The sequence of DNA is a code that contains all the information that is required for life (as we know it). DNA is stored inside the nucleus of cells and its sequence is replicated during cell division to ensure that the genetic information is transmitted to the daughter cells. The information contained in DNA is copied into RNA by a process called transcription. RNA acts as a messenger (mRNA) to carry the information between the nucleus and the cytoplasm, where it is used as a template to produce proteins through a process called translation. Proteins are the main effectors of all biological functions in the cell. However, the information required to make proteins (called “coding DNA sequence”) comprises only a small portion (~2%) of the entire human genome sequence. For several decades, it was generally accepted that the remaining 98% of the genome sequence had no biological function and, because of that, it was dubbed “junk DNA”. The discovery of non-coding DNA sequences that control the expression of genes challenged this idea, and revealed that there is biological function beyond protein-coding sequences. These non-coding sequences are called “regulatory elements” and they are classified into four classes according to their function: promoters, enhancers, insulators and silencers. Among them, enhancers play a critical role in activating the expression of genes in response to intra- and extra-cellular stimuli – which is essential for the development of complex organisms. Previous studies suggest that the human genome might contain more than one million enhancers – a much higher number compared to the
