Mutations in a Lung Cancer Genome
In a recently published article by Lee et al. the genome of a lung cancer tumor was sequenced and compared to normal tissue. The number of single nucleotide variants (SNV) in the tumor was over 50,000. It is insane amount! The patient had smoked 25 cigarettes a day for 15 years, which makes about one mutation for every 2.7 cigarettes! The study also shows that the rate of mutations is lower for expressed genes compared to non-expressed genes. So, something is reducing the amount of mutations in those areas. It could indicate the presence of a repairing mechanism or maybe the mutations affecting actively expressed genes make the cells non-viable. I recommend reading the excellent blog entry commenting the article.
All this reminds me of a comparison between Linux call graph and the transcriptional regulatory network of E. coli bacterium. DNA can be considered as a source code of life or an operating system of life. Also, genes can be considered as functions in software code. Genes (and functions in Linux) can be divided into three categories:
- master regulators: they switch other genes on and off, but are not regulated by other genes
- middle management: genes that are regulated and further regulate other genes.
- work horses: genes that do all the work and do not regulate other genes.
In the light of the tumor example above, we can see that living organisms are prone to errors but can tolerate quite a bit of damage before breaking down. Linux, however, has a large community of developers fixing all bugs emerged into the source code. Given this information, which system contains large number of work horses and which only few? Think about it for a while before reading the result (N.B. the graph!)