Somatic mutations in TET2 occur in about 15% of patients with various myeloid cancers.

MicroRNAs belong to a class of small noncoding RNAs of ‫ف‬ 21 nt that control the expression of many genes ( 1, 2 ). MicroRNAs are preferentially transcribed by RNA polymerase II and can be derived from individual microRNA genes, introns of protein-coding genes, or polycistronic transcripts. They are fi rst transcribed as primary microRNAs (pri-microRNAs) that CORRESPONDENCE Pierre Brousset: brousset.p@chu-toulouse.fr C. Quelen and R. Rosati contributed equally to this paper. The online version of this article contains supplemental material. Most chromosomal translocations in myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML) involve oncogenes that are either up-regulated or form part of new chimeric genes. The t(2;11)(p21;q23) translocation has been cloned in 19 cases of MDS and AML. In addition to this, we have shown that this translocation is associated with a strong up-regulation of miR-125b (from 6-to 90-fold). In vitro experiments revealed that miR-125b was able to interfere with primary human CD34 + cell differentiation, and also inhibited terminal (monocytic and granulocytic) differentiation in HL60 and NB4 leukemic cell lines. Therefore, miR-125b up-regulation may represent a new mechanism of myeloid cell transformation, and myeloid neoplasms carrying the t(2;11) translocation defi ne a new clinicopathological entity. Myeloid cell diff erentiation arrest

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