Factors which affect the fibre output of isolated wool follicles maintained in vitro

Abstract

A technique for growing individual wool follicles in vitro was developed to test the hypothesis that endocrine growth factors are responsible for the regulation of wool growth. Examination of the fibres produced showed that they were morphologically similar to fibres grown on the sheep, with the rate of wool growth being approximately half of that measured in vivo. This observation was consistent across all sheep breeds examined. Isolated wool follicles continued fibre production for4.1±0.2 days (mean ±-S.E.M.) with a range of zero to twelve days. Follicle culture was therefore regarded as an appropriate in vitro model of in vivo fibre growth.

Follicles grown in culture were used to investigate the mechanisms by which fibre growth is regulated. Wool growth became dissociated from seasonal and nutritional regulation when follicles were isolated from the sheep. Marked seasonal changes (P < 0.001) in in vivo wool growth rates were recorded over a ten month period for English Leicester sheep, but were not observed when follicles from the same sheep were grown in vitro. Similarly, in vivo wool growth responses to increased dietary energy and nitrogen were not carried over into cultured follicles. These results are consistent with the regulation of follicle growth rate being achieved through extrafollicular mechanisms.

The inclusion of adult ovine serum and specific growth factors in the nutrient medium provides further support for the hypothesis that systemic regulation of wool growth occurs. Ovine serum was inhibitory for fibre growth in a season and breed dependent manner. Wool growth inhibition was most apparent in follicles isolated during winter and in follicles supplemented with serum collected during winter. Fibre growth by follicles isolated from an English Leicester sheep was more sensitive to inhibition by ovine serum than growth by follicles from Drysdale sheep. Fractionation of ovine serum enabled preliminary identification of the key inhibitory components as a 55kD protein (possibly albumin), and either a > 350kD protein (possibly α₁-lipoprotein) or an unidentified 130kD protein.

A reduction in the fibre growth rate was also observed following the addition of basic fibroblast growth factor (45% reduction, P=0.003), epidermal growth factor (33%, P=0.05) or transforming growth factor alpha (20%, P = 0.16) to the tissue culture medium. At high concentration, minoxidil also inhibited fibre growth (45%, P < 0.001). In contrast, insulin, insulin-like growth factor-1, prolactin, melatonin and aqueous deer antler extract had no effect on the rate of fibre growth.

These results suggest that wool growth regulation by environmental stimuli may be achieved through inhibition of a biochemical pathway. They also indicate that specific growth factors may act on components of this pathway. This study therefore supports the hypothesis that the systemic regulation of wool production occurs through the expression of endocrine growth factors rather than via modification of the wool follicle itself.