Fig. 3. The scapular blade is severely affected in Tbx15/Gli3 and Alx4/Cart1/Tbx15 compound mutants. (A-N) Skeletal staining of the shoulder girdle of E16.5 embryos. Black arrowheads (B,D,F,I,K-N) indicate the reduced acromion in Tbx15/Gli3 and Alx4/Cart1/Tbx15 mutants; white arrowheads (C) indicate the indentations in the scapular blade of Gli3 mutants; black arrows (H-J,M) indicate the reduction of the anterior part of the scapular blade in Alx3/Alx4, Alx4/Cart1 and Alx4/Cart1/Tbx15 compound mutants. Note the severely reduced acromion and the remaining posterior part of the scapular blade in the Alx4^–/–Cart1^–/–Tbx15^–/– mutant shoulder girdle (N). (O,P) Side view of the intact skeleton of wild-type (O) and Alx4^–/–/Cart1^–/–/Tbx15^–/– (P) embryos at E16.5. Green arrowhead in O indicates the clavicle, which is missing in Alx4/Cart1/Tbx15 mutants (green arrowhead in P). Red arrowhead indicates the scapula; black arrowhead indicates the acromion. (Q-V) Clavicles of Alx3/Alx4/Cart1/Tbx15 compound mutants. The clavicle size is slightly reduced in Alx3/Alx4 double mutants (T), but only a small remnant of the clavicle is visible in Alx4/Cart1 (U) and Alx4^–/–Cart1^–/–Tbx15^+/– mutants (V). (W) Schematic representation of the elements of the shoulder girdle. (X) Schematic representation of the distinct functions of Alx4/Cart1 (red), Gli3 (blue) and Tbx15 (green) during shoulder girdle development. Alx4, Cart1 and Tbx15 (red/green) have functions during clavicle development.