The functions of many genes are illuminated by the study of mice with visible phenotypes (e.g. changes in development morphology, behavior, or metabolism) induced by ENU. Mutations in these mice are positionally cloned with interest. Recently, mutations in Tmprss6 and Ptpn6 were found to cause iron deficiency due to impaired iron uptake (18) and autoimmune and inflammatory disease (14), respectively. The phenotypes were first discovered in unchallenged mice because of visible defects: hair loss in Tmprss6mask/mask mice, and spontaneous foot inflammation in Ptpn6spin/spin mice. Of particular interest in the case of the Ptpn6 mutant spin, the autoimmune and autoinflammatory phenotypes were shown to depend upon both a microbial trigger and IL-1 receptor signaling (Figure 1).
Because of the link between pigmentation and immune function, a wide variety of mutants with variations in coat color are also under investigation (Figure 2).
Behavioral mutations such as Possum have revealed links between the peripheral nervous system and the central nervous system that would not otherwise have been suspected (19). And circling mutants, such as add, led to the identification of a new cause of deafness in humans (20). To date, 379 transmissible mutations that cause discernable phenotypes have been set aside for positional cloning in the Beutler laboratory; 254 mutations have been mapped to chromosomes and in 230 instances, molecular identification of the causative mutation has been made. These mutations fall within 156 genes. 215 of the mutations studied affect immunity, and about half of the mutations affecting immunity that are cloned prove to be novel in the sense that no such phenotype had been predicted by knockout mutations, or knockouts had not been generated.
While we specialize in the forward genetic approach, our current method of finding mutations, whole exome sequencing, permits us to identify most, if not all, of the changes ENU makes in every mouse genome. By saving sperm from G1 mutant male mice, we have begun to accumulate an allelic series at all loci in the mouse. Within a few years, putative null alleles for most loci should be readily available as a result.
The lab is sustained by dedicated staff highly trained in mutation mapping, DNA sequencing, and mutation finding (much of which is performed robotically and computationally). A core devoted to germline cryopreservation, intracytoplasmic sperm injection (ICSI), transgenesis, stem cell work, and gene targeting has also been established. These facilities make it possible to positionally clone many targets each year. A skilled and dedicated postdoctoral fellow or graduate student may expect to identify 5 to 10 mutations over the course of his or her stay in the laboratory (and some have found more than 30 mutations).
The long-range goal of the laboratory is to identify the key genes required for resistance to infection (the mammalian "resistome") and determine how they interact with one another. But as genetics is a form of exploration in which surprising phenotypes can and do arise, many different lines of inquiry are pursued. In this way the lab has solved basic questions in multiple fields. Please visit our Mutagenetix website to view the expanding list of mutations that we have produced and solved.