LET-99, GOA-1/GPA-16, and GPR-1/2 Are Required for Aster-Positioned Cytokinesis

Abstract

At anaphase, the mitotic spindle positions the cytokinesis furrow [1]. Two populations of spindle microtubules are implicated in cytokinesis: radial microtubule arrays called asters and bundled nonkinetochore microtubules called the spindle midzone [2-4]. In C. elegans embryos, these two populations of microtubules provide two consecutive signals that position the cytokinesis furrow: The first signal is positioned midway between the microtubule asters; the second signal is positioned over the spindle midzone [5]. Evidence for two cytokinesis signals came from the identification of molecules that block midzone-positioned cytokinesis [5-7]. However, no molecules that are only required for, and thus define, the molecular pathway of aster-positioned cytokinesis have been identified. With RNAi screening, we identify LET-99 and the heterotrimeric G proteins GOA-1/GPA-16 and their regulator GPR-1/2 [10-12] in aster-positioned cytokinesis. By using mechanical spindle displacement, we show that the anaphase spindle positions cortical LET-99, at the site of the presumptive cytokinesis furrow. LET-99 enrichment at the furrow depends on the G proteins. GPR-1 is locally reduced at the site of cytokinesis-furrow formation by LET-99, which prevents accumulation of GPR-1 at this site. We conclude that LET-99 and the G proteins define a molecular pathway required for aster-positioned cytokinesis.

Cytokinetic furrowing in toroidal, binucleate and anucleate cells inC. elegansembryos

“…Bringmann and colleagues (Bringmann et al, 2007) conducted a screen for components of the 'astral pathway'. Assuming that spd-1 mutants, lacking a central spindle, must depend solely on the astral mechanism, they sought genes required for zygote cytokinesis in a spd-1 background but not wild-type cells, and concluded that the astral pathway depends on LET-99, heterotrimeric G-proteins, and the G-protein regulator GPR-1/2.…”

“…Assuming that spd-1 mutants, lacking a central spindle, must depend solely on the astral mechanism, they sought genes required for zygote cytokinesis in a spd-1 background but not wild-type cells, and concluded that the astral pathway depends on LET-99, heterotrimeric G-proteins, and the G-protein regulator GPR-1/2. These are implicated in spindle positioning (Rose and Kemphues, 1998;Tsou et al, 2002;Tsou et al, 2003), and LET-99 localizes to the cortex in a band prefiguring the furrow (Bringmann et al, 2007;Tsou et al, 2002). However, LET-99 localization cannot explain the 'astral pathway' in AB: previous reports show that LET-99 is uniformly distributed in AB (Tsou et al, 2002), but we show here that AB has the same propensity as zygotes to furrow between two asters.…”

Cortical centralspindlin and Gα have parallel roles in furrow initiation in earlyC. elegansembryos

“…It would be intriguing to determine to which of the furrows ZEN-4::GFP localized in asymmetric spindle-severing assays, and whether depletion of par-2 and G␣ differentially affect these furrows. It has recently been proposed that LET-99 and the G-proteins are required for the aster-derived signal (Bringmann et al, 2007). The authors found that disruption of LET-99 and GPR-1/2 disrupted but did not completely block furrowing in spd-1(oj5) mutants and prevented furrow ingression in embryos in which the midzone was disrupted using laser ablation.…”

Cytokinesis microtubule organisers at a glance

“…The central spindle localisation of CLASP depends upon its interaction with PRC1 (Liu et al, 2009), similarly to its Schizosaccharomyces pombe orthologue cls1p (also called peg1p) (Bratman and Chang, 2007). Depletion of one of the three CLASPs in C. elegans causes a synthetic cytokinesis failure in PRC1 mutant embryos, which show only mild cytokinesis failure in the first cell division (Bringmann et al, 2007).…”