Keratan sulphate is present in developing chick skin in vivo where it could constitute a barrier to advancing neurites as observed in vitro

Abstract

Proteoglycans play an important role in axonal guidance. The glycosaminoglycan chondroitin sulphate is known to be inhibitory. Keratan sulphate is structurally similar and may play a similar role. The lectin peanut agglutinin potentially labels chondroitin or keratan sulphate rich areas. In order to elucidate the mechanisms by which the regular nerve pattern develops in chick skin, keratan sulphate epitopes and peanut agglutinin binding sites were localized in chick embryos and compared to previous studies of chondroitin sulphate. The markers all display specific, developmentally regulated staining patterns, thus reflecting their individuality. Their maximal expression coincides with the formation of feathers and their nerve pattern in both time and space. Furthermore, culture experiments using dorsal root ganglia demonstrate the avoidance of keratan sulphate by the growing sensory neurites, although outgrowth and elongation occur if they grow directly on the keratan sulphate substrate. Thus, keratan sulphate proteoglycans in developing chick skin are potentially involved in guidance of sensory neurites or maintenance of the new nerve pattern, but are clearly different to the chondroitin sulphate proteoglycans which have a complementary distribution. Furthermore, peanut agglutinin binding sites are independent of both proteoglycans.