Variation in protein expression levels in cell populations

Dissertation presented to obtain the Ph.D degree in Systems Biology

A widespread observation is that of variation in the expression levels of a molecule when analyzing a snapshot of single cells from a population. One possible explanation for this variation is that there are asynchronous fluctuations throughout time in the expression level of each cell, for example due to noise in gene expression. Another explanation is that there are so-called stable variants, groups of cells that have a permanent bias for a limited range of expression levels compared with the levels observed in a snapshot of the population. In an extreme scenario, each cell of the population would be a single stable variant with an expression level that is constant as a function of time, without any fluctuations. Stable variants could occur if the population is genetically diverse, with each clone being associated with a particular expression level.(...)