Pitstop 2 does not affect microtubule nucleation from the mitotic spindle poles. A, Metaphase synchronized HeLa cells were treated as described in Figure 2C then subjected to a MT regrowth assay whereby the MTs were allowed to regrow for 5 mins following depolymerization. Cells were fixed and stained for γ-tubulin (green), α-tubulin (red), and DNA (DAPI, blue). B-C, The dot blots show the length of the longest MT grown from each spindle pole in HeLa cells treated with the indicated siRNA (B) or drugs (C) as described in A. The median MT length in each experimental condition is indicated by the solid black line. n≥30 per sample. Statistical significance was determined by a Student’s t-test (* p < 0.05, ** p < 0.01).