Asymmetric spindle positioning

Abstract

SummaryWhen a spindle is positioned asymmetrically in a dividing cell, the resulting daughter cells are unequal in size. Asymmetric spindle positioning can be driven by regulated forces that can pull or push a spindle. The physical and molecular mechanisms that can position spindles asymmetrically have been studied in a number of systems, and some themes have begun to emerge from recent research. Recent work in budding yeast has presented a model for how cytoskeletal motors and cortical capture molecules can function in orienting and positioning a spindle. The temporal regulation of microtubule-based pulling forces that move a spindle has been examined in one animal system. Although the spindle positioning force generators have not been identified in most animal systems, the forces have been found to be regulated by both PAR polarity proteins and by G-protein signaling pathways in more than one animal system.

The Mos-MAPK pathway regulates Diaphanous-related formin activity to drive cleavage furrow closure during polar body emission in starfish oocytes

“…In these immature oocytes the germinal vesicle (GV) is positioned at the center (mammals) or close to the animal pole (echinoderms, amphibians and fish) (Johnson et al, 2011;Lénárt et al, 2003). Upon hormonal stimulation, oocyte maturation begins, germinal vesicle breakdown (GVBD) occurs, and small polar bodies are extruded from large oocytes by asymmetric spindle localization [polar body extrusion (PBE)] ( McCarthy and Goldstein, 2006). GVBD is a hallmark of the resumption of meiosis I and the first PBE is the hallmark of the completion of meiosis I.…”

The Spindle Midzone Microtubule-Associated Proteins Ase1p and Cin8p Affect the Number and Orientation of Astral Microtubules in Saccharomyces cerevisiae

“…[1][2][3][4] Mechanism that control nuclear positioning play a key role during animal development, such as in Caenorhabditis elegans embryos, Drosophila neuroblasts or more generally in stem cells, where asymmetric cell divisions are essential for proper cell fate. 3,4 Moreover, in some of these systems, perturbation of the asymmetrical division seems to be involved in tumor formation. 4,5 In budding yeast, the position of the division plane is defined by the neck between the mother cell and the bud, whereas in fission yeast it is defined by the position of the interphase nucleus.…”

Stu1 inversely regulates kinetochore capture and spindle stability

“…Cin8 and Kip1 (Saunders and Hoyt 1992), as well as a MT-binding protein Stu1 (Yin et al 2002), are important for establishing and maintaining this metaphase spindle; however, it is unclear how these proteins get activated upon prometaphase-to-metaphase transition. Astral MTs, emanating from the cytosolic side of the spindle pole bodies, interact with the cell cortex and position the metaphase spindle in the mother-bud axis (McCarthy and Goldstein 2006). Bipolar attachment of all sister KTs also satisfies the spindle assembly checkpoint (SAC).…”