Figure 4

Sfrp1 _NTR but not Sfrp1 _CRD , rescues the phenotype induced by knocking-down Sfrp1. (a-e') All the panels are dorsal (a-e) and lateral (a'-e') views of embryos at stage 19–20 injected with GFP mRNA alone (a,a'), Mo-olSfrp1 alone (b,b') or co-injected with Sfrp1 (c,c'), Sfrp1 _CRD (d,d') or Sfrp1 _NTR (e,e') mRNAs as indicated in the panels. Embryos were hybridised for rx3 (eye field) and foxA2 (axial mesoderm) both visualised in blue. Optic vesicles fail to develop in embryos injected with Mo-Sfrp1, as judged by the reduction in rx3 expression (b,b'). This defect is reverted by the co-injection of Sfrp1 and Sfrp1 _NTR mRNAs in 50% of the embryos (c,c',e,e',f) but not by that of Sfrp1 _CRD (d,d',f) mRNA, where the reduction of the eye field is even more pronounced than that observed with the Mo-Sfrp1 alone. Note that Sfrp1 mRNA not only rescues the effect of Mo-Sfrp1 but also induces a partial over-expression phenotype (compare (c,c') with Figure 2a,j). (f) Quantification of the rescue efficiency in the different conditions. Scale bar: 0.2 mm.