Close link between cutaneous nerve pattern development and feather morphogenesis demonstrated by experimental production of neo-apteria and ectopic feathers: Implication of chondroitin sulphate proteoglycans and other matrix molecules

In chick skin, nerve arcades develop around the base of feathers. In order to understand the mechanisms of their formation, we have tried to dissociate arcade formation from feather morphogenesis in various ways. Nerve patterns were analysed (1) in hydrocortisone-treated embryos that are partially devoid of feathers, (2) after retinoic acid treatment that produces ectopic feathers, (3) in dorsal root ganglia-skin co-cultures. Whenever tested, immunochemistry revealed that nerve arcades form around chondroitin sulphate proteoglycan-rich areas. Hydrocortisone treatment modifies the distribution of two out of three chondroitin sulphate proteoglycan epitopes tested, as well as the shapes of the feathers and nerve arcades, but not fibronectin, tenascin or laminin localizations. Chondroitinase digestion in cocultures eliminated the nerve arcade formation and produced abnormally thin feathers, but nevertheless with a normal spatial distribution. Thus, chondroitin sulphate proteoglycans are probably not involved in the overall arrangement of feathers, but appear to play a fundamental role in both the formation of nerve arcades and the morphogenesis of the feather.