Fig. 2. Forced expression of Hoxa2 in the endogenous posterior diencephalic neural fold and the facial phenotype. (A,B) Bilateral co-electroporation of Hoxa2 RCAS (BP)B (red) or control RCAS (BP)B (blue), and GFP constructs (green) in the anterior neural fold of a 5 ss chick embryo. Bilateral extirpation (broken lines) of the cephalic neural fold extending from mid-mesencephalic level down to r2/r3 boundary in the electroporated chick embryo. (C,D) In E3 control and Hoxa2-transfected embryos, in situ hybridization for Hoxa2 shows the endogenous pattern of gene expression at the rhombencephalic level (arrowhead), and in the second branchial arch (open arrow). (D) In Hoxa2-transfected embryos, the ectopic expression is evidenced at the diencephalic level (arrows) where the neural crest cells have started to migrate over the forebrain. Facial morphology and skeleton of a control embryo (E,F) and Hoxa2-transfected embryo (G,G',H) at E7. The latter exhibits severe morphological defects: its face consists in underdeveloped nasal and maxillary buds (G,G') in which no skeletal components of the upper face or lower jaw form as shown in H, representing an embryo treated with Alcian Blue (compare with F). Mxb, maxillary bud; Nlb, nasolateral bud; Nmb, nasomedial bud; T, tongue.