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Fig. 6
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Figure Caption
Fig. 6. Aplnrb-sfGFP internalization allows detection of a Toddler concentration gradient.
(A) Schematic representation of transplantation assay in a wild-type host embryo. Transplantation of Aplnrb-sfGFP–expressing toddler−/− cells to the animal pole and margin of the host embryo. Insets display representative confocal images of transplanted cells at animal pole and margin in a wild-type host embryo. (B) Quantification Aplnrb-sfGFP internalization levels of marginal (M) and animal pole (AP)–located transplanted cells in wild-type [n(M) = 22, n(AP) = 29], toddler−/− [n(M) = 16, n(AP) = 21], or aplnrMO [n(M) = 17, n(AP) = 18] host embryos, as determined by the ratio of membrane to cytoplasm fluorescence intensity. (C) Ratio of membrane to cytoplasm fluorescence intensity of transplanted cells relative to their distance to the margin. P value indicates significance of regression being different to 0 as determined by F test. (D) Schematic representation of the self-generated Toddler gradient: (i) Toddler is ubiquitously expressed throughout the embryo cap. Mesodermal progenitors internalize at the margin and express Aplnr, which acts as a scavenger receptor for Toddler. (ii) Aplnr binds and internalizes Toddler, which generates a local Toddler concentration gradient in front of the mesodermal cells, providing a directional cue. (iii) Aplnr also acts as a chemokine receptor to sense the self-generated Toddler guidance cue and induces the directed migration of mesodermal cells toward the animal pole, while continuously internalizing Toddler and shaping the local gradient. Data are means ± SD. Significance was determined using one-way ANOVA with multiple comparison; ****P < 0.0001; **P < 0.01; *P < 0.05.
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