DYNAMICS OF BASEMENT-MEMBRANE FORMATION BY KERATINOCYTE-FIBROBLAST INTERACTIONS IN ORGANOTYPIC SKIN CULTURE

The cutaneous basement membrane zone, composed of numerous macromolecu les, plays a multifunctional role in tissue regeneration and maintenan ce. To elucidate the cellular origin and dynamics of basement membrane formation, de novo synthesis, deposition, and ultrastructural assembl y of its components were analyzed in organotypic cultures of adult ski n keratinocytes on collagen gels with or without collagen-embedded der mal cells. Collagen IV and laminin-1 deposition occurred only in the p resence of mesenchymal cells: patchy at day 4 and continuous after 1 w eek. Chain-specific mRNA expression started at day 2 in both keratinoc ytes and fibroblasts. It steadily increased up to day 10, however, wit h a reciprocal induction pattern, mRNA abundance shifting from keratin ocytes to fibroblasts. On the other hand, laminin-5 staining was first observed at day 4, but in keratinocyte both mono-and cocultures. This was followed by nidogen, which was detected in cocultures but also in dermal monocultures. Laminin-5 protein persisted throughout day 21, w hereas nidogen steadily increased in intensity. Expression kinetics re vealed high levels of laminin-5 transcripts early and in keratinocytes only, whereas nidogen was expressed later and predominantly in fibrob lasts. Although basement membrane protein deposition was continuous at day 14, the ultrastructural organization was still fragmentary, event ually normalizing at 3 weeks. These data demonstrate a dynamic interac tion and cooperation of epithelial and mesenchymal skin cells in basem ent membrane formation. This interaction is supposedly mediated via di ffusible factors. Our findings further extend the scope of epithelial- mesenchymal interactions stressing that both cell compartments are ess ential to constitute a tissue-specific extracellular matrix structure. (C) 1998 Academic Press.