**2.4.1 Skin tissue**

Readily-accessible and as well-tolerated as punch biopsies (Camidge et al., 2005), skin is comprised of various layers of cells, making it useful for phenotypic and histological studies. Moreover, as a constantly dividing tissue with cells at various stages of development, skin provides insight into important signaling networks such as EGF, Wnt, Notch and cell proliferation (Phillips & Sachs, 2005).

Wee1 inhibitors have been examined as a way to bypass the G2 checkpoint, sensitizing p53 negative cells to DNA-damaging agents (Wang et al., 2001). In research conducted by Mizuarai et al., p53 negative rat skin xenograft tumors, p53 positive and negative cultured cancer cells, and p53 positive rat skin tissues were subjected to gemcitabine alone or in combination with the Wee-1 inhibitor MK-1775 (Mizuarai et al., 2009). Gene expression data identified five genes as potential biomarkers present in both tumor and skin.

Because of its strong potential as a surrogate tissue, it is important to address storage and handling challenges faced when using skin. Due to its protective nature, skin is shielded by nucleases and difficult to homogenize. We have found immediate preservation in RNAlater following the manufacturer's protocol (rather than flash-freezing) and thorough pulverization are paramount to extracting sufficient quantities of high-quality nucleic acid (data not shown).
