The outer plate in vertebrate kinetochores is a flexible network with multiple microtubule interactions

Abstract

Intricate interactions between kinetochores and microtubules are essential for the proper distribution of chromosomes during mitosis. A crucial long-standing question is how vertebrate kinetochores generate chromosome motion while maintaining attachments to the dynamic plus ends of the multiple kinetochore MTs (kMTs) in a kinetochore fibre. Here, we demonstrate that individual kMTs in PtK(1) cells are attached to the kinetochore outer plate by several fibres that either embed the microtubule plus-end tips in a radial mesh, or extend out from the outer plate to bind microtubule walls. The extended fibres also interact with the walls of nearby microtubules that are not part of the kinetochore fibre. These structural data, in combination with other recent reports, support a network model of kMT attachment wherein the fibrous network in the unbound outer plate, including the Hec1-Ndc80 complex, dissociates and rearranges to form kMT attachments.

Long tethers provide high-force coupling of the Dam1 ring to shortening microtubules

“…We suggest that the fibrillar network observed at the outer kinetochore of all eukaryotic cells examined (29,30) plays a critical role in providing an environment suitable for stable and mechanically optimal attachments between chromosomes and spindle fibers through a ring, directly through the fibrils (31), or with the help of some other MT binding component, such as the Ska1 complex (32).…”

The perpetual movements of anaphase

“…Kinetochore and non-kinetochore microtubules in close proximity have been widely reported in the literature, with the best evidence provided by 3D-electron microscopy reconstructions of spindles and kinetochore microtubules [199,200] (Figure 4). Indeed, it has been estimated that every vertebrate kinetochore is tangentially associated with 3-8 non-kinetochore microtubules [200].…”

“…Indeed, it has been estimated that every vertebrate kinetochore is tangentially associated with 3-8 non-kinetochore microtubules [200]. Additionally, several proteins such as dynein and its co-factor NuMA, kinesin-14 members or the Drosophila microtubule associated protein ASP have also been implicated in spindle pole focusing by mediating microtubule crosslinking [91,201,202].…”

Rings, bracelets, sleeves, and chevrons: new structures of kinetochore proteins

“…The symmetry more closely matches that of the underlying microtubule, which may preclude the loose attachment required to maintain a floating grip on a dynamic microtubule and hints at an ordered interaction between the bound kinesin-13 motor domains on the longitudinal protofilament spiral and the wall of the microtubule lattice. Finally, recent tomography of the mammalian kinetochore found no rings (28).…”