Although it is generally believed that microtubules have minus ends bound to the centrosome and free plus ends that exhibit dynamic instability, recant observations show that the minus ends can be free and that modulation of dynamic instability at both ends can result in treadmilling and flux in interphase calls.
Waterman-Storer, C. M., & Salmon, E. D. (2004). Microtubule dynamics: Treadmilling comes around again. Current Biology, 7(6), R369–R372. https://doi.org/10.1016/s0960-9822(06)00177-1