Fig. 1. Hox PG1 genes have overlapping expression domains during Xenopus laevis development. Hoxa1 (A-H), Hoxb1 (I-P) and Hoxd1 (Q-X) have overlapping expression patterns. Gastrula stage embryos (A,B,I,J,Q,R) are shown from the vegetal side, dorsal up. When compared with Otx-2 expression (^* in A,I,Q), it can be seen that the Hox expression does not reach the presumptive midbrain region. Neurula embryos are shown from the dorsal side, anterior to the right (C,E,K,M,S,U) or from the anterior side, dorsal up (D,F,L,N,T,V). Later embryos are shown from the lateral side, anterior to the right (G,H,O,P,W,X). Note pharyngeal arch expression of all three PG1 genes (arrows in G,H,O,P,W,X).