SMAD4 and malignant colon neoplasm: Gut epithelium differentiation (Chgb, Klf4, Klf6, Sst), cell death/apoptosis of microglia (Btg1, Casp3, Casp9, Cx3cl1, Grin1, Myd88), uptake of prostaglandin E2 (Slco2a1), tumorigenesis of brain tumor (Nf2, Stat2), tumorigenesis of polyp (Asph, Smad4), aggregatability of colon cancer cell lines (Cd82), cell spreading of colon cancer cell lines (Smad4), contact inhibition of colon cancer cell lines (Prkg1)