Wool follicles from sheep have long been a subject of biological research. In addition to their relevance to the wool industry, ovine follicles provide an interesting comparison to follicles from humans and other species. We have developed two cell culture models for studying aspects of wool follicle biology. In the first, keratinocytes are grown from explants comprising the follicle germinative epithelium, still attached to the adjacent dermal papilla. Preservation of attachment between the two tissues is necessary for the initiation of keratinocyte growth. However once these keratinocytes are established in culture, they can be cloned by limiting dilution and will continue to proliferate extensively. The behaviour of these cells suggests that the germinative epithelium of the follicle bulb is not composed solely of transit amplifying cells with inherently limited proliferative potential, but that their growth characteristics are strongly influenced by their culture environment.
In the second model, serially-passaged dermal papilla cells spontaneously aggregate to form papilla-like structures in vitro. The size of these aggregates can be experimentally manipulated with bioactive compounds that impinge on signalling pathways implicated in follicle development. Lithium chloride, dorsomorphin and SU5402 (which act via Wnt, inositol phospholipid, phosphotyrosine phosphatase, BMP, FGF, VEGF and PDGF signalling) all induced dose-dependent reductions in aggregate size. The alopecia drug, minoxidil, reversed the effect of lithium chloride. Dysregulation of papilla size is thought to underlie follicle miniaturisation in alopecia and follicle enlargement in hypertrichosis. These ovine papilla cells provide a new model for studying the morphogenetic mechanisms that regulate papilla size.