Cigarette smoke carcinogens such as benzo[a]pyrene are implicated in the development of lung cancer. The distribution of benzo[a]pyrene diol epoxide (BPDE) adducts along exons of the P53 gene in BPDE-treated HeLa cells and bronchial epithelial cells was mapped at nucleotide resolution. Strong and selective adduct formation occurred at guanine positions in codons 157, 248, and 273. These same positions are the major mutational hotspots in human lung cancers. Thus, targeted adduct formation rather than phenotypic selection appears to shape the P53 mutational spectrum in lung cancer. These results provide a direct etiological link between a defined chemical carcinogen and human cancer.

Down syndrome (DS) is caused by the presence of an extra copy of human chromosome 21 (Hsa21) and is the most common genetic cause for developmental cognitive disability. The regions on Hsa21 are syntenically conserved with three regions located on mouse chromosome 10 (Mmu10), Mmu16 and Mmu17. In this report, we describe a new mouse model for DS that carries duplications spanning the entire Hsa21 syntenic regions on all three mouse chromosomes. This mouse mutant exhibits DS-related neurological defects, including impaired cognitive behaviors, reduced hippocampal long-term potentiation and hydrocephalus. These results suggest that when all the mouse orthologs of the Hsa21 genes are triplicated, an abnormal cognitively relevant phenotype is the final outcome of the elevated expressions of these orthologs as well as all the possible functional interactions among themselves and/or with other mouse genes. Because of its desirable genotype and phenotype, this mutant may have the potential to serve as one of the reference models for further understanding the developmental cognitive disability associated with DS and may also be used for developing novel therapeutic interventions for this clinical manifestation of the disorder.

Down syndrome is caused by a genomic imbalance of human chromosome 21 which is mainly observed as trisomy 21. The regions on human chromosome 21 are syntenically conserved in three regions on mouse chromosomes 10, 16 and 17. Ts65Dn mice, the most widely used model for Down syndrome, are trisomic for approximately 56.5% of the human chromosome 21 syntenic region on mouse chromosome 16. To generate a more complete trisomic mouse model of Down syndrome, we have established a 22.9 Mb duplication spanning the entire human chromosome 21 syntenic region on mouse chromosome 16 in mice using Cre/loxP-mediated long-range chromosome engineering. The presence of the intact duplication in mice was confirmed by fluorescent in situ hybridization and BAC-based array comparative genomic hybridization. The expression levels of the genes within the duplication interval reflect gene-dosage effects in the mutant mice. The cardiovascular and gastrointestinal phenotypes of the mouse model were similar to those of patients with Down syndrome. This new mouse model represents a powerful tool to further understand the molecular and cellular mechanisms of Down syndrome.