Much has been learned about actin dynamics from studying cultured cells in vitro; however, we know little about this process in the context of collective migration events, or how cytoskeletal regulators influence morphogenetic processes. Now, John Wallingford and colleagues (Devitt et al., 2021) investigate the role of actin modulators during morphogenesis in vivo. The authors use live imaging, as well as confocal and total internal reflection fluorescence imaging, to study lamellipodial protrusions in the Xenopus dorsal gastrula mesoderm, or dorsal marginal zone (DMZ). They find that the dynamics and composition of the Xenopus DMZ are similar to those in single migrating cells. Turning their attention to Cofilin2, the authors define its in vivo interactome in this tissue, and then focus on Twinfilin1, the most highly enriched interactor. They show that Twinfilin1 is required for axis elongation and convergent extension, as well as actin node and cable formation. Although the loss of Twinfilin1 does not seem to affect lamellipodial morphology, the dynamics of lamellipodial assembly are severely disrupted in the DMZ. Finally, the authors developed a method for in vivo fluorescent speckle microscopy to assess the impact of Twinfilin1 loss on actin turnover during convergent extension, finding that Twinfilin1 is required for rapid actin turnover and dynamic actin treadmilling. These data complement our existing knowledge of the action of Twinfilin1 in vitro and provide a link between the actin regulation machinery and the specialised cell behaviours that drive vertebrate development.
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