Biomedical subjects

Gunnar Wrobel

Publications and source records attributed to Gunnar Wrobel.

7 recordsLinked to original sources

PubMed2003

Optimization of high-density cDNA-microarray protocols by 'design of experiments'.

Expression analysis using microarray technology implies a complex experimental procedure with a large number of parameters affecting the final result. We have demonstrated that optimization of such a complex protocol can be far better handled using design of experiments (DOE) than by working on a single parameter at a time. Based on the results of a screening design, we developed a spotting buffer composed of formamide, betaine and nitrocellulose. This buffer provides a 2-fold increase in signal-to-background ratio compared to 3x SSC. Comparison to seven other buffers tested on 10 different substrates revealed it had the highest sensitivity. DNA dissolved in this buffer can be spotted on epoxysilane-coated microscope slides at a density of up to 70 000 spots per slide. A second DOE approach characterized the RNA labeling process with regard to the concentration of fluorescent dyes, dNTPs and reverse transcriptase. Adjust ments of the concentrations of dNTPs, as well as reverse transcriptase, towards the optimum, produced an improvement in the performance of the labeling procedure by a factor of 3 (Cy3) and 10 (Cy5). These results demonstrate that the process of establishing a stable expression profiling protocol and its further optimization can be significantly shortened and improved by DOE.

Buffers↗

PubMed2003

Profile of gene expression induced by the tumour promotor TPA in murine epithelial cells.

Malignant transformation of mouse skin by chemical carcinogens and tumour promoters, such as the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA), is a multistage process that leads to squamous cell carcinoma (SCC) formation. In an effort to identify tumour-associated genes, we studied the influence of short-term TPA-treatment on the gene expression profile of murine skin. A comprehensive microarray with some 5,000 murine gene specific cDNA fragments was established and hybridised with pooled RNA derived from control and TPA-treated dorsal skin samples. Of these genes, 54 were up- and 35 were down-regulated upon TPA application. Additionally, we performed suppression subtractive hybridisation (SSH) with respective RNA pools to generate and analyse a cDNA library enriched for TPA-inducible genes. Expression data of selected genes were confirmed by quantitative real-time PCR and Northern blot analysis. Comparison of microarray and SSH data revealed that 26% of up-regulated genes identified by expression profiling matched with those present in the SSH library. Besides numerous known genes, we identified a large set of unknown cDNAs that represent previously unrecognised TPA-regulated genes in murine skin with potential function in tumour promotion. Additionally, some TPA-induced genes, such as Sprr1A, Saa3, JunB, Il4ralpha, Gp38, RalGDS and Slpi exhibit high basal level in advanced stages of skin carcinogenesis, suggesting that at least a subgroup of the identified TPA-regulated genes may contribute to tumour progression and metastasis.

Animals↗

PubMed2003

Hidden gene amplifications in aggressive B-cell non-Hodgkin lymphomas detected by microarray-based comparative genomic hybridization.

DNA amplifications are important mechanisms for proto-oncogene activation. Comparative genomic hybridization (CGH) to metaphase chromosome preparations has revealed amplifications in 10-20% of B-cell lymphomas (B-NHL). We analysed a series of 16 aggressive non-Hodgkin lymphomas by the new approach termed Matrix-CGH (M-CGH) using genomic DNA microarrays as hybridization target. For M-CGH, a dedicated B-cell lymphoma chip was constructed containing 496 genomic targets covering oncogenes, tumor suppressor genes as well as chromosome regions frequently altered in B-NHL. In 10 of 16 samples a total of 15 DNA amplifications were identified. The amplicons included BCL2, REL, CCND1, CCND2, JAK2, FGF4 and MDM2. Four of the 15 amplifications remained undetected by chromosomal CGH. The respective amplicons mapped to bands 2p13, 9p13-p21 and 12q24 and, were confirmed by fluorescence in situ hybridization. Furthermore, for four genomically amplified genes real-time quantitative reverse transcription polymerase chain reaction revealed elevated mRNA expression levels. These data show the superior diagnostic sensitivity of the newly developed diagnostic tool. As only a small portion of the genome (approximately 1.5%) has been analysed by the present DNA array, it is likely that gene amplifications are much more common in aggressive lymphomas than previously assumed.

Burkitt Lymphoma↗

PubMed2003

QuickLIMS: facilitating the data management for DNA-microarray fabrication.

SUMMARY: QuickLIMS is a Microsoft Access-based laboratory information and management system, capable of processing all information for microarray production. The program's operational flow is protocol-based, dynamically adapting to changes of the process. It interacts with the laboratory robot and with other database systems over the network, and it represents a complete solution for the management of the entire manufacturing process. AVAILABILITY AND SUPPLEMENTARY INFORMATION: http://www.dkfz-heidelberg.de/kompl_genome/Other/QuickLims/index.html

Computer Communication Networks↗

PubMed2002

Microarray-based copy number and expression profiling in dedifferentiated and pleomorphic liposarcoma.

Sixteen dedifferentiated and pleomorphic liposarcomas were analyzed by comparative genomic hybridization (CGH) to genomic microarrays (matrix-CGH), cDNA-derived microarrays for expression profiling, and by quantitative PCR. Matrix-CGH revealed copy number gains of numerous oncogenes, i.e., CCND1, MDM2, GLI, CDK4, MYB, ESR1, and AIB1, several of which correlate with a high level of transcripts from the respective gene. In addition, a number of genes were found differentially expressed in dedifferentiated and pleomorphic liposarcomas. Application of dedicated clustering algorithms revealed that both tumor subtypes are clearly separated by the genomic profiles but only with a lesser power by the expression profiles. Using a support vector machine, a subset of five clones was identified as "class discriminators." Thus, for the distinction of these types of liposarcomas, genomic profiling appears to be more advantageous than RNA expression analysis.

Algorithms↗

PubMed2002

Classical Hodgkin lymphoma is characterized by recurrent copy number gains of the short arm of chromosome 2.

Hodgkin- and Reed-Sternberg (HRS) cells microdissected from 41 classical Hodgkin lymphomas (cHL) of 40 patients comprising 8 lymphocyte-rich (cHL-LR), 16 nodular sclerosis (cHL-NS), 15 mixed-cellularity (cHL-MC), and 2 lymphocyte-depletion (cHL-LD) subtypes were analyzed by comparative genomic hybridization for recurrently imbalanced chromosomal subregions. Chromosomal gains most frequently involved chromosome 2p (54%), 12q (37%), 17p (27%), 9p and 16p (24% each), and 17q and 20q (20% each), whereas losses primarily affected chromosome 13q (22%). Using fluorescence in situ hybridization, amplification of the REL oncogene was demonstrated within a distinct 2p15-p16 amplicon. The high frequency of 2p overrepresentations including REL, particularly in cHL-NS (88%), suggests that an alternative mechanism of constitutive activation of nuclear factor NF-kappaB is a hallmark of HRS cells. Hierarchical cluster analysis of chromosomal imbalances revealed a closer relationship among cHL-NS than other subtypes. Furthermore, there is a tendency for different subtypes of cHL-MC tumors characterized by different ages at the time of tumor onset and gain of chromosome 17p. The imbalance pattern of cHL subtypes suggests that different molecular pathways are activated, with REL or other genes on chromosomal band 2p15-p16 playing a fundamental role in the pathogenesis of classical Hodgkin lymphoma.

Adolescent↗

PubMed2002

Automated screening for genomic imbalances using matrix-based comparative genomic hybridization.

Genome-wide screening for chromosomal imbalances using comparative genomic hybridization (CGH) revealed a wealth of data on previously unrecognized tumor-specific genomic alterations. CGH to microarrays of DNA, an approach termed matrix-CGH, allows detection of genomic imbalances at a much higher resolution. We show that matrix CGH is also feasible from small tissue samples requiring universal amplification of genomic DNA. Because widespread application of matrix-CGH experiments using large numbers of DNA targets demands a high degree of automation, we have developed a protocol for a fully automated procedure. The use of specialized instrumentation for the generation of DNA chips, their hybridization, scanning, and evaluation required numerous alterations and modifications of the initial protocol. We here present the elaboration and testing of automated matrix-CGH. A chip consisting of 188 different genomic DNA fragments, cloned in bacterial artificial chromosome (BAC) or P1-derived artificial chromosome (PAC) vectors and immobilized in replicas of 10, was used to assess the performance of the automated protocol in determining the gene dosage variations in tumor cell lines COLO320-HSR, HL60, and NGP. Although ratios of matrix-CGH were highly concordant with results of chromosomal CGH (85%), the dynamic range of the matrix-CGH ratios was highly superior. Investigation of the two amplicons on 8q24 in COLO320-HSR and HL60, containing the MYC gene, revealed a homogeneous amplicon in COLO320-HSR but a heterogeneous amplification pattern in HL60 cells. Although control clones for normalization of the signal ratios can be predicted in cases with defined chromosomal aberrations, in primary tumors such data are often not available, requiring alternative normalization algorithms. Testing such algorithms in a primary high-grade B-cell lymphoma, we show the feasibility of this approach. With the matrix-CGH protocol presented here, robust and reliable detection of genomic gains and losses is accomplished in an automated fashion, which provides the basis for widespread application in tumor and clinical genetics.

Chromosome Aberrations↗