1. Department of Zoology, The University of Hong Kong (R.T.-K.P., S.S.-M.N., B.K.-C.C.), Hong Kong, Special Administrative Region, Peoples Republic of China
2. the Department of Biochemistry, Chinese University of Hong Kong (C.H.-K.C.), Hong Kong, Special Administrative Region, Peoples Republic of China
3. The Center for Basic Research in Digestive Diseases, Mayo Clinic and Foundation (M.H.H., L.J.M.), Rochester, Minnesota 55905