Chromosomal localization of the rat Harvey-ras-1 gene (HRAS) by in situ hybridization

Genomewide assessment of genetic alterations in DMBA-induced rat sarcomas: cytogenetic, CGH, and allelotype analyses reveal recurrent DNA copy number changes in rat chromosomes 1, 2, 4, and 7

Rat sarcomas, induced by subcutaneous injections of 7,12-dimethylbenz[a]anthracene (DMBA), were studied with the objective of identifying critical chromosome regions associated with tumorigenesis. We employed three genomewide screening techniques-cytogenetics, CGH, and allelotyping-in 19 DMBA-induced sarcomas in F1 (BN/Han x LE/Mol) rats. The most conspicuous finding in the cytogenetic analysis was a high incidence of trisomy for rat chromosome 2 (RNO2). Signs of gene amplification (hsr) were also seen in several tumors. The CGH analysis revealed that gains in copy number were much more common than losses. The gains mostly affected RNO2 (10/19), RNO12q (7/19), and RNO19q (5/19), as well as the proximal part of RNO4 (8/19) and the distal part of RNO7 (7/19). Reduction in copy number was seen in RNO17 (2/19). For the allelotyping, we used 318 polymorphic microsatellite marker loci covering the entire genome. We identified regions of allelic imbalance affecting most of the rat chromosomes. The highest incidences of recurrent allelic imbalance were observed at loci in certain regions in RNO1, 2, 4, and 7 and at lower incidences in parts of RNO12, 16, 18, and 19. The combined results suggested that genetic alterations detected in RNO2 and RNO12 usually corresponded to complete or partial trisomy, whereas those in RNO1 and RNO7 seemed to involve regional deletions and/or gains. Furthermore, we could confirm that copy number gains occur proximally in RNO4, where a previous study showed amplification of the Met oncogene in a subset of these tumors.

Recurrent alterations of the short arm of chromosome 3 define a tumor suppressor region in rat mammary tumor cells

Cytogenetic alterations associated with different stages in carcinogenesis can be distinguished in cultured human or rodent cells transformed by carcinogenic agents. Three tumorigenic rat mammary epithelial cell lines transformed in vitro with 7,12, -dimethylbenz[a]anthracene alone or in combination with 12-O-tetradecanoylphorbol-13-acetate were examined cytogenetically. Non-random alterations consisting of translocations involving the short arm of chromosome 3 and trisomy of chromosomes 14 and X were identified in all three lines. Deletion and inversion of chromosome 1 with the breakpoint at band 1q22 and a duplication 1q 32-43 and trisomy of chromosome 2 were observed in two cell lines. The accumulation of structural alterations and chromosome imbalances during the process of cell immortalization and acquisition of tumorigenicity are required for normal rat mammary cells to become malignant. Unbalanced translocations of chromosome 3 resulting in loss of the short arm had the breakpoint at 3p11. This site is a hotspot of breakage and recombination in various rat tumors and may represent a region of tumor suppressor gene critical to the development of rat mammary tumors, as well as other types of tumors.

Rat chromosome 1: regional localization of seven genes (Slc9a3, Srd5a1, Esr, Tcp1, Grik5, Tnnt3, Jak2) and anchoring of the genetic linkage map to the cytogenetic map

Seven genes were regionally localized on rat Chromosome (Chr) 1, from 1p11 to 1q42, and two of these genes were also included in a linkage map. This mapping work integrates the genetic linkage map and the cytogenetic map, and allows us to orient the linkage map with respect to the centromere, and to deduce the approximate position of the centromere in the linkage map. These mapping data also indicate that the Slc9a3 gene, encoding the Na+/H+ exchanger 3, is an unlikely candidate for the blood pressure loci assigned to rat Chr 1. These new localizations expand comparative mapping between rat Chr 1 and mouse or human chromosomes.

Allelic imbalance in mammary carcinomas induced by either 7,12-dimethylbenz[a]anthracene or ionizing radiation in rats carrying genes conferring differential susceptibilities to mammary carcinogenesis

To identify and compare the genetic lesions associated with tumorigenesis in rats carrying the mammary carcinoma suppressor (MCS) 1 gene, we induced mammary carcinomas in (Wistar Furth (WF) x Copenhagen (Cop))F1 rats by using either 7,12-dimethylbenz[a]anthracene (DMBA) or radiation. The tumors were screened for allelic imbalances by using polymerase chain reaction and 65 polymorphic microsatellite markers spanning the genome. No allelic imbalance was detected at the mapped location of MCS-1 on chromosome 2; however, a scan of the genome revealed random allelic imbalances in the radiation-induced tumors. In addition, non-random loss of heterozygosity (LOH) on chromosome 1 in the DMBA-induced tumors was documented. We then screened three other subsets of DMBA- and radiation-induced mammary carcinomas from (WF x Fischer (F344))F1, (Wistar Kyoto x F344)F1, and (F344 x Cop)F1 rats for imbalance on chromosomes 1 and 2. No allelic imbalance was detected in the MCS-1 region of chromosome 2 in any of the tumors screened. Nonrandom imbalance on chromosome 1 was detected but only in the DMBA-induced tumors from the (F344 x Cop)F1 rats. Thus, only Cop-derived F1 rats have mammary tumors with the chromosome 1 imbalance; however, the imbalance does not favor the Cop parental allele. We also analyzed the DMBA-induced tumors with LOH at chromosome 1 for Ha-ras codon 61 mutation and found no association. These results suggest that loss of the MCS-1 Cop allele is not required for tumor formation, that the genetic background of the F1 rat appears to influence the type of genetic lesion identified in the mammary tumors, and that there is no association between Ha-ras codon 61 mutation and chromosome 1 imbalance in our model system.

Karyotype evolution of the clonal rat liver cell line CL 52 during progression in vitro and in vivo

Liver cell line CL 52, derived from a diethylnitrosamine-treated rat at the stage of preneoplasia/early neoplasia, had an inconspicuous 2n karyotype when analyzed 6 months after in vitro propagation. Malignant progression was accompanied by cytogenetic alterations of chromosomes 1, 3, and 11. In addition, trisomy of chromosomes 4, 6, and 7 led to a significant reduction of the tumor latency period after retransplantation. During 4 years of cytogenetic observation, the once clonal 2n population showed a characteristic karyotype evolution: loss of diploidy, occurrence of polyploid sidelines, deletions followed by unbalanced rearrangements, clonal diversification, and selection of the in vitro most rapidly growing or in vivo most malignant cell type. The karyotype alterations in the four sublines of CL 52 are discussed with special reference to oncogenesis-related genes assigned to the involved rat chromosomes 1, 3, 11, 12, 4, 6, 7, 10. The observed karyotype evolution of this cell line exemplifies genetic/ chromosome instability of carcinogen-induced preneoplastic/early neoplastic liver cells and provides a tool for analyzing, under controlled conditions, stage-dependent sequences of molecular genetic alterations in liver carcinogenesis.

Establishment of immortalized alveolar type II epithelial cell lines from adult rats

We developed methodology to isolate and culture rat alveolar Type II cells under conditions that preserved their proliferative capacity, and applied lipofection to introduce an immortalizing gene into the cells. Briefly, the alveolar Type II cells were isolated from male F344 rats using airway perfusion with a pronase solution followed by incubation for 30 min at 37 degrees C. Cells obtained by pronase digestion were predominantly epithelial in morphology and were positive for Papanicolaou and alkaline phosphatase staining. These cells could be maintained on an extracellular matrix of fibronectin and Type IV collagen in a low serum, insulin-supplemented Ham's F12 growth medium for four to five passages. Rat alveolar epithelial cells obtained by this method were transformed with the SV40-T antigen gene and two immortalized cell lines (RLE-6T and RLE-6TN) were obtained. The RLE-6T line exhibits positive nuclear immunostaining for the SV40-T antigen and the RLE-6TN line does not. PCR analysis of genomic DNA from the RLE-6T and RLE-6TN cells demonstrated the T-antigen gene was present only in the RLE-6T line indicating the RLE-6TN line is likely derived from a spontaneous transformant. After more than 50 population doublings, the RLE-6T cells stained positive for cytokeratin, possessed alkaline phosphatase activity, and contained lipid-containing inclusion bodies (phosphine 3R staining); all characteristics of alveolar Type II cells. The RLE-6TN cells exhibited similar characteristics except they did not express alkaline phosphatase activity. Early passage RLE-6T and 6TN cells showed a near diploid chromosome number.(ABSTRACT TRUNCATED AT 250 WORDS)

Loss of heterozygosity at chromosome 1q loci in rat mammary tumors

To better characterize abnormalities affecting rat chromosome 1 during mammary carcinogenesis, tumors were induced by nitrosomethylurea in F1 hybrid rats polymorphic at multiple chromosome 1 loci. By means of restriction fragment length polymorphism and microsatellite length polymorphism analyses, we observed loss of heterozygosity or allelic imbalance affecting various loci on the q arm of chromosome 1 in a high percentage of the 49 tumors analyzed. Fifty percent of the tumors showed loss or imbalance affecting the most distal (1q55) INS1 (rat insulin 1 gene) locus. The MT1PA (metallothionein-1 pseudogene a) locus was observed to be affected in 58% of tumors induced in BUF/NCr x ACI/Vsp rats. Most of the losses appeared to have occurred by mitotic recombination. No parental bias was observed on the affected chromosome 1. Tumors were also screened for mutations in codon 12 of the Ha-ras-1 gene, which is located on 1q. We observed an association between the presence of mutation and allelic imbalance. These studies confirm our previous cytogenetic observations of a high level of nonrandom instability affecting rat chromosome 1 during mammary carcinogenesis. The observed loss of heterozygosity may indicate the existence of a putative tumor suppressor gene within the distal half of the 1q arm. These abnormalities, however, could also be related to the early stages of Ha-ras amplification.