Growth Factors, Cell-Cell and Cell-Matrix Interactions in Skin during Follicle Development and Growth

Summary

Pattern and form are morphological expressions of an ordered sequence of events, the genetic components of which encode instructions that are delivered via related, but possibly distinct, pathways. In skin such processes include the specification of cells both with respect to the morphogenesis of a variety of cutaneous structures and their distribution. The developmental programme for the hair follicle population, for example, may first be discerned as a loss of homogeneity in epidermal and dermal tissues. Cells accumulate at sites on either side of the basement membrane as a result of altered interactions amongst themselves and the surrounding matrices. The expression of growth factor receptors suggests that peptides may be involved both in initial cellular differentiation, movements within the matrix and in proliferation.

A close association is maintained between epidermal and dermal components of the developing follicles which persists after maturation. Similarly, the distribution of cell surface receptors and matrix components in adult skin suggests continuing roles for growth factors and matrices in tissue organisation and fibre growth. As yet, the nature and function of these interactions remain unclear. Studies, in vitro indicate that skin cells also elaborate a variety of growth-regulating factors. Whilst many remain to be characterised, those identified have been shown to induce changes in cell shape, migratory patterns and the synthesis and secretion of collagen, adhesion glycoproteins and proteoglycans. Furthermore, such factors may alter the rates of movement of cells through particular stages of the cycle. A clearer understanding of this network of interactions must await the development of methods that permit discrimination of the individual actions of the factors from those in combination with other regulatory molecules and matrix components in vivo.