Oligoclonality of Moloney leukemias

The common viral insertion site Evi12 is located in the 5'-noncoding region of Gnn, a novel gene with enhanced expression in two subclasses of human acute myeloid leukemia

The leukemia and lymphoma disease locus Evi12 was mapped to the noncoding region of a novel gene, Gnn (named for Grp94 neighboring nucleotidase), that is located immediately upstream of the Grp94/Tra1 gene on mouse chromosome 10. The Gnn gene is conserved in mice and humans. Expression of fusion constructs between GFP and Gnn cDNA isoforms in HEK-293 cells showed that Gnn proteins are located mainly in the cytoplasm. Immunoblotting experiments demonstrated the presence of multiple Gnn protein isoforms in most organs, with the lowest levels of expression of the protein detected in bone marrow and spleen. The Evi12-containing leukemia cell line NFS107 showed high levels of expression of a approximately 150-kDa Gnn isoform (Gnn107) that was not observed in control cell lines. Overexpression may be due to the viral insertion in Evi12. The Gnn107 protein is probably encoded by a Gnn cDNA isoform that is expressed exclusively in NFS107 cells and that includes sequences of TU12B1-TY, a putative protein with homology to 5'-nucleotidase enzymes. Interestingly, using Affymetrix gene expression data of a cohort of 285 patients with acute myeloid leukemia (AML), we found that GNN/TU12B1-TY expression was specifically increased in two AML clusters. One cluster consisted of all AML patients with a t(8;21) translocation, and the second cluster consisted of AML patients with a normal karyotype carrying a FLT3 internal tandem duplication. These findings suggest that we identified a novel proto-oncogene that may be causally linked to certain types of human leukemia.

Large-scale identification of novel potential disease loci in mouse leukemia applying an improved strategy for cloning common virus integration sites

The identification of common virus integration sites (cVIS) in retrovirally induced tumors in mice provides a powerful strategy to isolate novel transforming genes. Applying virus LTR-specific inverse-PCR and RT-PCR combined with automated sequencing on CasBr-M Murine Leukemia Virus (MuLV) induced myeloid leukemias, 126 virus integration sites were cloned. Using locus- and LTR-specific primers, a nested-PCR/Southern-blotting procedure was developed on genomic DNA from a large panel of MuLV-induced leukemias, to analyse whether a particular virus insertion represented a cVIS. In fact 39 out of 41 integrations analysed this way appeared to represent a common virus integration. We recognized six previously cloned cVISs, i.e. Evi1, Hoxa7, c-Myb, Cb2/Evi11, Evi12, and His1 and 33 novel common insertions, designated Cas-Br Virus Integration Site (Casvis). Among this group we found integrations in or near genes encoding nuclear proteins, e.g. Dnmt-2, Nm23-M2, Ctbp1 or Erg, within receptor genes, e.g. Cb2 or mrc1, novel putative signaling or transporter genes, the ringfinger-protein gene Mid1 and a panel of genes encoding novel proteins with unknown function. The finding that 39 out of 41 integrations analysed represented a cVIS, suggests that the majority of the other virus insertions that were not yet analysed by the PCR/Southern-blotting method are located in a cVIS as well and may therefore also harbor novel disease genes.

The ftsZ gene as a tool for detection of Mycoplasma fermentans

Mycoplasma fermentans was reported as a common contaminant of cell cultures, and was shown to either induce or suppress several immunological functions. A strain of M. fermentans was recently isolated from a mouse T-lymphoma cell line, which differs from other M. fermentans strains by its growth characteristics and was designated (in the authors' records) as strain 609. Using the differential display technique (DD), a differentially expressed gene that was identified as the M. fermentans 609 ftsZ gene was isolated. Comparison of the nucleotide sequence of the M. fermentans 609 ftsZ gene to other ftsZ genes showed a 98% homology with Mycoplasma fermentans strain K7 and approximately 50% homology with Mycoplasma pulmonis and Mycoplasma genitalium. Comparison of the putative amino acid sequences of the FtsZ proteins showed similar homology. A polymerase chain reaction (PCR) assay to detect the presence of this ftsZ gene was established; it is a fast and convenient assay to detect infection of cells by the M. fermentans species. This work demonstrates that: (i) DD can be used as a useful technique to identify and isolate mycoplasmal genes from infected cells; and (ii) the ftsZ gene can be a useful marker to distinguish between different species of mycoplasma.

Early metastatic stage of 2,7-FAA-induced leukemia in rats

The development from primary focus to metastasis was histologically investigated in 2,7-FAA-induced leukemia in rats. The Wistar and Sprague-Dawley strains were used, and the results were similar in both strains. The spread of lesions was classified as solitary, scattered or diffuse. Scattered leukemia lesions were divided into two groups: A and B: (A) consisted of one or a few conspicuously large foci and many small foci, and (B) had no such large foci. The interval from the first appearance of orthochromatic erythroblasts to autopsy was short in animals with solitary lesions, slightly longer in those with scattered lesions in group (A), and still longer in group (B). Conspicuously large foci were predominantly localized in the bone marrow, while small foci were scattered in the bone marrow, spleen and liver. The (A) scattered lesions were considered to represent the early metastatic stage, since they consisted of the combination of large and small foci, and the time interval from the first appearance of erythroblasts to autopsy was between that of solitary lesions and (B) scattered lesions. The leukemia induced in rats by 2,7-FAA occurred predominantly in the bone marrow, which was the primary site. It was thought that this leukemia spread rapidly to other regions of the bone marrow, and to the spleen and liver, by hematogenous metastasis.

Multiple pre-neoplastic events and clonal selection of radiation induced mouse thymic lymphomas shown by TCR gene rearrangements

After split-dose irradiation, pre-lymphoma cells develop from a tumor-specific surface antigen TL-2+ thymocyte subpopulation. To analyze the clonality of pre-lymphoma cells, various numbers of TL-2+ thymocytes from a single irradiated mouse were intra-thymically injected to Thyl congenic recipient mice. The incidence of donor type thymic lymphoma(s) was subsequently examined in a group of recipient mice. We chose several lymphomas derived from a single donor mouse and analyzed the TCR gene rearrangements and V(D)J junctional diversity as genetic markers of clonality. These results indicate multiple initial neoplastic events and clonal selection into lymphoma.