Fig. 2. Premature neural differentiation of the epiblast occurs in Bmpr1a^-/- embryos. (A,B) At 5.5 dpc, Oct4 expression is observed throughout the epiblast of control and Bmpr1a mutant mouse embryos (n=5). (C,D) At 6.5 dpc, Oct4 is expressed in the epiblast of controls but its expression is downregulated in 50% of Bmpr1a^-/- embryos (n=4/8). (E,F) Nanog expression is observed in the proximal posterior epiblast at 6.5 dpc in controls, but not in Bmpr1a mutant embryos (n=6). (G,H) At 6.5 dpc, Fgf5 is expressed throughout the epiblast of controls but is strongly downregulated or absent in Bmpr1a^-/- embryos (n=5). (I-L) At 7.5 dpc, Six3 and Hesx1 are expressed in the anterior neural ectoderm of controls, but in Bmpr1a mutant embryos expression of both these genes is observed throughout the epiblast (n=7/8 and n=4/6, respectively). (M,N) Sox1 expression is not observed at 7.5 dpc in control embryos, but in Bmpr1a^-/- embryos expression is observed in the entire epiblast (n=7/8). (O,P) No Foxg1 expression is observed in control embryos at 7.5 dpc, but in Bmpr1a^-/- embryos Foxg1 is expressed in a discrete patch of cells at the boundary between the embryonic and extra-embryonic region (n=4/6). (Q,R) At 6.5 dpc, Six3 is not expressed in control embryos but is present throughout the epiblast of two-thirds of Bmpr1a^-/- embryos (n=3/5). (S,T) Hesx1 is expressed in the anterior visceral endoderm at 6.5 dpc, but in a third of Bmpr1a mutant embryos expression is observed throughout the epiblast (n=3/10).