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Biomedical subjects

U Tantravahi

Publications and source records attributed to U Tantravahi.

At least 37 records · Page 2Linked to original sources
PubMed1989

Prenatal diagnosis of Duchenne muscular dystrophy: prospective linkage analysis and retrospective dystrophin cDNA analysis.

The accuracy of DNA-based prenatal diagnosis of Duchenne muscular dystrophy (DMD) was determined by study of 174 families. Only 60% of families had a living affected male, and 63% had history of a single affected male. Prenatal diagnosis was declined by 47% of mothers whose DNA studies predicted a carrier risk below 2%, and none have had affected sons. Fetal risk was estimated prospectively by linkage analysis using intragenic and flanking RFLPs and retrospectively using dystrophin cDNA analysis for families whose linkage estimates lacked precision. Diagnostic accuracy was determined by comparing predictions with 40 male pregnancy outcomes. On the basis of linkage analysis, we anticipated 3.2 DMD males and observed 3.0. Retrospective cDNA analysis identified deletions in 2 of these 3 males. The combined use of linkage and cDNA deletion analysis provided a highly accurate method for prenatal diagnosis of DMD.

DNA↗
PubMed1988

Isolation of DNA sequences on human chromosome 21 by application of a recombination-based assay to DNA from flow-sorted chromosomes.

By merging two efficient technologies, bivariate flow sorting of human metaphase chromosomes and a recombination-based assay for sequence complexity, we isolated 28 cloned DNA segments homologous to loci on human chromosome 21. Subregional mapping of these DNA segments with a somatic cell hybrid panel showed that 26 of the 28 cloned DNA sequences are distributed along the long arm of chromosome 21, while the other 2 hybridize with sequences on the short arm of both chromosome 21 and other chromosomes. This new collection of probes homologous to chromosome 21 should facilitate molecular analyses of trisomy 21 by providing DNA probes for the linkage map of chromosome 21, for studies of nondisjunction, for chromosome walking in clinically relevant subregions of chromosome 21, and for the isolation of genes on chromosome 21 following the screening of cDNA libraries.

Animals↗
PubMed1987

Immunocytochemical evidence for methylation of the inactive X chromosome in human fetal oogonia.

The state of DNA methylation of the X chromosomes of human interphase oogonia from a 46,XX and a 46,XX/47,XXX fetus at 17 weeks of gestation was tested immunocytochemically with an antibody to 5-methylcytosine (5MeC). Of 1637 oogonial nuclei from the 46,XX fetal ovary, 313 (19.1%) contained Barr bodies, of which 93.6% were positive for 5MeC. Of 1780 oogonia from the 46,XX/47,XXX fetus 327 (18.4%) contained Barr bodies; 175 oogonia had one Barr body and 152 had two. Of the single Barr bodies 145 (82.8%) had positive 5MeC reaction product. Of the 152 oogonia from the XXX line, 97 (63.8%) had positive 5MeC on both Barr bodies, 35 (23%) had one positive and one negative, and 20 (13.1%) had no product on either Barr body. This immunocytochemical evidence supports the hypothesis that the DNA of the inactive X-chromosome of the human 17-week gestation oogonium is methylated.

DNA↗
PubMed1986

Repeated DNA sequences in the distal long arm of the human X chromosome.

Two DNA probes from within a single large insert from a recombinant phage-DNA library that was constructed from flow-sorted chromosomes enriched for the human X chromosome were shown to hybridize with repeated X-specific and autosomal DNA sequences. The X-chromosomal repeated sequences were assigned to the distal long arm of the X chromosome by both hybrid mapping and in situ hybridization. Fine mapping places these repeats in a region of Xq28 between DX13 (DXS15, in distal Xq28) and factor VIII (F8C, in proximal Xq28). The location of the X-specific repeats makes them potentially useful for future investigations of diseases mapping to the distal long arm of the X chromosome, such as the fragile X syndrome.

Animals↗
PubMed1986

Use of Y chromosome specific probes to detect low level sex chromosome mosaicism.

An individual found to be a true hermaphrodite at laparotomy, is presented. Cytogenetic studies which initially disclosed a 46,XX karyotype, conflicted with the anatomic presence of a testis. More extensive analysis of peripheral lymphocytes and skin fibroblasts revealed low level 46,XX/69,XXY mosaicism. DNA hybridization studies, using highly repeated Y chromosome specific probes, confirmed the rare presence of Y chromosome bearing cells. Such combined clinical and molecular studies can have an important impact on diagnosis and management of cases in which sex chromosome mosaicism is suspected.

Child, Preschool↗
PubMed1986

Physical mapping of the factor VIII gene proximal to two polymorphic DNA probes in human chromosome band Xq28: implications for factor VIII gene segregation analysis.

Genomic DNA segments for the coagulation factor VIIIc gene (F8C), which exhibits only limited restriction length polymorphism, map to the proximal region of band Xq28 by somatic cell hybridization analysis and in situ hybridization. Using somatic cell hybrids, we have obtained data which place probes DX13 (used to detect locus DXS15) and St14 (used to detect DXS52) distal to F8C, within band Xq28. Previous studies have mapped the factor IX gene (F9) and probe 52A (used to detect DXS51) proximal to F8C, in Xq26----q27 and Xq27, respectively (Camerino et al., 1984; Drayna et al., 1984; Mattei et al., 1985). Thus, the relative order of genetic marker loci in the Xq27----qter region is most likely cen-F9-DXS51-F8C-(DXS15, DXS52)-Xqter. The collection of these molecular probes is thus potentially useful in three-factor crosses of factor VIII gene segregation.

Animals↗
PubMed1985

Homogeneously staining regions (HSRs) of a rat hepatoma cell line are not early replicating.

The rat hepatoma cell line H4-IIE-C3 (H4) has homogeneously staining regions (HSRs) which contain multiple, tandemly repeated copies of ribosomal RNA (rRNA) genes. We determined the time of replication of the DNA within these HSRs autoradiographically after incorporation of [3H]thymidine and by Hoechst 33258 and Giemsa staining after 5-bromodeoxyuridine (5-BrdU) incorporation. The DNA within the H4 HSRs is not early replicating, unlike that in other HSRs. It begins replicating later than much of the other nuclear DNA, continues replicating throughout most of the S phase, and is completed 1-2 h before mitosis.

Animals↗
PubMed1985

Isolation and characterization of two repetitive DNA fragments located near the centromere of the mouse X chromosome.

Two repetitive DNA fragments located on the mouse X chromosome are described. The fragments were isolated from a lambda phage library enriched in X-chromosomal sequences by flow sorting. Both fragments, which are repeated 20 to 50 times in the genome, were mapped to the mouse X chromosome by Southern blot hybridization to DNA from hybrid cells retaining the mouse X chromosome, by dosage analysis, and by in situ hybridization to mouse chromosomes. In mouse strain C57BL/10BK, one fragment appeared to be located only on the X chromosome, while the other fragment had homologous sequences on chromosome 11 in addition to the X chromosome. The latter fragment showed DNA variants between mouse strains, which are potentially useful for mapping. Both fragments cross-hybridized to another mouse species: Mus caroli. In this species, each fragment appeared to be located on the X chromosome, indicating that some X-chromosome repetitive sequences are partially conserved. In addition, one fragment cross-hybridized to human DNA.

Animals↗
PubMed1984

A novel alteration in the structure of an activated c-myc gene in a variant t(2;8) Burkitt lymphoma.

We have characterized a variant Burkitt lymphoma in which translocation joins the immunoglobulin kappa locus on chromosome 2 to the c-myc gene on chromosome 8. This Burkitt lymphoma is especially interesting because, in contrast to the more common lymphomas that carry 8;14 translocations, it carries a translocation that involves a light chain locus and occurs 3' to and at least 20 kb downstream of the c-myc gene. Furthermore, the c-myc gene from the translocated chromosome is abnormally expressed in that there is a characteristic shift in c-myc promoter utilization and an increase in c-myc transcript. These disturbances could be explained by novel structural alterations that occur in the c-myc gene and include a duplication of a 2.5 kb segment of DNA containing the two c-myc promoters and their untranslated leader exons. Interestingly, these alterations arise at a considerable distance from the translocation breakpoint.

Base Sequence↗
PubMed1984

A strategy to reveal high-frequency RFLPs along the human X chromosome.

Fifteen human X-chromosome-specific DNA fragments, localized to particular regions of that chromosome, were used to search for restriction fragment length polymorphisms. A screening panel prepared by digesting DNA from only two females and one male with 24 restriction enzymes was sufficient to reveal two-allele polymorphisms among one-third of the probes tested. These polymorphisms, as theoretically anticipated, showed minor allele frequencies above 20%, as a rule. Such high-frequency polymorphism allowed identifying females, from pedigrees segregating three X-linked diseases, who were multiply heterozygous for polymorphic loci spread throughout the X chromosome. In addition, two of the 24 enzymes tested with these X-specific probes, Msp I and Taq I, generate fragment sizes in DNA-blotting experiments that, on average, are significantly larger than expected from nearest neighbor predicted recognition site frequencies.

Alleles↗
PubMed1984

Molecular genetic approaches to human diseases involving mental retardation.

Recombinant DNA techniques provide new approaches to the diagnosis and analysis of inherited human diseases associated with mental retardation. Examples of such diseases include the Lesch-Nyhan syndrome, phenylketonuria, the Fragile X syndrome, Down syndrome, and those associated with deletions or duplications of subchromosomal regions, e.g., the proximal short arm of human chromosome #15. For a limited but increasing number of diseases, the DNA sequences responsible for the phenotype (e.g., sequences coding for abnormal proteins) can be isolated directly. In many other cases, DNA segments mapping near genes responsible for diseases of interest can be isolated, e.g., from recombinant phage libraries enriched for specific regions of the genome by metaphase chromosome flow-sorting and then used in molecular linkage studies to "track" the abnormal gene in a pedigree. Both the necessary technology and the methods for its application continue to improve, and the impact of recombinant DNA studies in the field of mental retardation should increase markedly in the very near future.

Animals↗
PubMed1983

Identification and isolation of transcribed human X chromosome DNA sequences.

A human X chromosome specific phage library has been used as a source of X-specific genomic DNA clones which hybridize with cellular RNA. Random cDNA clones were mapped for X chromosome sequence localization and 8 were identified as hybridizing to X chromosome Hind III fragments. All eight also hybridized with autosomal Hind III fragments. The X chromosome genomic sequences corresponding to two of these cDNA clones were isolated from a phage library constructed with the Hind III endonuclease digest products of X enriched DNA. One genomic DNA segment, localized to the short area of the X, shared sequence homology with at least one region of the human Y chromosome. The methodology developed represents a rapid means to obtain a specific genomic DNA clone from a single chromosome when multiple different genomic loci homologous to an expressed DNA sequence exist.

Animals↗
PubMed1983

High resolution analysis of the timing of replication of specific DNA sequences during S phase of mammalian cells.

A new method, utilizing selective photodegradation of 5-bromo-deoxyuridine (BUdR)-substituted DNA and flow cytometry, has been developed for analyzing the timing of replication of specific DNA sequences. Chemically synchronized Chinese hamster ovary cells were given a pulse of the deoxythymidine analogue, BUdR, at different times during S phase, and flow sorted according to DNA content, before DNA isolation. Newly-replicated, unifilarly BUdR-substituted DNA was selectively degraded by treatment with 33258 Hoechst plus near UV light followed by S1 nuclease digestion; the resistant DNA was analyzed for its content of 18s and 28s rDNA or dihydrofolate reductase (DHFR) sequences via Southern blot analysis. Both the rDNA and DHFR sequences were found to replicate almost entirely during the first quarter of S phase. The approach described should have general utility for analyzing replication kinetics of specific DNA sequences in mammalian cells.

Animals↗
PubMed1983

Cytologic and molecular analysis of 46,XXq- cells to identify a DNA segment that might serve as a probe for a putative human X chromosome inactivation center.

Cloned human X chromosome-specific DNA segments, derived from a recombinant phage library enriched for the human X and previously localized to different regions of the X, were used as probes in Southern blots to confirm the nature of a deletion of the long arm of the X chromosome as del(X)(q13) in a patient with some features of Turner's syndrome and suspected from cytologic studies to have a 46,XXq- karyotype. Two dimensional scanning densitometry of autoradiograms of the Southern blots was used to quantitate hybridization of the 32P-labeled probes, reinforcing visual analysis and permitting distinction between sequences present at one or two copies per diploid genome. Once thus characterized, DNA from the patient's cells was used in quantitatively analyzed Southern blots to refine the location of an additional DNA segment, previously mapped to somewhere in the proximal part of the long arm of the X chromosome, to the juxtacentromeric region of Xq, which has been hypothesized to be critical for X-inactivation. Cloned DNA probes such as that localized to the juxtacentromeric region of Xq should be useful for evaluating this hypothesis.

Absorptiometry, Photon↗
PubMed1982

Regional localization on the human X of DNA segments cloned from flow sorted chromosomes.

Fluorescence activated sorting of chromosomes from 49,XXXXY human lymphoblasts has been used to obtain DNA enriched for the human X. This DNA was cloned in lambda phage Charon 21A to obtain a library of approximately 60,000 pfu. Phage inserts free of human highly repeated DNA sequences are localized to different regions of the human X by two independent hybridization analyses. The first utilized comparative hybridization to rodent-human hybrid cell DNA samples containing all or known portions of the human X, while the second was based on hybridization dosage to DNA samples from human cell lines differing in the number of X chromosomes or X chromosome segments. Of five unique sequence inserts tested, three were X chromosome specific and were localized to regions Xpter leads to Xcen, Xql leads to Xq22 and Xq24 leads to Xqter, respectively. The library presented here represents a highly enriched source of human X chromosome-specific DNA sequences.

Animals↗
PubMed1982

The rat XC sarcoma cell line: ribosomal RNA gene amplification and banded karyotype.

Ribosomal RNA gene amplification has been demonstrated in the rat XC sarcoma cell line. Cells of this rat line have a fairly stable karyotype with several unusual features, which have been clarified by in situ hybridization, silver staining, and binding of antibodies to 5-methylcytosine. There are one or two tiny acrocentric chromosomes containing transcriptionally active 18S and 28S ribosomal RNA (rRNA) genes. The short arm of one chromosome No. 12 has been replaced by a GC-rich, C-band negative, differentially staining region (DSR) containing an increased number of rRNA genes; most of these are transcriptionally inactive and located in regions containing highly methylated DNA. The short are of a small chromosome, probably a No. 20, has been replaced by a GC-rich, C-band negative, homogeneously staining region (HSR) that presumably represents amplification of a DNA sequence other than the 18S and 28S rRNA coding sequences. The DNA in this HSR is not enriched in 5-methylcytosine and neither is that in the HSRs of methotrexate-resistant Syrian hamster cells.

Animals↗