Fig. 4. Effects exerted by ectopic expression of FoxA4a/Pintallavis and Xvent2, and repression and activation constructs on the expression of endogenous Xanf1. All embryos were microinjected with a mixture of FLD and mRNA. (AD) Ectopic expression of EnRFoxA4a/Pintallavis and EnRXvent fusions elicit inhibition of Xanf1 expression. Microinjection of mRNA: FoxA4a/Pintallavis (A,A'); Xvent2 (B,B'); EnR FoxA4a/Pintallavis (C,C'); EnRXvent2 (D,D'). (B1,B1',B2,B2') Representative histological sections at two sagittal levels (1 and 2) of the embryo shown in B and B' demonstrate that descendants of the microinjected blastomeres labelled with FLD are primarily localised in the neurectoderm. Only single labelled cells are found in underlying endomesoderm. (E-G) Ectopic expression of dominant-negative versions of FoxA4a/Pintallavis and Xvent2 result in posterior expansion of endogenous Xanf1 expression. Red and black arrows indicate position of the posterior border of the Xanf1 expression domain within microinjected and non-microinjected (normal) zones, respectively. Microinjection of mRNA: VP-16-FoxA4a/Pintallavis (E,E'); VP16-Xvent2 (F,F'); Xvent2-P40 (G,G'). (E1,E1') Representative histological section at level 1 of the embryo shown in E and E' illustrates that microinjected blastomeres primarly populate the neurectoderm and that endogenous Xanf1 is now expressed in these cells.