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Biomedical subjects

B Horsthemke

Publications and source records attributed to B Horsthemke.

At least 163 records · Page 9Linked to original sources
PubMed1989

Maternal origin of a de novo chromosome 8 deletion in a patient with Langer-Giedion syndrome.

The anonymous DNA probe L32, which defines the D8S48 locus within the Langer-Giedion syndrome chromosome region on the long arm of chromosome 8, was used to search for a common restriction fragment length polymorphism. A HindIII and an MspI polymorphism were detected (polymorphism information contents 0.25 and 0.19, respectively). Both polymorphisms were informative in the family of a Langer-Giedion patient carrying a de novo interstitial deletion 8q23-24.1. Lack of transmission of a maternal haplotype indicates that this deletion occurred during maternal gametogenesis. This finding contrasts with the frequent paternal origin of mutations in other microdeletion syndromes.

Chromosome Banding↗
PubMed1989

Epigenetic changes may contribute to the formation and spontaneous regression of retinoblastoma.

Epigenetic models for tumor formation assume that oncogenic transformation results from changes in the activity of otherwise normal genes. Since gene activity can be inhibited by DNA methylation, and inactivation of tumor suppressor genes is a fundamental process in oncogenesis, we investigated the methylation status of the retinoblastoma suppressor gene (RB gene) on chromosome 13, in blood and tumor cells from 21 retinoblastoma patients. Using methylation-sensitive restriction enzymes and a cloned DNA probe for the unmethylated CpG island at the 5' end of RB gene, we obtained evidence of hypermethylation of this gene in a sporadic unilateral retinoblastoma tumor. The closely linked esterase D gene and a CpG-rich island on chromosome 15 were not affected. We suggest that changes in the methylation pattern of the RB gene play a role in the development and spontaneous regression of some retinoblastoma tumors.

DNA Restriction Enzymes↗
PubMed1989

Mechanism of i(6p) formation in retinoblastoma tumor cells.

Isochromosome (6p) represents a highly characteristic cytogenetic abnormality of human retinoblastoma (RB) cells and may be important for tumor progression. To elucidate the mechanism by which this abnormal chromosome is formed, 24 RB tumors and three cell lines were studied by means of DNA polymorphisms specific for the short arm and the long arm of chromosome 6. Our results indicate that mitotic nondisjunction leading to trisomy 6 precedes the isochromosome formation. The isochromosome may then be formed by transverse division of the centromere or intrachromosomal chromatid exchange.

Alleles↗
PubMed1988

Construction of a chromosome 15-specific linking library and identification of potential gene sequences.

We have tested a strategy for the construction of a total restriction fragment map of a human chromosome and the rapid isolation of a great number of genes from a specific chromosome. The strategy is based on the cloning of chromosome-specific CpG-rich DNA sequences which are present at the 5' end of many genes. This approach has two important implications: (i) the clones can be used to probe pulsed-field gradient gel blots and link restriction fragments generated by CpG restriction endonucleases, and (ii) the finding of tight genetic or physical linkage between one of these gene probes and a given hereditary disease would make the marker a good candidate gene for this disease. We have constructed a chromosome 15-specific linking library and identified potential gene sequences.

Base Sequence↗
PubMed1988

Application of linkage analysis to genetic counselling in families with hereditary retinoblastoma.

Six families with retinoblastoma in more than one member were investigated with DNA markers linked to the retinoblastoma locus because direct analysis had not disclosed the gene defect. In all of the families we could identify the affected chromosome and predict the genetic risk with a high level of confidence (90 to 99%). In one patient the test helped to detect tumour development earlier than usually possible. Several subjects were found not to carry a mutation, thus obviating frequent ophthalmological examinations under anaesthesia as would be necessary otherwise. These results show that linkage analysis can be successfully applied to genetic counselling in families with hereditary retinoblastoma.

Adult↗
PubMed1987

Unequal crossing-over between two alu-repetitive DNA sequences in the low-density-lipoprotein-receptor gene. A possible mechanism for the defect in a patient with familial hypercholesterolaemia.

We have previously identified a patient with familial hypercholesterolaemia (FH), where the defect appears to be caused by a deletion in the 3' region of the low-density lipoprotein (LDL)-receptor gene. We have now isolated the LDL-receptor gene from the patient and have studied the defect at the DNA level. Restriction mapping and sequence analysis demonstrate that a 4-kb DNA deletion has occurred between two alu-repetitive sequences that are in the same orientation, one in intron 12 and the other in intron 14. This deletion eliminates exons 13 and 14, and changes the reading frame of the resulting spliced mRNA such that a stop codon is created in the following exon. Immuno- and ligand-blot analysis using cultured fibroblasts from this patient revealed the normal gene product, but failed to detect any smaller receptor protein. This implies that the truncated receptor protein that is synthesised is rapidly degraded. We suggest that in this patient the deletion is caused by an unequal crossing-over event that occurred between two homologous chromosomes at meiosis.

Chromosome Deletion↗
PubMed1987

Detection of submicroscopic deletions and a DNA polymorphism at the retinoblastoma locus.

DNA samples from 60 unrelated patients with retinoblastoma were screened by Southern blot hybridization using two probes that are closely linked to the retinoblastoma locus within human chromosome band 13q14. Seven of 44 patients with bilateral or multifocal unilateral retinoblastoma and one patient with unifocal unilateral retinoblastoma were found to have a heterozygous deletion for the anonymous DNA sequence H3-8. Three of the eight deletions did not include the esterase D locus and were undetectable by conventional cytogenetic analysis. The findings are compatible with the deletions being the cause of retinoblastoma in these cases and provide a basis for DNA diagnosis in nearly 20% of patients with bilateral and multifocal unilateral retinoblastoma. The H3-8 probe also detects a restriction fragment length polymorphism that is a useful genetic marker in some families.

Child↗
PubMed1987

Identification of deletions in the human low density lipoprotein receptor gene.

DNA samples from 70 unrelated UK patients with heterozygous familial hypercholesterolaemia were screened by Southern blot hybridisation with a 5' fragment of the human low density lipoprotein (LDL) receptor cDNA. In the majority of cases, the restriction fragment pattern of the LDL receptor gene was indistinguishable from that observed in normal subjects. However, three patients were found to have a deletion of approximately 1 kb in the central portion of the gene. Mapping experiments indicated that in two patients a similar deletion has occurred that includes all or part of exon 5, and in the third patient a deletion has occurred that includes exon 7. Taking into account our previously described patient with a deletion in the 3' part of the gene, this means that in four out of 70 UK patients with familial hypercholesterolaemia (6%), the defect is caused by a detectable deletion of part of the coding portion of the low density lipoprotein receptor gene.

Chromosome Deletion↗
PubMed1985

A common DNA polymorphism of the low-density lipoprotein (LDL) receptor gene and its use in diagnosis.

A cloned gene probe coding for the low-density lipoprotein (LDL) receptor was used to detect a restriction fragment length polymorphism with the enzyme Pvu II. The frequency of the rare allele is approximately 0.2 both in normal controls and individuals with familial hypercholesterolaemia (FH). About 30% of individuals are heterozygous for the polymorphism, and are potentially informative for family studies and for early diagnosis of FH. This polymorphism was used to follow the inheritance of the LDL receptor gene in two families with FH. In these families, the polymorphism co-segregates with the disease unambiguously, and therefore can be used for early diagnosis.

Alleles↗
PubMed1985

Identification of a deletion in the low density lipoprotein (LDL) receptor gene in a patient with familial hypercholesterolaemia.

DNA samples from 60 unrelated UK patients with familial hypercholesterolaemia (FH) were screened by Southern blot hybridisation to detect gross alterations in the low density lipoprotein (LDL) receptor gene. One patient was found to have a 2kb deletion in the 3' part of the gene. The deletion cosegregates with the FH phenotype in his family. This finding is compatible with the deletion being the cause of FH in this case and makes a presymptomatic test based on DNA analysis available for this family. The defects in most of the other patients are likely to be due to point mutations.

Chromosome Deletion↗
PubMed1985

A study of DNA polymorphisms around the human apolipoprotein AI gene in hyperlipidaemic and normal individuals.

We have used a 2.2 kb fragment of the human apolipoprotein AI (apo AI) gene to screen a number of unrelated individuals for common restriction fragment length polymorphisms (RFLPs) of the gene. As well as the previously reported SstI RFLP (allele frequencies in normolipidaemic individuals 0.94 and 0.06) we have detected RFLPs with the enzymes PstI and XmnI (allele frequencies in normolipidaemic individuals 0.88 and 0.12 for both polymorphisms). In the population studied, the RFLPs appear to be in linkage equilibrium and can be used in conjunction as a haplotype, with a PIC value (polymorphism information content) of 0.5. Significant differences in allele frequency were observed between subgroups of hyperlipidaemic patients and normolipidaemic controls. There is no strong population association in our patient group between any allele of the RFLPs studied and hypertriglyceridaemia.

Alleles↗
PubMed1984

Degradation of substance P by neurones and glial cells.

Neuronal and astroblast-rich cultures from rat brain degrade exogenously added substance P. The rate of degradation is decreased by diisopropylfluorophosphate, phosphoramidon and bacitracin, but not by N-ethylmaleimide or bestatin. When diisopropylfluorophosphate, phosphoramidon and bacitracin are simultaneously present in the culture medium, the degradation of substance P is completely inhibited. These results indicate that the hydrolysis of substance P by intact cells is catalyzed by the post-proline dipeptidylaminopeptidase (EC 3.4.14.5), the thermolysin-like metallopeptidase ("enkephalinase", EC 3.4.24.11) and a yet uncharacterized bacitracin-sensitive activity. While the thermolysin-like metallopeptidase is mainly associated with glial cells, the specific activity of the other enzymes is five times higher in the neuronal culture.

Animals↗
PubMed1984

Subcellular distribution of particle-bound neutral peptidases capable of hydrolyzing gonadoliberin, thyroliberin, enkephalin and substance P.

Subcellular fractions from rat anterior pituitary homogenates were obtained by differential and gradient centrifugation, identified with the help of marker enzymes and screened for peptidases capable of hydrolyzing gonadoliberin, thyroliberin, enkephalin and substance P. Since each neuropeptide is susceptible to cleavage by more than one enzyme, specific substrates or inhibitors have been used for the selective determination of the individual peptidasic activities. Among the various enzymes tested, the angiotensin-converting enzyme, the thermolysin-like metalloendopeptidase ('enkephalinase'), a thyroliberin-degrading enzyme and some aminopeptidasic activities were found to be associated with the plasma membrane. Other aminopeptidases, a gonadoliberin-degrading and a substance-P-degrading enzyme are associated with the mitochondria and thus are most likely not involved in the biological inactivation of neuropeptides.

Animals↗
PubMed1984

Characterization of a neutral endopeptidase localized in the mitochondrial matrix of rat anterior pituitary tissue with GnRH as a substrate.

We have determined the subcellular localization of an endopeptidase activity able to degrade gonadotropin releasing hormone (GnRH) and present in the rat adenohypophysis. After fractionation of tissue homogenates in 0.25 M sucrose by differential centrifugation, about 25% of the total cellular GnRH degrading activity was found to be sedimentable and recovered from heavy (M) and light (L) mitochondrial fractions with a distribution pattern similar to that of the mitochondrial and lysosomal reference enzymes cytochrome oxidase and beta-galactosidase. Upon further fractionation on sucrose density gradients, the activity comigrated with mitochondria. The peptidase appears endowed with a structure-linked latency; the activity is low in a freshly prepared mitochondrial fraction and increases upon treatment with membrane disrupting agents in a manner similar to that of malate dehydrogenase, a component of the mitochondrial matrix. Determination of GnRH cleavage sites was performed by amino acid analysis of the fragments obtained after incubation of the peptidase with (3H)-GnRH labelled on the pyroglutamic acid residue, in presence of carboxypeptidase and peptidyldipeptidase inhibitors. The fragments were separated by ion-exchange chromatography on an Aminex Q-15S column and purified by chromatography on silica gel plates. Fragments 1-2, 1-3, 1-4, 1-5 and 1-6 were all present as early as 1 min after the beginning of incubation. Formation of each of them was inhibited to the same extent by EDTA, mersalyl acid, dithioerythritol and Na deoxycholate. The same fragmentation pattern was observed after partial purification of the enzyme by gel filtration. These data indicate that cleavage of several peptide bonds may result from a possibly single endopeptidase located in the mitochondrial matrix space.

Animals↗