Erature. First, we verified that temperature had no impact on theErature. First, we verified that

Erature. First, we verified that temperature had no impact on the
Erature. First, we verified that temperature had no impact on the MFI of fixed cells (not shown) demonstrating that the observed effect was not due to a GSK089 clinical trials higher brilliance of an identical number of proteins. We then checked whether or not the temperature could induce changes in either cell size or cells number. Cells were grown for 5 days at different temperatures and analyzed. Regarding the cell division rate, we did not notice any significant effect of the temperature on its value, as assessed by blue trypan counting (Additional file 3: Figure SD3B). The cell volume (as assessed by flow cytometry, see “Methods”, Additional file 3: Figure SD3A) was affected by the temperature: we noted an increase by 20 of the cell size after 5 days at 35 and a decrease by 15 at 39 . One reason to check the effect of the temperature on the cell size and the cell growth rate was to be sure that the higher mCherry content measured at low temperature was not due to a reduction of the division rate and thus to an accumulation of the proteins in the cell. In such a case, we would notice a diminution of the growth rate and an increase of the cell size at 35 and the inverse would be true at 39 . Here, we do not notice any effect of temperature on the growth rate, which allows usrejecting this hypothesis. However, we do notice a size variation that is positively correlated with the overall in gene expression level. These two phenomena may therefore be part of the cellular response to PubMed ID:https://www.ncbi.nlm.nih.gov/pubmed/28461567 the variation of temperature (see “Discussion” below). Thus, the observed MFI variations are neither the consequence of a modification of the cell cycle, nor of intrinsic protein brilliance. It thus became reasonable to examine whether MFI variations may result from an effect of temperature on gene expression dynamics. We therefore examined how temperature changes could influence the fit of a two-state model of gene expression, which we previously demonstrated to account for fluorescent reporter gene expression distributions [9].Transcription burst sizes are systematically affected by temperatureThe two-state model describes the protein production process as a three-step process: transcription (that depends on the gene on ff cycling), mRNA dynamics (production vs. degradation) and protein dynamics (production vs. degradation). It thus incorporates six parameters, three of which cannot be distinguished in the conditions considered here and are thus treated as an aggregated parameter (see “Methods”), resulting in a 4 parameters model. Among these parameters, two can be measured experimentally: the protein and mRNA halflife (respectively 1/ and 1/ ). We therefore determined whether temperature variation was susceptible to influence their value. We observed that temperature had no influence on protein stability (Fig. 5). mRNA stability was differently affected: a significant threefold increase was detected at 39 , with no significant variation observed at 35 . Interestingly, this is exactly the oppositeArnaud et al. BMC Molecular Biol (2015) 16:Page 7 ofFig. 6). A suitable mathematical treatment (see “Methods”) allows to fit the experimental curves at the different temperatures, and to infer the underlying parameters. As can be observed on the example shown on Fig. 6a, the scale of the curve is significantly modified (horizontal dilatation), while the shape remains comparable. In other words, each transcription burst produces fewer proteins at higher temperatures,.