Evidence for a reaction/diffusion system in the control of cell proliferation and differentiation in the wool follicle.

Specific mechanisms responsible for the control of cell proliferation and differentiation in growing hair fibres are still uncharacterized. However, the Reaction-Diffusion (RD) system of morphogens advanced by Nagorcka and Mooney (1982) makes specific quantitative predictions about wavelike patterns of putative morphogen distributions as functions of wool follicle bulb size and shape and dermal papilla volume. These theoretical morphogen distributions can then be used to predict patterns of cell proliferation and differentiation in the growing wool fibre. In order to test these predictions, we used the BrdU/anti-BrdU technique in conjunction with a monoclonal antibody (Hewish and French 1986) specific for fibre orthocortex cells to visualize patterns of cell proliferation and differentiation in the wool follicle bulb. Sheep were injected with BrdU and skin samples embedded in paraffin and serially sectioned before immunohistochemical staining. Individual follicles were followed from their base to the level at which cortical differentiation was obvious. For every follicle examined to date (n=15) from one sheep whose fibres exhibit bilateral cortical segmentation, there is good agreement between the observed asymmetric pattern of cell proliferation and the predicted morphogen gradient.