title: Keratin expression provides novel insight into the morphogenesis and function of the companion layer in hair follicles.
abstract: Hair follicles cycle between stages of growth (anagen) and metabolic quiescence (telogen) throughout life. In mature follicles, transition from telogen back into anagen involves the activation, proliferation, and differentiation of epithelial stem cells located in the bulge, a specialization of the outer root sheath. Recent studies identified keratin 6a (K6a) transcripts as enriched in bulge epithelial stem cells in mouse skin. We used messenger RNA probes, antibodies, a LacZ reporter mouse model, and whole-mount staining assays to investigate the regulation of mK6a during mouse postnatal hair cycling, and compare it to mK75, a companion layer (Cl) marker. We find that mK75 regulation parallels that of inner root sheath (IRS) markers, with expression onset at anagen IIIa above the new hair bulb and subsequent spreading towards the bulge. Although also occurring in the Cl, mK6a expression begins at anagen IIIb in differentiating cells located proximal to the bulge, and subsequently spreads towards the hair bulb. mK6a and mK75 thus exhibit temporally distinct, and spatially opposed, expression patterns in the Cl during postnatal anagen. These findings provide novel insight into the morphogenesis and properties of the Cl, and raise the distinct possibility that it is an integral part of the IRS compartment.
authors.affiliation: Department of Biological Chemistry, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
authors.forename: Li-Hong
authors.initials: LH
authors.lastname: Gu
authors.forename: Pierre A
authors.initials: PA
authors.lastname: Coulombe
mesh_terms: D000818:Animals; D049109:Cell Proliferation; D004847:Epithelial Cells / Q000166:cytology / Q000502:physiology; D005786:Gene Expression Regulation; D018859:Hair Follicle / Q000166:cytology / Q000502:physiology*; D007381:Intermediate Filament Proteins; D007633:Keratins / Q000235:genetics / Q000502:physiology*; D053564:Keratins, Hair-Specific / Q000235:genetics / Q000502:physiology; D051379:Mice; D008822:Mice, Transgenic; D023421:Models, Animal; D009024:Morphogenesis / Q000502:physiology*; D011401:Promoter Regions, Genetic / Q000235:genetics; D011498:Protein Precursors / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012867:Skin / Q000166:cytology
chemical_list: D007381:Intermediate Filament Proteins; C519389:K75 protein, mouse; D053564:Keratins, Hair-Specific; D011498:Protein Precursors; D012333:RNA, Messenger; C016159:trichohyalin; D007633:Keratins