Establishing an experimental-evolution-based method for understanding an incomplete penetrance mechanism in a model of C. elegans.

There is a wide range of diseases that manifest a not-fully-penetrant phenotype; however, the mechanism of the phenomena is still not clear. Incomplete penetrance is characterized by variability in the manifestation of the phenotypes, despite identical mutant alleles. In this work, we employ experimental evolution to reveal a compensatory mechanism developed through successive generations of selective pressure that eliminate the impaired phenotype.

We chose Caenorhabditis elegans due to its cellular complexity, and conservation of the disease pathways of interest while being much simpler than other animal models.

We then analyzed a population of c. elegans bearing a mutation in the fourth exon of daf-18, an ortholog of the human PTEN gene, which causes the protein to be truncated. Previous studies showed that human PTEN can replace DAF-18 in C. elegans, suggesting that human PTEN and DAF-18 are functionally similar and the regulation of PTEN is highly conserved in C. elegans.

The experiment was performed by application of strong selection for the desired starvation resistant phenotype. Fluctuation in the penetrance rate was observed shortly after beginning application of the selective pressure and till stabilization of a low penetrance phenotype. The adaptation occurred in less than 100 generations. Subsequent examination revealed several possible mechanisms of compensation. Genotyping of the evolving populations revealed a “wild type” phenotype in the background of mutation.

We are currently working to understand the molecular mechanism of compensation in the evolved population. Additionally, we are examining the evolutionary aspects of the adaptation using fitness-evaluation-genome-stability-analysis.