Spatiotemporal patterns of fibronectin distribution during embryonic development. II. Chick branchial arches.

It has recently been demonstrated with the chick limb in ovo that successive nonrandom patterns of fluorescent staining with specific antibodies to fibronectin indicate the cartilagenous primordia prior to overt chondrogenesis. Given the apparent nonequivalence of embryonic cartilages, the purpose of this study was to determine whether this phenomenon was unique to developing chick limbs or is a more general characteristic of chondrogenesis. The appearance and distribution of fibronectin during chick first and second branchial arch development in ovo was investigated by indirect immunofluorescence techniques in H.H. stages 15-26. Fibronectin can be detected in early stages in areas presumed to be composed mainly of ectomesenchyme. During later stages of development, successive nonrandom patterns of fibronectin distribution appear to precede overt chondrogenesis as demonstrated by alcian blue staining. Pretreatment of cartilage with testicular hyaluronidase, prior to fibronectin staining, revealed that fibronectin was still present, suggesting that it was masked by proteoglycans. Fibronectin was also detected in the developing membrane bones of the mandible. The nonrandom patterning of fibronectin distribution in ovo in chick branchial arches and limb buds, respectively derived from neural crest and somatic mesoderm, were similar. It appears that specific patterns of fibronectin distribution were characteristic of chondrogenesis, regardless of the embryonic origin of the cartilage. This phenomenon may prove to be an extremely useful probe for early developmental skeletal abnormalities.