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Biomedical subjects

L J Shapiro

Publications and source records attributed to L J Shapiro.

At least 91 records · Page 5Linked to original sources
PubMed1984

Inherited chondrodysplasia punctata due to a deletion of the terminal short arm of an X chromosome.

We studied two families with an inherited deletion of the short arm of an X chromosome (Xp) in which affected male offspring have epiphyseal stippling in infancy (chondrodysplasia punctata), nasal hypoplasia, ichthyosis, and mental retardation. The presence of ichthyosis and the apparent pattern of X-linked recessive inheritance prompted investigation of the short arm of the X chromosome through studies of genetic markers and focused cytogenetic analysis. Biochemical studies suggested that there was a deletion of three genes previously mapped to the X-chromosome short arm, including the steroid sulfatase locus, the Xg locus, and the M1C2X locus. Prometaphase chromosomes demonstrated a deletion of Xp at p22.32 in the affected boys, in their obligate-carrier mothers, and in 11 of 25 women at risk as potential carriers. The women carrying the Xp deletion had normal gonadal function and fertility but were shorter than the noncarriers in their families (P less than 0.00001). These findings have implications for the genetic organization of this portion of the human X chromosome and demonstrate that small cytogenetic abnormalities may account for disorders with apparent mendelian patterns of inheritance.

Adolescent↗
PubMed1984

Isolation of genomic clones homologous to transcribed sequences from human X chromosome.

Several X chromosome DNA clones homologous to transcribed sequences were isolated from a human X chromosome library. The clones were selected for their ability to hybridize either with 32P-labeled human cDNA in the presence of an excess of unlabeled human repetitive DNA or with mouse fibroblast cDNA. The X chromosome specificity of these sequences was demonstrated by two criteria: A dosage effect was seen when the clones were hybridized to Southern blots of DNA from 1X and 5X cells, and they hybridized to DNA from mouse-human hybrid cells containing only the human X chromosome. The presence of transcribed sequences in these X clones was detected by hybridization with mouse cDNA or with human cDNA in the presence of unlabeled human repetitive sequences, by identifying restriction fragments which hybridize with cDNA but not with human repetitive DNA, and by hybridization with poly A+ RNA on Northern blots. These clones were mapped on the human X chromosomes using a panel of mouse-human somatic cell hybrids carrying various translocated human X chromosomes.

Cloning, Molecular↗
PubMed1984

Differential methylation of hypoxanthine phosphoribosyltransferase genes on active and inactive human X chromosomes.

Previous theoretical considerations and some experimental data have suggested a role for DNA methylation in the maintenance of mammalian X chromosome inactivation. The isolation of specific X-encoded sequences makes it possible to investigate this hypothesis directly. We have used cloned fragments of the human hypoxanthine phosphoribosyltransferase (HPRT) gene and methylation-sensitive restriction enzymes to study methylation patterns in genomic DNA of individuals with different numbers of X chromosomes and in somatic cell hybrid lines containing human X chromosomes that are either active or inactive or have been reactivated by treatment with 5-azacytidine. The results of these analyses show that there is hypomethylation of active X chromosomes relative to inactive X chromosomes in the 5' region of this gene. In the middle region of the gene, however, a site that is consistently undermethylated on inactive X chromosomes was identified. Taken together, the data suggest that the overall pattern of methylation, rather than methylation of specific sites, plays a role in the maintenance of X chromosome inactivation.

Base Sequence↗
PubMed1984

Frequency of reactivation and variability in expression of X-linked enzyme loci.

A mouse-human cell hybrid clone retaining an inactive human X chromosome was treated with 5-azacytidine. Following treatment, expression of the X-linked enzyme markers, hypoxanthine-guanine phosphoribosyltransferase (HPRT), glucose-6-phosphate dehydrogenase (G6PD), phosphoglycerate kinase (PGK), and alpha-galactosidase A (GLA) was examined. Results presented here show that 45 of the 62 clones positive for human HPRT expressed human GLA, while only four of 68 clones negative for human HPRT expressed human GLA. These results strongly suggest that there is coordinate reactivation of GLA and HPRT. Reactivated expression of G6PD was studied in detail. The studies show that 5-azacytidine can induce heritable changes in the inactive human X chromosome resulting in the expression of G6PD activity at a level lower than that from an active human X chromosome.

Animals↗
PubMed1984

Recombinant DNA in medicine.

Studies in bacteria and bacterial viruses have led to methods to manipulate and recombine DNA in unique and reproducible ways and to amplify these recombined molecules millions of times. Once properly identified, the recombinant DNA molecules can be used in various ways useful in medicine and human biology. There are many applications for recombinant DNA technology. Cloned complementary DNA has been used to produce various human proteins in microorganisms. Insulin and growth hormone have been extensively and successfully tested in humans and insulin has been licensed for sale. Mass production of bacterial and viral antigens with recombinant DNA technology is likely to provide safe and effective vaccines for some disorders for which there is no prevention. The cloned probes for the human alpha- and beta-globin loci, for specific disease genes, such as the Z allele of alpha-antitrypsin, and for random genomic sequences are proving useful for prenatally diagnosing human genetic disorders and preventing their clinical consequences.

Bacterial Infections↗
PubMed1984

The cell surface antigen locus, MIC2X, escapes X-inactivation.

Recently, it was shown that the cell surface antigen defined by the monoclonal antibody 12E7 is expressed by both the human X and Y chromosomes; the gene loci on the X and Y chromosomes are referred to as MIC2X and MIC2Y, respectively. It was also shown that MIC2X is located in the region Xp22.3----Xpter and MIC2Y is in the region Ypter-Yq1.1. Here, we show that MIC2X escapes X-inactivation on structurally normal and abnormal inactive human X chromosomes.

Animals↗
PubMed1984

The steroid sulfatase locus on structurally abnormal inactive X chromosomes is expressed.

In mammalian somatic cells, sex-chromosome dosage compensation is achieved by random inactivation of one of the two X chromosomes. The Xg blood group antigen (Xg) and steroid sulfatase (STS) loci on the distal end of the short arm of the X chromosome have been shown to escape this inactivation. However, it has been reported that on structurally abnormal inactive X chromosomes Xg and STS are inactivated. This discrepancy requires further consideration since whatever process accounts for the lack of inactivation of these loci on structurally normal, inactive X chromosomes might be anticipated to be operative on structurally abnormal, inactive X chromosomes. To investigate this issue, we examined the expression of STS activity in mouse-human somatic-cell hybrids retaining two different, deleted, inactive human X chromosomes. These studies provide evidence for lack of inactivation of STS on structurally abnormal, inactive X chromosomes.

Animals↗
PubMed1982

Differential expression of steroid sulphatase locus on active and inactive human X chromosome.

The X chromosome in mammalian somatic cells is subject to unique regulation--usually genes on a single X chromosome are expressed while those on other X chromosomes are inactivated. The X-locus for steroid sulphatase (STS; EC 3.1.6.2), the microsomal enzyme that catalyses the hydrolysis of various 3 beta-hydroxysteroid sulphates, is exceptional because it seems to escape inactivation. Evidence for this comes from fibroblast clones in females heterozygous for mutations that result in a severe deficiency of this enzyme in affected males; all clones from these heterozygotes have STS activity, and enzyme-deficient clones that are expected if the locus were subject to inactivation, have not been found. Further evidence that the STS locus escapes inactivation is that the human inactive X chromosomes contributes STS activity to mouse-human hybrid cells. On the basis of these hybrid studies the STS locus has been mapped to the distal half of the short arm (p22-pter) of the human X chromosome. Although the STS locus on both X chromosomes in human female cells is expressed, quantitative measurements of STS activity in males and females do not accurately reflect the sex differences in number of X chromosomes (Table 1). The ratio of mean values for normal females to that of normal males is greater than 1:1 but less than the ratio of 2:1 expected if STS loci on all X chromosomes were equally expressed. The incomplete dosage effect suggests that the STS locus on the inactive X chromosome might not be fully expressed. To test this hypothesis, we examine two heterozygotes for X-linked STS deficiency who were also heterozygous for the common electrophoretic variants of glucose-6-phosphate dehydrogenase (G6PD A and B). Studies of fibroblast clones from these females provide evidence, presented here, for differential expression of STS loci on the active and inactive X chromosome.

Dosage Compensation, Genetic↗
PubMed1982

Cell cycle-specific reactivation of an inactive X-chromosome locus by 5-azadeoxycytidine.

Three cytidine analogs containing modifications in the 5-position of the cytosine ring (5-azacytidine, 5-aza-2'-deoxycytidine and pseudoisocytidine) induced the expression of human hypoxanthine/guanine phosphoribosyltransferase (IMP; pyrophosphate phosphoribosyltransferase, EC 2.4.2.8) gene (HPRT) from a structurally normal inactive human X chromosome retained in a mouse-human somatic cell hybrid. Between 0.1% and 8% of the cells surviving treatment with these analogs were able to form colonies in selective medium (hypoxanthine/aminopterin/thymidine/glycine medium), but two other analogs, 5-fluoro-2'-deoxycrytidine and 5.6-dihydro-5-azacytidine, did not induce HPRT expression. The inactive X chromosome present in the hybrid, was found to be late replicating, and experiments with synchronized cells showed that the induction of HPRT expression by 5-aza-2'-deoxycytidine occurred maximally in cells treated in the latter half of the S phase. Two division cycles were required after analog treatment for the highest frequency of expression of the induced gene. Because these analogs are powerful inhibitors of the methylation of cytosine residues in DNA, the results imply that demethylation of specific DNA sequences may be required for the reexpression of human HPRT.

Animals↗
PubMed1982

Transformation with DNA from 5-azacytidine-reactivated X chromosomes.

It has been shown that 5-azacytidine (5-Aza-Cyd) can reactivate genes on the inactive human X chromosome. It is assumed that the 5-Aza-Cyd acts by causing demethylation of the DNA at specific sites, but this cannot be demonstrated directly without a cloned probe. Instead, we have utilized the technique of DNA-mediated transformation to show that the 5-Aza-Cyd-induced reactivation occurs at the DNA level. DNAs from various mouse-human or hamster-human hybrid cell lines, deficient for mouse or hamster hypoxanthine phosphoribosyltransferase (HPRT, EC 2.4.2.8) and varying in whether they contained either an active or inactive human X chromosome, were used in transformation of HPRT- cells. DNA from the active human X chromosome-containing cell lines yielded HPRT+ transformants, whereas DNA from the inactive X chromosome-containing cells lines did not. The inactive X chromosomal DNA was able to transform thymidine kinase-deficient mouse cells, indicating that the DNA solution was normal. These results confirm that inactivation of the X chromosome involves a DNA modification. Furthermore, DNAs from three cell lines with a 5-Aza-Cyd-reactivated X chromosome also transform HPRT- cells, demonstrating that the 5-Aza-Cyd has altered the DNA structure and supporting the idea that methylation plays a role in X chromosome inactivation.

Animals↗
PubMed1982

Placental steroid deficiency: association with arylsulfatase A deficiency.

A family with an obstetric history consistent with placental sulfatase deficiency has X-linked ichthyosis. Steroid sulfatase deficiency was confirmed in placenta, leukocytes, and cultured skin fibroblasts of affected males; arylsulfatase A diminution was also observed in these tissues of both affected males and 2 generations of related females. No symptoms of metachromatic leukodystrophy are present in any family members. In this family, placental sulfatase deficiency, and arylsulfatase A pseudodeficiency are nonallelic.

Alleles↗