SKIN FIBROBLASTS ARE THE ONLY SOURCE OF NIDOGEN DURING EARLY BASAL LAMINA FORMATION IN-VITRO

The purpose of this study was to determine whether nidogen, the linkag e protein of the basal lamina, is of epidermal or dermal origin. The d evelopment of the basal lamina was studied in an in vitro skin model, Preputial fibroblasts seeded onto a nylon mesh attached, proliferated, and developed a rich extracellular matrix (dermal model). Preputial k eratinocytes were added to the dermal model to form a keratinocyte der mal model that ultrastructurally resembled in many respects human skin . Ultrastructural analysis revealed early stages of dermal development , including an incomplete basal lamina, aggregates of dermal filamento us material connecting to the lamina densa, bundles of 10-nm microfibr ils, formation of premature hemidesmosomes, anchoring filaments, and a nchoring fibrils. The cell origin of nidogen was determined in the der mal model and in the epidermal and dermal components of the keratinocy te dermal model. Specific antibodies and a cDNA probe for nidogen were used for immunofluorescence microscopy, Western and Northern blots, a nd for in situ hybridization studies. Our data show that fibroblasts a re the only source of nidogen during early basal lamina formation. Alt hough fibroblasts can synthesize nidogen and deposit it in the dermal matrix, no basal lamina will form unless they are recombined with kera tinocytes. This suggests that the epidermis plays a major regulatory r ole in the production and assembly of nidogen into the basal lamina.