Heterotypic Cell Contacts and Basal Lamina Morphology During Hair Follicle Development in the Mouse: A Light, Scanning, and Electron Microscopic Study at the Site of Tissue Interaction

The study examined the interface between the epithelial hair matrix and the mesenchymal dermal papilla in developing mouse vibrissa follicles to test the hypothesis that heterotypic cell contacts mediate the differentiation of hair matrix cells. Using embryos aged 14.0 to 15.5 days, the researchers separated the upper lip skin into epithelium and mesenchyme with ethylene diamine tetraacetic acid or trypsin, and sometimes used tape-stripping or cryofracture before scanning electron microscopy. The chelating agent was effective in producing clean preparations of intact basal lamina on mesenchyme. Transmission electron microscopy revealed that gaps appeared in the previously intact lamina densa surrounding the dermal papilla and persisted through three stages of follicle development. Mesenchymal cell processes from the papilla were found in close contact with epithelial hair matrix cells through these gaps just before and during differentiation, suggesting these contacts might be involved in transmitting differentiation instructions.