Fear Deficits in Hypomyelinated Tppp Knock-Out Mice

Oligodendrocytes in the central nervous system (CNS) produce myelin sheaths that insulate axons to facilitate efficient electrical conduction. These myelin sheaths contain lamellar microtubules that enable vesicular transport into the inner sheath. Mechanistically, oligodendrocytes rely on Golgi outpost organelles and the associated protein tubulin polymerization promoting protein (TPPP) to nucleate or form new microtubules outside of the cell body. Consequently, elongation of lamellar microtubules is defective in Tppp knock-out (KO) mice, which have thinner and shorter myelin sheaths. We now explore the behavioral phenotypes of Tppp KO mice using a number of different assays. In open-field assays, Tppp KO mice display similar activity levels and movement patterns as wild-type mice, indicating that they do not display anxiety behavior. However, Tppp KO mice lack fear responses by two types of assays, traditional fear-conditioning assays and looming fear assays, which test for innate fear responses. Deficits in fear conditioning, which is a memory-dependent task, as well as in spatial memory tests, support possible short-term memory defects in Tppp KO mice. Together, our experiments indicate a connection between CNS myelination and behavioral deficits.