Fig. 7

Cartoon illustrating expression of HoxA11 and HoxA13 during development of paired fins in the little skate (Leucoraja erinacea). Expression of HoxA13 and HoxA11 mirror expression of Wnt3 in novel AER domains in the anterior pectoral and pelvic fins, respectively. Wnt3 is expressed in both anterior AER domains, but each is patterned by a different HoxA gene. HoxA11 expression is associated with developing fin rays, and marking a broad domain in the posterior half of pelvic fin at stage 28, which attenuates to posterior pelvic fin by stage 29. While HoxA11 is expressed in the pelvic fins of both males and females, at stage 32, HoxA11 is in clasper only, and we see a reverse collinear expression pattern, where HoxA13 is broadly expressed in the entire clasper while HoxA11 is a more restricted domain (see Additional file 3). Wnt3 expression provided by Nakamura et al. [20], while photographs of pelvic fin expression provided by Tetsuya Nakamura