Tracking lineages of single cells in lines using a microfluidic device.

Cells within a genetically identical population exhibit phenotypic variation that in some cases can persist across multiple generations. However, information about the temporal variation and familial dependence of protein levels remains hidden when studying the population as an ensemble. To correlate phenotypes with the age and genealogy of single cells over time, we developed a microfluidic device that enables us to track multiple lineages in parallel by trapping single cells and constraining them to grow in lines for as many as 8 divisions. To illustrate the utility of this method, we investigate lineages of cells expressing one of 3 naturally regulated proteins, each with a different representative expression behavior. Within lineages deriving from single cells, we observe genealogically related clusters of cells with similar phenotype; cluster sizes vary markedly among the 3 proteins, suggesting that the time scale of phenotypic persistence is protein-specific. Growing lines of cells also allows us to dynamically track temporal fluctuations in protein levels at the same time as pedigree relationships among the cells as they divide in the chambers. We observe bursts in expression levels of the heat shock protein Hsp12-GFP that occur simultaneously in mother and daughter cells. In contrast, the ribosomal protein Rps8b-GFP shows relatively constant levels of expression over time. This method is an essential step toward understanding the time scales of phenotypic variation and correlations in phenotype among single cells within a population.