Fig. 5. Wnt3a-mediated repulsion requires RhoA function, and dominant-negative or constitutively active forms of RhoA cause cardia bifida. (A) HH3 primitive streak cells electroporated with a constitutively active form of RhoA, RhoA-V14, were repelled by Wnt3a-expressing cells (yellow asterisk) in area opaca explants. (B) HH3 primitive streak cells electroporated with a dominant-negative form of RhoA, RhoA-N19, ignored the source of Wnt3a and behaved like unchallenged explants or explants transfected with DN-Wnt3a (see Fig. 3C,G), migrating in all directions away from the graft. (C) RhoA transcripts were expressed in the primitive streak at HH4. (D) vMHC in situ hybridisation showed that embryos electroporated with RhoA-V14-IRES-GFP developed cardia bifida. (E) Graph showing the percentage of embryos with cardia bifida. Embryo treatment is indicated below each bar. ccp, control cell pellet; ep, electoporation. (F) Long-term video microscopy followed by image processing revealed the movement trajectories of RhoA-V14-IRES-GFP labelled cardiac progenitors. Still images at the time points indicated are shown. (G) Corresponding bright-field images show the location of GFP cells within the embryo. The bilateral heart fields are indicated by a white outline in HH8 embryos.