13-cis-retinoic acid affects sheath-shaft interactions of equine hair follicles in vitro

Abstract

A major challenge to the study of hair follicle growth is an appropriate assay system. Because equine mane follicles are large and noncurved, enabling easy dissection; are readily accessible from a single defined source; and possess a long anagen growth phase, we initiated a study of them in culture. As ire our previous studies of human and sheep follicles (Dev Biol 165:469, 1994), we found in this system that transection level dictates the pattern of follicle growth in vitro: follicles transected below the sebaceous gland show a type 1 growth pattern (the shaft grows out with an adherent sheath), while nontransected follicles show a-type 2 growth pattern (a naked Shaft grows out lacking a sheath). In the present study, we searched for compounds that might influence type 1. or type 2 patterns of growth. We found that 13-cis-retinoic acid induced, in a concentration-dependent fashion, a type 1-like pattern of growth under conditions for which a type 2 pattern was expected. All-trans-retinoic acid, SR11237 (a synthetic retinoid X receptor-specific ligand), and meta-carboxy-TTNPB (an inactive synthetic retinoid) did not have these properties. We hypothesize that sheath growth/processing is mediated by the follicle at the level of the sebaceous gland, or by the sebaceous gland itself, and that persistence of the follicle sheath about the out-growing shaft in vitro (i) in the physical absence of the sebaceous portion of the follicle, or (ii) in the presence of 13-cis-retinoic acid, is due to the reduced expression of a factor that regulates important shaft-sheath interactions.