Keratinocytes- Ectodermal derivation : keratinocytes comprise approximately 80–85% of epidermal cells
- Total epidermal turnover time: average 45–60 days (30–50 days from stratum basale to stratum corneum and approximately 14 days from stratum corneum to desquamation)
- Epidermal self-renewal maintained via stem cells in basal layer of interfollicular epithelium and the bulge region of hair follicles (latter location only activated with epidermal injury)
- Keratinocytes produce keratin filaments (syn: intermediate filaments or tonofilaments), which form the cell’s cytoskeletal network; this provides resilience, structural integrity, along with serving as a marker for differentiation (i.e., basal layer: K5/14)
- Six different types of keratin filaments: type I/II are epithelial/hair keratins, type III–VI include desmin, vimentin, neurofilaments, nuclear lamins, and nestin
- >50 different epithelial/hair keratins, expressed as either type I (acidic) or type II (basic), and type I/II coexpressed together as a heterodimer (i.e., K5/14)
| | | | | | Of note, second
cytoskeletal network
formed by actin filaments | | | | | |
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- Type I (acidic) hair keratins: K31–40 (old nomenclature: hHa1-hHa8, Ka35, Ka36)
- Type II (basic) epithelial keratins: K1–8 and K71–80, chromosome 12
- Type II (basic) hair keratins: K81–86 (old nomenclature: hHb1–hHb6)
| | | | | | | Table 1-2 Keratin Filament Expression Pattern | | Type II | | Type I | | Location of Expression | | Associated Diseases | | 1 | | 10 | | Suprabasal keratinocytes | | Epidermolytic hyperkeratosis (EHK), Unna-Thost palmoplantar keratoderma (PPK) | | 1 | | 9 | | Palmoplantar suprabasal keratinocytes | | Vorner PPK | | 2(2e) | | 10 | | Granular and upper spinous layer | | Ichthyosis bullosa of Siemens | | 3 | | 12 | | Cornea | | Meesman corneal dystrophy | | 4 | | 13 | | Mucosal epithelium | | White sponge nevus | | 5 | | 14 | | Basal keratinocytes | | Epidermal bullosa simplex (EBS), Dowling-Degos disease | | 6a | | 16 | | Outer root sheath | | Pachyonychia congenita I | | 6b | | 17 | | Nail bed | | Pachyonychia congenita II | | 8 | | 19 | | Simple epithelium | | Cryptogenic cirrhosis | | K81 K86 | | | | Hair | | Monilethrix | | | | 19 | | Stem cells | | | | | | | | | | |
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(Do not confuse with Dowling-Degos with Degos disease Dowling-Degos: AD, reticulated pigmentation; over skin folds Degos disease (malignant atrophic papulosis): occlusion + tissue infarction) | | | | | |
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