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Lieven Thorrez (Katholieke Universiteit Leuven, Leuven, Belgium)Pancreatic beta cells regulate blood glucose level via insulin secretion. When destroyed or disfunctional, this leads respectively to type 1 or type 2 diabetes. Beta cells remain plastic after birth and adapt beta cell mass through cell apoptosis and renewal. Recently, it became apparent that beta cell mass increases during pregnancy. To gain insight in timing and mechanism of this phenomenon we studied gene transcription by means of expression microarrays. Samples were taken from female C57/Bl6 mice at different timepoints before, during and after pregnancy. This generated data for 45000 probesets over 7 timepoints in at least 3 replicates. To give a meaningful overview in a single picture, both for time dynamics and function, we visualized differentially expressed genes in the five largest functional categories by a network adapted from String. The main conclusion of this study -clearly apparent in the visualization- is that upregulation of cell cycle genes is the largest transcriptional change, leading to the observed increase in beta cell mass. This wave of cell cycle activation starts very early during pregnancy, peaks at day 9.5 and completely renormalizes at lactation.