In recent years significant steps have been made in enhancer-biology. Studies investigating enhancers have revealed two classes of enhancers: active or primed. Despite this recent advance it is still largely unknown how epigenetic marks functionally interact and in which order events take place during enhancer priming in the early embryo. In order to address these questions I will study enhancers during early zebrafish development, allowing easy access to large numbers of early stage embryos. I set myself three goals: 1) identify active enhancers at different time points during zebrafish development, 2) determine the order of events during enhancer priming and 3) determine the factors involved in enhancer priming. Importantly, all in the context of a developing embryo and as such free of potential cell-culture artifacts. To achieve this, DNA methylation profiling and ChIP-Seq of multiple epigenetic marks will be performed on zebrafish embryos at various early stages of development. From this data primed enhancers will be identified and will be further characterized using enhancer bulk assays such as 4C-Seq and CRISPR-mediated enhancer knock-outs, but importantly I will also aim for single-cell based methods using super high-resolution microscopy. Finally, factor(s) involved in priming/poising enhancers will be identified by motif search analysis and mass spectrometry-based experiments, followed by validation using reverse genetics techniques.During the course of this fellowship there will be a strong mix of guidance and the space to freely develop my own thoughts and experiments. In the hosting lab (Rene Ketting) postdocs really get the possibility to pursue their own ideas and this proposal is an excellent example of this. In summary, this project, in combination with the scientific environment available in the hosting laboratory, will be an excellent stepping-stone to reach full independence and start my own research group at a renowned institute.