Fig. 5. Cauterization of the CR does not change the dorsoventral level of rib growth. (A-C) Transverse sections of a stage 14 P. sinensis embryo fixed just after unilateral microcauterization. (A) Enlargement of the experimental side of the embryo (B) shows necrosis of the CR tissue (arrowhead). (C) Enlargement of the left side of the same embryo showing the intact CR as the negative control. (D-G) In situ hybridization of an embryo 1 day after cauterization with a probe for CRABP1 (D,E) or for APCDD1 (F,G). The left panels represent the operated sides, and the right panels represent the corresponding control sides. In both cases, CR-specific gene expression is lost from the epidermis of the cauterized CR. (H-J) Three days after the microcauterization of the CR performed at stage 14. (H) A magnified view of the experimental side of the embryo; the image on the right shows an enlargement of the intact CR. Note that the intact CR comprises a thickened epidermis covering the accumulated mesenchyme (J), whereas on the operated side, these characteristic features of the CR have been lost (H). (I) Also note that the transversely viewed patterns of the ribs (r) are identical on the control and operated sides. (K-N) A whole-mount embryo 12 days after CR cauterization. Control (K) and operated (L) sides. Note the arrested growth of the carapacial margin at the site of cauterization (arrowhead). Dorsal (M) and lateral (N) views of the skeleton of the same embryo stained with Alcian Blue. Two successive ribs approximate each other distally (red arrowheads) at the site of CR cauterization (black brackets). Compare with the normal fan-shaped pattern on the control side (white brackets). Note that the ribs at the CR ablation do not grow ventrally across the level of the ablated CR (black arrowhead in N). (O-R) A whole-mount embryo 10 days after the cauterization of the apical ectodermal ridge of the forelimb. Control (O,P) and operated (Q,R) sides. (P,R) Alcian Blue-stained embryo. Note the severely disfigured autopod on the operated side (Q,R). Scale bars: 50 µm for A,C,H,J; 100 µm for B,D-G; 500 µm for I; 1 mm for K-R.