Figure 1

In situ hybridizations of chicken wing buds with probes against the chondrogenic markers Sox9 (A, B) and Coll2a (C, D), after removal of the dorsal ectoderm at HH-stage 20-21 and 24 or 48 h reincubation. On the left side is the control limb, the right limb has been manipulated. Arrowheads indicate the site of ectoderm removal. A Expression of Sox9 after 24 h. Expression is stronger on the operated side. a Transverse section of the control limb showing low Sox9 expression. a' Transverse section of the operated limb showing strong Sox9 expression, which is extending ectopically towards the dorsal surface of the limb. B Expression of Sox9 after 48 h. Expression is stronger on the operated side. b Transverse section of the control limb showing normal Sox9 expression. b' Transverse section of the operated limb showing enhanced Sox9 expression, which is extending ectopically towards the dorsal surface of the limb. C Expression of ColIIA after 24 h. Expression is stronger on the operated side. Dislocated fragments of gold foil are still visible. c Transverse section of the control limb showing low ColIIA expression. c' Transverse section of the operated limb showing strong ColIIA expression, which is extending ectopically towards the dorsal surface of the limb. D Expression of ColIIA after 48 h. Expression is stronger on the operated side. d Transverse section of the control limb showing normal ColIIA expression. d' Transverse section of the operated limb showing enhanced ColIIA expression, which is extending ectopically towards the dorsal surface of the limb. Scale bar 500 μm.