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S T Warren

Publications and source records attributed to S T Warren.

108 records · Page 6Linked to original sources
PubMed1987

The fragile X site in somatic cell hybrids: an approach for molecular cloning of fragile sites.

Fragile X syndrome is a common form of mental retardation associated with a fragile site on the human X chromosome. Although fragility at this site is usually evident as a nonstaining chromatid gap, it remains unclear whether or not actual chromosomal breakage occurs. By means of somatic cell hybrids containing either a normal human X or a fragile X chromosome and utilizing two genes that flank the fragile site as markers of chromosome integrity, segregation of these markers was shown to be more frequent if they encompass the fragile site under appropriate culture conditions. Hybrid cells that reveal marker segregation were found to contain rearranged X chromosomes involving the region at or near the fragile site, thus demonstrating true chromosomal breakage within this area. Two independent translocation chromosomes were identified involving a rodent chromosome joined to the human X at the location of the fragile site. DNA analysis of closely linked, flanking loci was consistent with the position of the breakpoint being at or very near the fragile X site. Fragility at the translocation junctions was observed in both hybrids, but at significantly lower frequencies than that seen in the intact X of the parental hybrid. This observation suggests that the human portion of the junctional DNA may contain part of a repeated fragility sequence. Since the translocation junctions join heterologous DNA, the molecular cloning of the fragile X sequence should now be possible.

Animals↗
PubMed1985

Linkage and recombination between fragile X-linked mental retardation and the factor IX gene.

Linkage analysis on a family with fragile X-linked mental retardation was performed using a Taq 1 restriction fragment length polymorphism detected by a cloned human coagulation factor IX cDNA. Two affected brothers in this sibship were found to have different factor IX RFLP alleles, indicating a recombinational event occurred between the two genes. Our data therefore indicate that the gene responsible for fragile X-linked mental retardation is not as tightly linked to the factor IX gene as the previously published data may suggest.

Alleles↗
PubMed1984

Isolation and characterization of human factor IX cDNA: identification of Taq I polymorphism and regional assignment.

Hemophilia B or Christmas disease is an X-linked condition caused by absent or reduced levels of functional coagulation factor IX. Based upon the peptide sequence of bovine factor IX, we synthesized a 17-base pair oligonucleotide probe to screen a human liver cDNA library. A recombinant clone was identified with a 917-nucleotide insert whose sequence corresponds to 70% of the coding region of human factor IX. This factor IX cDNA was used to probe restriction endonuclease digested human DNA to identify a Taq I polymorphism associated with the genomic factor IX gene as well as to verify that there is a single copy of this gene per haploid genome. The factor IX cDNA was also used to map the locus for factor IX to a region from Xq26 to Xqter. The cloning of human factor IX cDNA and identification of a Taq I polymorphism and its regional localization will provide a means to study the molecular genetics of hemophilia B and permit linkage analysis with nearby loci.

Amino Acid Sequence↗
PubMed1984

Expression of fragile X chromosome in human-rodent somatic cell hybrids.

The fragile X chromosome, associated with a common form of X-linked mental retardation, is cytologically observed most often as a gap or fragile site near the distal end of the long arm in band Xq28. Expression of this site is variable and dependent upon lowered thymidylate pools. In order to examine the behavior of this fragile site in a foreign genetic background, interspecific somatic cell hybrids were isolated from crosses of hamster cells and lymphoblastoid cells derived from male patients with fragile X-linked mental retardation. Three hybrid cell lines containing the human X chromosome were analyzed. Following induction with 5-fluorodeoxyuridine, all three hybrids expressed the fragile site in approximately 10% of the metaphases examined. Our data indicate that expression of the fragile site in band Xq27 is dependent neither on the integrity of the human genome nor on the expression of human autosomal genes.

Animals↗
PubMed1982

Evaluation of the carcinogenic potential of 2,4-dinitrofluorobenzene and its implications regarding mutagenicity testing.

Tumor promoters are compounds which dramatically enhance the appearance of tumors when chronically applied after an initiating dose of a carcinogen. Initiators are generally considered mutagens while promoters have previously been shown not to induce either DNA damage or mutations. 2,4-Dinitrofluorobenzene (2,4-DNFB), a compound used in the identification of N-terminal amino acids of polypeptides, had been previously reported to be a tumor promoter in mouse skin, while other investigators have found it to be a mutagen in bacteria and yeast. To investigate this apparent discrepancy, we chose to study the carcinogenic potential of 2,4-DNFB utilizing various methods available in V79 Chinese hamster cells. 2,4-DNFB exposure did not result in any unscheduled DNA synthesis a measure of DNA excision repair, nor did it increase the frequency of sister chromatid exchanges in V79 cells either in the presence or absence of rat liver postmitochondrial supernatant (S-15). Forward mutations in V79 cells, either to ouabain or 6-thioguanine resistance, were not induced by 2,4-DNFB, in the presence or absence of S-15. 2,4-DNFB was, however, able to induce reversions in methionine-requiring E. coli auxotrophs in a dose-dependent fashion. Phylogenetic differences between lower organisms and mammals may account for this discordance. 2,4-DNFB was found to inhibit metabolic cooperation, in a dose dependent manner, in V79 cells. This property has previously been shown to be correlated with tumor promoting ability in mouse skin. Therefore, we conclude that the carcinogenic potential of 2,4-DNFB might reside in its ability as a tumor promoter and not as a carcinogenic initiator. Furthermore, these studies serve to illustrate the need for caution when extrapolating bacterial data for risk assessment in humans.

Animals↗
PubMed1981

Familial occurrence of congenital pulmonary lymphangiectasis. Genetic implications.

Congenital pulmonary lymphangiectasis (CPL) is a rare, generalized disease of the lung, consisting of lymphatic cysts in the subpleural and interlobular connective tissue. This disorder typically manifests a clinical picture of acute respiratory distress with cyanosis shortly after birth, with death occurring in the neonatal period. Several cases of this disorder have been described in the literature, but there has been no family with more than one affected child. We report the first instance, to our knowledge, of familial cases of CPL, which raises an important question regarding a possible genetic component in this disorder. The implications of this are discussed.

Female↗
PubMed1981

Isolation and characterization of a UV-sensitive hypermutable aphidicolin-resistant Chinese hamster cell line.

Aphidicolin is a specific inhibitor of DNA polymerase alpha and blocks DNA synthesis in vivo. The inhibition of purified alpha-polymerase has been shown to be competitive with dCTP but not with the other three deoxynucleoside triphosphates (dNTPs). In order to study the various roles that the alpha-polymerase might play in DNA replication and/or repair, we have attempted to isolate Chinese hamster V79 cells that are resistant to aphidicolin. Four resistant mutants were isolated from BrdU--black light- and UV-mutagenized cells. None of the mutants isolated contains an alpha-polymerase that is resistant, in crude extract measurements, to aphidicolin. Three mutants isolated, however, were found to be resistant to araC. Two mutants tested were found to be sensitive to cytidine and have elevated levels of dCTP or all 4 dNTPs. These results indicate that they are nucleotide pool mutants instead of alpha-polymerase mutants. One mutant, aphr-4, is characterized by the following: (1) high level of dCTP; (2) thymidine (or CdR, UdR) auxotrophic; (3) sensitive to thymidine (and AdR, GdR); (4) slow-growing; (5) cytidine sensitive; (6) UV sensitive and hypermutable at the ouabain-resistant locus; and (7) a ninefold increase in frequency of chromatid gaps and breaks when cells are exposed to BrdU-containing medium. Revertants of aphr-4 which are partially aphidicolin-resistant and retain the first three characteristics listed above, but not the others, have been isolated. The appearance of this type of revertant indicates that either aphr-4 or its "revertant" is a double mutant.

Animals↗
PubMed1981

Elevated spontaneous mutation rate in Bloom syndrome fibroblasts.

The rates of spontaneous mutation to 6-thioguanine resistance were determined in fibroblasts derived from normal and two Bloom syndrome individuals (GM 2548 and GM 1492). Two methods were utilized to determine the rates. Method I obtained the spontaneous mutation rate from the increase in the mutation frequency of a cell population in logarithmic-phase growth over 10 days. The two Bloom syndrome strains had spontaneous mutation rates of 16 X 10(-6) and 17 X 10(-6) mutations per cell per generation, whereas two normal strains had rates of 1.5 X 10(-6) and 1.1 X 10(-6). Method II utilized fluctuation analysis to measure the rate of spontaneous mutation. This method resulted in rates of 19 X 10(-6) and 23 X 10(-6) mutations per cell per generation in Bloom syndrome cells, compared to rates of 4.6 X 10(-6) and 4.9 X 10(-6) in the control strains. These data suggest that Bloom syndrome may be a mutator mutation, a previously unrecognized phenomenon in humans, and that an elevated spontaneous mutation rate in vivo may be responsible for the clinical phenotype of primordial dwarfism and increased cancer incidence.

Abnormalities, Multiple↗
PubMed1975

Genetic variation in Nigeria. I. The genetics of phenylthiourea tasting ability.

Phenylthiourea (PTC) taste sensitivity thresholds have been measured for 2,013 Nigerians using a modified sorting technique. The frequency of non-tasters was observed to be 12.5% and the t gene frequency was 0.354. There was a significant difference between the sexes at the 0.01 level for the overall population. However, when the data are analyzed according to the geographical origin of the subject, the sex difference is found only in one of three geographical regions. Also, there may be geographical influences on PTC taste sensitivity, although this was not statistically significant. The estimates reported in this population differ considerably from some of the previously published estimates for black populations.

Adolescent↗
PubMedDate not supplied

Strategy for molecular cloning of the fragile X site DNA.

Fragile X syndrome is a common form of mental retardation associated with a fragile site on the human X chromosome. We have recently demonstrated that the fragile X chromosome, when isolated within a somatic cell hybrid, often participates in translocations involving rodent chromosome arms. Cytogenetic and molecular evidence strongly suggests that the human breakpoint of these translocations is within the fragile X sequence. Hence, the joining of heterologous DNA (i.e. from two species) may permit the molecular cloning of the fragile X site. We describe here the cloning approach employed to enhance the isolation of interspecific chromosome translocation junctions. The human portion of the translocation junction should be derived from the fragile X site sequence.

Animals↗
PubMedDate not supplied

Fragile X syndrome: a hypothesis regarding the molecular mechanism of the phenotype.

Among all the human chromosomal fragile sites currently recognized, the fragile site mapping to Xq27.3 is the only one associated with an abnormal phenotype. This phenotype, referred to as the Martin-Bell or fragile X syndrome, has mental retardation as its most important manifestation. We propose that this site is associated with an abnormal phenotype due its location on the X chromosome, particularly it's proximity to the q telomere. Thus, if an in vivo break should occur with loss of Xq28 in the fra(X) male, the cell would be nullisomic for the genes distal to the fragile site. Similarly, a female cell would be functionally nullisomic if the break occurred on the active X. Breakage and loss of genetic material at other fragile sites either would have no impact due to complementation by homologous genes or would be lethal if X-linked with a significant deletion (i.e. fra(Xq22]. This leads to the proposal that the fragile X syndrome is due to mosaic nullisomy of distal genes. We describe below the implications of this model and a means to test this hypothesis.

Chromosome Deletion↗
PubMedDate not supplied

Intragenic probe used for diagnostics in fragile X families.

The intragenic (FMR-1) probe pE5.1 was used for DNA analysis in fragile X families. With this probe fragments of altered size can be detected in female carriers, affected individuals and transmitting males. The length of the altered fragments was found to vary from one generation to another as well as between sibs. This instability of the DNA detected by pE5.1 was also seen in peripheral blood within single individuals. These phenomena are illustrated by 4 exemplary families segregating the fragile X syndrome. We demonstrate the diagnostic contribution of intragenic analysis to carrier detection as well as the identification of normal transmitting males carrying premutations. One of the families illustrates the passage of a premutation to a male through 2 generations.

DNA↗
PubMedDate not supplied

In vitro assay for tumor promoters and anti-promoters.

Tumor promoters and anti-promoters have been shown to modify the induction of ornithine decarboxylase, the production of plasminogen activator, and the recovery of induced mutations. Data were presented to show that the recovery of mutagen-induced ouabain-resistant mutations in cultured Chinese hamster cells is increased with a tumor-promoter treatment and reduced by anti-promoter treatments. The results suggest that many induced mutations can either be repressed or derepressed by promoters or anti-promoters. The results also support the hypothesis that tumor initiation is due to a mutagenic event, while tumor promotion is the result of an epigenetic process involving cyclic nucleotide modulation of gene expression.

Animals↗