Gene expression in sight: Single-molecule studies of gene expression control

Humans are multicellulair organisms, which means that the human body consists out of many individual cells. On average, the human body comprises an astounding number of 20 to 30 trillion cells. These cells are not all the same: for example there are skin cells, muscle cells, and nerve cells. Nowadays, it is estimated that over 400 different cell types can be found in the human body. The differences between our cells is not explained by the DNA that they contain. Instead, the differences arise because cells use or ‘read’ the DNA in distinct ways. The DNA consists of an enormous amount of nucleotides that together contain the information for approximately 30.000 genes. By controlling which genes are expressed, a cell can control if it becomes a skin cell or a muscle cell. Taken together this process is referred to as gene expression regulation. In this thesis we have studied three distinct processes that are involved in gene regulation. To study these processes we have used methods such as single-molecule imaging and single cell RNA sequencing. Using these methods we have studied how Argonaute2 finds and cleaves its RNA targets in a living cell. We have investigated how mRNA degradation is involved in remodelling the transcriptome during and after cell division. And, finally, we have set-up a method to assess how promoter-enhancer interactions result in active transcription.