Stochastic protein expression in individual cells at the single molecule level

Abstract

In a living cell, gene expression--the transcription of DNA to messenger RNA followed by translation to protein--occurs stochastically, as a consequence of the low copy number of DNA and mRNA molecules involved. These stochastic events of protein production are difficult to observe directly with measurements on large ensembles of cells owing to lack of synchronization among cells. Measurements so far on single cells lack the sensitivity to resolve individual events of protein production. Here we demonstrate a microfluidic-based assay that allows real-time observation of the expression of beta-galactosidase in living Escherichia coli cells with single molecule sensitivity. We observe that protein production occurs in bursts, with the number of molecules per burst following an exponential distribution. We show that the two key parameters of protein expression--the burst size and frequency--can be either determined directly from real-time monitoring of protein production or extracted from a measurement of the steady-state copy number distribution in a population of cells. Application of this assay to probe gene expression in individual budding yeast and mouse embryonic stem cells demonstrates its generality. Many important proteins are expressed at low levels, and are thus inaccessible by current genomic and proteomic techniques. This microfluidic single cell assay opens up possibilities for system-wide characterization of the expression of these low copy number proteins.

Discreteness-induced concentration inversion in mesoscopic chemical systems

“…For now, we consider m to be a time-independent constant. Later, we also study the case where m is itself a stochastic quantity, as it is typically in burst phenomena associated with protein production 32 .…”

“…Experiments have shown that proteins are produced in bursts, where the number of molecules per burst is distributed according to an exponential distribution 32 . We therefore study the situation where the burst size m is sampled, independently for each input event, from a geometric probability distribution, P(m) = p(1 − p) m − 1 , where p = 〈m〉 − 1 , and 〈m〉 is the average burst size.…”

Dynamic Single-Cell Analysis for Quantitative Biology

“…Because of the heterogeneity within a population, increased emphasis has been put on analyzing a large quantity of individual cells and determining the distributions of responses (18,21,22). Although population heterogeneity appears to be partly due to stochastic behavior within signaling pathways, a lack of control of the cellular microenvironment also may play a large role in the broadening of population distributions.…”

Hasard et destinée cellulaire

“…Ces mesures ont été ensuite reproduites dans les levures [2], organismes eucaryotes, démontrant qu'il ne s'agissait pas d'une spécificité des procaryotes. Ces conclusions ont été rapidement étoffées par comptage de molécules uniques au sein de cellules uniques [3], révélant que durant les phases d'activation du promoteur, les ARN sont transcrits de manière aléatoire sous la forme de « bouffées » ( Figure 1C). Une fois établie l'existence de sources de bruit, se pose la question de sa transmission à travers les réseaux d'interactions génétiques et de réactions enzymatiques.…”