To determine if Atrx loss would decrease the time to tumor initiation, we added a floxed Atrx allele (Atrxfl/fl/y) to the Osx-Cre+p53fl/flRbfl/fl to create Osx-Cre+p53fl/flRbfl/flAtrxfl/fl/y. Here, SP7 is linked to neoplasm.