Ectodermal Placodes and the Epidermis

Several factors stimulate development of the epidermis (see Figure 16.12). Dermal fibroblasts activate epidermal stem cell division through the production of Fgfs, insulin-like growth factor, and receptor ligands for the appropriately named epidermal growth factor (Hsu et al. 2014). Bmps help initiate epidermal production by inducing the p63 transcription factor in the basal layer. This transcription factor’s multiple roles may depend in part on different splicing isoforms of p63 that are expressed in the epidermis. The p63 protein is required for keratinocyte proliferation and differentiation (Truong and Khavari 2007); it also appears to stimulate the production of the Notch ligand Jagged. Jagged is a juxtacrine protein in the basal cells that activates the Notch protein on the cells above them, activating the keratinocyte differentiation pathway and preventing further cell divisions (see Mack et al. 2005; Blanpain and Fuchs 2009). Thus, Notch signaling is necessary for the transition from the basal layer to the spinous layer.

Literature Cited

Blanpain, C. and E. Fuchs. 2009. Epidermal homeostasis: A balancing act of stem cells in the skin. Nat. Rev. Mol. Cell Biol. 10: 207–217.
PubMed Link

Hsu, Y. C., L. Li and E. Fuchs. 2014. Emerging interactions between skin stem cells and their niches. Nat. Med. 20: 847–856.
PubMed Link

Mack, J. A., S. Anand and E. V. Maytin. 2005. Proliferation and cornification during development of the mammalian epidermis. Birth Def. Res. C Embryol. Today 75: 314–329.
PubMed Link

Truong, A. B. and P. A. Khavari. 2007. Control of keratinocyte proliferation and differentiation by p63. Cell Cycle 6: 295–299.
PubMed Link

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