Figure 2.
Live imaging reveals the dynamics of cellular protrusions in different tissue contexts. (A) Schematic indicates embryonic stage and the red box shows imaging location in the migrating heart field. A indicates anterior and P, posterior. Mesodermal cardiac progenitor cells extend filopodia toward the surrounding tissues as the bilateral heart fields migrate toward the midline over the Anterior Intestinal Portal (AIP). White arrowhead indicates leading cardiac progenitor cells extending filopodia towards each other. The tissues surrounding the cardiac progenitor cells are pseudocoloured for clarity. (B) Inset of boxed region in A, 3 m later shows the first contact via a filopodium (white arrow) between the leading cardiac progenitor cells from each side. (C) Time series of filopodia projecting from cardiac progenitor cells towards the AIP. Filopodia contacting AIP cells (dark blue arrowheads) are longer and have higher persistence than free filopodia (light blue arrowheads). (D and E) Quantified in D and E, n = 86 filopodia from 4 embryos. *** P < 0.001 (Welch’s test for D and two-sided Mann-Whitney test for E). Violin plots show mean and first and third quartiles. (F) Schematic indicates the embryonic stage, and the red box shows the imaging location in the neural tube. Cellular protrusions of varying morphologies (white arrowheads) extend from the edges of the neural folds into the open lumen of the neural tube. (G) Protrusions reach across the neural tube lumen (white arrowhead) and contact the opposite neural fold close to the zippering point. (H and I) Neural tube (NT) closure is faster in embryos with more protrusions, n = 9 embryos. Shaded area in H indicates 95% C.I. **P < 0.01 (Student’s t test) in I. Violin plots show mean and first and third quartiles, n < 8: five embryos and n > 8: four embryos (Student’s unpaired two-sided t test). (J) High spatiotemporal resolution imaging reveals the highly dynamic nature of the neural tube protrusions. (K) Computationally masking the protrusions (left panel) allowed measurement of the area change over time, three examples shown from two embryos. (L) Schematic indicates the embryonic stage, and the red box shows the imaging location in the ectoderm. The ectodermal sheet contains transient apertures indicated by orange box. (M) Higher magnification of inset from L, pseudocoloured with a temporal code to reveal dynamic actin-based structures. (N) Kymographs made from regions indicated demonstrate contractile pulsations in cell junctions (1) and formation of lamellipodia by actin flow (2). (O) Speed of actin flow measured at lamellipodia, n = 39 flow waves from four cells. Graph shows mean ± SD.

Live imaging reveals the dynamics of cellular protrusions in different tissue contexts. (A) Schematic indicates embryonic stage and the red box shows imaging location in the migrating heart field. A indicates anterior and P, posterior. Mesodermal cardiac progenitor cells extend filopodia toward the surrounding tissues as the bilateral heart fields migrate toward the midline over the Anterior Intestinal Portal (AIP). White arrowhead indicates leading cardiac progenitor cells extending filopodia towards each other. The tissues surrounding the cardiac progenitor cells are pseudocoloured for clarity. (B) Inset of boxed region in A, 3 m later shows the first contact via a filopodium (white arrow) between the leading cardiac progenitor cells from each side. (C) Time series of filopodia projecting from cardiac progenitor cells towards the AIP. Filopodia contacting AIP cells (dark blue arrowheads) are longer and have higher persistence than free filopodia (light blue arrowheads). (D and E) Quantified in D and E, n = 86 filopodia from 4 embryos. *** P < 0.001 (Welch’s test for D and two-sided Mann-Whitney test for E). Violin plots show mean and first and third quartiles. (F) Schematic indicates the embryonic stage, and the red box shows the imaging location in the neural tube. Cellular protrusions of varying morphologies (white arrowheads) extend from the edges of the neural folds into the open lumen of the neural tube. (G) Protrusions reach across the neural tube lumen (white arrowhead) and contact the opposite neural fold close to the zippering point. (H and I) Neural tube (NT) closure is faster in embryos with more protrusions, n = 9 embryos. Shaded area in H indicates 95% C.I. **P < 0.01 (Student’s t test) in I. Violin plots show mean and first and third quartiles, n < 8: five embryos and n > 8: four embryos (Student’s unpaired two-sided t test). (J) High spatiotemporal resolution imaging reveals the highly dynamic nature of the neural tube protrusions. (K) Computationally masking the protrusions (left panel) allowed measurement of the area change over time, three examples shown from two embryos. (L) Schematic indicates the embryonic stage, and the red box shows the imaging location in the ectoderm. The ectodermal sheet contains transient apertures indicated by orange box. (M) Higher magnification of inset from L, pseudocoloured with a temporal code to reveal dynamic actin-based structures. (N) Kymographs made from regions indicated demonstrate contractile pulsations in cell junctions (1) and formation of lamellipodia by actin flow (2). (O) Speed of actin flow measured at lamellipodia, n = 39 flow waves from four cells. Graph shows mean ± SD.

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