Student Research: Cecile Krejsa
Tumor development is a multi-step process which can be divided into stages of initiation, promotion, and progression. We used a two step tumorigenesis model to induce skin tumors using the carcinogen 7, 12-dimehylbenz-[a]-anthracene (DMBA) and the tumor promoter 12-O-teradecanoylphorbol-13-acetate (TPA) in wild-type, p19ARF-, and p53-deficient mice. To identify novel genetic alterations required for tumor development during each stage and to identify any differences in genetic alterations when two of the commonly altered tumor suppressor genes, p19ARF or p53, are missing, micro-array based comparative genome hybridization (array-CGH) was used to detect chromosomal aberrations from skin tumors. We transformed the array-CGH data using the bacterial artificial chromosome (BAC) clone map locations to identify chromosomal gains and losses by spatial structure of the array-CGH. We used the BAC clone log2 ratio to determine statistically significant changes in tumor sample DNA compared to normal tissue DNA to identify unique chromosomes with gains or losses in different tumor stages. Our method showed malignant carcinomas had a higher number of chromosomes with gains or losses compared to benign papillomas and duplication of chromosomes 6, 7, and 15 were consistently observed. Regardless of genotypes, a duplication of chromosome 7 was present in both carcinomas and papillomas while a duplication of chromosomes 6 and 15 were present mostly in the carcinoma but not in the papilloma. We also show that carcinomas from p19ARF- and p53-deficient mice had higher number of chromosomes with gains or losses compared to the carcinomas from wild-type mice. These findings indicate that tumor progression is associated with increase in chromosomal gains or losses, that duplication of chromosome 7 is an early event while duplication of chromosome s 6 and 15 is a late event, and that p19ARF- and p53-deficiency leads to increase in genomic instability in this skin tumorigenesis model.