The reaction-diffusion (RD) theory of wool (hair) follicle initiation and development. II. Original secondary follicles

Abstract

In an accompanying paper it was shown that a spatial prepattern mechanism based on a biochemical reaction referred to as a reaction-diffusion (RD) system is able to account for many aspects of the initiation and development of primary (P) wool follicles. In this paper the same RD system is applied to the initiation and development of original secondary (SO) follicles. Prepatterns are generated by solving the equations describing the reaction and diffusion of the chemical components of the RD system in early stage follicles. It is demonstrated that the prepattern mechanism can account for the loss of a sweat gland causing a change from P follicle initiation to SO follicle initiation. The RD system equations are also solved in the epidermis. The time sequence of prepatterns obtained in the epidermis account for the tendency of SO follicles to group with P follicles, by initiating in-between members of the trio group of P follicles as well as in between existing SO follicles. The prepatterns obtained did not account for the tendency of secondary follicles to initiate on the posterior side of the trio group. Good agreement was obtained between the predicted increase in total follicle density and the increase in follicle density observed during follicle initiation by Carter and Hardy (1947), provided full account was taken of the interaction between existing follicles and each new future generations of follicles. The prepattern mechanism provides a fundamental basis for an inverse genetic correlation between total P and SO follicle density and fibre diameter.