The maintenance of a stable stem cellpopulation in the epidermis is important for robust regenerationof the stratified epithelium. The population size is usuallyregulated by cell secreted extracellular signalling molecules aswell as intracellular molecules. In this paper, a simple modelincorporating both levels of regulation is developed to examinethe balance between growth and differentiation for the stem cellpopulation. In particular, the dynamics of a known differentiationregulator c-Myc, its threshold dependent differentiation, andfeedback regulation on maintaining a stable stem cell populationare investigated.

Tocotrienols have been shown to inhibit proliferation and induce apoptosis in cancer cells. However, the molecular mechanisms involved in tocotrienol-induced apoptosis are still unclear. In the present study, γ-tocotrienol induced apoptosis in human gastric adenocarcinoma SGC-7901 cell line through down regulation of the extracellular signal-regulated kinase (ERK) signalling pathway. Furthermore, γ-tocotrienol-induced apoptosis was accompanied by down regulation of Bcl-2, up regulation of Bax, activation of caspase-3, and subsequent poly (ADP-ribose) polymerase cleavage. These results indicated that up or down regulation of Bcl-2 family proteins play a major role in the initiation of γ-tocotrienol-induced apoptosis as an activator of caspase-3.γ-Tocotrienol also down regulated the activation of the Raf-ERK signalling pathway, and down regulated c-Myc by decreasing the expressions of Raf-1 and p-ERK1/2 proteins. The results suggest that key regulators in tocotrienol-induced apoptosis may be Bcl-2 families and caspase-3 in SGC-7901 cells through down regulation of the Raf-ERK signalling pathway.