Ultrastructural immunocytochemical localization of fibronectin in the early chick embryo.

Fibronectin was localized using peroxidase and biotin-avidin-ferritin techniques in developmental stages of the chick embryo from laying to primitive streak formation. The primary location of fibronectin at all stages examined was the basal lamina of the epiblast and its associated extracellular material. The remaining tissues showed little or no immunochemical deposit. At the primitive streak stage of development there were some regional differences in the density of the deposit on the basal lamina. Closely adjacent to the primitive streak, where the basal lamina is fragmentary, deposit was sparse or absent. In this, and other regions, mesoderm cell surfaces did not stain except where they closely approached the stained basal lamina or interstitial bodies. Staining was variable in the basal lamina anterior to the primitive streak, but in a number of cases particularly heavy deposit was noted overlying the crescent of late hypoblast. This area seemed to correspond with the anterior fibronectin-rich band reported by others using immunofluorescence localization.