Environmentally-modulated changes in fluorescence distribution in cells with oscillatory genetic network dynamics.

We investigated the distribution of green fluorescent protein (GFP) expression levels in a population of E. coli cells expressing an artificial genetic regulatory network, known as the "repressilator". This network originally constructed by Elowitz and Leibler in 2000 consists of three cyclically-inhibiting promoter-repressor pairs.

Cell population heterogeneity in expression of a gene-switching network with fluorescent markers of different half-lives.

We studied the distribution of expression levels amongst the cells of an Escherichia coli population carrying a gene-switching network, known as the genetic toggle. We employed two green fluorescent protein (GFP) reporter proteins with different half-lives and characterized the effect of isopropyl-beta-D-thiogalactopyranoside (IPTG) inducer concentration on fluorescence distribution characteristics. Our flow cytometric measurements indicated that there is a spread of fluorescence phenotypes of one to three orders of magnitude, due to the highly heterogeneous nature of the cell populations under investigation.