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Fig. 3. Inhibition of myosin function leads to defects in the recruitment of cortical ß-catenin to the furrow. Control (A,B,E,F,I,J), blebbistatin-treated (C,D,G,H,K,L) and ML7-treated (M,N) embryos labeled with anti-ß-catenin (green) and anti-
-tubulin (red) antibodies. In control embryos, ß-catenin is initially recruited at the first furrow as aligned punctae of aggregates (arrowheads in A,B) and later forms a contiguous line (arrowheads in E,F,I,J). During these stages, a field of ß-catenin-rich cortical aggregates can be observed centered on the prospective second cleavage furrow (bracket in A). These aggregates will also coalesce into a contiguous line as the second furrow develops (arrow in I). In blebbistatin-treated embryos, the enrichment of aggregates centered on the prospective furrow occurs (bracket in C) and some ß-catenin punctae align at the forming furrow (arrowhead in C,D), but there is no further recruitment of ß-catenin at the furrow as a contiguous structure (arrowheads and arrows in G,H,K,L). Instead, ß-catenin cortical aggregates remain dispersed. A ß-catenin-free region often develops flanking the furrow center (brackets in G), which may correspond to the region where internal membrane has undergone localized exocytosis. Microtubule labeling shows the lack of FMA remodeling in myosin-inhibited embryos (shown in detail in Fig. 4). (M,N) Embryos treated with ML7 also exhibit defects ß-catenin recruitment to the furrow and in FMA remodeling. Arrowheads, arrows and asterisks indicate first, second and third cleavage furrows, respectively. Bar, 50 µm (A,C,E,G,I,K,M) and 16 µm (B,D,F,H,J,L,N).
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