Changes in fibronectin, laminin and type IV collagen distribution relate to basement membrane restructuring during the rat vibrissa follicle hair growth cycle.

Hair growth in adult mammals involves continuous dermal-epidermal interaction across the follicular basement membrane, and repeated reorganisation of lower follicle structure during the hair growth cycle. The immunolocalisation of 3 extracellular matrix components, fibronectin, laminin and type IV collagen was investigated during the course of the rat vibrissa follicle growth cycle, and their distribution correlated with changes in cellular and extracellular ultrastructure, particularly around the basement membrane zone. Laminin and type IV collagen were omnipresent at the follicular dermal-epidermal junction, but were also seen in granular extracellular form within the inner dermal component of the follicle, the dermal papilla. Both the inner papilla-epidermal junction and the thick specialised outer basement membrane (the glassy membrane) revealed labelling by these 2 antibodies around telogen (the period of nonfibre production). By contrast, fibronectin was abundant within the anagen dermal papilla but at telogen stained the dermal-epidermal junction heterogeneously, when it disappeared from the inner papilla-epidermal interface but intensified externally. These changes to extracellular matrix distribution coincided with a modification of basement membrane ultrastructure from a relatively uniform line at anagen, to one which became much broader and multilayered at telogen with a loss of definite structure within the papilla. This shows that the lower part of the vibrissa follicle retains the capacity for very rapid basement membrane modification and remodelling, and implies that it is part of the biological process which enables dermal-epidermal signalling, rather than a secondary product of physical changes to the appendage. The work supports the idea that dermal papilla cells could contribute to basement membrane formation, and also that fibronectin may be involved in regulating cellular activities within the follicle. In the vibrissa follicle, dynamic cellular activity clearly takes place throughout the duration of the hair cycle.