TAB1 and neoplasm: Transplantation of immunodeficient host mice with either Tab1−/− or Map3k1mPHD ES cells causes aberrant tumors to form, and these have altered tissue composition and are of smaller mass and size.72 Add-back of Tab1, but not lysine-mutated (Lys294Ala, Lys319Ala, Lys335Ala and Lys350Ala) Tab1, into Tab1−/− ES cells restores normal ES cell differentiation and tumorigenesis, demonstrating that the lysines in Tab1 ubiquitinated by the Map3k1 PHD motif are critically important for ES cell differentiation and tumor formation in mice.72