Control of the mitotic spindle by dynein light chain 1 complexes.

Robust control mechanisms ensure faithful inheritance of an intact genome through the processes of mitosis and cytokinesis. Different populations of the cytoplasmic dynein motor defined by specific dynein adaptor complexes are required for the formation of a stable bipolar mitotic spindle. This study analysed how different dynein subcomplexes contribute to spindle formation and orientation. Various dynein subpopulations were identified by mass spectrometry. I have shown that the dynein light chain 1 (DYNLL1) directly interacts with the kinetochore localised Astrin-Kinastrin complex as well as the spindle microtubule associated complex formed by CHICA and HMMR. I have characterised both complexes and identified unique functions in chromosome alignment and mitotic spindle orientation, respectively. I have found that Kinastrin (C15orf23) is the major Astrin-interacting protein in mitotic cells and is required for Astrin targeting to microtubule plus ends proximal to the plus tip tracking protein EB1. Fixed cell microscopy revealed that cells over-expressing or depleted of Kinastrin mislocalise Astrin. Additionally, depletion of the Astrin-Kinastrin complex delays chromosome alignment and causes the loss of normal spindle architecture and sister chromatid cohesion before anaphase onset (Dunsch et al., 2011). Using immunoprecipitation and microtubule binding assays, I have shown that CHICA and HMMR interact with one another, and target to the spindle by a microtubule-binding site in the amino-terminal region of HMMR. CHICA interacts with DYNLL1 by a series of conserved TQT motifs in the carboxy-terminal region. Depletion of DYNLL1, CHICA or HMMR causes a slight increase in mitotic index but has little effect on spindle formation or checkpoint function. Fixed and live cell microscopy reveal, however, that the asymmetric distribution of cor tical dynein is lost and the spindle in these cells fails to orient correctly in relation to the culture surface (Dunsch et al., 2012). These findings presented here suggest that the Astrin-Kinastrin complex is required for normal spindle architecture and chromosome alignment, and that per turbations of this pathway result in delayed mitosis and non-physiological separase activation, whereas HMMR and CHICA act as par t of a dynein-DYNLL1 complex with a specific function defining or controlling spindle orientation.This thesis is not currently available in ORA