Immunolocalization of basal lamina components during development of chick otic and optic primordia.

Immunolocalization of laminin, fibronectin, and type IV collagen was examined during early morphogenetic shape changes of the avian inner ear and eye. The ear was studied from formation of the otic placode to invagination of the otic pit and the eye from the optic vesicle stage to formation of an optic cup. Distribution and intensity of immunoreactivity were compared in the two organ primordia and in adjacent epithelial layers. Laminin formed a continuous layer at the basal surface of the otic ectoderm and adjacent neural tube at all stages. The basal surfaces of the optic and lens epithelia also were continuously covered with laminin throughout development. The otic placode became attached to the neural ectoderm through a single layer of fibronectin and collagen IV between the layers of laminin. The ring-like attachment between the edges of the optic cup and lens primordium had the same structure. In addition, the central regions of the optic and lens primordia were attached by fibrils containing type IV collagen, whereas finer strands containing fibronectin and laminin also connected the otic epithelium and neural tube. The results are discussed in terms of models of invagination for the two primordia.