Cancer is an evolutionary process driven by mutagenesis and selection for malignant phenotypes. Correspondingly, mutations that elevate mutation rates, producing a “mutator phenotype,” accelerate tumor formation. Heterozygous mutator alleles affecting the catalytic subunit of DNA polymerase (Pol) epsilon (encoded by the POLE gene) or bi-allelic mutations affecting mismatch repair (MMR) components, such as MSH2, arise frequently in a subset of colorectal and endometrial cancers. In some tumors, mutator alleles from both classes occur together and synergistically cause tremendous genetic instability. A key unanswered question is whether the severe mutation accumulation compromises tumor cell fitness and imposes a selection for “antimutator” phenotypes that allow the tumor to escape extinction. Evidence supporting the selection for antimutator alleles in strong mutator cells have been obtained using budding yeast, whose DNA replication and repair machinery are highly conserved with their mammalian counterparts. Our initial studies in haploid yeast show that mutations in the pol2 mutator alleles represent a major class of antimutator alleles. However, mutator suppression in diploid cells remains understudied. The strongest mutator allele known in human disease is POLE-P286R, which corresponds to pol2-P301R in yeast. We previously evolved diploid pol2-P301R/POL2 msh2Δ/msh2Δ mutator yeast strains to identify candidate antimutators that may arise in diploid cells. We also identified putative human antimutator alleles from The Cancer Genome Atlas database. Here, we test whether these alleles do indeed exert antimutator phenotypes by re-engineering them into diploid yeast. Our findings will provide a direct test of the relevance of antimutators for tumor evolution and define likely antimutator candidates for further study.

Pigs often have an anterior crossbite (underbite), where the maxillary incisors (upper anterior teeth) are positioned behind the mandibular incisors (lower anterior teeth) instead of in front as found in a normal dental relationship. In humans, when this condition is severe, proper feeding, speaking, and breathing can be impeded. An anterior crossbite can occur due to dental and/or skeletal malformations. Retro-inclination of the maxillary incisors or excessive pro-inclination of the mandibular incisors are dental contributors to this problem, whereas excessive growth of the mandible (lower jaw) or deficient growth of the maxilla (upper jaw) are skeletal causes. Pigs are a novel model for anterior crossbites in humans, yet it is unclear which dental or skeletal condition is the primary cause in pigs. Therefore, it is necessary to characterize this condition in pigs to translate this model to humans effectively. The purpose of this project is to determine if improper inclination of the incisors, mandibular prognathism, or maxillary retrognathism is the primary cause of anterior crossbites in pigs. A total of 150 pig skulls (120 dry skulls and 30 CT images) were included in this study. The angle of inclination of maxillary and mandibular incisors, length of the mandible, and length of the maxilla (estimated by the length of the hard palate) were measured in dry skulls using a metric protractor and ruler to the nearest degree or mm. The same measurements were taken on CT images using ImageJ software. Measurements will be compared between normal and affected pigs using t-tests and correlated to the severity of anterior crossbite using Pearson correlations. Based on the data I have acquired, I expect that the primary cause of anterior crossbites in pigs is maxillary retrognathism, also termed maxillary hypoplasia, and thus serves as a model for this specific condition in humans.