Previous work by Képiró et al. describing the photostable blebbistatin derivative para-nitroblebbistatin was inadvertently omitted from the reference list of this Article and should have been cited at instances where this inhibitor is referred to. For example, in the Results section, Képiró et al. should have been cited as follows: ‘To test this hypothesis, we used a non-phototoxic form of Blebbistatin (para-nitroblebbistatin), which impairs cell migration (Supplementary Fig. 2c) and is compatible with GFP imaging (Képiró et al.)’.Képiró, M. et al. para-Nitroblebbistatin, the non-cytotoxic and photostable myosin II inhibitor. Angew. Chem. Int. Ed. Engl. 53, 8211–8215 (2014).