Anastral meiotic spindle morphogenesis: role of the non-claret disjunctional kinesin-like protein.

Abstract

Abstract. We have used time-lapse laser scanning confocal microscopy to directly examine microtubule reorganization during meiotic spindle assembly in living Drosophila oocytes. These studies indicate that the bipolarity of the meiosis I spindle is not the result of a duplication and separation of centrosomal microtubule organizing centers (MTOCs). Instead, microtubules first associate with a tight chromatin mass, and then bundle to form a bipolar spindle that lacks asters. Analysis of mutant oocytes indicates that the Non-Claret Disjunctional (NCD) kinesin-like protein is required .... for normal spindle assembly kinetics and stabilization of the spindle during metaphase arrest. Immunolocalization analyses demonstrate that NCD is associated with spindle microtubules, and that the centrosomat components ~/-tubulin, CP-190, and CP-60 are not concentrated at the meiotic spindle poles. Based on these observations, we propose that microtubule bundling by the NCD kinesin-like protein promotes assembly of a stable bipolar spindle in the absence of typical MTOCs.

An ATM- and ATR-dependent checkpoint inactivates spindle assembly by targeting CEP63

“…However, mitotic spindles can form in the absence of centrosomes through actions of motor proteins and structural elements (Theirkauf and Hawley, 1992;Bartolini and Gundersen, 2006;Walczak et al, 1998;Compton, 1998;McKim and Hawley, 1995;Matthies et al, 1996;Heald et al, 1997). It is commonly believed that centrosome functions have not been fully elucidated.…”

“…Anastral spindle assembly is prevalent in higher plants, meiotic cells and in some other cell types (Theirkauf and Hawley, 1992;Bartolini and Gundersen, 2006). In the process of spindle self-assembly, chromatin promotes microtubule polymerisation and actions of motor proteins aid sorting and organisation of microtubules into a bipolar spindle array (McKim, and Hawley, 1995;Heald et al, 1997;Theurkauf and Hawley, 1992;Matthies et al, 1996;Khodjakov and Rieder, 2001). …”

Emerging molecular mechanisms that power and regulate the anastral mitotic spindle of flowering plants

“…ATK5 tracks to the plus end of microtubules in all stages of the cell cycle, independent of the motor domain, but its motor activity is minus-end-directed [Ambrose et al, 2005]. These authors propose that the plus-end tracking targets ATK5 to the spindle midzone, from where it helps to focus the poles by crosslinking parallel microtubules and walking toward the minus ends, as has also been suggested for NCD in Drosophila [Matthies et al, 1996].…”

“…In animals and fungi, these motor proteins are responsible for the inward directed forces on the spindle, balancing the outward forces, focusing the poles, and drawing the spindle halves together. The founder member of the family is nonclaret disjunctional (NCD), discovered on the basis of a Drosophila loss-of-function mutant that caused chromosome nondisjunction and spindles with broad, unfocused poles in oocytes and embryos [Hatsumi and Endow, 1992;Matthies et al, 1996].…”

Spindle assembly in the oocytes of mouse and Drosophila – similar solutions to a problem

“…The role of interpolar microtubules in mouse acentrosomal spindle assembly has not been investigated. in the sections that follow, is based on both fixed (Theurkauf & Hawley 1992, Jang et al 2005 and living (Matthies et al 1996, Skold et al 2005 oocytes. The organization of the microtubules in early prometaphase I is promoted by the chromosomes, which recruit and/or nucleate the microtubules.…”