Search PubMed⌕ Search

Biomedical subjects

B N White

Publications and source records attributed to B N White.

At least 55 records · Page 3Linked to original sources
PubMed1987

Carrier detection in the hemophilias.

The subject of carrier detection in the hemophilias has received new impetus in the past several years. Treatment complications arising from clotting factor concentrates have become more evident and earlier prenatal diagnosis and new genetic markers for the clotting factor genes have focused interest on this area. Until now, carrier diagnosis has relied upon standard pedigree analysis and clotting factor assays. The results obtained using these methods are probabilistic, and the coagulation tests are unavoidably influenced by the effects of random X chromosome inactivation and the inherent variability of the methods involved. With the cloning and characterization of both factor IX and factor VIII genes, has come the capability of using gene analysis to diagnose the carrier state. This usually involves the detection of restriction fragment length polymorphisms (RFLPs) and their use as linked markers for the defective clotting factor gene. In hemophilia A, the combined use of three intragenic RFLPs and two closely linked, highly polymorphic extragenic markers will make carrier information available to approximately 90% of kindred. In hemophilia B, phenotypic analysis has been complicated by the more heterogeneous expression of the gene defect. To date, five intragenic and one closely linked RFLP have been reported, as well as two protein polymorphisms detectable by monoclonal antibody immunoassays. With the combined use of these genetic markers it is likely that accurate carrier assignment will be available to more than 80% of hemophilia B families.

Female↗
PubMed1987

Recombination between the factor VIII gene and the DXS52 locus gives the most probable genetic order as centromere-fra(X)-DXS15-DXS52-F8C-telomere.

The linkage relationship between the factor VIII gene (F8C) and the DXS52 locus was examined in 8 families. Two recombinations were identified in 35 informative meioses (Zmax = 5.67; theta = 0.05), one in a family with hemophilia A, the other in a family with the fra(X) syndrome. Based on the latter recombination, the most probable order of loci was determined to be centromere-fra(X)-DXS15-DXS52-F8C-telomere. When these data are added to those reported previously the most probable genetic distance between F8C and DXS52 is 3 cM (Z = 14.62). Identification of these and other recombinations suggests that the use of DXS52 as a genetic marker for carrier detection and prenatal diagnosis of hemophilia A has an error rate between 3-5%.

Chromosome Fragility↗
PubMed1987

A DNA marker closely linked to the factor IX (haemophilia B) gene.

We have isolated a DNA segment, pX58dIIIc, from an X-chromosome library which identifies an SstI restriction fragment length polymorphism (RFLP) at locus DXS99. Linkage analysis in six informative families has shown that the DXS99 locus lies close to the factor IX gene (F9). No recombination was detected between these loci in 39 informative meioses (Z = 9.79, theta = 0.0). Therefore, DXS99 will be useful as a DNA marker for the assessment of carrier status in families with haemophilia B where intragenic markers are not informative. Heterozygosity at DXS99 is approximately 50% and, in conjunction with the RFLPs at F9, 90% of females at risk for being haemophilia B carriers should be diagnosed.

Factor IX↗
PubMed1987

Linkage analysis of multiple endocrine neoplasia type 2A (MEN-2A) and three DNA markers on chromosome 20: evidence against synteny.

Members of four families in which multiple endocrine neoplasia type 2A (MEN-2A) is segregating were genotyped for three chromosome #20 DNA markers. Close linkage is excluded for the genetic locus of MEN-2A (MEN2A) with each marker locus tested. Using multipoint analysis, the MEN2A locus was excluded from a region 32.5 cM in length encompassing D20S5 and D20S6, two loci that previously had been mapped to the chromosome 20p12.2 region containing the putative deletion associated with MEN-2. In total, we excluded approximately 90.5 cM of chromosome #20 as a possible location of the MEN2A locus. The data from this study do not support increased recombination on the short arms of chromosome #20 and were insufficient to support heterogeneity of MEN-2A as possible explanations for failure to detect linkage between MEN2A and D20S5 or D20S6.

Chromosome Banding↗
PubMed1987

Evidence for unequal crossing-over as the mechanism for amplification of some homogeneously staining regions.

The mechanism of DNA amplification in homogeneously staining regions (HSR) was studied in the human melanoma cell line MeWo. Three karyotypically distinguishable cell types within this cell line contain HSR on four different chromosomes, but all HSR contain the same amplified sequences derived from the short arm of chromosome #15. We examined metaphases of MeWo cells from different passages for changes in the length and location of the HSR. In addition, we examined the replication patterns of the HSR sequences and the organization of repeated sequences within these structures. We found that variation in the lengths of the HSR was due to fewer or more copies of a unit that consisted of a later-replicating, distamycin A/DAPI-positive block and active nucleolar organizing regions (NOR). Lateral asymmetry studies suggested that the satellite DNA sequences that are present within the HSR are organized in large inverted repeats. This organization would account for the pairing in both orientations with exchanges resulting in the types of derivative chromosomes observed. The frequency of sister chromatid exchanges (SCE) within the HSR was increased over other chromosomal regions and four examples of unequal SCE within the HSR, with prominent looping out of the longer chromatids, were seen. These results support a model of unequal SCE, rather than saltatory replication for the amplification of DNA sequences in these HSR.

Cell Line↗
PubMed1987

Cloning and 5' end nucleotide sequences of two juvenile hormone-inducible vitellogenin genes of the African migratory locust.

Screening of lambda libraries prepared with locust (Locusta migratoria) genomic DNA yielded overlapping clones containing two complete vitellogenin genes, designated A and B, along with extensive 3'- and 5'-flanking sequences. Genes A and B are about 12 kb and 10.5 kb long, respectively, and both hybridize on Northern blots with 6300-nucleotide RNAs previously identified as vitellogenin mRNAs. Each gene contains a large intron near the 5' end and must also contain other introns. Repetitive "Lm1 elements," similar to the human Alu repetitive DNA elements, and other repeated sequences occur within the large intron and in the 3'- and 5'-flanking regions of each gene. Southern blots showed no cross-hybridization between the major portions of mRNA-coding sequences of genes A and B. DNA sequences have been determined for the 5' terminal exons and flanking regions of both genes. Both genes contain short (56-58 nucleotide) 5' leader exons, which, unlike the rest of the coding region, are highly conserved in sequence (87% identical) and code for amino acids that resemble the amino-terminal sequences of vertebrate vitellogenins. The upstream 5'-flanking sequences of the two genes contain several short stretches of similarity that may be involved in juvenile hormone regulated expression.

Animals↗
PubMed1987

Identification of restriction-fragment-length polymorphisms in genomic DNA of the lesser snow goose (Anser caerulescens caerulescens).

A genomic library of partially EcoRI-digested DNA from the lesser snow goose, Anser caerulescens caerulescens, was constructed in the phage vector Charon 4. Phage containing only unique sequences were identified by screening plaques with 32P-labeled genomic DNA. Restriction-fragment-length polymorphisms (RFLPs) were identified by probing DNA from 11-13 male birds from the breeding colony at La Perouse Bay. Of the 17 probes examined, all detected RFLPs with at least one of EcoRi, HindIII, Msp1, and Taq1. Several of them identified highly variable regions with multiple alleles. These RFLPs are valuable DNA markers that can be used for (1) the examination of DNA variation, relatedness, and genetic distance and (2) assessing paternity and maternity. These data suggest that there are higher levels of variation of DNA sequence in birds than had previously been thought to exist.

Alleles↗
PubMed1987

Carrier detection of haemophilia A using DNA markers in families with an isolated affected male.

The carrier status of women in five families with an isolated haemophilia male was assessed by pedigree analysis, coagulation factor assays and DNA markers. In three families, ten women could be given very low risks of being carriers based on DNA analysis. In two of the families the DNA markers identified the mutation as originating in either the maternal or maternal grandfather's germ cell. Combined DNA and coagulation data suggested that the affected male in a third family was a de novo mutation. DNA analysis of the affected male in another family identified a large deletion of the F8 gene which was present in his mother and three sisters, suggesting that the grandmother was a carrier. A combination of coagulation factor data and DNA marker assessment can determine the carrier status of the majority of females in families with isolated affected haemophilia A males.

DNA↗
PubMed1987

Localization and linkage of three polymorphic DNA sequences on human chromosome 20.

The D20S6 locus has been sublocalized by in situ hybridization using the pD3H12 probe to human chromosome band 20p12 and the D20S4 locus using the pMS1-27 probe to 20q13.2. A rare new restriction fragment length polymorphism detected in MspI-digested DNA by the pMSI-27 probe is reported. Linkage studies in nine families have shown that the D20S6 locus is linked to D20S5 (formerly mapped to 20p12 by in situ hybridization) with a maximum likelihood estimate of 0.07 for the recombination frequency (lod score = 9.07) and a confidence interval of 0.02 to 0.14. Estimated recombination frequencies were similar in males and females. Using both two- and multipoint analyses, linkage of D20S4 with the D20S5 and D20S6 loci was excluded and the suggested order for the three loci on chromosome 20 is D20S5-D20S6-centromere-D20S4. D20S5 and D20S6 are very useful markers for linkage studies because of their close proximity and reasonably good polymorphic information content values.

Chromosome Banding↗
PubMed1987

An efficient strategy for gene mapping using multipoint linkage analysis: exclusion of the multiple endocrine neoplasia 2A (MEN2A) locus from chromosome 13.

Members of four families in which multiple endocrine neoplasia type 2A (MEN-2A) is segregating were typed for seven DNA markers and one red cell enzyme marker on chromosome 13. Close linkage was excluded between the MEN2A locus and each marker locus tested. By means of multipoint analysis and the genetic map of chromosome 13 developed by Leppert et al., MEN2A was excluded from any position between the most proximal marker locus (D13S6) and the most distal marker locus (D13S3) and from within 12 cMorgans outside these two loci, respectively. However, the support of exclusion within an interval was diminished under the assumption of a substantially larger genetic map in females. The strategy of multipoint analysis, which excluded between 1.5 and 2.0 times more chromosome 13 than did two-point analysis, demonstrates the utility of linkage maps in mapping disease genes.

Chromosome Mapping↗
PubMed1986

Rearrangements of chromosomal regions containing ribosomal RNA genes and centromeric heterochromatin in the human melanoma cell line MeWo.

A chromosomal examination of cells from the earliest available passage of the human melanoma cell line MeWo revealed the presence of seven hypodiploid cell types that shared common complex marker chromosomes. Two of the cell types had long homogeneously staining regions (HSR) by Q-banding on three different chromosomes. Distamycin A/DAPI staining and silver staining for active nucleolar organizing regions (NOR) confirmed that the HSR were derived from chromosome #15. All HSR-containing cells had 4-9 pairs of large NOR distributed along the length of each HSR, with all acrocentric chromosomes being negative. The HSR-lacking cells differed primarily with respect to the morphology of the short arm of one #13 chromosome and NOR activity. One cell type had four chromosomes with active NOR, whereas all other cell types had a single active NOR on one #13. One of these cell types had a satellited #8 with NOR. Cells from three other MeWo cultures at higher passages were examined. Two of these contained both hypodiploid and hypotetraploid cells, some of which had satellited X chromosomes or satellited #3 chromosomes with active NOR. The majority of the new chromosomal rearrangements in cells from the later cultures involved the NOR-containing regions, many of which were associated with the distamycin A/DAPI-positive centromeric heterochromatin from chromosome #15. These results indicate that the chromosomal instability in the MeWo cultures is mainly limited to sequences containing active NOR and centromeric heterochromatin from chromosomes #13 and #15. This may be due to a selective pressure to increase the number of active NOR in the MeWo cells. If this is so, it would appear that amplification of active NOR occurs more readily than the activation of the many silent NOR present in these cells.

Cell Line↗
PubMed1986

Isolation and characterization of an alpha-satellite repeated sequence from human chromosome 22.

We constructed a library in lambda L47.1 with DNA isolated from flow-sorted human chromosome 22. Over 50% of the recombinants contained the same highly repetitive sequence. When this sequence was used to probe Southern blots of EcoRI-digested genomic DNA, a ladder of bands with increments of about 170 bp was observed. This sequence comigrates with satellite III in Ag+/Cs2SO4 gradients and may account for at least part of the 170 bp Hae III ladder seen in isolated satellite III DNA. Partial sequence analysis revealed homology to the 171 bp monomeric repeat unit of alpha-R1-DNA and the X specific alpha-satellite consensus sequence. After low stringency in situ hybridization, silver grains were found over the centromeres of a number of chromosomes. Under high stringency conditions, however, the labeling was concentrated over the centromeric region of chromosome 22. This localization was confirmed using DNA from a panel of human/hamster cell lines which showed that the homologous 2.1 and 2.8 kb EcoR1 restriction fragments were chromosome 22 specific. These clones therefore contain chromosome 22 derived alpha-satellite sequences analogous to other chromosome-specific satellite sequences described previously.

Animals↗
PubMed1986

IS222, a new insertion element associated with the genome of Pseudomonas aeruginosa.

A new insertion element, IS222, was identified to be associated with the DNA of a mutant strain of the converting Pseudomonas aeruginosa bacteriophage D3. The insertion sequence was 1,350 base pairs in size and possessed terminal inverted repeats. The nucleotide sequence contained single cleavage sites for EcoRI and PvuI but none for BamHI, PstI, HindIII, SmaI, or SalI. By Southern hybridization analysis, no homology was found with genomic DNA from P. aeruginosa PAT or Escherichia coli. Genomic DNA from the phage host, P. aeruginosa PAO, contained two sequences homologous to IS222.

DNA Restriction Enzymes↗