Molecular and cytogenetic studies on nucleolar cistrons (rDNA) in mouse leukemia cells

7,12-DMBA-induced rat leukemia: a review with insights into future research

7,12-Dimethylbenz[a]anthracene (DMBA) elicits leukemia in Long-Evans rats (LE). This leukemia is mostly erythroblastic and 30% of leukemias have total and partial trisomy of #2 chromosome and the rest have diploid karyotype. The common duplication site is in 2q26-q34 and N-ras gene is located in 2q34. 7,8,12-Trimethylbenz[a]anthracene (TMBA) also induces similar leukemias. These leukemias reveal a highly specific mutation of N-ras gene as in human leukemias. N-ras mutation is induced 48h after DMBA treatment. Wild type N-ras allele is frequently lost in diploid leukemias but not in trisomy type. Therefore, a gene dosage problem related to the mutant N-ras gene is involved in development of leukemia. Some secondary genetic rearrangements involving abl and H-ras are also observed in cultured leukemia cells. DMBA-induced chromosome aberrations as well as leukemia are enhanced by erythropoietin and blocked by Sudan III given prior to DMBA treatment. This leukemia will provide an important tool for chemical carcinogenesis and leukemia studies.

Structural alterations of the ribosomal RNA genes in leukemic cells

Cloned 6.7 kb EcoR1 fragment of mice rDNA was used as a hybridization probe for rDNA structure analysis in mice, rat and calf haemopoietic tumor and normal cells. EcoR1, BglII and Pst1 restriction fragment length polymorphism (RFLP) was found in neoplastic rDNA and was not revealed in normal ones. The rRNA gene rearrangements were observed not only in spacer region but in coding sequences of the genes. Leukemic cells reveal also rDNA amplification. A role of genetic rearrangements of rDNA for mechanisms of carcinogenesis is suggested.

Chromosome 14 Abnormality with a Breakpoint of p12 in Adult T-cell Leukemia

We describe a patient with adult T-cell leukemia (ATL) with a 14p chromosomal abnormality. Cytogenetic study revealed two clonal populations of leukemic cells in the peripheral blood sample. Both clones were karyotypically related to each other. One of them showed rearrangement of chromosome 14 at break band p 12 (14p12) in addition to + 3, + 7, -X and del(6) (q14q21). The nucleolar organizer region (NOR) is assigned to the band 14p12 and the role of the rearrangement of chromosome 14p12 in the pathogenesis of ATL is discussed.

Establishment and characterization of mouse leukemia cell lines L615K and L7212K derived from transplantable murine leukemias maintained in China

Two culture cell lines L615K and L7212K were established from transplanted murine leukemias L615 and L7212, which had been established and maintained in China for years. Based on morphological, immunological and gene rearrangement analyses, L7212K cells are considered to be of T-cell origin while L615K cells might be immature T-cells. Immunofluorescence assays of viable leukemia cells and fluorescence focus assays of their culture supernate for infectious viruses suggested that recombinant mink cell focus-inducing viruses were significantly involved in both leukemic cell lines. Chromosome analysis of the L615K cells revealed a translocation t(12;17) which probably involved the c-fos locus on chromosome 12, since the DNA rearrangement of c-fos was demonstrated by Southern blot analysis with Hind III, and c-fos has been assigned to this chromosome. Although the expression of this gene was not detected by RNA Northern blot analysis, c-myc was slightly expressed in both L615K and L7212K cells.

Spontaneous in vitro neoplastic evolution of cultured Chinese hamster cells. Nucleolus organizing region activity

Silver staining to demonstrate active nucleolus organizing regions (NORs) was performed at four different stages of the spontaneous tumorigenic progression in vitro of Chinese hamster WCHE/5 cells. The number of active NORs increased for fully transformed, highly tumorigenic, late passage cells. The increase of NOR material was due to additional NOR-bearing chromosomes or chromosome arms, i.e., trisomy 5, trisomy 8, and the marker chromosome i(3q). Intermediate stages of the neoplastic evolution showed changing patterns of NOR activity, but not an overall increase. We postulate that the increase of active rDNA enhances cell growth and provides undefined selective advantage, and that this supports our previous conclusion that selectable karyotype changes provide competitive advantages rather than being essential for neoplastic evolution in vitro.

Cytogenetic analyses of somatic chromosomes in a transplantable monomyelocytic leukemia in BALB/c mice

In vivo cytogenetic analyses have been performed using G-, C-, and nuclear organizing region (NOR)-banding techniques, and sister chromatid exchanges (SCE) on a transplantable monomyelocytic leukemia (MML) initially induced in female BALB/c mice by the Rauscher leukemia virus (RLV). Centromeric associations have been found to be greatly increased in MML transplanted mice. Transplantability of the disease has been demonstrated at the cytogenetic level by the presence of female cells in males transplanted with MML cells. G-banding analysis has shown the existence of a marker deleted chromosome 18 in all tissues examined (bone marrow, spleen, and peripheral blood) restricted to female transplanted cells. The NOR-banding analysis has shown a slight increase in the number of Ag-NOR sites per metaphase in MML transplanted mice compared with controls and the existence of an extra chromosome having NOR in MML transplanted mice. No differences were found in C banding between controls and MML transplanted mice. In MML transplanted males, female transformed cells showed a significant reduction in SCE frequency compared with host male cells or controls.