Fig. 4. Ependymal cells and tail blastema cells express the hedgehog receptor Ptc1. (A-F) In situ hybridization of Ptc1 on cross-sections. Sense probe shows no staining of the entire cross-section both in control (A) and agonist-treated (D) regenerates. Ptc1 is expressed in the ventral ependymal cells (dashed line marks the ependymal tube) and in the blastema, but not in the epidermis (B,C). Note that the staining in the blastema is strongest in the cells surrounding the ventral spinal cord. C is taken at twice the magnification of B. A-C is 4 dpa. Ptc1 expression is increased in agonist-treated regenerates (E,F). Now all the ependymal cells express Ptc1 and the vast majority of ventral blastema cells do (compare ventral to dorsal blastema cells). F is taken at twice the magnification of E. D-F is 5 dpa. Scale bars: 100 µm.