Development of hemidesmosomes: an intramembranous view.

Hemidesmosomes of the skin are adhesive structures involved in the anchoring of the epidermis to structures of the basement membrane and the underlying dermis. The plasma membrane of the basal cells is an integral component of hemidesmosomes. This freeze fracture study shows the intramembranous changes that occur during hemidesmosome formation in the epidermis during human embryonic/fetal development. The first indication of hemidesmosomes is the presence of groups of intramembranous particles on the E fracture face of basal cells. Each group of intramembranous particles represents a hemidesmosome. With progressive development the number of intramembranous particles per hemidesmosome and the number of hemidesmosomes increases. Concomitant with these changes the plasma membrane bows toward the dermis at the hemidesmosome sites. The distribution of hemidesmosomes in the plane of the basal plasma membrane is non-uniform with the majority found in the center. The outline of the hemidesmosomes is variable although the elongate shape is the most common.