Cnn1 inhibits the interactions between the KMN complexes of the yeast kinetochore

Abstract

Kinetochores attach the replicated chromosomes to the mitotic spindle and orchestrate their transmission to the daughter cells. Kinetochore–spindle binding and chromosome segregation are mediated by the multi-copy KNL1Spc105, MIS12Mtw1 and NDC80Ndc80 complexes that form the so-called KMN network. KMN–spindle attachment is regulated by the Aurora BIpl1 and MPS1Mps1 kinases. It is unclear whether other mechanisms exist that support KMN activity during the cell cycle. Using budding yeast, we show that kinetochore protein Cnn1 localizes to the base of the Ndc80 complex and promotes a functionally competent configuration of the KMN network. Cnn1 regulates KMN activity in a spatiotemporal manner by inhibiting the interaction between its complexes. Cnn1 activity peaks in anaphase and is driven by the Cdc28, Mps1 and Ipl1 kinases.

Regulation of outer kinetochore Ndc80 complex-based microtubule attachments by the central kinetochore Mis12/MIND complex

“…It could also explain why Ndc80 is detected only at the kinetochore whereas other microtubule binding components of the kinetochore are also detected all along the spindle microtubules (36). Cnn1 provides a distinct Ndc80 receptor during anaphase (13,15,16). It will therefore be interesting to learn whether and how Cnn1 affects Ndc80's microtubule affinity.…”

“…However, it is unknown whether these structural changes correlate with changes in microtubule affinity. The Ndc80 complex also interacts with a second kinetochore receptor, CENP-T/Cnn1 (13)(14)(15)(16). It is unclear how central kinetochore components influence the activity of the Ndc80 complex throughout mitosis.…”

The Centromere: Epigenetic Control of Chromosome Segregation during Mitosis

“…For example, the role of a CENP-T-containing complex in recruiting the Ndc80 complex and the function of CENP-C in recruiting of the Mis12 complex, suggests different functions of the kinetochore are brought to centromeres through different activities of core centromere proteins. However, despite this modularity, there is significant cross talk between centromere components to stably form a functional centromere and kinetochore; Mis12 and CENP-T compete for Ndc80 binding (Bock et al 2012;Schleiffer et al 2012;Nishino et al 2013) and a CENP-N/L heterodimer binds CENP-C (Carroll et al 2009;Hinshaw and Harrison 2013), presumably as part of a CENP-A nucleosome-containing complex. Pinpointing how and when different centromere modules interact remains an exciting challenge.…”

“…A nonphosphorylatable CENP-T amino-terminal tail disrupts kinetochore function as it cannot fulfill these functions (Gascoigne et al 2011). Interestingly, the Mis12 complex also binds Spc24/25 in the same manner as CENP-T, and CENP-Tand Mis12 compete for Ndc80 binding, which may influence the stability of kinetochore microtubule attachments (Bock et al 2012;Schleiffer et al 2012). Furthermore, phosphoregulation of Mis12 and/ or CENP-T could control switching between different microtubule-binding modes within kinetochores.…”

“…A second essential step in KMN protein assembly at centromeres is binding of the Spc24/25 components of the Ndc80 complex by the phosphorylated aminoterminal tail of CENP-T. This conserved interaction forms stable, load-bearing attachments to microtubules via the Ndc80 complex (Bock et al 2012;Schleiffer et al 2012;Malvezzi et al 2013;Nishino et al 2013). A nonphosphorylatable CENP-T amino-terminal tail disrupts kinetochore function as it cannot fulfill these functions (Gascoigne et al 2011).…”