Tea4-phosphatase I landmark promotes local growth by dual Cdc42 GEF recruitment and GAP exclusion

Abstract

Cell polarization relies on small GTPases, such as Cdc42, which can break symmetry through self-organizing principles, and landmarks that define the axis of polarity. In fission yeast, microtubules deliver the Tea1-Tea4 complex to mark cell poles for growth, but how this complex activates Cdc42 is unknown. Here, we show that ectopic targeting of Tea4 to cell sides promotes the local activation of Cdc42 and cell growth. This activity requires that Tea4 binds the type I phosphatase (PP1) catalytic subunit Dis2 or Sds21, and ectopic targeting of either catalytic subunit is similarly instructive for growth. The Cdc42 guanine-nucleotide-exchange factor Gef1 and the GTPase-activating protein Rga4 are required for Tea4-PP1-dependent ectopic growth. Gef1 is recruited to ectopic Tea4 and Dis2 locations to promote Cdc42 activation. By contrast, Rga4 is locally excluded by Tea4, and its forced colocalization with Tea4 blocks ectopic growth, indicating that Rga4 must be present, but at sites distinct from Tea4. Thus, a Tea4-PP1 landmark promotes local Cdc42 activation and growth both through Cdc42 GEF recruitment and by creating a local trough in a Cdc42 GAP.

Casein kinase 1γ acts as a molecular switch for cell polarization through phosphorylation of the polarity factor Tea1 in fission yeast

“…; Kokkoris et al . ) supports this notion. Third, there may be additional phosphorylation sites within Tea1 that are carried out by another kinase (Kim et al .…”

“…Of note, the cell length of entrapment strains was somewhat longer than that of the WT cells, with some cells showing irregular shapes (in particular cells containing Cki3 KD -GFP and Tea1-GBP-mCherry), the reason for which is currently not yet being investigated further. It should, however, be noted that it was previously reported ectopic recruitment of Tea4 to cell sides leads to Cdc42 activation and growth initiation from these sites (Kokkoris et al 2014). As shown below, under this condition Tea4 is also colocalized with entrapped Tea1 (see below), which may account for these abnormal cell morphologies.…”

“…It should, however, be noted that it was previously reported ectopic recruitment of Tea4 to cell sides leads to Cdc42 activation and growth initiation from these sites (Kokkoris et al . ). As shown below, under this condition Tea4 is also colocalized with entrapped Tea1 (see below), which may account for these abnormal cell morphologies.…”

Cell Polarity in Yeast

“…Aligned microtubules deliver tip factors to the cell ends; such factors include Tea1 and its binding partner Tea4, which is a targeting subunit for protein phosphatase 1 (PP1) (Alvarez-Tabares et al 2007, Martin et al 2005, Mata & Nurse 1997, Tatebe et al 2005). In turn, local PP1 promotes activation of Cdc42 by affecting the localization of its regulators Gef1 (a GEF) and Rga4 [a GTPase-activating protein (GAP)] (Kokkoris et al 2014). PP1 may promote local association of Gef1 at cell tips by reversing the Gef1 phosphorylation catalyzed by Orb6 (a NDR/LATS-family kinase).…”

“…Orb6-mediated Gef1 phosphorylation promotes binding to 14-3-3, which displaces Gef1 from the cortex (Das et al 2009, 2015). In contrast to Gef1, the GAP Rga4 is excluded from cell tips through an unresolved mechanism (Kokkoris et al 2014, Tatebe et al 2008). Thus, cylindrical cell shape leads to aligned microtubules, which promote activation of Cdc42 at cell ends.…”