Fig. 7. Inhibition of activin function causes an upregulation of Xnr2 expression and a downregulation of Derrière. (A) Embryos were injected with the indicated antisense morpholino oligonucleotides and allowed to develop to early gastrula stage 10.5, when they were assayed for expression of nodal-related genes and Derrière by real-time RT PCR. (B-G) Upregulation of Xnr2 expression is not accompanied by an expansion of its expression domain. Embryos were subjected to in situ hybridisation to detect Xnr2 RNA and viewed from the vegetal pole (B-D) or from the side (E-G). Transcription of Xnr2 in embryos injected with MO1 (C,D) or MO3 (F,G) is not observed beyond its normal expression domain. (H-J) Downregulation of Derrière is not accompanied by a restriction in its normal expression domain. All embryos were injected at the two-cell stage, with 20 ng MO1 or 15 ng MO3 into each blastomere.