Morales, A. M. | Search bioRxiv

bioRxiv2023

The molecular clock in long-lived tropical trees is independent of growth rate

The rates of appearance of new mutations play a central role in evolution. However, mutational processes in natural environments and their relationship with growth rates are largely unknown, particular in tropical ecosystems with high biodiversity. Here, we examined the somatic mutation landscapes of two tropical trees, Shorea laevis (slow-growing) and S. leprosula (fast-growing), in central Borneo, Indonesia. Using newly-constructed genomes, we identified a greater number of somatic mutations in tropical trees than in temperate trees. In both species, we observed a linear increase in the number of somatic mutations with physical distance between branches. However, we found that the rate of somatic mutation accumulation per meter of growth was 3.7-fold higher in S. laevis than in S. leprosula. This difference in the somatic mutation rate was scaled with the slower growth rate of S. laevis compared to S. leprosula, resulting in a constant somatic mutation rate per year between the two species. We also found that somatic mutations are neutral within an individual, but those mutations transmitted to the next generation are subject to purifying selection. These findings suggest that somatic mutations accumulate with absolute time and older trees have a greater contribution towards generating genetic variation. Significance StatementThe significance of our study lies in the discovery of an absolute time-dependent accumulation of somatic mutations in long-lived tropical trees, independent of growth rate. Through a comparative analysis of somatic mutation landscapes in slow- and fast-growing species, we observed a clock-like accumulation of somatic mutations in both species, regardless of their growth rates. Although the majority of somatic mutations were restricted to a single branch, we also identified mutations present in multiple branches, likely transmitted during growth. Our findings suggest that older trees make a greater contribution towards generating genetic variation.

evolutionary biology↗

bioRxiv2023

Cancer Cell`s Seven Achilles Heels: Consideration for desing of anti-cancer drug combinations.

Loss of function screens using shRNA and CRISPR are routinely used to identify genes that modulate responses of tumor cells to anti-cancer drugs. Here, by integrating GSEA and CMAP analyses of multiple published shRNA screens, we identified a core set of pathways that affect responses to multiple drugs with diverse mechanisms of action. This suggests that these pathways represent "weak points" or "Achilles heels", whose mild disturbance should make cancer cells vulnerable to a variety of treatments. These "weak points" include proteasome, protein synthesis, RNA splicing, RNA synthesis, cell cycle, Akt-mTOR, and tight junction-related pathways. Therefore, inhibitors of these pathways are expected to sensitize cancer cells to a variety of drugs. This hypothesis was tested by analyzing the diversity of drugs that synergize with FDA-approved inhibitors of the proteasome, RNA synthesis, and Akt-mTOR pathways. Indeed, the quantitative evaluation indicates that inhibitors of any of these signaling pathways can synergize with a more diverse set of pharmaceuticals, compared to compounds inhibiting targets distinct from the "weak points" pathways. Our findings described here imply that inhibitors of the "weak points" pathways should be considered as primary candidates in a search for synergistic drug combinations.

cancer biology↗