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Chapter 2 - University of British Columbia

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gain and loss. When examining major oncogenes and tumor suppressor genes, while most<br />

oncogenes were associated with frequent areas <strong>of</strong> gain, we found a subset <strong>of</strong> both known and<br />

novel oncogenes that were frequently affected by UPD. Finally, examining oncogenes with<br />

homozygous mutation in multiple cancer types, we observe frequent UPD at these genes<br />

suggesting this mechanism <strong>of</strong> oncogene activation is prevalent across multiple cancer types.<br />

4.2 Methods<br />

4.2.1 Genome wide pr<strong>of</strong>iling <strong>of</strong> clinical lung adenocarcinoma specimens<br />

Forty-six lung adenocarcinoma cases were obtained from Vancouver General Hospital under<br />

approved ethics. Cases were reviewed by a pathologist and tumors were microdissected to<br />

ensure maximal tumor cell content (≥ 70%). Five hundred nanograms <strong>of</strong> genomic DNA were<br />

extracted from each tumor and adjacent non-malignant tissue were prepared and hybridized to<br />

the Affymetrix Genome-Wide Human SNP 6.0 array platform as per manufacturer's instructions.<br />

CEL files, the raw data files generated, were then processed using the Affymetrix Genotyping<br />

Console version 3.0.2 to generate .chp files using the birdseed v2 genotyping algorithm.<br />

4.2.2 Determination <strong>of</strong> regions <strong>of</strong> uniparental disomy (UPD) in clinical lung tumors<br />

CEL files and .chp files were imported into Partek Genomics Suite (PGS) using the s<strong>of</strong>tware's<br />

recommended default settings. First, to determine total copy number, paired copy number<br />

intensities were calculated for each sample using the intensity in the tumor vs. it's matched non-<br />

malignant sample. Paired copy number intensities were then analyzed using the Genomic<br />

Segmentation method in PGS with all parameters run at default except for the number <strong>of</strong><br />

markers which was set to 50. Subsequently, allele specific copy number (ASCN) analysis was<br />

used to determine regions <strong>of</strong> allelic imbalance. A region was deemed imbalanced if the<br />

imbalance proportion was ≥ 0.15 (as recommended by PGS). Finally, a region was called UPD<br />

if the region was imbalance and no change in total copy number was present.<br />

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