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BP: Fachverband Biologische Physik
BP 45: Systems biology
BP 45.5: Vortrag
Donnerstag, 19. März 2015, 16:00–16:15, H 1028
Competition between nucleosomes and transcriptional machinery determines the timing of genome activation in the zebrafish embryo — •Stefanie Belohlavy1, Jens Karschau1, Shai R. Joseph2, Mukesh Kumar2, Andrej Shevchenko2, Nadine L. Vastenhouw2, and Vasily Zaburdaev1 — 1MPI PKS, Dresden, Germany — 2MPI CBG, Dresden, Germany
In a developing embryo, many identical cells are formed by rapid cell divisions from one single egg cell. Initially, DNA is not readable for protein synthesis, and cells only rely on egg-provided resources. Then, once a certain number cells have been produced, DNA transcription starts. Why DNA is initially transcriptionally silent is a topic of strong debate. Previously, biological models of a repressor silencing DNA were proposed. In analogy to this idea, we experimentally show nucleosomes to act as a highly abundant repressor in zebrafish. To fully explain transcriptional activation, we propose a theoretical competition model. It consists of an activator (which only binds to specific sites) and a repressor (which has uniform probability to bind anywhere on the DNA). The exponential increase of DNA lowers the free repressor pool. Whenever a repressor leaves an activator site, activators rebind to it instead of a repressor triggering DNA transcription. Our model is consistent with our experimental advances: variations in the ratio of DNA to repressor shift the time of transcriptional onset. Future modifications to the strength of binding sites will help us to identify particular activators as theory and experiment continue to advance side by side.