Kinetochore fibers increase spindle microtubule density. (A) Relationship between spindle area and total tubulin fluorescence intensity for spindle types showing differences in microtubule density among spindle types. Large plot shows data averaged across 21 equally sized cross-sectional area bins, and small plots show raw data for X. laevis cycled and CSF spindles. (B) Example images and microtubule density violin plots for IgG control (n = 117) and Nuf2 antibody inhibition (n = 230) showing decreased microtubule density after interfering with kinetochore microtubule formation. ***, P < 10⁻¹³ for a two-sample Kolmogorov–Smirnov test.