Showing papers on "X chromosome published in 1985"
TL;DR: It is reported that animals with maternal duplication/paternal deficiency and its reciprocal for each of two particular chromosome regions show anomalous phenotypes which depart from normal in opposite directions, suggesting a differential functioning of gene loci within these regions.
Abstract: Although both parental sexes contribute equivalent genetic information to the zygote, in mammals this information is not necessarily functionally equivalent. Diploid parthenotes possessing two maternal genomes are generally inviable, embryos possessing two paternal genomes in man may form hydatidiform moles, and nuclear transplantation experiments in mice have shown that both parental genomes are necessary for complete embryogenesis. Not all of the genome is involved in these parental effects, however, because zygotes with maternal or paternal disomy for chromosomes 1, 4, 5, 9, 13, 14 and 15 of the mouse survive normally. On the other hand, only the maternal X chromosome is active in mouse extraembryonic membranes, maternal disomy 6 is lethal, while non-complementation of maternal duplication/paternal deficiency or its reciprocal for regions of chromosome 2, 8 and 17 has been recognized. We report that animals with maternal duplication/paternal deficiency and its reciprocal for each of two particular chromosome regions show anomalous phenotypes which depart from normal in opposite directions, suggesting a differential functioning of gene loci within these regions. A further example of non-complementation lethality is also reported.
691 citations
TL;DR: Analysis of 81 unique segments derived from cloned reassociated DNA molecules has led to the identification of 4 (5%) human DNA fragments that are absent from the male patient's DNA.
Abstract: A method that allows the specific cloning of DNA fragments absent from patients homozygous or hemizygous for chromosomal deletions is described. The method involves phenol-accelerated competitive DNA reassociation and subsequent molecular cloning of appropriately reassociated molecules. The deletion DNA sample utilized in the competition was isolated from a patient with a minute interstitial deletion in the short arm of the X chromosome. Sheared DNA isolated from a male child, who was diagnosed as having Duchenne muscular dystrophy, chronic granulomatous disease, and retinitis pigmentosa, was combined in a 200-fold excess with Mbo I-cleaved DNA isolated from a 49, XXXXY human lymphoid cell line, and the mixture was subjected to a phenol-enhanced reassociation technique. Analysis of 81 unique segments derived from cloned reassociated DNA molecules has led to the identification of 4 (5%) human DNA fragments that are absent from the male patient's DNA. The 4 clones were localized, on the basis of hybridization with restriction nuclease-digested genomic DNA from a panel of human and human-rodent hybrid cell lines, into three regions surrounding band 21 of the short arm of the normal human X chromosome. These clones are potential linkage markers for the diseases affecting this boy. Each clone, as well as others obtainable by this approach, may also serve as a starting point in the eventual cloning of these three X-linked-disease loci. Extension of this approach to other loci, including human tumors potentially homozygous for small deletions, should also be possible.
440 citations
Journal Article•
TL;DR: Southern blot analysis with 20 single-copy probes led to the discovery of one (probe 754) that is missing from this patient's X chromosome and also from his total DNA, proving that he has a deletion rather than a balanced insertion.
Abstract: We are reporting a male patient who suffered from chronic granulomatous disease associated with cytochrome b−245 deficiency and McLeod red cell phenotype, Duchenne muscular dystrophy, and retinitis pigmentosa. On cytogenetic analysis, he seemed to have a very subtle interstitial deletion of part of band Xp21. Since it was impossible to know whether this material was truly deleted or inserted elsewhere in the genome, somatic cell and molecular studies were carried out. In somatic cell hybrids, the deleted X chromosome was isolated on a Chinese hamster background. Southern blot analysis with 20 single-copy probes, that had been mapped to the X short arm, led to the discovery of one (probe 754) that is missing from this patient's X chromosome and also from his total DNA. This proves that he, indeed, has a deletion rather than a balanced insertion. The results provide cytological mapping information for the X-linked phenotypes present in this patient. Furthermore, probe 754 recognizes a restriction fragment length polymorphism of high frequency that makes it the most powerful probe currently available for linkage studies with X-linked muscular dystrophy.
419 citations
TL;DR: Five DMD males are shown to exhibit deletions for one of the cloned DNA segments and at least 38 kb of surrounding DNA, which will complement the existing Xp21 probes for use in carrier detection and prenatal diagnosis of DMD.
Abstract: The Duchenne muscular dystrophy (DMD) locus has been localized to the short arm of the human X chromosome (Xp21) by detection of structural abnormalities and by genetic linkage studies A library highly enriched for human DNA from Xp21 was constructed using DNA isolated from a male patient who had a visible deletion and three X-linked disorders (DMD, retinitis pigmentosa and chronic granulomatous disease) Seven cloned DNA probes from this library and the probe 754 (refs 5, 8) are used in the present study to screen for deletions in the DNA isolated from 57 unrelated males with DMD Five of these DMD males are shown to exhibit deletions for one of the cloned DNA segments and at least 38 kb of surrounding DNA In addition, two subclones from the same region detect four restriction fragment length polymorphisms which exhibit no obligate recombination with DMD in 34 meiotic events These new DNA segments will complement the existing Xp21 probes for use in carrier detection and prenatal diagnosis of DMD Elucidation of the end points of the five deletions will help delineate the extent of the DMD locus and ultimately lead to an understanding of the specific sequences involved in DMD
373 citations
TL;DR: By the use of a series of closely linked DNA probes detecting restriction fragment length polymorphisms (RFLPs), a double crossover was detected in a Duchenne muscular dystrophy carrier and an affected male fetus was diagnosed at 12 weeks of gestation.
365 citations
TL;DR: In this article, the authors used rRNA sequences as probes to clone the region spanning the translocation breakpoint, which was then used to detect a restriction fragment length polymorphism (RFLP) which was closely linked to the DMD gene and uncovers chromosomal deletions in some male DMD patients.
Abstract: Duchenne muscular dystrophy (DMD) is an X-linked recessive disorder which affects approximately 1 in 3,300 males, making it the most common of the neuromuscular dystrophies (see ref. 1 for review). The biochemical basis of the disease is unknown and as yet no effective treatment is available. A small number of females are also affected with the disease, and these have been found to carry X;autosome translocations2,3 involving variable autosomal sites but always with a breakpoint within band Xp21 of the X chromosome (implicated by other kinds of genetic evidence as the site of the DMD lesion4–6. In these female patients the normal X chromosome is preferentially inactivated, which it is assumed silences their one normal DMD gene, leading to expression of the disease. In one such affected female the autosomal breakpoint lies in the middle of the short arm of chromosome 21 (ref. 2), within a cluster of ribosomal RNA genes7. Here we have used rRNA sequences as probes to clone the region spanning the translocation breakpoint. A sequence derived from the X-chromosomal portion of the clone detects a restriction fragment length polymorphism (RFLP) which is closely linked to the DMD gene and uncovers chromosomal deletions in some male DMD patients.
351 citations
TL;DR: An aqueous spreading procedure that permits simultaneous analysis of human chromosomes by Q-banding and indirect immunofluorescence and anticentromere antibodies from an autoimmune patient is developed and it is shown that a family of structurally related human centromere proteins is detectable only at the active centromeres.
Abstract: We developed an aqueous spreading procedure that permits simultaneous analysis of human chromosomes by Q-banding and indirect immunofluorescence. Using this methodology and anticentromere antibodies from an autoimmune patient we compared the active and inactive centromeres of an isodicentric X chromosome. We show that a family of structurally related human centromere proteins (CENP-A, CENP-B, and CENP-C) is detectable only at the active centromere. These antigens therefore may be regarded both as morphological and functional markers for active centromeres.
234 citations
TL;DR: A collection of human Y-derived cosmid clones was screened with a plasmid insert containing a member of the human X chromosome alphoid repeat family, DXZ1, and a 5500 base EcoRI fragment was found to be characteristic of a Y-specific alphoids repeat.
227 citations
TL;DR: The results confirm the predictions of the model in that when the inactivation centre is deleted from one of the X-chromosomes neither X present in a diploid cell can be inactivated, and in addition considerably further localize the position of the in activation centre on theX- chromosome.
Abstract: The predictions of a model for the initiation of X-chromosome inactivation based on a single inactivation centre were tested in a cytogenetic study using six different embryo-derived (EK) stem cell lines, each with a different-sized deletion of the distal part of one of the X-chromosomes. Metaphase chromosomes were prepared by the Kanda method from each cell line in the undifferentiated state and after induction of differentiation, and cytogenetic evidence sought for a dark-staining inactive X-chromosome. The results confirm the predictions of the model in that when the inactivation centre is deleted from one of the X-chromosomes neither X present in a diploid cell can be inactivated, and in addition considerably further localize the position of the inactivation centre on the X-chromosome.
213 citations
TL;DR: A developmental and genetic analysis of the X-linked vital locus l(1)EC7 in Drosophila melanogaster and gynandromorphic genetic mosaics shows that the gene function is autonomously essential in the eye and is not necessary in most major imaginal-disc cell derivatives with the exception of the eye disc.
Abstract: We report a developmental and genetic analysis of the X-linked vital locus l(1)EC7 in Drosophila melanogaster. The locus maps in the salivary band region 1B4-5 to 1B8-9, a part of the X chromosome previously shown to be essential for normal neural development. Certain mutant alleles at the locus can cause embryonic lethality, indicating that the function provided by the gene is essential during embryo-genesis. A developmental analysis of gynandromorphic genetic mosaics shows that: (l)the gene function is autonomously essential in the eye; (2) the gene function is essential for normal development of the optic lobes; and (3) the gene function is not necessary in most major imaginal-disc cell derivatives with the exception of the eye disc. Conclusions from the developmental analysis of a temperature sensitive allele are consistent with those from the mosaic analysis. The embryonic lethality caused by the mutant alleles and abnormalities observed in the genetic mosaics have led us to rename the locus l(1)EC7 ...
199 citations
TL;DR: Comparison of the gene maps of the human and mouse X chromosomes suggests that myelin proteolipid protein may be involved in X-linked mutations at the mouse jimpy locus and has implications for Pelizaeus-Merzbacher disease, a human inherited X- linked myelin disorder.
Abstract: Several inherited disorders in humans and in rodents result in myelin dysgenesis and a deficiency of the molecular constituents of myelin. A complementary DNA to one of the two major myelin proteins, myelin proteolipid protein (also known as lipophilin), has been used with Southern blot analysis of somatic cell hybrid DNA to map the human proteolipid protein gene to the middle of the long arm of the human X chromosome (bands Xq13-Xq22) and to assign the murine proteolipid protein gene to the mouse X chromosome. Comparison of the gene maps of the human and mouse X chromosomes suggests that myelin proteolipid protein may be involved in X-linked mutations at the mouse jimpy locus and has implications for Pelizaeus-Merzbacher disease, a human inherited X-linked myelin disorder.
TL;DR: Analysis of the recombinational behavior of fully marked chromosomes suggests that the number of recombination events on the X chromosome may be nonrandom and that the normal linkage map of this chromosome should be especially valuable in the mapping of rare X-linked diseases.
Abstract: A database useful for mapping the human X chromosome has been established. The data consist of the genotypic characterizations obtained at more than 20 DNA marker loci from a set of 38 selected families. Multilocus linkage analysis has provided an initial genetic map completely spanning the distance from the distal short arm to the distal long arm of the chromosome, for a total genetic length of at least 185 recombination units. Analysis of the recombinational behavior of fully marked chromosomes suggests that the number of recombination events on the X chromosome may be nonrandom. Linkage studies of six families that carry the mutation which causes Duchenne muscular dystrophy were combined with linkage data from a large number of normal families. This permitted mapping of the locus for Duchenne muscular dystrophy with greater precision and statistical confidence than studies in which disease families alone provided the genotypic database. This observation suggests that the normal linkage map of this chromosome should be especially valuable in the mapping of rare X-linked diseases.
TL;DR: Using their X-chromosomal probes and a set of autosomal probes, isolated and examined in an identical way, the authors found a significantly lower RFLP frequency for the X chromosome as compared to the autosomes.
Abstract: We have isolated 23 human X chromosome-specific DNA fragments from λ libraries, prepared from flow-sorted X chromosomes. To increase diagnostic potential for X-linked genetic disorders, including Duchenne muscular dystrophy (DMD), the fragments were tested for restriction fragment length polymorphisms (RFLPs) with six restriction enzymes. All fragments were regionally mapped to segments of the X chromosome with a panel of somatic cell hybrids and with human cell lines carrying unbalanced chromosomal abnormalities. Two of the isolated probes detected a high frequency RFLP. One, 754, maps between Xp11.3 and Xp21 and detects a PstI polymorphism with an allele frequency of 0.38. The other, 782, maps between Xp22.2 and Xp22.3 and reveals an EcoRI polymorphism with an allele frequency of 0.40. According to a pilot linkage study of families at risk for Duchenne muscular dystrophy, 754 gives a maximum Lod score of 7.6 at a recombination fraction of 0.03. Probe 782 lies telomeric to DMD with a maximum Lod score of 2.2 at a recombination fraction of 0.17. Using our X-chromosomal probes and a set of autosomal probes, isolated and examined in an identical way, we found a significantly lower RFLP frequency for the X chromosome as compared to the autosomes.
TL;DR: Data indicate that the 2.0 kb repeat consists of twelve alpha satellite monomers arranged in imperfect, direct repeats, and provides strong support for the hypothesis that individual human chromosomes are characterized by different alpha satellite families.
Abstract: The pericentromeric region of the human X chromosome is characterized by a tandemly repeated family of 2.0 kilobasepair (kb) DNA fragments, initially revealed by cleavage of human DNA with the restriction enzyme BamHI. We report here the complete nucleotide sequence of a cloned member of the repeat family and establish that this X-linked DNA family consists entirely of alpha satellite DNA. Our data indicate that the 2.0 kb repeat consists of twelve alpha satellite monomers arranged in imperfect, direct repeats. Each of the alpha X monomers is approximately 171 basepairs (bp) in length and is 60-75% identical in sequence to previously described primate alpha satellite DNAs. The twelve alpha X monomers are 65-85% identical in sequence to each other and are organized as two adjacent, related blocks of five monomers, plus an additional two monomers also related to monomers within the pentamer blocks. Partial nucleotide sequence of a second, independent copy of the 2.0 kb BamHI fragment established that the 2.0 kb repeat is, in fact, the unit of amplification on the X. Comparison of the sequences of the twelve alpha X monomers allowed derivation of a 171 bp consensus sequence for alpha satellite DNA on the human X chromosome. These sequence data, combined with the results of filter hybridization experiments of total human DNA and X chromosome DNA, using subregions within the 2.0 kb repeat as probes, provide strong support for the hypothesis that individual human chromosomes are characterized by different alpha satellite families, defined both by restriction enzyme periodicity and by chromosome-specific primary sequence.
TL;DR: In this article, the authors examined the frequency of new chromosomal rearrangements, that appeared only in the progeny of hybrid individuals, and found that 30 times higher mutation frequency was found in hybrid males than in hybrid females.
Abstract: Introgression of a chromosome segment from Drosophila serido into the genome of its sibling D. buzzatii brought about the release of mutator potential in the hybrids. Mutator activity was determined by examining the frequency of new chromosomal rearrangements, that appeared only in the progeny of hybrid individuals. Mutation frequency was 30 times greater in the progeny of hybrid males than in that of hybrid females. There was a remarkable influence of the D. buzzatii genetic background on the frequency of production of these new rearrangements. The appearance of a new rearrangement did not depend on the genotype of the larva that bore it, but only on that of its hybrid progenitor. Among the new rearrangements there were inversions, translocations, and duplications. The number of translocations was significantly lower than that of inversions or duplications; this last type was the most frequently recorded. The distribution of the aberrations among the four major autosomes seemed to be homogeneous, although the total number of breakpoints was significantly greater in chromosome 4 than in the others. No rearrangement was found on the X chromosome. Breakpoints within three of the four affected autosomes were not randomly distributed.
TL;DR: Probe St14 reveals one of the most polymorphic loci known to date in the human genome and should be of great use for the genetic study of three important diseases: hemophilia A, mental retardation with a fragile X chromosome, and adrenoleukodystrophy.
Abstract: A DNA fragment (named St14) derived from the human X chromosome reveals a small family of related sequences that have been mapped to the Xq26-Xq28 region by using a panel of rodent-human somatic cell hybrids. The probe detects in human DNA digested by Taq I a polymorphic system defined by a series of at least eight allelic fragments with a calculated heterozygosity in females of 80%. With Msp I, we found three additional restriction fragment length polymorphisms, each of them being defined by two alleles. These polymorphisms are also common in Caucasian populations. The genetic locus defined by probe St14 has been localized more precisely to the distal end of the X chromosome (in band q28) by linkage analysis to other polymorphic DNA markers. The results obtained suggest that the frequency of recombination is distributed very unevenly in the q27-qter region of the X chromosome, with a cluster of seven tightly linked loci in q28 showing about 30% recombination with the gene for coagulation factor IX located in the neighboring q27 band. Probe St14 reveals one of the most polymorphic loci known to date in the human genome, and 17 different genotypes have already been observed. It constitutes the best marker on the X chromosome and should be of great use for the genetic study of three important diseases: hemophilia A, mental retardation with a fragile X chromosome, and adrenoleukodystrophy.
TL;DR: Analysis of genes within the 2C-D area of the X chromosome indicates the presence of an embryonic zygotic lethal locus, as yet unidentified, which produces central nervous system and ventral hypoderm degeneration in deficiency-hemizygous embryos.
Abstract: We have conducted a genetic and developmental analysis of genes within the 2C-D area of the X chromosome. Phenotypes of 33 mutations representing nine adjacent complementation groups including eight recessive lethals and one visible homeotic mutation (polyhomeotic) are described. Germline clonal analysis of the eight zygotic lethals has revealed three types of gene requirements: (1) normal activity at two pupal lethal loci (corkscrew and C204) and one larval lethal locus (ultraspiracle) is required for normal embryogenesis; (2) normal activity at three larval lethal loci (DF967, VE651 and Pgd) is required for normal oogenesis; and (3) activity at only one locus (EA82), a larval lethal, appears to have no maternal requirement. Ambiguous results were obtained for the GF316 lethal complementation group. Analysis of mitotic figures of the pupal lethals indicates that C204 disrupts an essential mitotic function. This result correlates with the preblastoderm arrest observed among embryos derived from germline clones of C204. Embryos derived from germline clones of corkscrew (csw) exhibit a "twisted" phenotype. The recessive lethal ultraspiracle (usp) disrupts the organization of the posterior tip of the larva both zygotically and maternally: second instar usp/Y larvae derived from heterozygous usp/+ mothers possess an extra set of spiracles, whereas usp/Y embryos derived from females possessing a germline clone (usp/usp) exhibit a localized ventral defect in the ninth or posterior eighth abdominal segment. Analysis of the phenotypes of deficiency-hemizygous embryos indicates the presence of an embryonic zygotic lethal locus, as yet unidentified, which produces central nervous system and ventral hypoderm degeneration. Additional information on the genetic organization of loci within the adjacent 2E area are also described. The implications of this analysis to our understanding of the maternal of zygotic lethal loci in development are discussed.
TL;DR: Close linkage was found with the pDP34 probe (DXYS1 locus, Xq13-q21), suggesting that the gene responsible for the disease is located on the proximal long arm of the X chromosome.
Abstract: A large kindred with the X-linked dominant form of peroneal muscular atrophy (Charcot-Marie-Tooth disease) was analyzed for individual variation in the length of DNA fragments after restriction endonuclease digestion. A systematic search was performed for linkage with a series of cloned single-copy DNA sequences of known regional assignment to the human X chromosome. Close linkage was found with the pDP34 probe (DXYS1 locus, Xq13-q21), suggesting that the gene responsible for the disease is located on the proximal long arm of the X chromosome.
TL;DR: Although conventional genetic analysis of the Y chromosome is difficult, this chromosome is particularly suited to molecular analysis and may soon become the best defined human chromosome at the molecular level and may become the model for other chromosomes.
Abstract: Despite its central role in sex determination, genetic analysis of the Y chromosome has been slow. This poor progress has been due to the paucity of available genetic markers. Whereas the X chromosome is known to include at least 100 functional genetic loci, only three or four loci have been ascribed to the Y chromosome and even the existence of several of these loci is controversial. Other factors limiting genetic analysis are the small size of the Y chromosome, which makes cytogenetic definition difficult, and the absence of extensive recombination. Based on cytogenetic observation and speculation, a working model of the Y chromosome has been proposed. In this classical model the Y chromosome is defined into subregions; an X-Y homologous meiotic pairing region encompassing most of the Y chromosome short arm and, perhaps, including a pseudoautosomal region of sex chromosome exchange; a pericentric region containing the sex determining gene or genes; and a long arm heterochromatic genetically inert region. The classical model has been supported by studies on the MIC2 loci, which encode a cell surface antigen defined by the monoclonal antibody 12E7. The X linked locus MIC2X, which escapes X inactivation, maps to the tip of the X chromosome short arm and the homologous locus MIC2Y maps to the Y chromosome short arm; in both cases, these loci are within the proposed meiotic pairing region. MIC2Y is the first biochemically defined, expressed locus to be found on the human Y chromosome. The proposed simplicity of the classical model has been challenged by recent molecular analysis of the Y chromosome. Using cloned probes, several groups have shown that a major part of the Y chromosome short arm is unlikely to be homologous to the X chromosome short arm. A substantial block of sequences of the short arm are homologous to sequences of the X chromosome long arm but well outside the pairing region. In addition, the short arm contains sequences shared with the Y chromosome long arm and sequences shared with autosomes. About two-thirds of XX males contain detectable Y derived sequences. As the amount of Y sequences present varies in different XX males, DNA from these subjects can be used to construct a map of the region around the sex determining gene. Assuming that XX males are usually caused by simple translocation, the sex determining genes cannot be located in the pericentric region. Although conventional genetic analysis of the Y chromosome is difficult, this chromosome is particularly suited to molecular analysis. Paradoxically, the Y chromosome may soon become the best defined human chromosome at the molecular level and may become the model for other chromosomes.
TL;DR: Findings suggest that dosage compensation, at least at the G6PD locus, has not been well established or maintained in placental tissue and paternal X inactivation in extraembryonic lineages is not an essential feature of mammalian X dosage compensation.
Abstract: Studies of glucose-6-phosphate dehydrogenase (G6PD) in heterozygous cells from chorionic villi of five fetal and one newborn placenta show that the locus on the allocyclic X is expressed in many cells of this trophectoderm derivative. Heterodimers were present in clonal populations of cells with normal diploid karyotype and a late replicating X chromosome. The expression of the two X chromosomes was unequal, based on ratios of homodimers and heterodimers in clones. Studies of DNA, digested with Hpa II and probed with cloned genomic G6PD sequences, indicate that expression of the locus in chorionic villi is associated with hypomethylation of 3' CpG clusters. These findings suggest that dosage compensation, at least at the G6PD locus, has not been well established or maintained (or both) in placental tissue. Furthermore, the active X chromosome in these human cells of trophoblastic origin can be either the paternal or maternal one; therefore, paternal X inactivation in extraembryonic lineages is not an essential feature of mammalian X dosage compensation.
TL;DR: It is reported here that these related XX males, like the sporadic cases, contain portions of the Y chromosome.
Abstract: Human ‘XX males’ are sterile males whose chromosomes seem to be those of a normal female. About 1 in 20,000 males has a 46, XX karyotype, and most cases are sporadic, that is, they are without familial clustering1. It has long been argued that maleness in XX males may result from the undetected presence of a small, testis-determining fragment of the Y chromosome2, and there is strong evidence for this in sporadically occurring XX males3–5. Indeed, the genomes of three of four sporadic XX males tested were found to contain certain Y-specific DNA sequences6. A pedigree in which three XX males occur has been interpreted as being consistent with autosomal recessive inheritance of maleness7,8, and it has been argued that the basis of XX maleness in this family is fundamentally different from that in the sporadic cases9. However, we report here that these related XX males, like the sporadic cases, contain portions of the Y chromosome. The portion of the Y chromosome present in one of the three XX males differs from that present in the other two.
Journal Article•
TL;DR: The ornithine transcarbamylase gene and four anonymous DNA sequences map within band Xp21, flanking the presumed locus for Duchenne muscular dystrophy, as well as five different regions of the short arm of the X chromosome.
Abstract: Panels of somatic cell hybrid lines carrying various structural rearrangements of the human X chromosome short arm were analyzed with 21 X-chromosome-specific cloned DNA fragments We mapped these molecular markers to five different regions of the short arm of the X chromosome The results were confirmed by gene-dosage studies of human lymphoblasts with structurally abnormal X chromosomes The ornithine transcarbamylase gene and four anonymous DNA sequences map within band Xp21, flanking the presumed locus for Duchenne muscular dystrophy
TL;DR: It is shown that 5-aza-C causes a dramatic increase in the DNase-I sensitivity of the entire inactive X chromosome of female G. gerbillus cells and this increase in nuclease sensitivity correlates with a large shift in the time of replication of the inactive X chromosomes from late S phase to early S phase.
Abstract: We have examined the effect of 5-azacytidine (5-aza-C) induced hypomethylation of DNA on the time of replication and DNase I sensitivity of the X chromosomes of female Gerbillus gerbillus (rodent) lung fibroblast cells. Using in situ nick translation to visualise the potential state of activity of large regions of metaphase chromosomes we show that 5-aza-C causes a dramatic increase in the DNase-I sensitivity of the entire inactive X chromosome of female G. gerbillus cells and this increase in nuclease sensitivity correlates with a large shift in the time of replication of the inactive X chromosome from late S phase to early S phase. These effects of 5-aza-C on the inactive X chromosome are associated with a 15% decrease in DNA methylation. Our results indicate that DNA methylation concomitantly affects both the time of replication and the chromatin conformation of the inactive X chromosome.
TL;DR: It appears that Drosophila heterochromatin contains developmentally important genetic elements, and that a functional concomitant ofheterochromatic location is gene action at a developmental stage during which the activity of the euchromatic genome is as yet undetectable.
Abstract: We examined the behavior of an autosomal recessive maternal-effect mutation, abnormal-oocyte (abo), that is located in the euchromatin of the left arm of chromosome 2. When homozygous in females, abo results in a marked reduction in the probability that an egg produced by a mutant mother will develop into an adult. However, this probability is increased if the fertilizing sperm delivers to the egg either a normal allele of the maternal-effect gene or a specific type of heterochromatin (called ABO) that is located in small regions of the X and Y chromosome constitutive heterochromatin as well as in some autosomal heterochromatin. These regions, moreover, all react to Hoechst 33258 fluorescent dye identically and specifically. The amelioration of the maternal effect produced by this heterochromatin differs temporally from that caused by the normal allele of the euchromatic gene: the heterochromatin reduces only precellular blastoderm mortality, whereas the normal allele of the euchromatic gene reduces only postblastoderm mortality. Thus, although the genome of the preblastoderm Drosophila embryo is apparently mostly silent, the ABO-containing heterochromatin functions at this early time. Finally, preliminary data indicate that abo is but one member of a cluster of linked genes, each of which interacts with its own normal allele and with a different, locus-specific, heterochromatic factor. From these observations, it appears that Drosophila heterochromatin contains developmentally important genetic elements, and that a functional concomitant of heterochromatic location is gene action at a developmental stage during which the activity of the euchromatic genome is as yet undetectable. Some general implications of these inferences are considered.
TL;DR: Two unrelated girls who present some clinical features of severe incontinentia pigmenti (IP) with characteristic skin pigmentation have balanced de novo X/autosome translocations involving band Xp11, which suggests this band may be the site of the IP gene locus.
Abstract: We report two unrelated girls who present some clinical features of severe incontinentia pigmenti (IP), with characteristic skin pigmentation. Both have balanced de novo X/autosome translocations involving band Xp11. The coincidence of the probable de novo expression of an X-linked disorder in these two girls with translocations involving similar breakpoints on the X chromosome suggests that this band may be the site of the IP gene locus.
TL;DR: A BrdU late-labeling technique is used to determine the X-inactivation pattern in 45,X and 47,XXX lymphocytes of older women to elucidate the mechanism of X-chromosome aneuploidy in aging females and evidence is presented in favor of the former hypothesis.
Abstract: It has been known for some time that there is an association between chronological aging and X-chromosome aneuploidy in peripheral blood lymphocyte cultures from females. In an attempt to elucidate th
TL;DR: It is concluded that this housekeeping gene is subject to tissue-specific transcriptional regulation, which in turn correlates with methylation of specific sites located at and near the 3' end of the gene.
Abstract: Glucose-6-phosphate dehydrogenase (G6PD) is a ubiquitous enzyme that supplies the cell with NADPH required for a variety of reductive reactions and biosynthetic processes. Therefore, the gene G6PD, located in mammals on the X chromosome, that specifies G6PD can be regarded as a typical housekeeping gene. We have investigated the expression of human G6PD in eight different fetal and adult tissues by determining the level of enzyme activity, the level of G6PD mRNA, and the methylation pattern of the 3' end of the gene, for which we have nucleic acid probes. By combining sequence information with results of Southern blot analysis of DNA samples digested with the methylation-sensitive restriction enzyme Hpa II, we have identified five specific sites that are unmethylated in all tissues examined, a number of sites that are uniformly methylated, and a number of sites that are sometimes methylated. A subset of Hpa II sites, designated on our restriction map as H37-H55, exhibit positive correlation between degree of methylation, level of mRNA, and level of G6PD activity. A comparison of these methylation patterns with those we previously have observed in the G6PD gene on the inactive X chromosome [Toniolo, D., D'Urso, M., Martini, G., Persico, M.G., Tufano, V., Battistuzzi, G. & Luzzatto, L. (1984) EMBO J. 3, 1987-1995] indicates that different sites are associated with X-inactivation and with the regulation of G6PD on the active X chromosome. We conclude that this housekeeping gene is subject to tissue-specific transcriptional regulation, which in turn correlates with methylation of specific sites located at and near the 3' end of the gene.
TL;DR: It is demonstrated that these probes are localised at Xq27/Xq28-Xqter, close physically to the fragile site, and the importance of these data for the genetic mapping of this region of the human X chromosome is discussed.
Abstract: One of the commonest forms of X-linked mental retardation is associated with a fragile site at Xq27 on the human X chromosome which can be visualised structurally after culturing cells in folate-deficient media. Unusually, the mutation can be transmitted through a phenotypically normal male. There is already some evidence that the gene loci for G6PD and factor IX are linked to this mental retardation locus. We have followed the inheritance of a DNA sequence 52A, in fragile site families that are also informative for factor IX. We demonstrate that these probes are localised at Xq27/Xq28-Xqter, close physically to the fragile site. We did not find close linkage between 52A, factor IX, and the fragile site in the families studied despite 52A and factor IX showing linkage in normal families. We discuss the importance of these data for the genetic mapping of this region of the human X chromosome and the implication for the use of these DNA probes for clinical diagnosis.
TL;DR: The results indicated that the thickness of enamel and that of 'dentin' are increased in the teeth of 47,XYY males compared with normal controls, and that the difference in tooth size between males and females is explained by a differential growth-promoting effect of the Y chromosome compared to the X chromosome.
Abstract: Enamel thickness of the maxillary permanent central incisors and canines in 14 47,XYY males, their male and female relatives and population-control males and females were determined from radiographs. The results indicated, although not fully unambiguously, that the thickness of enamel and that of 'dentin' (distance between mesial and distal dentino-enamel junctions) are increased in the teeth of 47,XYY males compared with normal controls. Earlier results have indicated a direct growth-promoting effect of the Y chromosome on tooth growth by influencing both enamel formation and, possibly through cell proliferations, growth of dentin. The present results can be considered additional evidence for the presence of the factors within the Y chromosome controlling different growth processes. Tooth size measurements in two males with deletions of the parts of the y chromosome suggested that there may be a specific growth-promoting gene(s) in the non-fluorescent part of the long arm. It is suggested that the way of influence of the Y chromosome on the amelogenesis is regulatory, and that the difference in tooth size between males and females is explained by a differential growth-promoting effect of the Y chromosome compared to the X chromosome.
TL;DR: The XLR gene family is closely linked to the X-linked immunodeficiency described in the CBA/N mouse strain (xid) by restriction fragment length polymorphism (RFLP) analysis of DNA from mice congeneic for xid, indicating that this gene family either includes the locus defined by the xid mutation or is adjacent to it in a gene complex which may be important in lymphocyte differentiation.
Abstract: The striking number of human and murine immunodeficiency disorders which map to the X chromosome (Table 1) suggests that genes localized on this chromosome must have important roles in lymphocyte development. At least seven distinct disorders in the human and two in the mouse disrupt lymphocyte maturation, particularly that of B cells, at characteristic stages1,2. As functional genes mapping to the X chromosome in one mammal are found on the X chromosome in all other mammals3, the same genes regulating lymphocyte development are expected to be found on the X chromosome in mouse and man. Investigations into the possible mechanisms of these X-linked disorders have been hampered by the lack of molecular probes for the genes or gene products affected; because of this, and the possibility of correlating one or more of the several hundred B- or T-cell-specific genes4 with a specific mutation, we surveyed 15 different B- and T-cell-specific cDNA clones for localization to the X chromosome. We report here the characterization of one of these murine cDNA clones, which hybridizes with a large, X-linked gene family, designated XLR (X-linked, lymphocyte-regulated). We show that the XLR gene family is closely linked to the X-linked immunodeficiency described in the CBA/N mouse strain (xid)5, by restriction fragment length polymorphism (RFLP) analysis of DNA from mice congeneic for xid. This finding, together with data on the expression of the XLR locus in B cells (see accompanying paper6), indicates that this gene family either includes the locus defined by the xid mutation or is adjacent to it in a gene complex which may be important in lymphocyte differentiation.