title: Sox9, more than a marker of the outer root sheath: spatiotemporal expression pattern during human cutaneous embryogenesis.
abstract: BACKGROUND
  The sex-determining gene Sox9 was recently unexpectedly found to have an essential role in outer root sheath differentiation. It was also characterized as a general marker of basal cell carcinoma. Herein, we describe its spatiotemporal expression pattern outside the hair follicle during human cutaneous embryogenesis.
  
  
  METHODS
  We examined immunohistochemically samples from embryonic and fetal human skin for the expression of SOX9 using standard techniques. For comparison reasons, we also included scalp skin from adults.
  
  
  RESULTS
  SOX9 is expressed in the developing nail organ, eccrine glands, blood vessels and melanocytes/melanoblasts. In the nail organ, the nail bed but not the nail matrix was immunoreactive for SOX9. In plantar skin, SOX9 specifically labels the evolving eccrine glands but not the interfollicular keratinocytes.
  
  
  CONCLUSIONS
  The distinctive expression pattern of SOX9 during human cutaneous embryogenesis indicates a key role in skin homeostasis that includes but goes beyond its role in outer root sheath differentiation. Studying immunohistochemical markers in developing human skin has the potential to further our understanding of adult skin physiology and to deepen our concepts especially of the histogenesis of adnexal tumors (including those of the nail unit) and the relationship of the various adnexal structures to each other.
authors.affiliation: Institut für Dermatohistologie, Heidelberg, Germany.
authors.forename: Dieter
authors.initials: D
authors.lastname: Krahl
authors.forename: Klaus
authors.initials: K
authors.lastname: Sellheyer
mesh_terms: D000328:Adult; D049109:Cell Proliferation; D018507:Gene Expression Regulation, Developmental; D018859:Hair Follicle / Q000196:embryology* / Q000378:metabolism; D006801:Humans; D007150:Immunohistochemistry; D009262:Nails / Q000196:embryology* / Q000378:metabolism; D055758:SOX9 Transcription Factor / Q000378:metabolism*; D012867:Skin / Q000196:embryology* / Q000378:metabolism
chemical_list: D055758:SOX9 Transcription Factor; C527932:SOX9 protein, human