Measuring dynamic behavior of trinucleotide repeat tracts in vivo in Saccharomyces cerevisiae

Trinucleotide repeat (TNR) tracts are inherently unstable during DNA replication, leading to repeat expansions and/or contractions. Expanded tracts are the cause of over 40 neurodegenerative and neuromuscular diseases. In this chapter, we focus on the (CNG)_n repeat sequences that, when expanded, lead to Huntington’s disease (HD), myotonic dystrophy type 1 (DM1), and a number of other neurodegenerative diseases. We describe a series of in vivo assays, using the model system Saccharomyces cerevisiae, to determine and characterize the dynamic behavior of TNR tracts that are in the early stages of expansion, i.e., the so-called threshold range. Through a series of time courses and PCR-based assays, dynamic changes in tract length can be observed as a function of time. These assays can ultimately be used to determine how genetic factors influence the process of tract expansion in these early stages.