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Hardy, 56). The second step of this two step process involves elongation and differentiation, cells in the placode grow and differentiate into the mature hair follicle (Oro, 575;Kashiwagi, 22-23). During this step the final signaling event produced by the dermal layer initiates proliferation and differentiation of the epithelial portion to form the hair follicle proper (Gat, 605; Hardy, 56; Oro, 576). The processes of hair follicle development are regulated by cell-cell interactions through soluble signaling molecules or direct cell contacts (Kashiwagi, 22). The regulations of these processes require gene responses in order to produce effects. Transcription factors are molecules that cause gene effects, and thus must be involved in the signaling pathway for gene responses to occur.

Transcription Factors:Transcription factors are proteins that control, where, when, and how genes are expressed by binding directly to DNA (Klug). Transcription factors contain two domains, one that binds to the DNA (DNA binding domain) and another that affects transcription through protein-protein interactions (Trans- activating domain) (Klug). TBX2 is a transcription factor encoded by the Tbx2 mRNA, and is expressed virtually in all areas of epithelium-mesenchyme interactions including the mouse lung, limb, and mammary gland (Chapman 379- 381). At 12.5 dpc Tbx2expression was observed in the facial region (Chapman, 381-382). We predict that Tbx2is expressed in the 13.5 dpc whisker pad due to its location in the facial region combined with the epithelium-mesenchyme

©Cebra-Thomas, 2000

Last Modified: 05 May 2000

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