Biology subjects

Chuang, J.

Publications and source records attributed to Chuang, J..

3 recordsLinked to original sources

bioRxiv2018

Spt6 is required for the fidelity of promoter selection

Spt6 is a conserved factor that controls transcription and chromatin structure across the genome. Although Spt6 is viewed as an elongation factor, spt6 mutations in Saccharomyces cerevisiae allow elevated levels of transcripts from within coding regions, suggesting that Spt6 also controls initiation. To address the requirements for Spt6 in transcription and chromatin structure, we have combined four genome-wide approaches. Our results demonstrate that Spt6 represses transcription initiation at thousands of intragenic promoters. We characterize these intragenic promoters, and find sequence features conserved with genic promoters. Finally, we show that Spt6 also regulates transcription initiation at most genic promoters and propose a model of initiation-site competition to account for this. Together, our results demonstrate that Spt6 controls the fidelity of transcription initiation throughout the genome and reveal the magnitude of the potential for expressing alternative genetic information via intragenic promoters.

genomics↗

bioRxiv2018

Distribution-based measures of tumor heterogeneity are sensitive to mutation calling and lack strong clinical predictive power

Mutant allele frequency distributions in cancer samples have been used to estimate intratumoral heterogeneity and its implications for patient survival. However, mutation calls are sensitive to the calling algorithm. It remains unknown whether the relationship of heterogeneity and clinical outcome is robust to these variations. To resolve this question, we studied the robustness of allele frequency distributions to the mutation callers MuTect, SomaticSniper, and VarScan in 4722 cancer samples from The Cancer Genome Atlas. We observed discrepancies among the results, particularly a pronounced difference between allele frequency distributions called by VarScan and SomaticSniper. Survival analysis showed little robust predictive power for heterogeneity as measured by Mutant-Allele Tumor Heterogeneity (MATH) score, with the exception of uterine corpus endometrial carcinoma. However, we found that variations in mutant allele frequencies were mediated by variations in copy number. Our results indicate that the clinical predictions associated with MATH score are primarily caused by copy number aberrations that alter mutant allele frequencies. Finally, we present a mathematical model of linear tumor evolution demonstrating why MATH score is insufficient for distinguishing different scenarios of tumor growth. Our findings elucidate the importance of allele frequency distributions as a measure for tumor heterogeneity and their prognostic role.

bioinformatics↗

bioRxiv2017

Uncertainties In Tumor Allele Frequencies Limit Power To Infer Evolutionary Pressures

We read with great interest the paper by Williams, et. al.[1], who argued for neutral evolution in tumors by analyzing The Cancer Genome Atlas (TCGA) data. They supported this conclusion by showing high R2 values for fits to a neutral evolution model predicting M {propto} 1 / f, where M is the number of somatic mutations with allele frequency [≥] f. However, we believe a conclusion of neutrality must be treated cautiously, as high R2 values are consistent with many evolutionary models.

cancer biology↗