…Dr. Holly A. Wichman
L1 elements have been active in mammals for over 150 million years and make up about 20% of the genome. Most of the copies in the genome are ancient molecular fossils, so it is a challenge to sift through all of the old copies to find those that have been recently active. Using a vector system developed in the lab to identify markers from recently transposed elements, we have examined the evolution of L1 retroposons in 7 orders of mammals. We recently identified a group of South American rodents in which L1s appear to have ceased transposition.
This group will be a useful model system to study the impact of L1s on the genome. In addition to their direct effects on genes and genomes, L1s are thought to provide the transpositional machinery that moves small, non-autonomous elements and produces pseudogenes. It has also been proposed that L1s play a role in X chromosome inactivation. We are currently testing these ideas in South American rodents with and without active L1s.
Short-term adaptation to the environment can be observed in real time, and it is short-term evolution that contributes to health problems such as drug resistance and host switching. We study short-term adaptation at the molecular level to ask whether it is possible to learn the rules of molecular evolution on this time scale. We are currently using the bacteriophage phiX174 and its relatives to study the molecular basis of host switching. We have identified specific residues important for host recognition. During experimental evolution, these residues undergo repeated forward and backward substitutions which each host switching event. We can now study the generality of these results by evolving to different hosts.