive de novo methylation of one allele at the preimplantation stage is associated with its permanent inactivation. We applied X chromosome inactivation toward understanding human breast morphogenesis by examining the nonmalignant breast epithelium from two reduction mammaplasties and a mastectomy. We found that entire lobules and large ducts of normal breast tissue have the same X chromosome inactivated, suggesting that they are derived from the same stem cell. The regions of inactivation of a particular X chromosome do not extend over an entire breast, so that ducts and lobules with opposite chromosomes inactivated are present within a single breast. Potential relevance of these observations for malignant transformation is discussed.
Journal Article•
TL;DR: This work has attempted to uncover evidence for genetic control of X-chromosome inactivation in the human by examining X chromosome-inactivation patterns in 255 females from 36 three-generation pedigrees, to determine whether this quantitative character exhibits evidence of heritability.
Abstract: One of the two X chromosomes in each somatic cell of normal human females becomes inactivated very early in embryonic development. Although the inactivation of an X chromosome in any particular somatic cell of the embryonic lineage is thought to be a stochastic and epigenetic event, a strong genetic influence on this process has been described in the mouse. We have attempted to uncover evidence for genetic control of X-chromosome inactivation in the human by examining X chromosome-inactivation patterns in 255 females from 36 three-generation pedigrees, to determine whether this quantitative character exhibits evidence of heritability. We have found one family in which all seven daughters of one male and the mother of this male have highly skewed patterns of X-chromosome inactivation, suggesting strongly that this quantitative character is controlled by one or more X-linked genes in some families.
TL;DR: In many features, it appears that humans and, particularly, mice are the weird mammals that break more general mammalian, or even vertebrate rules.
Abstract: ▪ Abstract Marsupials and monotremes, the mammals most distantly related to placental mammals, share essentially the same genome but show major variations in chromosome organization and function. Rules established for the mammalian genome by studies of human and mouse do not always apply to these distantly related mammals, and we must make new and more general laws. Some examples are contradictions to our assumption of frequent genome reshuffling in vertebrate evolution, Ohno's Law of X chromosome conservation, the Lyon Hypothesis of X chromosome inactivation, sex chromosome pairing, several explanations of Haldane's Rule, and the theory that the mammalian Y chromosome contains a male-specific gene with a direct dominant action on sex determination. Significantly, it is not always the marsupials and monotremes (usually considered the weird mammals) that are exceptional. In many features, it appears that humans and, particularly, mice are the weird mammals that break more general mammalian, or even vertebr...
TL;DR: Double FISH experiments demonstrated that the 5S rDNA which is not sex linked is located at the NOR bearing arm close to the major ribosomal RNA genes, similar to the situation observed in Atlantic salmon.
Abstract: The karyotype of the rainbow trout is characterized by a primitive XX/XY sex-determining chromosomal system. (Thorgaard et al., 1977). In the present study using FISH we have physically linked the 5S rRNA genes to the partially undifferentiated X chromosome pair. PCR amplified 5S rDNA was used for FISH and hybridization signals indicated that the genes were duplicated, present in one acrocentric and one metacentric pair of chromosomes. After analyzing several individuals, the female metaphases showed four fluorescent signals whereas males presented only three signals. Two of the three signals obtained in males corresponded to the metacentric pair whereas the single signal was mapped to the heterochromatin that cytologically differentiates the X chromosome from the Y chromosome. Double FISH experiments demonstrated that the 5S rDNA which is not sex linked is located at the NOR bearing arm close to the major ribosomal RNA genes (5.8S, 18S and 28S), similar to the situation observed in Atlantic salmon (Pendas et al., 1994a).
TL;DR: The requirement of faf for normal oocyte development in Drosophila combined with the map location and escape from X-inactivation of DFFRX raises the possibility that the human homologue plays a role in the defects of oocyte proliferation and subsequent gonadal degeneration found in Turner syndrome.
Abstract: EST 221 derived from human adult testis detects homology to the Drosophila fat facets gene (faf) and has related sequences on both the X and Y chromosomes mapping to Xp11.4 and Yq11.2 respectively. These two loci have been termed DFFRX and DFFRY for Drosophila fat facets related X and Y. The major transcript detected by EST 221 is -8 kb in size and is expressed widely in a range of 16 human adult tissues. RT-PCR analysis of 13 different human embryonic tissues with primers specific for the X and Y sequences demonstrates that both loci are expressed in developing tissues and quantitative RT-PCR of lymphoblastoid cell lines carrying different numbers of X chromosomes reveals that the X-linked gene escapes X-inactivation. The amino acid sequence (2547 residues) of the complete open reading frame of the X gene has 44% Identity and 88% similarity to the Drosophila sequence and contains the conserved Cys and His domains characteristic of deubiquitinating enzymes, suggesting its biochemical function may be the hydrolysis of ubiquitin from protein-ubiquitin conjugates. The requirement of faf for normal oocyte development in Drosophila combined with the map location and escape from X-inactivation of DFFRX raises the possibility that the human homologue plays a role in the defects of oocyte proliferation and subsequent gonadal degeneration found in Turner syndrome.
TL;DR: The findings show that ovarian carcinomas reveal consistent chromosomal abnormalities, and further detailed studies of these regions with specific molecular genetic techniques may lead to the identification of oncogenes and/or tumor suppressor genes playing an important role in the tumorigenesis of ovarian carcinoma.
Abstract: In order to define the ability of comparative genomic hybridization (CGH) to detect and map genetic imbalances, we investigated 47 malignant ovarian tumors and 2 ovarian tumors of low malignant potential. The most common genetic changes in order of frequency included DNA gains of chromosome arms 8q (53%), 3q (51%), 20q (43%), 1p (32%), 19q (30%), 1q (28%), 12p (28%), 6p (21%), and 2q (19%). The smallest regions of overrepresentation could be defined in 3q26-qter, 8q23-qter, 1p35-pter, 12p12, and 6p21-22, respectively. Losses were detected on 18q (23%), chromosome 4 (23%), 13q (17%), and 16q (17%) with the smallest underrepresented regions on 18q22-qter, 13q21, and 16q23-qter. Also, losses of the X chromosome (19%) were detected, correlating with higher ages of the patients. Therefore, some of these X chromosome losses might be due to a well-known aging phenomenon and in these cases will be more preferably lost during cell division and tumor progression. Our findings show that ovarian carcinomas reveal consistent chromosomal abnormalities. Further detailed studies of these regions with specific molecular genetic techniques may lead to the identification of oncogenes and/or tumor suppressor genes playing an important role in the tumorigenesis of ovarian carcinomas. Genes Chromosom Cancer 16:46–54 (1996). © 1996 Wiley-Liss, Inc.
TL;DR: A novel effect in hybrids between different mouse species that manifests itself in abnormal growth of the placenta is described, which is mainly caused by abnormal development of the spongiotrophoblast of the conceptus.
Abstract: Interspecific hybridization between closely related species is commonly associated with decreased fertility or viability of F1 hybrids. Thus, in mouse interspecific hybrids, several different hybrid sterility genes that impair gametogenesis of the male hybrids have been described. We describe a novel effect in hybrids between different mouse species that manifests itself in abnormal growth of the placenta. Opposite phenotypes, that is, placental hypotrophy versus hypertrophy, are observed in reciprocal crosses and backcrosses. The severity of the phenotype, which is mainly caused by abnormal development of the spongiotrophoblast, is influenced by the sex of the conceptus. In general, placental hypertrophy is associated with increased fetal growth. Hypotrophy of the placenta frequently leads to growth impairment or death of the fetus. One of the major genetic determinants of placental growth maps to the proximal part of the mouse X chromosome.
TL;DR: The DPY-26 protein is required in the nematode Caenorhabditis elegans for X-chromosome dosage compensation as well as for proper meiotic chromosome segregation, and was shown to mediate both processes through its association with chromosomes.
Abstract: The DPY-26 protein is required in the nematode Caenorhabditis elegans for X-chromosome dosage compensation as well as for proper meiotic chromosome segregation. DPY-26 was shown to mediate both processes through its association with chromosomes. In somatic cells, DPY-26 associates specifically with hermaphrodite X chromosomes to reduce their transcript levels. In germ cells, DPY-26 associates with all meiotic chromosomes to mediate its role in chromosome segregation. The X-specific localization of DPY-26 requires two dosage compensation proteins (DPY-27 and DPY-30) and two proteins that coordinately control both sex determination and dosage compensation (SDC-2 and SDC-3).
TL;DR: It is demonstrated that a mutation in a type V collagen gene, COL5A1, results in EDS type I, and shows the involvement of L1 sequences in a constitutional chromosomal translocation.
Abstract: Ehlers-Danlos syndrome (EDS) is a genetically and pathogenetically heterogeneous group of disorders of which at least 11 types have been described. All are connective tissue disorders characterized by defects of the skin, ligaments and blood vessels with the clinical spectrum ranging from innocuous findings to lethality. Mutations in the genes encoding the major fibrillar collagen types I and III have been demonstrated in EDS types VII and IV, respectively, while mutations in the lysyl hydroxylase and ATP7A genes, with roles in collagen cross-linking, are responsible for EDS types VI and IX. The biochemical and molecular bases for the most common forms of EDS (types I, II and III) are unknown. Here, we describe a balanced translocation between chromosome 9 and an X chromosome that disrupts the minor fibrillar collagen type V gene COL5A1 in a patient with both EDS type I and hypomelanosis of Ito. The breakpoint occurs at 9q34 within COL5A1 intron 24 and interestingly, within a LINE-1 (L1) element at Xp21.1. A fusion mRNA between COL5A1 and an Alu sequence is produced, but no aberrant protein is detectable. Rather, the amount of type V collagen is reduced in the patient's fibroblasts, suggesting haploinsufficiency as a cuase of the phenotype. This demonstrates that a mutation in a type V collagen gene, COL5A1, results in EDS type I, and shows the involvement of L1 sequences in a constitutional chromosomal translocation. Because collagen type V is a heteromorphic protein in which molecules may be composed of polypeptides encoded by three COL5A genes, this suggests all three genes as candidates for mutations in EDS.
TL;DR: This work has shown that dosage compensation results in equivalent X‐linked gene expression in males (XY) and females (XX) and that four proteins are required for dosage compensation and associate with the X chromosome in males but not in females.
Abstract: Background: Dosage compensation results in equivalent X-linked gene expression in males (XY) and females (XX). In Drosophila, both X chromosomes are active in females, and the single male X must double its transcriptional activity to allow male development. Four proteins (encoded by the male-specific lethal genes) are required for dosage compensation and associate with the X chromosome in males but not in females.
Results : In this report, we focus on the maleless (MLE) protein. The MLE protein sequence contains motifs common to members of a family of RNA-dependent ATPases. We have found that association of MLE with the male X chromosome is RNase sensitive, and that mutations in the ATPase motifs affect MLE function. Overexpression of MLE or its carboxyl terminus, which includes glycine-rich repeats, reveals an RNase-sensitive affinity for all chromosome arms.
Conclusions: Our results suggest that nascent transcripts or a hypothetical RNA component of chromatin play a critical role in the biochemical mechanism of dosage compensation. The potential relationship between interaction with RNA and transcriptional control of the X chromosome suggests that the mechanism of dosage compensation is distinct from classical models for transcriptional activation.
TL;DR: Data suggest that the paternal X chromosome carries the de novo alpha-galactosidase A mutation and that uneven X inactivation is the underlying mechanism for disease expression in this novel female MZ twin pair.
Abstract: We describe two female monozygotic (MZ) twins heterozygous for Fabry disease, an X linked disorder resulting from the deficient activity of alpha-galactosidase A. While one of the twins was clinically affected, the other was asymptomatic. Enzymatic assay of alpha-galactosidase in blood leucocytes, skin fibroblasts, Epstein-Barr virus transformed lymphoid cell lines, and hair follicles of the twins and their parents confirmed the heterozygous status of the twins and indicated that Fabry disease had occurred as a result of a de novo mutation. The son of the unaffected twin sister was shown to be hemizygous. Molecular analysis of the alpha-galactosidase A gene permitted the identification of an as yet undescribed point mutation at position 10182 of exon 5 which causes an Asp to Asn substitution at codon 231. Single strand conformation polymorphism (SSCP) analysis again showed the heterozygous status of the twins and a normal pattern in their parents. The basis for the discordant expression of this d novo mutation in the twins was investigated by studying their X inactivation status. Analysis of the inactive X specific methylation at the androgen receptor gene showed unbalanced inactivation in the twins' fibroblasts and in opposite directions. While the maternally derived X chromosome was preferentially active in the asymptomatic twin, the paternal X chromosome was active in the other, affected twin and was found in her hemizygotic nephew. These data suggest that the paternal X chromosome carries the de novo alpha-galactosidase A mutation and that uneven X inactivation is the underlying mechanism for disease expression in this novel female MZ twin pair. This is the first documented case of female twins discordant for Fabry disease.
TL;DR: Data support a model for regulation of X-inactivated genes that involves at least two levels of control: (i) large chromosomal domains are placed into a transcriptionally nonpermissive state by late replication and (ii) transcription is blocked at the local level by promoter methylation.
Abstract: Cytosine methylation at promoter regions and late replication timing have both been implicated in the regulation of genes subject to X chromosome inactivation. Reported here are studies of X-linked gene replication in normal male and female cells as well as in cell hybrids that contain either a normal active X, a normal inactive X, or an inactive X chromosome that has been treated with the demethylating agent, 5-azacytidine (5aC). The relationship between replication timing and transcriptional activity was examined for XIST, XPCT, PGK1, HPRT, F9, FMR1, IDS, and G6PD, and earlier replication was generally found to be associated with increased transcriptional activity. The HPRT and G6PD genes in an untreated inactive X hybrid were among the few exceptions to this correlation in that they remain inactive, yet replicate earlier than their inactive X alleles present in normal human diploid cells. This condition of earlier replication timing may contribute to the high rates of 5aC-induced reactivation for HPRT and G6PD in this hybrid relative to other inactive X hybrids. Other anomalous cases include 5aC-induced advances in replication time for genes such as XIST and F9 whose transcription was unaltered by treatment. These and other data support a model for regulation of X-inactivated genes that involves at least two levels of control: (i) large chromosomal domains are placed into a transcriptionally nonpermissive state by late replication and (ii) transcription is blocked at the local level by promoter methylation. In addition, our observations of continued XIST expression in 5aC-treated hybrids with reactivated genes indicates that such expression is not sufficient for the maintenance of X inactivation.
University of Brescia1, University of Oslo2, Nancy-Université3, John Radcliffe Hospital4, University of Padua5, Royal Free Hospital6, Necker-Enfants Malades Hospital7, University of Haifa8, Karolinska Institutet9, University of Helsinki10, Robert Koch Institute11, Soroka Medical Center12, University of Pavia13, Casa Sollievo della Sofferenza14, University of Turin15, Leiden University16, University of Washington17, Keio University18, Boston Children's Hospital19, Mitsubishi20
TL;DR: A database (CD40Lbase) of CD40L mutations has now been established, and the resultant information, together with other mutations reported elsewhere in the literature, is presented here.
TL;DR: It is reported that the sex- and chromosome-specific binding of three of the msl proteins (MSLs) occurs in other drosophilid species, spanning four genera, and it is shown that MSL binding correlates with the evolution of the sex chromosomes.
Abstract: IN species where males and females differ in number of sex chromosomes, the expression of sex-linked genes is equalized by a process known as dosage compensation. In Drosophila melanogaster, dosage compensation is mediated by the binding of the products of the male-specific lethal (msl) genes to the single male X chromosome. Here we report that the sex- and chromosome-specific binding of three of the msl proteins (MSLs) occurs in other drosophilid species, spanning four genera. Moreover, we show that MSL binding correlates with the evolution of the sex chromosomes: in species that have acquired a second X chromosome arm because of an X-autosome translocation, we observe binding of the MSLs to the 'new' (previously autosomal) arm of the X chromosome, only when its homologue has degenerated. Moreover, in Drosophila miranda, a Y-autosome translocation has produced a new X chromosome (called neo-X), only some regions of which are dosage compensated. In this neo-X chromosome, the pattern of MSL binding correlates with the known pattern of dosage compensation.
TL;DR: Most TSC hamartomas are clonal in origin, which is an intriguing finding, since these lesions are composed of more than one cell type.
Abstract: Tuberous sclerosis (TSC) is an autosomal dominant condition characterised by tumour-like malformations (hamartomas) in the brain and other organs. A proportion of hamartomas from patients with TSC show loss of heterozygosity (LOH) for DNA markers in the region of either the TSC1 gene on chromosome 9q34 or the TSC2 gene on 16p13.3. This implies that these lesions are clonal. We have studied X-chromosome inactivation, as a marker of clonality, in 13 hamartomas from females with TSC. The hamartomas comprised five renal angiomyolipomas, three fibromas and seven other lesions. In previous studies, four of the lesions showed LOH. A polymerase chain reaction assay was used to analyse differential methylation of an HpaII restriction site adjacent to the androgen-receptor triplet-repeat polymorphism on Xq11-12. In 12 of the lesions, there was a skewed inactivation pattern with one X chromosome being fully methylated and the other unmethylated. Normal tissue showed a random pattern of inactivation. These data confirm that most TSC hamartomas are clonal in origin. This is an intriguing finding, since these lesions are composed of more than one cell type.
TL;DR: Fibroblast subclones from a biopsy at the boundary of a skin lesion in a newborn IP2 patient were isolated, and clones with either one or the other X active were identified, demonstrating that cells with the active disease-bearing X chromosome are still present in stage I skin lesions.
Abstract: Incontinentia Pigmenti 2 (IP2) is an X-linked dominantdisorder with male lethality. Affected females display acharacteristic skin eruption that evolves through fourclassic stages, frequently accompanied by dental andretinal abnormalities. Non-random (skewed)X-inactivation in peripheral blood leukocytes and infibroblasts has been observed in females with IP2;however, sample sizes have been small and methods ofanalysis varied. We have examined X-inactivation in alarge group of multigenerational IP2 families, in smallerfamilies, and in isolated cases. Ninety-eight percent ofaffected females in multigenerational IP2 pedigreesshow completely skewed patterns of X-inactivation,while only ∼10% of a normal control population isskewed. Results both in small families and in newmutation cases with subsequent segregation consistentwith Xq28 linkage are similar. Isolated cases show alower percentage (85%) of skewed affected individuals;this difference may be due to inaccurate clinicalascertainment. The parent of origin of new mutationscould be determined in 15 families; paternal newmutations were twice as common as maternal. Fibro-blast subclones from a biopsy at the boundary of a skinlesion in a newborn IP2 patient were isolated, andclones with either one or the other X active wereidentified, demonstrating that cells with the activedisease-bearing X chromosome are still present instage I skin lesions.INTRODUCTIONFamilial Incontinentia Pigmenti (IP2) is a neurocutaneousgenodermatosis which segregates as an X-linked dominant traitwith prenatal male lethality (for review, see ref. 1). In affectedfemales, its most prominent phenotypic features involve the skinand its derivatives, the eye and the central nervous system. Thisdisorder is diagnosed in affected females at or soon after birth bythe presence of a progressive erythematous and vesicular rash. Thisrash becomes sequentially verrucous, pigmented, then atrophic, andmay leave adolescents and adults with areas of linear and reticularhypopigmentation. Other manifestations include cicatricial al opecia,hypodontia or anodontia, eosinophilia (in the early stages),peripheral vascular abnormalities and cicatrization of the retina,and other secondary ocular findings. The penetrance of the diseaseapproaches 100%, but its expressivity is highly variable, evenwithin families.Linkage of IP2 to Xq28 markers was demonstrated in 1989 ( 2);subsequently, IP2 was localized more precisely to the regionsurrounding and most likely telomeric to DXS52 (3). Morerecently, the region of interest has been narrowed to Xq28 distalto Factor VIII; the highest LOD scores are found with DXS1108(θ = 0.00) (4).Non-random X inactivation in patients with IP2 has beenreported by several groups. Migeon et al. (5), using G6PDvariants and an RFLP at the HPRT locus which detects adifferentially methylated HpaII site, observed that thechromosome bearing the normal allele at the IP locus is the activeX in the majority of skin fibroblasts in affected females in threefamilies. Variable skewing in peripheral blood leukocytes wasalso observed in these families, which was unexpected since thistissue had not previously been thought to be involved in thisdisease. Analysis of G6PD isozymes showed a more randomdistribution in red blood cells, suggesting that red cell progenitorsare less likely to be affected negatively by the IP mutation thanare white cell progenitors. Other investigators (6) used somaticcell hybrid analysis to compare skin biopsies taken from normaland hyperpigmented (stage III) areas of the skin; the same Xchromosome was found to be active in every clone, regardless ofwhether it was derived from normal or hyperpigmented skin.These authors concluded that invasion of affected skin by normalcells most likely takes place at the transition from theinflammatory (I) to the verrucous (II) stage, and that their resultssupport the model that normal cells have a proliferativeadvantage. A third study ( 7), again with RFLP analysis, producedcontradictory results. Extreme skewing was found in a minorityof cases, and in most of these cases it was not possible todetermine parental origin of the inactive X chromosome; in theone fully informative family with extreme skewing, the X