Fig. 1. Effect of QT6-Shh cell graft in BA1 presumptive territory on lower-jaw morphogenesis. (A) Graft of QT6-Shh cells (outlined), under the ectoderm, lateral to the posterior mesencephalon, in a 5 ss chick embryo, on its right side. (B) Cross-section at the level of the graft at 10 ss. In situ hybridization for Shh shows the QT6-Shh cells in contact with lateral ectoderm (Ect) and foregut endoderm (End). (C) Lateral right view of the head at E11 showing the normal lower beak (1) and two supernumerary hemi-lower-beaks (2,3) with mirror-image polarities (1/2 and 2/3). (D) Skeleton preparation of the embryo shown in C. The right lower jaw shows a large proximal Meckel's cartilage (arrow) prolonged by three distinct branches of cartilage (1-3). The quadrate and articular (arrowhead) are not perturbed. (E) Higher magnification of D showing that each branch of Meckel's cartilage (1-3) is associated with a dentary bone (white arrows) oriented in mirror image. (F) Higher magnification of structures 1 and 2 viewed through the left side (control side) allows the comparison of the normal left Meckel's cartilage (nMc) and the larger right experimental one (eMc), and shows mirror-image duplication of splenial (black arrows) and dentary bones (white arrows). Scale bar: 50 µm in B.