Figure 3.

Analysis of variability in expression across tissues as a function of the total 5'UTR intron length. (a) Transcripts with low mean expression have higher normalized expression variability. A standardized measure of the variability in gene expression across tissues was calculated and plotted against the natural logarithm of mean expression level. The black vertical line represents the lowest 25th percentile in mean expression. Since transcripts with low levels of mean expression tend to exhibit an artificially high variability in expression, they are removed from further analysis. (b) Boxplot of the coefficient of variation (standard deviation-to-mean ratio) of genes grouped by the total length of 5'UTR intron. The width of the boxes represents the relative number of data points in each category. There are no apparent differences between the three groups (c) Boxplot of log₁₀ of total 5'UTR intron length of genes grouped by their across-tissue variability. Genes are divided into six categories depending on their coefficient of variation. Error bars correspond to standard deviation of the mean. No obvious dependence of expression variability to total 5UI length can be observed except for the most highly variable genes, which tend to have slightly shorter 5'UTR introns. (d) Boxplot of log₁₀ of total 5'UTR intron length for gene groups defined by the number of tissues in which expression of each gene was detected. A gene was defined to have detectable expression in a given tissues if its expression was higher than the 25th percentile of mean expression of all genes. We found no differences in total 5'UTR intron length amongst the different gene groups. (e) Histogram of number of genes divided by the presence of 5'UTR introns and by the number of tissues in which expression was detected. The number of tissues in which expression was detected was independent of the presence of 5'UTR introns.