Xenbase Image ID: 129981

Figure 4. Xcnn2 Governs the Formation of the Polarized Cortical Actin Network in Migratory NCCs (A–C) Xenopus NCC explants from WT (A) and Xcnn2 morphant (B) embryos were cultured and the actin cytoskeleton was visualized by phalloidin staining. Nuclei were counterstained with DAPI. Panels show cells derived from the epithelioid-mesenchymal transition zone of explants. Magnifications of single WT (A′) and morphant (B′) cells are shown. Broken arrows in (A′) and (B′) indicate cell protrusions. (C) Wind rose diagrams depict the distribution of protrusion angles into eight segments spanning 45° each. Note that in WT explants, cell protrusions (n = 541 from 28 cells derived from six embryos) predominantly point in the distal direction, whereas morphant vectors (n = 521 protrusions, 22 cells, 5 embryos) are randomized. Bottom: Quantification of vector analysis. Morphant cells display significantly fewer distal protrusions (dark gray) and more proximal protrusions (light gray), caused by a loss of cortical actin and a gain of stress fibers. (D) Model of RhoA and Cnn2 acting downstream of PCP to polarize the actin cytoskeleton and direct NCC migration, and a schematic depiction of different migration states in NCC explant. Left: Epithelioid premigratory NCCs are characterized by actin stress fibers. They express RhoA at the plasma membrane (red), leading to Cnn2 phosphorylation and degradation. Middle: Cells at the margin of the epithelioid cell layer, which are about to leave the lattice, are polarized and characterized by central stress fibers and a peripheral cortical actin network. RhoA and Cnn2 (green) are expressed in a mutually exclusive manner such that Cnn2 is found where the cortical actin is localized and RhoA is found in the part of the cells that harbors stress fibers. Right: Migratory mesenchymal NCCs lack stress fibers and possess peripheral actin with colocalized Cnn2 throughout. RhoA is present in migratory mesenchymal cells but absent from the cortical actin network. Image published in: Ulmer B et al. (2013) Copyright © 2013. Image reproduced with permission of the publisher and the copyright holder. This is an Open Access article distributed under the terms of the Creative Commons Attribution License. Larger Image Printer Friendly View

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