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Discovery of Basement Membrane Zone Ultrastructural Entities by Electron Microscopy

  • Robin A.J. Eady
    Correspondence
    St John’s Institute of Dermatology, King’s College London, St Thomas’ Hospital, London SE1 7EH, UK
    Affiliations
    St John’s Institute of Dermatology, King’s College London, St Thomas’ Hospital, London, UK
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      Although electron microscopy studies of the DEJ have been valuable in defining key steps in processes such as normal development, ageing and carcinogenesis, a major application has been in the studies of blistering disorders, both hereditary and acquired.
      • Pearson R.W.
      Studies on the pathogenesis of epidermolysis bullosa.
      delineated the differences between the primary levels of skin separation in the three main types of hereditary epidermolysis bullosa, and others drew attention to disorders of anchoring fibrils in the dystrophic forms of the disease (
      • Briggaman R.A.
      • Wheeler C.E.
      Epidermolysis bullosa dystrophica—recessive: a possible role of anchoring fibrils in the pathogenesis.
      ,
      • Briggaman R.A.
      • Wheeler C.E.
      The dermal–epidermal junction.
      ,
      • Anton-Lamprecht I.
      • Hashimoto I.
      Epidermolysis bullosa dystrophica dominans Pasini)—a primary structural defect of the anchoring fibrils.
      ,
      • Tidman M.J.
      • Eady R.A.J.
      Evaluation of anchoring fibrils and other components of the dermal-epidermal junction in dystrophic epidermolysis bullosa by a quantitative ultrastructural technique.
      ) when the association between anchoring fibrils and type VII collagen was still unknown. Yet these observations provided an important clue to the later discovery that mutations of type VII collagen, an anchoring fibril component, cause dystrophic epidermolysis bullosa. Other research underscored the importance of structural abnormalities of hemidesmosomes in both the Herlitz (
      • Hashimoto I.
      • Gedde-Dahl Jr., T.
      • Schnyder U.W.
      • Anton-Lamprecht I.
      Ultrastructural studies in epidermolysis bullosa hereditaria. IV. Recessive dystrophic types with junctional blistering. (Infantile or Herlitz–Pearson type and adult type).
      ) and non-Herlitz (
      • Tidman M.J.
      • Eady R.A.J.
      Hemidesmosome heterogeneity in junctional epidermolysis bullosa revealed by morphometric analysis.
      ) forms of junctional epidermolysis bullosa.
      Localizing antigens in the DEJ at the ultrastructural level has been of lasting interest, especially in studies of autoimmune or congenital bullous disorders. Preliminary research (for example,
      • Schreiner E.
      • Wolff K.
      Systemic lupus erythematosus: electron microscopic localization of in vivo bound globulins at the dermal–epidermal junction.
      ) used horseradish peroxidase to provide an insoluble marker to localize immunoglobulin deposition in lupus erythematosus. However, it was much later, when colloidal gold was introduced to immunoelectron microscopy, that precise molecular localization became possible. Thus, for the first time, we could see convincingly that type VII collagen localized to anchoring fibrils (
      • Sakai L.Y.
      • Keene D.R.
      • Morris N.P.
      • Burgeson R.E.
      Type VII collagen is a major structural component of anchoring fibrils.
      ) and that kalinin (now known as laminin 5) (
      • Rousselle P.
      • Lunstrum G.P.
      • Keene D.R.
      • Burgeson R.E.
      Kalinin: an epithelium-specific basement membrane adhesion molecule that is a component of anchoring filaments.
      ) was associated with anchoring filaments. The immunolocalization of intracellular proteins, such as bullous pemphigoid antigen 1, was more problematic, initially requiring permeabilization of the cell membrane to allow access of the labelling antibody (
      • Westgate G.E.
      • Weaver A.C.
      • Couchman J.R.
      Bullous pemphigoid antigen localization suggests an intracellular association with hemidesmosomes.
      ). However, a new approach entailing freeze substitution and post-embedding (or on-section) labelling enabled both intracellular and extracellular antigen labelling with good membrane preservation (
      • Shimizu H.
      • McDonald J.N.
      • Kennedy A.R.
      • Eady R.A.
      Demonstration of intra- and extracellular localization of bullous pemphigoid antigen using cryofixation and freeze substitution for postembedding immunoelectron microscopy.
      ). Whereas one study (
      • Keene D.R.
      • Sakai L.Y.
      • Lunstrum G.P.
      • Morris N.P.
      • Burgeson R.E.
      Type VII collagen forms an extended network of anchoring fibrils.
      ) elegantly demonstrated that anchoring fibrils form an extensive network beneath the lamina densa and link with small discrete ‘anchoring plaques’, another (
      • Shimizu H.
      • Ishiko A.
      • Masunaga T.
      • Kurihara Y.
      • Sato M.
      • Bruckner-Tuderman L.
      • et al.
      Most anchoring fibrils in human skin originate and terminate in the lamina densa.
      ) found that nearly all anchoring fibrils insert at both ends in the lamina densa. These contrasting findings have probably come about because of major differences in skin sample processing and the mode of gold labelling. The former used a pre-embedding en-bloc labelling method, and the latter a post-embedding technique, as described above.

      References

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