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Abstract
During determination of the cell division plane, an actomyosin contractile ring is induced at the equatorial cell cortex by signals from the mitotic apparatus and contracts to cause cleavage furrow progression. Although the small GTPase RhoA is known to regulate the progression, probably by controlling actin filament assembly and enhancing actomyosin interaction, any involvement of RhoA in division plane determination is unknown. In this study, using a trichloroacetic acid (TCA) fixation protocol we recently developed, we show that RhoA accumulates at the equatorial cortex before furrow initiation and continues to concentrate at the cleavage furrow during cytokinesis. We also demonstrate that both Rho activity and microtubule organization are required for RhoA localization and proper furrowing. Selective disruption of microtubule organization revealed that both astral and central spindle microtubules can recruit RhoA at the equatorial cortex. We find that centralspindlin and ECT2 are required for RhoA localization and furrowing. Centralspindlin is localized both to central spindle microtubules and at the tips of astral microtubules near the equatorial cortex and recruits ECT2. Positional information for division plane determination from microtubules is transmitted to the cell cortex to organize actin cytoskeleton through a mechanism involving these proteins.
Highlights
Cytokinesis is the final event in cell division that causes a cell to split into two daughter cells
The mitotic apparatus consists of three types of microtubule organization: spindle microtubules formed between two spindle poles, astral microtubules emanating radially from spindle poles, and central spindle microtubules, anti-parallel overlapping microtubules formed between sister chromatids after chromosomal segregation
RhoA accumulates at the equatorial cortex before furrowing depending on its activity and microtubule organizations To understand the spatial relationship between RhoA localization and the area of furrow initiation, we examined HeLa cells during the cell cycle fixed according to a TCAfixation protocol (Hayashi et al, 1999; Kosako et al, 2002; Yonemura et al, 2004)
Summary
Cytokinesis is the final event in cell division that causes a cell to split into two daughter cells. The division plane in animal cells is determined by microtubules of the mitotic apparatus. The contraction of a ring consisting of actin filaments, myosin II and other proteins induces ingression of the cleavage furrow (Guertin et al, 2002). The mitotic apparatus consists of three types of microtubule organization: spindle microtubules formed between two spindle poles, astral microtubules emanating radially from spindle poles, and central spindle microtubules, anti-parallel overlapping microtubules formed between sister chromatids after chromosomal segregation. Central spindle microtubules are tightly connected to each other by associated proteins (Guertin et al, 2002; Mollinari et al, 2002). Astral or central spindle microtubules are considered to be important for determination of the cell division plane (Burgess and Chang, 2005)
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