title: The concept of the onychodermis (specialized nail mesenchyme): an embryological assessment and a comparative analysis with the hair follicle.
abstract: BACKGROUND
  Recently, an intriguing concept was introduced into the literature that defines the area underlying the nail bed as a specific mesenchymal substructure unique to the nail organ. It has been termed onychodermis. The onychodermis expresses CD10 with remarkable specificity. Herein, we compare adult and fetal human hair follicles with fetal nail organs in an attempt to draw analogies for the mesenchyme associated with both adnexal structures.
  
  
  METHODS
  We examined immunohistochemically samples from adult and fetal hair follicles for the expression of CD10, CD34 and the mesenchymal stem cell marker nestin and compared the antigen profile with that of the fetal nail organ.
  
  
  RESULTS
  The CD10-positive/CD34-negative onychodermis is prominently visible at the end of the second trimester. A corresponding follicular structure was not identified, either in the adult or in the developing hair follicle. Nestin staining does not define the onychodermis.
  
  
  CONCLUSIONS
  The concept of the onychodermis is equally valid in the developing nail organ where it is also defined by its expression for CD10. Its function may be related to the anchorage of the overlying nail bed but may also involve a more dynamic role in the induction of hard keratins in the latter, contributing to the formation of the nail plate.
authors: Department of Dermatology, Cleveland Clinic Foundation, Cleveland, OH, USA. klaus.sellheyer@gmail.com
authors: Klaus
authors: K
authors: Sellheyer
authors: Paula
authors: P
authors: Nelson
mesh_terms: D000328:Adult; D000367:Age Factors; D018952:Antigens, CD34 / Q000378:metabolism; D015415:Biomarkers / Q000378:metabolism; D005260:Female; D018859:Hair Follicle / Q000166:cytology / Q000196:embryology* / Q000378:metabolism; D006801:Humans; D007381:Intermediate Filament Proteins / Q000378:metabolism; D059630:Mesenchymal Stem Cells / Q000166:cytology / Q000378:metabolism; D008648:Mesoderm / Q000166:cytology / Q000196:embryology* / Q000378:metabolism; D009262:Nails / Q000166:cytology / Q000196:embryology* / Q000378:metabolism; D015260:Neprilysin / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000378:metabolism; D064231:Nestin; D011247:Pregnancy; D011262:Pregnancy Trimester, Second
chemical_list: D018952:Antigens, CD34; D015415:Biomarkers; D007381:Intermediate Filament Proteins; C577484:NES protein, human; D009419:Nerve Tissue Proteins; D064231:Nestin; D015260:Neprilysin