Negative control of cytokinesis by stress-activated MAPK signaling.

Mitogen-activated protein kinase (MAPK) signalling pathways regulate multiple cellular functions in eukaryotic organisms in response to environmental cues, including the dynamic remodeling of the actin cytoskeleton. The fission yeast S. pombe is an optimal model to investigate the conserved regulatory mechanisms of cytokinesis, which relies in an actomyosin-based contractile ring (CAR) that prompts the physical separation of daughter cells during cellular division. Our group has recently shown that p38 MAPK ortholog Sty1, the core component of the stress-activated pathway (SAPK), negatively modulates CAR assembly and integrity in S. pombe during actin cytoskeletal damage induced with Latrunculin A and in response to environmental stress. This response involves downregulation of protein levels of the formin For3, which assembles actin filaments for cables and the CAR, likely through an ubiquitin-mediated degradation mechanism. Contrariwise, Sty1 function positively reinforces CAR assembly during stress in the close relative dimorphic fission yeast S. japonicus. The opposite effect of SAPK signaling on CAR integrity may represent an evolutionary refined adaptation to cope with the marked differences in cytokinesis onset in both fission yeast species.