Pax3 regulates pax7 expression and alar plate patterning in the brain. (A) Pax3 depletion using an antisense morpholino (Pax3MO) specifically prevents Xenopus laevis pax3 translation in vitro (lane 3). Pax7MO and a control MO have no effect on Xenopus laevis pax3 translation while Mus musculus pax3 is unaffected by Pax3MO. (B) Following Pax3 depletion in vivo (bar 1), pax7 expression is severely reduced, Mus musculus Pax3 mRNA efficiently rescues the decrease in pax7 expression (bar 2). (C) Unilateral depletion of Pax3 results in loss in pax7 expression; (D) a similar effect is observed after Pax3-EnR over-expression. (E) Gain in Pax3 activity increases and expands pax7 expression. (F–I) Transverse sections show that the loss in pax7 (C, D, G, H) is accompanied by reduced alar plates development, while Pax3 increase results in expanded pax7-expressing alar plates (I). Bar=500 μm.