Experimental and computational analyses identify multiple cell populations during the epithelial-to-mesenchymal transition.

Natural variations in gene expression provide a mechanism for multiple phenotypes to arise in an isogenic bacterial population. In particular, a sub-group termed persisters show high tolerance to antibiotics. Previously, their formation has been attributed to cell dormancy. Here we demonstrate that bacterial persisters, under β-lactam antibiotic treatment, show less cytoplasmic drug accumulation as a result of enhanced efflux activity. Consistently, a number of multi-drug efflux genes, particularly the central component TolC, show higher expression in persisters. Time-lapse imaging and mutagenesis studies further establish a positive correlation between tolC expression and bacterial persistence. The key role of efflux systems, among multiple biological pathways involved in persister formation, indicates that persisters implement a positive defense against antibiotics prior to a passive defense via dormancy. Finally, efflux inhibitors and antibiotics together effectively attenuate persister formation, suggesting a combination strategy to target drug tolerance.

Significance: In a few milliliters of blood from a cancer patient, one can isolate a few circulating tumor cells (CTCs). Originating from the primary tumor, CTCs seed metastases, which account for the majority of cancer-related deaths. We demonstrate the analyses of the whole genome of single CTCs, which are highly needed for personalized treatment. We discovered that copy number variations (CNVs), one of the major genomic variations, are specific to cancer types, reproducible from cell to cell, and even from patient to patient. We hypothesize that CNVs at certain genomic loci are selected for and lead to metastasis. Our work shows the prospect of noninvasive CTC-based cancer diagnostics.