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Figure 1. (A) Illustration of a zebrafish embryo highlighting the somites (blue) and presomitic mesoderm (yellow). (B?E) Confocal images of integrin ?5-RFP (B and C) and ?V-GFP (D and E) in wild-type (WT) embryos. As the somite boundary (SB) forms, ?5 clusters to the basal side (dashed lines) of the anterior (A) and posterior (P) boundary cells (arrows). The white cross in (E) denotes a mesenchymal cell (MC) within a somite. Scale bars, 20 ?m. (F) Basal/apical ratio of integrin intensity in anterior (SB/A, solid line) and posterior (SB/P, dashed line) boundary cells. Data are mean ± SD from n = 15 cell pairs in six embryos. (G?L) Integrin ?5-Aquamarine (Aqm) and ?V-Aqm co-expressed with different integrin ? subunits tagged with mCitrine (mCit) in developing somites of MZ?5?/? embryos. (G) ?5?1, (H) ?V?1, (I) ?V?1-BiFC (bimolecular fluorescence complementation, used to increase heterodimer stability), (J) ?V?3, (K) ?V?5, and (L) ?V?6. Arrows in (H) indicate clustering on the somite border. Scale bars, 30??m. (M) Clustering quantification via the SB/MC intensity ratio. Details of ROI selection shown in Figure S1A. ?5?1, n = 18 measurements (12 embryos); ?V?1-BiFC, n = 21 (13 embryos); ?V?3, n = 18 (8 embryos); ?V?5, n = 16 (14 embryos); ?V?6, n = 19 (9 embryos). Data are mean ± SD. ???p < 0.0001; n.s., not significant (two-sided t test). See also Figure S1.