Ptprj is a candidate for the mouse colon-cancer susceptibility locus Scc1 and is frequently deleted in human cancers.

Only a small proportion of cancers result from familial cancer syndromes with Mendelian inheritance. Nonfamilial, 'sporadic' cancers, which represent most cancer cases, also have a significant hereditary component, but the genes involved have low penetrance and are extremely difficult to detect. Therefore, mapping and cloning of quantitative trait loci (QTLs) for cancer susceptibility in animals could help identify homologous genes in humans. Several cancer-susceptibility QTLs have been mapped in mice and rats, but none have been cloned so far. Here we report the positional cloning of the mouse gene Scc1 (Susceptibility to colon cancer 1) and the identification of Ptprj, encoding a receptor-type protein tyrosine phosphatase, as the underlying gene. In human colon, lung and breast cancers, we show frequent deletion of PTPRJ, allelic imbalance in loss of heterozygosity (LOH) and missense mutations. Our data suggest that PTPRJ is relevant to the development of several different human cancers.

Genetic analysis of three-dimensional shape of mouse lung tumors reveals eight lung tumor shape-determining (Ltsd) loci that are associated with tumor heterogeneity and symmetry.

Most lung tumor linkage studies focus on identifying loci that confer susceptibility or resistance irrespective of the tumor types developed. However, different mouse strains develop different types of lung tumors. A major obstacle for genetic studies of these differences is the lack of reproducible, quantitative, and uniform assessment of tumor type. We have previously described a new variable (Rratio) that assesses the three-dimensional shape of lung tumors in a quantifiable way and showed that nonspherical tumors are correlated with tumor heterogeneity and with a tendency to asymmetrical growth (N. Tripodis and P. Demant, Exp. Lung Res., 27: 521-531, 2001). In the present study, we use the Rratio variable to search for quantitative trait loci affecting tumor phenotype. We tested the F(2) cross between the susceptible strain O20 and the recombinant congenic strain OcB-9. Both develop mixed alveolar and papillary lung tumors, and the OcB9 tumors are, on average, more elongated than the O20 ones. We mapped eight new lung tumor shape-determining loci (Ltsd1-8) involved in mutual interactions. Two of these loci, Ltsd1 and Ltsd3, seem to play a major role in tumor shape formation. The Ltsd4 locus was confirmed in a second F(2) cross between strain O20 and the recombinant congenic strain OcB-6. Genotype-phenotype associations show that nonspherical tumors are correlated with tumor heterogeneity and nonsymmetrical (focal) development of structures. Most of the new Ltsd loci map in regions where susceptibility to lung cancer (Sluc) loci have been previously mapped, raising the question of whether they are identical or closely linked loci. Based on models of tumor growth indicating that supply of nutrients and the ability to create a capillary network may be shape-determining factors (G. P. Pescarmona et al., Med. Hypoth., 53: 497-503, 1999), we suggest as likely candidates for the Ltsd loci genes involved in angiogenesis, vascularization, and capillary patterning. This is the first set of loci that affects qualitative aspects of lung tumors and may provide biologically and clinically interesting indicators of lung tumor progression.

Dissecting the genetic complexity of human 6p deletion syndromes by using a region-specific, phenotype-driven mouse screen.

Monosomy of the human chromosome 6p terminal region results in a variety of congenital malformations that include brain, craniofacial, and organogenesis abnormalities. To examine the genetic basis of these phenotypes, we have carried out an unbiased functional analysis of the syntenic region of the mouse genome (proximal Mmu13). A genetic screen for recessive mutations in this region recovered thirteen lines with phenotypes relevant to a variety of clinical conditions. These include two loci that cause holoprosencephaly, two that underlie anophthalmia, one of which also contributes to other craniofacial abnormalities such as microcephaly, agnathia, and palatogenesis defects, and one locus responsible for developmental heart and kidney defects. Analysis of heterozygous carriers of these mutations shows that a high proportion of these loci manifest with behavioral activity and sensorimotor deficits in the heterozygous state. This finding argues for the systematic, reciprocal phenotypic assessment of dominant and recessive mouse mutants. In addition to providing a resource of single gene mutants that model 6p-associated disorders, the work reveals unsuspected genetic complexity at this region. In particular, many of the phenotypes associated with 6p deletions can be elicited by mutation in one of a number of genes. This finding implies that phenotypes associated with contiguous gene deletion syndromes can result not only from dosage sensitivity of one gene in the region but also from the combined effect of monosomy for multiple genes that function within the same biological process.