Natural and induced genetic variation in the rat

The laboratory rat is one of the most studied model organisms for human heath and disease. Researchers have developed many inbred strains that specifically mimic aspects of human genetic disease, like hypertension, diabetes, and neurological disorders, like anxiety, schizophrenia, and many others. The development of such models largely depends on the amount of natural occurring variation. In this thesis, I describe a method to induce genetic variation in the rat and discover the newly induced mutations. Using this method, called target-selected mutagenesis or TILLING, we developed mutant rats and more importantly, knockout rats, harboring a mutation that abolishes gene function in a directed way. Besides inducing genetic variation, I also describe studies on naturally occurring genetic variation. Since inbred rat strains are specifically selected to mimic certain aspects of a human genetic disease, it is of importance to gain insight in the genetic variation that may cause this disease. Therefore, we sampled genetic variation in coding regions of over 50 rat genes in 96 commonly used inbred strains. In addition, we studied variation in wild rats, caught in The Netherlands and compared this to laboratory strains. We found that 84 percent of wild rat alleles was still represented in a set of 36 commonly used rat strains, illustrating that rat strains are descending from a limited founder population of domesticated wild rats relatively recently. Moreover, we postulate that wild rat-based shotgun sequencing is an efficient approach to discover novel genetic variation in the rat. Despite the advances reported in this thesis, we are still at the beginning of full understanding of the function of the mammalian genome. Even if we know the exact sequence variation in each rat model, we still don't know which of the sequence variants is functionally important for establishment of the disease. Therefore, the need for development of genetic experiments for the rat is inevitable, as described in the Introduction