Stable kinetochore–microtubule interactions depend on the Ska complex and its new component Ska3/C13Orf3

Abstract

Ska1 and Ska2 form a complex at the kinetochore-microtubule (KT-MT) interface and are required for timely progression from metaphase to anaphase. Here, we use mass spectrometry to search for additional components of the Ska complex. We identify C13Orf3 (now termed Ska3) as a novel member of this complex and map the interaction domains among the three known components. Ska3 displays similar characteristics as Ska1 and Ska2: it localizes to the spindle and KT throughout mitosis and its depletion markedly delays anaphase transition. Interestingly, a more complete removal of the Ska complex by concomitant depletion of Ska1 and Ska3 results in a chromosome congression failure followed by cell death. This severe phenotype reflects a destabilization of KT-MT interactions, as demonstrated by reduced cold stability of KT fibres. Yet, the depletion of the Ska complex only marginally impairs KT localization of the KMN network responsible for MT attachment. We propose that the Ska complex functionally complements the KMN, providing an additional layer of stability to KT-MT attachment and possibly signalling completion of attachment to the spindle checkpoint.

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

“…8,9 The kinetochore protein assemblies, from the inner towards the outer plate, contain the large constitutive centromere associated network (CCAN), consisting of approximately 14 proteins, and the KMN complex, which contains ten proteins in three subunits, called the Knl1, Mis12 and Ndc80 complexes. In addition to these components, which are required for microtubule binding, 10 there are many others that may stabilize microtubule binding, such as the Ska/ Rama complex, [11][12][13] or regulatory complexes like the chromosome passenger complex (CPC), 14,15 the RZZ complex 16 as well as additional proteins that control microtubule dynamics, 17 and other proteins. 1 One very important property of the kinetochore microtubule binding sites is that they have to be robust enough to withstand the pulling forces of the mitotic spindle without blocking the dynamic instability of microtubules.…”

“…Upon binding of microtubules to Ndc80, the Ska complex assembles to stabilize these interactions and both complexes are essential for the formation of stable loadbearing end-on attachments. 12 The formation of microtubule attachments is, however, based on initially stochastic interactions in the cytoplasmic space of mitotic cells. Because mathematical calculations suggested that the originally proposed 'search-and-capture mechanism' 22 would ©2 0 1 1 L a n d e s B i o s c i e n c e .…”

Long non-coding RNA SPRY4-IT1 promotes the proliferation and invasion of U251 cells through upregulation of SKA2

“…SKA2 has been reported to locate to the kinetochore-microtubule interface during mitosis, whereas SKA-depleted cells cause chromosome congression defects and subsequently cell death (18,32). A prior study revealed that A549 cells were treated with a microRNA-301 inhibitor or SKA2-specific siRNA, the mitotic index of the cells significantly increased, with a corresponding decrease in the colony formation ability (33).…”

Divalent Cations Affect the Stability and Structure of Dad2p, a Subunit of the Candida Albicans Kinetochore Dam1 Complex

“…This difference has been postulated to reflect the more stringent requirement for maintaining connection with the depolymerizing microtubule when a single point of attachment is present; thus, under these circumstances, the ring may provide necessary stability (Burrack et al, 2011;Thakur & Sanyal, 2011). Outside of the yeasts, sequence-based homologues of the Dam1 complex proteins are not identifiable, though a variety of evidence suggests that the functional homologue in metazoans may be the Ska complex (Gaitanos et al, 2009;Guimaraes & Deluca, 2009;Hanisch, Sillje, & Nigg, 2006;Jeyaprakash et al, 2012;Welburn et al, 2009). …”