A model for FAM29A-mediated MT amplification in spindle assembly and in k-fiber maturation. (A) Three major pathways for MT nucleation in mitosis: centrosome-dependent (I), chromatin-dependent (II), and FAM29A/MT-dependent (III). (B and C) Role of FAM29A-mediated MT amplification in spindle assembly and in k-fiber maturation. FAM29A recruits the NEDD1–γ-tubulin complex to MTs derived from centrosomes and chromatin to promote their amplification (IIIa and IIIb, respectively). Similarly, FAM29A also targets the NEDD1–γ-tubulin complex to a kinetochore MT, which then nucleates additional MT to promote k-fiber maturation (IIIc). MT flux then transports newly synthesized MTs to spindle poles. Drawings for various cellular structures are representative, but not to scale.