Bmp Signaling Affects the Directionality of Cell Migration and the Functionality of Lamellipodia, but Not Lamellipodia Formation Per Se (A–C) Representative examples of time-lapse recordings of individual lateral mesodermal cells over 20 min with 1 min intervals (80%–85% epiboly stage). Dorsal is to the right, animal pole to the top; the start and end points are indicated by yellow and red asterisks, respectively. (D) Graphical illustrations of the total speed and the net dorsal speed of lateral mesodermal cells (in μm/hr; n = 20) in wild-type, has2 morphant, bmp2b morphant, and bmp2b-overexpressing embryos, calculated from time-lapse recordings as shown in (A)–(C). Error bars indicate standard errors, calculated by Excel software. (E) Newly formed lamellipodia per cell and hour in wild-type, bmp2b morphant, and bmp2b-overexpressing embryos from 80%–85% epiboly. Error bars indicate standard errors, calculated by Excel software. (F) 3D confocal reconstructions of individual mGFP-labeled lateral mesodermal cells at 85% epiboly stage; dorsal to the right. All cells form multiple lamellipodia, which project into random directions. Scale bar represents 10 μm. (G) Persistence (time between outgrowth and retraction in minutes) of dorsally (in blue) and ventrally (in red) projecting lamellipodia in embryos between 80% and 85% epiboly. Error bars indicate standard errors, calculated by Excel software. (H and I) Percentages of lamellipodia of mesodermal cells at 90° from the dorsal shield, for which lamellipodial retraction was coupled with a displacement of the cell body by at least half a cell diameter into the direction of their projection. Comparison of dorsally (in blue) and ventrally projecting (in red) lamellipodia in embryos between 75% and 80% epiboly (H) and between 85% and 90% epiboly (I). For every condition/column, 20–25 lamellipodia from 4–6 independent experiments were scored. See Figure S3 for examples. WT, wild-type; MO, bmp2b morphant; RNA, bmp2b-overexpressing. The data in (D), (E), and (G) are presented as mean ± SEM.
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