fig4: Steady-state expression levels of IEGs are adjusted according to glucose concentration. Min6 cells were cultured at indicated glucose concentrations for 20 h. mRNA levels for indicated genes were assessed by quantitative real-time RT-PCR and normalized with 18S rRNA. Results are expressed as mean of fold change compared to control condition (±SD, n = 3).

Mentions: Establishment of a new expression steady state upon sustained stimulation suggests that IEG induction is not solely a response to a sudden metabolic change, but rather that the levels of IEG expression are continuously adjusted according to metabolic status of the cell. We wondered whether this effect would occur on a longer time scale and whether this system will also sense subtle variations in the intensity of a metabolic stimulation. Thus, we determined the expression levels of two IEGs (c-fos and sgk1) after long-term culture (20 h) at various glucose concentrations (from 1 to 25 mM, but without co-stimulant). The results in Figure 4 show that the expression levels of both IEGs are gradually adjusted with increasing glucose levels. Notably, maximal variations occur within a physiological range of glucose concentrations between 5 and 10 mM. With these mild stimulations (as cpt-cAMP co-stimulant was not used), mRNA levels for the moderately-responding b3gt2 gene were not significantly affected (data not shown). However, after 20 h of co-stimulation with high glucose plus cpt-cAMP, we observed mRNA levels for b3gt2 and c-fos that were similar to those observed at 6 h (Figure 3 and data not shown).

Glauser DA, Schlegel W - Nucleic Acids Res. (2006)

Bottom Line: IEG expression persisted as long as stimulation was maintained, but was rapidly lost upon stimuli removal, abolishing the delayed induction.In conclusion, we propose that the network composed of IEGs and their dynamically functions to convert signal inputs of different durations into quantitative differences in global transcriptional adaptation.These findings provide a novel and more comprehensive view of dynamic gene regulation.

Affiliation: Fondation pour Recherches Médicales, University of Geneva, Switzerland.

Abstract: How cells convert the duration of signals into differential adaptation of gene expression is a poorly understood issue. Signal-induced immediate-early gene (IEG) expression couples early signals to late expression of downstream genes. Here we study how kinetic features of the IEG- system allow temporal integration of stimuli in a pancreatic beta cell model of metabolic stimulation. Gene expression profiling revealed that beta cells produce drastically different transcriptional outputs in response to different stimuli durations. Noteworthy, most genes (87%) regulated by a sustained stimulation (4 h) were not regulated by a transient stimulation (1 h followed by 3 h without stimulus). We analyzed the induction kinetics of several previously identified IEGs and . IEG expression persisted as long as stimulation was maintained, but was rapidly lost upon stimuli removal, abolishing the delayed induction. The molecular mechanisms coupling the duration of stimuli to quantitative transcription were demonstrated for the AP-1 transcription factor. In conclusion, we propose that the network composed of IEGs and their dynamically functions to convert signal inputs of different durations into quantitative differences in global transcriptional adaptation. These findings provide a novel and more comprehensive view of dynamic gene regulation.