An Equatorial Contractile Mechanism Drives Cell Elongation but not Cell Division
Figure 2
Localization of actin and actin-binding proteins in the equatorial region of notochord cells.
(A) A diagram of a notochord cell at 19 hpf. The notochord cells have a cylindrical shape, with two lateral domains at the anterior and posterior ends of the cell (designated as poles, arrowheads) to form contact with two adjacent notochord cells, and a single, circumferential, basal domain that contacts the notochordal sheath. During lumen formation the center of lateral domains differentiates into apical domain that contacts emerging lumen. The morphological constriction is located at the equator of the cell (arrow). (B and B′, section and projection) Colocalization of F-actin (green) and pS19 MRLC (red) in the equatorial region of the basal domain (yellow arrows). F-actin and pS19 MRLC are also localized in the lateral domains, where they partially overlap (arrowheads). (C) Maximal projection of notochord cells shows the localization of cofilin, α-actinin, tropomyosin, and talinA revealed by immunohistochemistry. Yellow arrows indicate the accumulation of these proteins in the equatorial region. (D) Maximal projection of notochord cells shows the localization of cofilin-mCherry, α-actinin-mCherry, mCherry-tropomyosin, and mCherry-talinA in live embryos. Whereas mCherry-α-actinin, mCherry-tropomyosin, and mCherry-talinA I/LWEQ localize in a broad region (yellow arrows), cofilin-mCherry consistently localizes in a narrow line at the equator (yellow arrowhead). Anterior to the left. Scale bars, 5 µm.