Tubulin Polymerization Promoting Protein Affects the Circadian Timing System in C57Bl/6 Mice

The circadian timing system (CTS) is a complex set of cyclic cellular mechanisms which serve to synchronize discrete cell groups across multiple organ systems to adapt the bodys physiology to a (roughly) 24-hour clock. Many genes and hormones have been shown to be strongly associated with the CTS, some of which include the genes Bmal1, Period1, Period2, Cryptochrome1, and Cryptochrome2, and the hormone melatonin. Previous data suggest that microtubule dynamics play an important role in melatonin function as it relates to the CTS in vitro, though this relationship has never been explored in vivo. The purpose of this study was to determine whether disruption of microtubule regulation in C57Bl/6 mice results in measurable changes to the CTS. To study the potential effects of microtubule dynamics on the CTS in vivo, we utilized a mouse model of microtubule instability, knocked out for the tubulin polymerization promoting protein gene (Tppp -/-), comparing them to their wild type (WT) littermates in three categories: locomotor activity (in light/dark and dark/dark photoperiods), serial clock gene expression, and serial serum melatonin concentration. These comparisons showed differences in all three categories, including significant differences in locomotor characteristics under dark/dark conditions. Our findings support and extend previous reports that microtubule dynamics are a modulator of circadian rhythm regulation likely through a mechanism involving melatonin induced phase shifting.