Göran Levan

Tumor etiology and chromosome pattern.

Fibrosarcomas induced in Chinese hamsters and rats by Rous sarcomla virus and 7,12-dimethylbenz(a)anthracene are associated with nonrandom chromosome variation. Although histologically indistinguishable, the tumors induced by the virus or chemical in each host species are characterized by completely different karyotypic patterns.

Amplification of Mycn, Ddx1, Rrm2, and Odc1 in rat uterine endometrial carcinomas.

The BDII rat is genetically predisposed to estrogen‐dependent endometrial adenocarcinoma and represents a valuable model for this type of tumor. Tumors arising in strain crosses involving the BDII rats had previously been screened for DNA copy number changes using comparative genome hybridization (CGH). It was found that extra copies of the proximal region of rat chromosome (RNO) 6 commonly could be detected in these tumors. Based on RH‐mapping data and comparative mapping with mouse and human, seven cancer‐related genes were predicted to be situated in RNO6q14–q16. Rat PACs were isolated for the N‐myc proto‐oncogene (Mycn), apolipoprotein B (Apob), the DEAD box gene 1 (Ddx1), ornithine decarboxylase 1 (Odc1), proopiomelanocortin (Pomc1), ribonucleotide reductase, M2 polypeptide (Rrm2), and syndecan 1 (Sdc1). The localization of the genes to the region was verified by FISH (fluorescence in situ hybridization) mapping, and the detailed order among them was determined by dual‐color FISH. By Southern blot analysis, it was found that the Mycn locus was highly amplified in two out of 10 cell cultures derived from the tumors. In one of them (designated RUT30), the amplification level of Mycn was estimated at 140×. Two other genes were coamplified (Ddx1 and Rrm2) at much lower levels. Similarly, in another culture (designated RUT2), Mycn was amplified more than 40×, whereas three of the other genes (Ddx1, Rrm2, and Odc1) were coamplified at lower levels. Using FISH on metaphase chromosomes from the cell cultures analyzed, the amplified sequences were shown to be located in typical HSRs. With competitive RT‐PCR, distinct overexpression of Mycn and Ddx1 could be demonstrated in both RUT2 and RUT30. In addition, Mycn was overexpressed in two other tumors not exhibiting Mycn amplification. Taken together, our results suggest that overexpression of Mycn plays an important role in the development of endometrial cancer in the BDII rat. In humans, Mycn amplification has been reported mainly from tumors of neuronal origin. To our knowledge, this is the first report of Mycn amplification and overexpression in hormone‐dependent tumors.

Between rat and mouse zoo-FISH reveals 49 chromosomal segments that have been conserved in evolution

Abstract.Mouse single chromosome paints were applied to rat prophase/prometaphase chromosomes to detect homologous chromosome regions. The analysis revealed 49 rat chromosomal regions ranging in size from whole chromosomes down to small bands near the limit of detection with this method, which was estimated to be 2–3 Mb. When all the painted regions were taken into account, the whole rat genome was covered with mouse-homologous regions, with the exception of small segments near the centromeres and the short arms of Chromosomes (Chrs) 3, 11, 12, and 13. These regions were shown to contain high levels of rat-specific repetitive DNA. The number of conserved segments between rat and mouse detected by our high-resolution zoo-FISH method was significantly higher than that reported in previous studies.

High-density marker loss of heterozygosity analysis of rat chromosome 10 in endometrial adenocarcinoma.

Endometrial cancer is a disease with serious impact on the human population, but not much is known about genetic factors involved in this complex disease. Female BDII rats are genetically predisposed to spontaneous endometrial carcinoma, and the BDII inbred strain provides an experimental animal model for endometrial carcinoma development. In the present study, BDII females were crossed with males from two nonsusceptible inbred rat strains. Endometrial adenocarcinomas (EACs) developed in a proportion of the F1 and F2 progeny. We screened 18 EAC solid tumors and 9 EAC cell cultures for loss of heterozygosity (LOH) using fluorescent‐PCR‐based marker allelotyping methodology with 47 microsatellite markers covering the proximal part of rat chromosome 10 (RNO10). Conclusive evidence was obtained for LOH/deletion involving about 56 cM in the proximal part of RNO10 in DNA from six out of seven informative tumor cell cultures. Analysis of the solid tumors confirmed the presence of LOH in this part of RNO10 in 14 of 17 informative tumors. However, from the studies in the solid tumors it appeared that in fact three separate segments in the proximal part of RNO10 were affected. These three LOH/deletion regions were located approximately in cytogenetic bands 10q11‐12, 10q22, and 10q24.

Polycyclic hydrocarbon-induced rat sarcomas correlated to disturbances in the deoxyadenylate regions of the tumor DNAs☆

Abstract Ten separate groups containing a total of 51 rat sarcomas induced by the polycyclic hydrocarbons were examined for inducing agent-related abnormalities in their DNAs. The levels of deoxyadenylate (dA) regions in normal and tumor rat DNAs were estimated from annealing [ 3 H ]-polyuridylic acid to DNA and treatment of the resultant hybrids with ribonuclease A. All the tumor material had significant reductions in the (dA) regions of their DNAs when the levels were compared to normal rat DNA. Although the (dA) reductions were rather heterogeneous from one tumor group to the other no matter the inducing agent, the greatest decreases tended to be found with tumors induced by 20 -methylcholanthrene (MC) and 7,12 -dimethylbenz(a)anthracene (DMBA). No relationship was found between (dA) alterations and the types of chromosomal aberrations in the tumor cell populations. However, normal and tumor DNAs, fractionated into A + T rich and G + C rich DNA by thermal elution from hydroxylapatite columns, showed specific neoplastic-associated (dA) disturbances in the A + T rich DNA of tumors induced by 3,4 -benzopyrene (BP), MC and DMBA. The base compositions of the tumor material were also analyzed and compared to normal rat DNA. Tumors induced by DMBA showed highly significant decreases in % A + T whereas BP and MC induced tumors tended to show only small increases in % A + T. Some tumors induced by BP, MC and DMBA were unaltered in base composition. Together our results are consistent with the hypothesis that DMBA is the strongest carcinogen in the series because it interacts preferentially with A + T Trich DNA, which is the type of DNA most important for polycyclic hydrocarbon-induced neoplasm in the rat.