Kit is expressed by epithelial cells in vivo

Area of Science:

• Dermatology
• Cell Biology
• Molecular Biology

Background:

• Stem cell factor (SCF) and its receptor Kit are known to regulate mast cells and melanocytes in mammalian skin.
• Previous observations noted Kit-positive (Kit+) cells in murine hair follicles, distinct from typical cutaneous Kit+ cells.
• The identity and function of these intraepithelial Kit+ cells in hair follicles remained uncharacterized.

Purpose of the Study:

• To identify the nature of Kit+ cells within murine hair follicles.
• To investigate the role of Kit signaling in hair follicle biology and hair growth control.
• To explore potential novel functions of Kit signaling in epithelial cell biology.

Main Methods:

• Immunohistochemistry using markers like desmoplakin and Trp-1.
• Electron microscopy to analyze cellular ultrastructure, including tonofilaments, desmosomes, and melanosomes.
• Analysis of genetically modified mice (Kit(Sl)/Kit(Sl-d), Kit(W)/Kit(W-v)) and antibody-treated mice to assess Kit and SCF expression and function during the hair cycle.

Main Results:

• Kit immunoreactivity was identified in hair matrix keratinocytes within anagen hair follicles, separate from the pigmentary unit.
• These Kit+ cells were confirmed as keratinocytes via immunohistochemistry (desmoplakin+/Trp-1-) and electron microscopy (lacking melanosomes).
• Kit and SCF expression exhibited strong hair cycle dependency, and impaired Kit signaling (Kit(W)/Kit(W-v) mice) resulted in retarded anagen development.

Conclusions:

• Hair matrix keratinocytes express the stem cell factor receptor Kit.
• Epithelial Kit expression plays a significant role in regulating hair growth and the hair cycle.
• Kit signaling represents a novel pathway with potential unexplored functions in hair follicle epithelial cell biology.