Evidence of kinesin motors involved in stable kinetochore assembly during early meiosis

The characteristic ‘bi-lobed’ organization of the kinetochores observed during mitotic metaphase is a result of separation of the sister kinetochores into two clusters upon their stable end-on attachment to the microtubules emanating from opposite spindle poles. In contrast, during metaphase I of meiosis despite bi-orientation of the homologs, we observe that the kinetochores are linearly dispersed between the two spindle poles indicating that pole-distal and pole-proximal kinetochores are attached laterally and end-on, respectively to the microtubules. Colocalization studies of kinetochores and kinesin motors suggest that budding yeast kinesin 5, Cin8 and Kip1 perhaps localize to the end-on attached kinetochores while kinesin 8, Kip3 resides at all the kinetochores. Unlike mitosis in budding yeast, in meiosis, the outer kinetochores assemble much later after prophase I. From the findings including co-appearance of kinesin 5 and the outer kinetochore protein Ndc80 at the centromeres after prophase I and a reduction in Ndc80 level in Cin8 null mutant, we propose that kinesin motors are required for reassembly and stability of the kinetochores during early meiosis. Thus, this work reports yet another meiosis specific function of kinesin motor.