Hair follicle dermal cells: a morphological, behavioural and molecular study

Anatomy and smooth muscle a-actin expression in hair follicles from a variety of animal species (Mink, Polecat, Meerkat, Grey squirrel and stoat) was investigated. Smooth muscle ɑ-actin expression was related to follicle activity. Expression was greatest during anagen, with a marked reduction in expression during telogen. Follicular dermal cells were cultured from the above animal species. In vitro grey squirrel dermal papilla (DP) and dermal sheath (DS) cells both expressed smooth muscle ɑ -actin. Rat dermal papilla cell in vitro aggregative behaviour was characterized, by proliferation, chemotactic and molecular studies. Aggregation behaviour in these cells was not attributed to focal proliferation. However, fluctuations in cell motility correlated with the aggregation process, with the greatest motility between subconfluent and clumped cells. Motility was terminated within the clumped cells. Furthermore, DP cells in vitro secreted molecules that enhancer! motility in subconfluent DP cells and a variety of other cell types. As yet the type and specificity of this medium borne component is unknown. TGFP, bFGF and aFGF were all used as a comparison to the unknown molecule, however migration was rarely similar in magnitude to the response of the DP cell medium. Mouse cDNA probes of BMP 2 and BMP 4 were used to isolate rat homologues from a cDNA library. Wholemount in situ hybridization of BMP 4 expression was consistent with the data in the mouse, however BMP 4 was also expressed in adult rat telogen vibrissae. Molecular expression within in vitro DP cells was studied using a differential screen of a cDNA library. A number of clumped DP specific clones were differentially expressed, one of which having high homology with migration inhibitory factor. These results are discussed, and a hypothetical model is proposed to describe how DP aggregation occurs with reference to dermal condensation in vivo.