Abnormalities of chromosome 7q are common in myeloid malignancies, but no specific target genes have yet been identified. Here, we describe the finding of homozygous EZH2 mutations in 9 of 12 individuals with 7q acquired uniparental disomy. Screening of a total of 614 individuals with myeloid disorders revealed 49 monoallelic or biallelic EZH2 mutations in 42 individuals; the mutations were found most commonly in those with myelodysplastic/myeloproliferative neoplasms (27 out of 219 individuals, or 12%) and in those with myelofibrosis (4 out of 30 individuals, or 13%). EZH2 encodes the catalytic subunit of the polycomb repressive complex 2 (PRC2), a highly conserved histone H3 lysine 27 (H3K27) methyltransferase that influences stem cell renewal by epigenetic repression of genes involved in cell fate decisions. EZH2 has oncogenic activity, and its overexpression has previously been causally linked to differentiation blocks in epithelial tumors. Notably, the mutations we identified resulted in premature chain termination or direct abrogation of histone methyltransferase activity, suggesting that EZH2 acts as a tumor suppressor for myeloid malignancies.

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The contamination of cell cultures by mycoplasmas remains a major problem in cell culture. Mycoplasmas can produce a virtually unlimited variety of effects in the cultures they infect. These organisms are resistant to most antibiotics commonly employed in cell cultures. Here we provide a concise overview of the current knowledge on: (1) the incidence and sources of mycoplasma contamination in cell cultures, the mycoplasma species most commonly detected in cell cultures, and the effects of mycoplasmas on the function and activities of infected cell cultures; (2) the various techniques available for the detection of mycoplasmas with particular emphasis on the most reliable detection methods; (3) the various methods available for the elimination of mycoplasmas highlighting antibiotic treatment; and (4) the recommended procedures and working protocols for the detection, elimination and prevention of mycoplasma contamination. The availability of accurate, sensitive and reliable detection methods and the application of robust and successful elimination methods provide powerful means for overcoming the problem of mycoplasma contamination in cell cultures.

without detectable blast infiltration. At diagnosis of MDS, interface cytogenetic and RT-PCR analyses, respectively, showed trisomy 8 and absence of AF9-MLL rearrangement in Introduction the bone marrow (BM). On readmission with florid leukemia, his peripheral white blood cell count was 13 200/mm 3 , with A subtle, reciprocal translocation exchanging the terminal 56% leukemic blasts. His hemoglobin concentration was short and long arm segments of chromosomes 9 and 11, 15.0 g/dl, and his platelet count was 22 000/mm 3 . The bone respectively t(9;11)(p21-22;q23), is associated with acute marrow aspiration showed 92% leukemic blasts, and the mormyeloid leukemia (AML)-M5, 1 particularly the M5a subtype. 2 phological diagnosis was made as AML-M5a. Cytogenetic Ascertainment may be difficult in suboptimal preparations analysis was interpreted as: 47, XY, +8, t(9;11)(p22;q23). and, despite being regarded as the 'standard' cytogenetic Immunophenotyping analysis of fresh leukemia blasts change in acute monoblastic leukemia, its overall incidence revealed no significant expression of CD antigens associated and pattern of associations remain uncertain. 2 A recent study with the myelo-monocytic lineage. CD34 was 30% positive comparing AML-M1 and -M5 patients, analyzed simuland non-lineage-associated HLA-DR was found to be positive taneously by reverse transcriptase-polymerase chain reaction at 70%; whereas those indicative of lymphoid lineage includ-(RT-PCR), Southern blotting and fluorescence in situ hybridizing CD3, CD4, CD8, CD10, CD19 were absent or weakly ation (FISH) with an MLL-specific yeast artificial chromosome expressed. Myeloperoxidase activity was weakly detected on (YAC) probe, suggests the overall incidence of MLL rearrangethe fresh leukemic blasts. Despite receiving chemotherapy, he ment in AML-M5 may be as high as 60%. 3 It was apparent in succumbed to rapidly progressive leukemia on 15 August that study that approximately half the cases with MLL 1995. rearrangement went undetected by cytogenetic methods, including a cryptic t(6;11)(q27;q23) resulting from a cytogenetically invisible insertion juxtaposing AF6 and MLL.Materials and methods A case of AML-M5a with de novo MLL-AF9 fusion evolving from MDS with trisomy 8 present at all phases has recently Cell culture been described. 4 We describe a pair of cell lines, MOLM-13 During relapse, after chemotherapy, a heparinized peripheral blood specimen, obtained with informed consent, was proCorrespondence: Y Matsuo,

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