Tend to generate alternative splicing a widespread mechanism of gene regulation

We observe only sporadic nuclear localization of Msn2-GFP, similar to observations of unconstrained cells, indicating that the general stress response pathway is not activated as a result of culturing cells in our device. Thriving in the constantly changing environments that cells typically inhabit requires an ability to identify and respond to stresses. A single transcription factor is involved in the activation of hundreds of different stress response genes. Msn2p has unusual dynamics, with alternative modes of nuclear shuttling that lead to activation of different subsets of genes. Responding appropriately to stress involves prima facie careful regulation. A cell that fails to sense a significant and increasing stress could fail to respond and thus be removed from the gene pool. Alternatively, stress responses cause the mobilization of large numbers of proteins. If a cell responds to a stress that fails to materialize fully, it would be disadvantaged relative to cells that did not, paying the cost of the response yet receiving no benefit. Even if cells could sense the external environment perfectly, they may respond differently depending on their own history and MOPS, sodium salt intracellular state. Imaging cells over tens of divisions and providing repeated stimuli is an opportunity to observe how individual cells adapt and modulate their responses to stress. As proof of principle for the capabilities of ALCATRAS for such experiments, we observed the response of cells to repeated limitations of glucose. When cells that are exposed to high glucose suddenly experience a low glucose environment, Msn2p-GFP becomes nuclear localized. The cell thus recognizes this nutrient limitation and activates a stress response using a single period of sustained nuclear localization followed by more stochastic localizations. The cells were grown to log phase in 2% glucose, and then introduced to the device. We switched the media to low glucose for 2 hours and then to high glucose for 6 hours. This sequence was repeated three times, and the responses of individual cells varied substantially. Trends did emerge when the cells were viewed as a collective. Compared to the first glucose limitation, the fraction of cells with nuclear Msn2p-GFP is reduced NPPB during the second and third limitations. We classified cells as having nuclear localized Msn2p if the nuclear localization was greater than the population mean of all cells over the whole time course plus one standard deviation.

Leave a Reply