Effects of γ-Tubulin Complex Proteins on Microtubule Nucleation and Catastrophe in Fission Yeast

摘要

Although γ-tubulin complexes (γ-TuCs) are known as microtubule (MT) nucleators, their function in vivo is still poorly defined. Mto1p (also known as mbo1p or mod20p) is a γ-TuC–associated protein that recruits γ-TuCs specifically to cytoplasmic MT organizing centers (MTOCs) and interphase MTs. Here, we investigated γ-TuC function by analyzing MT behavior in mto1 Δ and alp4 (GCP2 homologue) mutants. These cells have free, extra-long interphase MTs that exhibit abnormal behaviors such as cycles of growth and breakage, MT sliding, treadmilling, and hyperstability. The plus ends of interphase and spindle MTs grow continuously, exhibiting catastrophe defects that are dependent on the CLIP170 tip1p. The minus ends of interphase MTs exhibit shrinkage and pauses. As mto1 Δ mutants lack cytoplasmic MTOCs, cytoplasmic MTs arise from spindle or other intranuclear MTs that exit the nucleus. Our findings show that mto1p and γ-TuCs affect multiple properties of MTs including nucleation, nuclear attachment, plus-end catastrophe, and minus-end shrinkage.