How to cope with (osmotic) stress

In the fission yeast S. pombe, the actin and microtubule cytoskeletons are crucial for polarised growth. Conditions of osmotic stress perturb growth in several ways (for instance, F-actin dissociates from growing tips and microtubules become static) – but what are the signalling pathways that mediate cell recovery? To address this question, Alasdair Robertson and Iain Hagan (p. 4055) investigate the impact of the stress-response MAP kinase pathway (SRP) and the actin-modulating kinase Ssp1 on the recovery of osmotically stressed S. pombe. The authors demonstrate that SRP signalling promotes the resumption of microtubule dynamics by activating the transcription factor Atf1. They show that the timely recovery of tip growth requires the activity of the SRP-pathway MAP kinase Sty1, whereas Ssp1 maintains correct polarity of tip growth. Moreover, Ssp1 and Wsh3 (an SRP-associated polarity factor) are required to select the correct site for polarised tip extension. Notably, the authors show that the cell-cycle kinase Polo – which is phosphorylated to promote recovery of tip growth in response to other environmental stresses – is not required for growth recovery after osmotic stress. These results identify key features of stress-response signalling in S. pombe, and highlight the specificity of cellular responses to distinct stresses.