Fig. 6. Knockdown of AmphiHox1 function with an antisense morpholino oligonucleotide mimics the effect of BMS009 treatments on the posterior limit of the pharynx in amphioxus. Scale bar=50 µm. (A,C,E,G) Embryos injected with the control morpholino. (B,D,F,H) Embryos injected with the AmphiHox1 antisense morpholino-oligonucleotide. (A,B) AmphiHox1 expression. In controls (A), the anterior limit of AmphiHox1 expression in the endoderm (arrowhead) coincides with the first pigment spot to form in the nerve cord, and is shifted slightly posteriorly in embryos injected with the AmphiHox1 morpholino (B). (C,D) AmphiPax1/9 expression. The posterior limit of AmphiPax1/9 expression in the endoderm (arrowhead) of an amphioxus larva injected with the control morpholino (C) coincides with the first pigment spot to form in the nerve cord (double arrowhead), whereas in larvae injected with the AmphiHox1-specific morpholino (D), the pharynx is expanded posteriorly and the posterior limit of AmphiPax1/9 expression in the pharyngeal endoderm (arrowhead) is posterior to the first pigment spot in the nerve cord (double arrowhead). (E-H) AmphiOtx expression. In control embryos (E,G), the posterior limit of AmphiOtx expression (arrowhead) coincides with the first pigment spot in the nerve cord (double arrowhead). AmphiOtx expression is expanded posteriorly in embryos injected with the AmphiHox1-specific morpholino (F,H). A,B,E,F=30 hours. C,D,G,H=40 hours.