The head and neck region (full-body shielded) of mice from each genotype were irradiated using a Varian 6 MV linear accelerator, at a dose rate of 200 cGy/min, according to previously published methods (15 (link)). Groups of mice received a single 30 Gy fraction, and other groups received 10 Gy daily fractions for four consecutive days. Mice were immobilized and irradiated while under Nembutal anesthesia as described elsewhere (14 (link), 15 (link)). Lower single- or fractionated radiation doses did not induce mucositis (14 (link), 15 (link)).