Spindly/CCDC99 Is Required for Efficient Chromosome Congression and Mitotic Checkpoint Regulation

Abstract

Human Spindly is required for kinetochore localization of cytoplasmic dynein, which is essential for poleward movement of chromosomes and for kinetochore protein streaming. In addition, Spindly controls the activity and kinetochore abundance of the RZZ complex, which contributes to microtubule attachment and mitotic checkpoint activity.

Spindly switch controls anaphase: Spindly and RZZ functions in chromosome attachment and mitotic checkpoint control

“…In human cells, however, neither Mad2 recruitment to unattached kinetochores nor its removal from bi-oriented kinetochores was strongly affected by loss of Spindly function. [32][33][34][35] The reasons for these differences are not clear at the moment but might be due to the different structures of kinetochores in these species. 91 The chromosome congression defect induced by Spindly knockdown in Drosophila was weaker than that observed in C. elegans and human cells and resembled a DHC depletion phenotype, previously shown to interfere with the onset of anaphase.…”

“…The strong chromosome congression defect seen in Spindly RNAi cells depended on the RZZ complex and was not seen when RZZ function was compromised, although in both cases Spindly-and dynein-were absent from kinetochores. 32,34 These observations rather suggested an important novel function of the RZZ complex in the maturation of stable "end-on" attachments and suggested a regulatory function of Spindly in this process (Fig. 2).…”

“…41,56 Kinetochore stripping commences with stable microtubule attachment and evidence has been obtained that this removal can be asymmetric, affecting only one of sister-kinetochore in the case of monopolar attachments. 32 Complete removal of the RZZ complex from kinetochores, however, depends on tension because residual RZZ levels are retained on kinetochores in taxol treated cells, to maintain Mad2-dependent mitotic arrest in an Aurora B kinase dependent manner. 82 Whether the RZZ is directly controlled by Aurora kinase B activity has not been established yet but it is possible that intrakinetochore stretching 54 could displace RZZ components from Aurora B kinase.…”

“…The localization of Spindly to kinetochores depends on RZZ and a direct physical, albeit weak, interaction between the RZZ complex and Spindly could be confirmed by co-immunoprecipitation experiments. [32][33][34] In addition, depletion of any of the RZZ subunits caused destabilization of the other subunits as well as Spindly, 32,33 suggesting that Spindly is part of the RZZ complex. Spindly is required for the kinetochore localisation of dynein.…”

The Spindle Assembly Checkpoint: Clock or Domino?

“…The spindle assembly checkpoint proteins Mad1, Mad2, and BubR1, are removed from kinetochores upon microtubule attachment and transported along microtubules to the spindle pole (Howell et al 2000, a transition that is supposed to silence the signal emanating from kinetochores. This spindle checkpoint protein depletion system uses the dynein/dynactin motor protein and specialized dynein binding partners on kinetochores, composed of the RZZ complex (Rod, ZW10 and Zwilch) and Spindly (Barisic et al 2010;Chan et al 2009;Clute and Pines 1999;Gassmann et al 2008Gassmann et al , 2010Griffis et al 2007;Howell et al 2001;Karess 2005;Yamamoto et al 2008). However, experimental evidence suggest that these proteins cannot be the only silencing system, as cells lacking Spindly still silence the checkpoint upon chromosome alignment (Gassmann et al 2010).…”