Split-signal FISH for detection of chromosome aberrations in acute lymphoblastic leukemia

Abstract

Chromosome aberrations are frequently observed in precursor-B-acute lymphoblastic leukemias (ALL) and T-cell acute lymphoblastic leukemias (T-ALL). These translocations can form leukemia-specific chimeric fusion proteins or they can deregulate expression of an (onco)gene, resulting in aberrant expression or overexpression. Detection of chromosome aberrations is an important tool for risk classification. We developed rapid and sensitive split-signal fluorescent in situ hybridization (FISH) assays for six of the most frequent chromosome aberrations in precursor-B-ALL and T-ALL. The split-signal FISH approach uses two differentially labeled probes, located in one gene at opposite sites of the breakpoint region. Probe sets were developed for the genes TCF3 (E2A) at 19p13, MLL at 11q23, ETV6 at 12p13, BCR at 22q11, SIL-TAL1 at 1q32 and TLX3 (HOX11L2) at 5q35. In normal karyotypes, two colocalized green/red signals are visible, but a translocation results in a split of one of the colocalized signals. Split-signal FISH has three main advantages over the classical fusionsignal FISH approach, which uses two labeled probes located in two genes. First, the detection of a chromosome aberration is independent of the involved partner gene. Second, split-signal FISH allows the identification of the partner gene or chromosome region if metaphase spreads are present, and finally it reduces false-positivity. Leukemia ( Chromosome aberrations play an important role in hematological malignancies. 1 In ALL, most of these aberrations concern balanced translocations involving genes that play key roles in the development and function of lymphoid cells, such as transcription factors, cell cycle regulators, and signal transduction molecules. Balanced translocations can result in fusion of two genes that encode leukemia-specific chimeric (fusion) proteins. The fusion proteins have functional features that differ from the corresponding wild-type proteins and mostly play a role in leukemogenesis. In addition to the new features of the fusion protein, loss of wild-type activity due to the translocation (in some translocations enhanced by deletion of the second allele) might contribute to oncogenesis. Alternatively, chromosome translocations can result in deregulated expression of (onco)genes as a direct consequence of a translocation to a regulatory element, for example, an immunoglobulin (Ig) or T-cell receptor (TCR) enhancer. 2,3 The most frequent translocations in precursor-B-ALL are t(1;19)(q23;p13) t(4;11)(q21;q23), t(12;21)(p13;q22), and t(9;22)(q34;q11), all four of which result in generation of fusion genes. The t(1;19)(q23;p13) fuses the transcription factorencoding gene TCF3 (E2A) with the transcription factor PBX1. In t(4;11)(q21;q23), the MLL gene at 11q23, which encodes a putative DNA-binding protein, is translocated to the MLLT2 (AF4) gene. The MLL gene is involved in many other translocations in ALL and acute myeloid leukemia (AML). Until now, more than 30 partner genes have been identified. 4 The t(12;21)(p13;q22) involves th...

New insights to the MLL recombinome of acute leukemias

“…Therefore, the identification of MLL gene fusions is necessary for rapid clinical decisions resulting in specific therapy regimens. Current procedures to identify MLL rearrangements include cytogenetic analysis, 3,4 fluorescence in situ hybridization (FISH) experiments (for example, MLL split-signal FISH), [5][6][7] specific reverse transcriptase (RT)-PCR 8 or genomic PCR methods. 9,10 This repertoire of technologies was recently extended by a long-distance inverse PCR (LDI-PCR) method that uses small amounts of genomic DNA to determine any type of MLL gene rearrangement on the molecular level.…”

Flow cytometric immunobead assay for the detection of BCR–ABL fusion proteins in leukemia patients

“…Detection of t(9;22) is generally carried out at the chromosome level using karyotyping or fluorescence in situ hybridization (FISH), 20,25 or at the mRNA level using PCR techniques. 26,27 The availability of these techniques is generally restricted to specialized laboratories in reference centers with well-trained personnel.…”

Diagnostic tool for the identification of MLL rearrangements including unknown partner genes

“…Current procedures to diagnose MLL rearrangements include cytogenetic analysis, FISH experiments (e.g., split-signal FISH) (8), and specific RT-PCR methods. However, results of RT-PCR analyses are influenced strongly by the quality of the investigated RNA samples.…”