Figure 5

The behaviour of anterior and posterior primitive streak explants is affected by Wnt3a and Wnt5a. Embryos were electroporated with pCS2⁺GFP and following GFP expression explants were dissected from anterior and posterior primitive streak as indicated in the drawings. Explants were placed on the area opaca of a host embryo (HH4). Labelled cells were imaged overnight and still images are shown at zero and 16 hours. Timelapse sequences were scored as migratory if they contained individual cells migrating away from the explant. χ² analysis was used to determine if changes in explant behaviour were statistically significant. (A) Control explants from a HH5 embryo; cells are migratory. (B) Explants from the anterior primitive streak of a HH8 embryo; cells remained cohesive and few individual cells moved away from the explants. This behavior was not affected by Wnt3a expressing cells, but in response to Wnt5a the explants dispersed and more migrating cells were observed. Anterior explants exposed to both Wnt3a and Wnt5a remained cohesive. (C) Explants from the posterior primitive streak of a HH8 embryo contained many cells migrating away and most of the explant dispersed by the end of imaging. In the presence of Wnt3a expressing cells posterior explants remained cohesive. Wnt5a expressing cells had no effect and migrating cells were observed. Posterior explants exposed to both Wnt3a and Wnt5a remained cohesive. Arrowheads indicate cells that have migrated from explants, circles indicate positions of cell pellets. (D) Summary of explant data. χ² analyses showed that the altered behavior in response to Wnt5a or Wnt3a was statistically significant. Black bars indicate the percentage of explants showing migratory behaviour, grey bars indicate explants with non-migratory behaviour.