Biomedical subjects

Bernhard Horsthemke

Publications and source records attributed to Bernhard Horsthemke.

7 recordsLinked to original sources

PubMed2003

Somatic mosaicism for maternal uniparental disomy 15 in a girl with Prader-Willi syndrome: confirmation by cell cloning and identification of candidate downstream genes.

Although uniparental disomy often results from the postzygotic rescue of a meiotic non-disjunction event, mosaicism is usually confined to the placenta. We describe a girl with Prader-Willi syndrome (PWS) who is mosaic for normal cells and cells with maternal uniparental disomy 15 [upd(15)mat] in blood and skin. Somatic mosaicism was confirmed by cloning and genotyping of skin fibroblasts. X inactivation studies indicated that upd occurred prior to X inactivation. RNA samples from the cloned cells were used in DNA microarray experiments to study the effect of upd(15)mat on the gene expression pattern of fibroblasts. Proof of principle was obtained by detecting several chromosome 15 genes known to be imprinted. We did not obtain any evidence for novel 15q genes showing imprinted expression in fibroblasts. Differentially expressed genes on other chromosomes are candidates for downstream genes regulated by an imprinted gene and may play a role in the pathogenesis of PWS. The finding of strongly reduced mRNA levels in upd(15)mat cells of the gene encoding secretogranin II (SCG2), which is a precursor of the dopamine releasing factor secretoneurin, raises the question whether hyperphagia in patients with PWS might be due to a defect in dopamine-modulated food reward circuits.

Adult↗

PubMed2003

The RING finger protein RNF4, a co-regulator of transcription, interacts with the TRPS1 transcription factor.

The TRPS1 gene encodes a repressor of GATA-mediated transcription. Mutations in this gene cause the tricho-rhino-phalangeal syndromes, but the affected pathways are unknown. In a yeast two-hybrid screen with the C-terminal part of the murine Trps1 protein as bait, we obtained three yeast clones encoding two overlapping fragments of the 194 amino acids RING finger protein 4 (Rnf4). The overlap narrows down the Trps1-binding region within Rnf4 to amino acids 6-65. This region in Rnf4 is also known to interact with several proteins including steroid receptors. By using truncated Trps1 constructs, the Rnf4-binding region in Trps1 could be assigned to amino acids 985-1184 of 1281. This 200 amino acid region of Trps1 does not contain any predicted protein-protein interacting motif. Complex formation between the human proteins TRPS1 and RNF4 was verified by co-immunoprecipitation from transfected and native mammalian cells. Confocal laser-scanning microscopy revealed that the endogenous proteins are located in distinct structures of the nucleus. Using a luciferase reporter assay, we could demonstrate that the repressional function of TRPS1 is inhibited by RNF4. This finding suggests that RNF4 is a negative regulator of TRPS1 activity.

Amino Acid Motifs↗

PubMed2003

Nuclear interaction of the dynein light chain LC8a with the TRPS1 transcription factor suppresses the transcriptional repression activity of TRPS1.

The TRPS1 gene codes for a 1281 amino acids nuclear transcription factor with an unusual combination of different types of zinc finger motifs, including GATA-type DNA-binding and IKAROS-like zinc fingers. TRPS1 is a repressor of GATA-regulated genes and implicated in the human tricho-rhino-phalangeal syndromes. We found that two distinct regions of TRPS1 can physically interact with the dynein light chain 8 protein, LC8a, that are at least 458 amino acids apart from each other. Region A covers 89 amino acids (635-723), spanning three potential C(2)H(2) zinc finger structures, and region B covers the 100 most C-terminal amino acids (1182-1281) containing the IKAROS-like motif. LC8a is known to interact with more than 10 different molecules, both proteins and nucleic acids. In most cases, LC8a was identified as a transport molecule in the cytoplasm. Interestingly, we found that LC8a co-localizes with TRPS1 in dot-like structures in the cell nucleus. In an electrophoretic mobility shift assay we could show that the interaction of LC8a and TRPS1 lowers the binding of TRPS1 to the GATA consensus sequence. In addition, GATA-regulated reporter gene assay indicated that LC8a is able to suppress the transcriptional repression activity of TRPS1.

Amino Acid Sequence↗

PubMed2003

Tumor classification based on gene expression profiling shows that uveal melanomas with and without monosomy 3 represent two distinct entities.

Uveal melanoma is the most common intraocular malignancy. About 50% of patients die of metastases, which almost exclusively originate from primary tumors that have lost one chromosome 3 (monosomy 3). To gain insight into the biological mechanisms that underlie the various metastasizing potential of uveal melanoma, we have determined gene expression levels in 20 primary tumors using oligonucleotide microarrays containing 12500 probe sets. The expression measurements of those 7902 genes that were expressed in more than 10% of tumors were analyzed using two different statistical approaches. We used a modified Wilcoxon rank-sum test to identify genes differentially expressed between tumors with and without monosomy 3. Seven genes showed complete loss of expression in tumors with monosomy 3 but were expressed in tumors with disomy 3. Two of them, CHL1 and fls485, are located within or close to the uveal melanoma susceptibility locus UVM2 at 3p25. However, mutation analysis of both genes in eight tumors with monosomy 3 did not reveal structural or epigenetic alteration. To identify tumor classes, we performed unsupervised hierarchical cluster analysis; this approach separated uveal melanomas into two groups. We found that this classification is strikingly robust because, when tested by "resampling," the same grouping is obtained from 47 of 50 subsamples of genes. In clusterings of the three remaining subsamples, the grouping of only one tumor does not conform with the original classification. Excluding this tumor, cluster analyses of subsamples containing as few as 300 randomly chosen genes consistently result in the same classification, thus indicating that the difference between the two tumor classes is pervasive. Interestingly, all of the tumors in one of the groups have disomy 3, whereas all of the others have monosomy 3. Our findings suggest that there are two distinct entities of uveal melanoma that were previously unrecognized because they are not obviously distinguishable by clinicopathological features.

Chromosomes, Human, Pair 3↗

PubMed2003

Epimutations in Prader-Willi and Angelman syndromes: a molecular study of 136 patients with an imprinting defect.

Prader-Willi syndrome (PWS) and Angelman syndrome (AS) are neurogenetic disorders that are caused by the loss of function of imprinted genes in 15q11-q13. In a small group of patients, the disease is due to aberrant imprinting and gene silencing. Here, we describe the molecular analysis of 51 patients with PWS and 85 patients with AS who have such a defect. Seven patients with PWS (14%) and eight patients with AS (9%) were found to have an imprinting center (IC) deletion. Sequence analysis of 32 patients with PWS and no IC deletion and 66 patients with AS and no IC deletion did not reveal any point mutation in the critical IC elements. The presence of a faint methylated band in 27% of patients with AS and no IC deletion suggests that these patients are mosaic for an imprinting defect that occurred after fertilization. In patients with AS, the imprinting defect occurred on the chromosome that was inherited from either the maternal grandfather or grandmother; however, in all informative patients with PWS and no IC deletion, the imprinting defect occurred on the chromosome inherited from the paternal grandmother. These data suggest that this imprinting defect results from a failure to erase the maternal imprint during spermatogenesis.

Angelman Syndrome↗

PubMed2003

Computer-based recognition of dysmorphic faces.

Genetic syndromes often involve craniofacial malformations. We have investigated whether a computer can recognize disease-specific facial patterns in unrelated individuals. For this, 55 photographs (256 x 256 pixel) of patients with mucopolysaccharidosis type III (n=6), Cornelia de Lange (n=12), fragile X (n=12), Prader-Willi (n=12), and Williams-Beuren (n=13) syndromes were preprocessed by a Gabor wavelet transformation. By comparing the feature vectors at 32 facial nodes, 42/55 (76%) of the patients were correctly classified. In another four patients (7%), the correct and an incorrect diagnosis scored equally well. Clinical geneticists who were shown the same photographs achieved a recognition rate of 62%. Our results prove that certain syndromes are associated with a specific facial pattern and that this pattern can be described in mathematical terms.

Craniofacial Abnormalities↗

PubMed2002

Intracytoplasmic sperm injection may increase the risk of imprinting defects.

In germ cells and the early embryo, the mammalian genome undergoes widespread epigenetic reprogramming. Animal studies suggest that this process is vulnerable to external factors. We report two children who were conceived by intracytoplasmic sperm injection (ICSI) and who developed Angelman syndrome. Molecular studies, including DNA methylation and microsatellite and quantitative Southern blot analysis, revealed a sporadic imprinting defect in both patients. We discuss the possibility that ICSI may interfere with the establishment of the maternal imprint in the oocyte or pre-embryo.

Adult↗