Yeast Division in Microdroplets – YEASTDROPLETS

A human body is composed of about 10tothe13 to 10tothe14 cells, and major biological processes such as cellular differentiation, immune response, offspring identity, or cancer emergence arise from single or very few cells. It is therefore essential to investigate the probabilistic rules of such rare events. Our current biological knowledge lacks individual-cell statistics because it is essentially based on biochemical dosage of samples of many cells. Many studies of the past 5 years dissected some of the rules governing cell-to-cell stochastic differences, mainly at the level of reporter gene expression regulations. This type of investigation is technically limited by the need for monitoring large numbers of living cells through time. We propose to study cell-to-cell variations beyond the regulation of reporter systems by monitoring a complex and integrative cellular process: the cell division. To this end, we propose to develop and use a novel technology which is based on emulsion droplets that travel in microfluidic channels. Individual yeast cells will be encapsulated in microdroplets of culture medium where they will undergo cell division. The droplets will be filmed regularly to determine generation times (achievement of a second cell). This experimental setup should allow to monitor about 10,000 cell divisions in about 2 hours, and will therefore be adapted to a systematic genetic analysis of 'noise' in generation time (random variation from one division to another). We will measure this noise in many divergent strains of S. cerevisiae and perform two types of quantitative genetics mapping to identify genes buffering this noise. A panel of divergent strains that are already genotyped at high resolution will be used for association study, and a particular pair of strains will be crossed to identify Quantitative Trait Loci of noise in the genome. This is a collaborative project between a laboratory of yeast quantitative genetics (partner 1) which already accumulated evidence of natural genetic variation of noise, and a laboratory of physics/chemistry (partner 2) which already developed parts of the experimental setup. We expect the study to reach a very large community because it will test a fundamental question about genetic predisposition to complex traits such as common diseases and because the technology that will be developped can be extended to other applications.