Stratum Basale (Germinativum)- Basal layer just above basement membrane; contains keratinocytes, melanocytes, merkel cells, and Langerhans cells (latter mainly in stratum spinosum)
- 10% of cells in basal layer are stem cells
- Expression of ornithine decarboxylase (ODC), which is a marker for proliferative activity (ODC stimulated by UVB and partially blocked by retinoic acid/corticosteroid/vitamin D3)
- De novo expression of K5/14 occurs, forming keratin filaments which insert into both desmosomes and hemidesmosomes and form keratinocyte cytoskeleton
- Hemidesmosomes allow attachment of basal keratinocyte to basement membrane.
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