Spectral karyotyping combined with locus-specific FISH simultaneously defines genes and chromosomes involved in chromosomal translocations

A der(8)t(8;11) chromosome in the Karpas-620 myeloma cell line expresses only cyclin D1: yet both cyclin D1 and MYC are repositioned in close proximity to the 3'IGH enhancer

The Karpas-620 human myeloma cell line (HMCL) expresses high levels of Cyclin D1 (CCND1), but has a der(8)t(8;11) and a der(14)t(8;14), and not a conventional t(11;14). Fluorescent in situ hybridization (FISH) and array comparative genomic hybridization (aCGH) studies suggest that der(14)t(11;14) from a primary translocation underwent a secondary translocation with chromosome 8 to generate der(8)t(8;[14];11) and der(14)t(8;[11];14). Both secondary derivatives share extensive identical sequences from chromosomes 8, 11, and 14, including MYC and the 3' IgH enhancers. Der(14), with MYC located approximately 700 kb telomeric to the 3'IGH enhancer, expresses MYC. By contrast, der(8), with both CCND1 and MYC repositioned near a 3'IGH enhancer, expresses CCND1, which is telomeric of the enhancer, but not MYC, which is centromeric to the enhancer. The secondary translocation that dysregulated MYC resulted in extensive regions from both donor chromosomes being transmitted to both derivative chromosomes, suggesting a defect in DNA recombination or repair in the myeloma tumor cell.

Spectral karyotyping of human, mouse, rat and ape chromosomes--applications for genetic diagnostics and research

Spectral karyotyping (SKY) is a widely used methodology to identify genetic aberrations. Multicolor fluorescence in situ hybridization using chromosome painting probes in individual colors for all metaphase chromosomes at once is combined with a unique spectral measurement and analysis system to automatically classify normal and aberrant chromosomes. Based on countless studies and investigations in many laboratories worldwide, numerous new chromosome translocations and other aberrations have been identified in clinical and tumor cytogenetics. Thus, gene identification studies have been facilitated resulting in the dissection of tumor development and progression. For example, different translocation partners of the TEL/ETV6 transcription factor that is specially required for hematopoiesis within the bone marrow were identified. Also, the correct classification of complex karyotypes of solid tumors supports the prognostication of cancer patients. Important accomplishments for patients with genetic diseases, leukemias and lymphomas, mesenchymal tumors and solid cancers are summarized and exemplified. Furthermore, studies of disease mechanisms such as centromeric DNA breakage, DNA double strand break repair, telomere shortening and radiation-induced neoplastic transformation have been accompanied by SKY analyses. Besides the hybridization of human chromosomes, mouse karyotyping has also contributed to the comprehensive characterization of mouse models of human disease and for gene therapy studies.

Multiple reciprocal translocations in salivary gland mucoepidermoid carcinomas

Mucoepidermoid carcinoma, the most common human malignant salivary gland tumor, can arise from both major and minor salivary glands, including sites within the pulmonary tracheobronchial tree. We performed comparative genomic hybridization (CGH) and spectral karyotyping (SKY) on two tumor cell lines: H3118, derived from tumor originating in the parotid gland, and H292, from tumor in the lung. In both cell lines, CGH showed a partial gain within the short arm of chromosome 7 and SKY revealed the presence of the previously reported reciprocal translocation t(11;19)(q21;p12). Additional chromosomal rearrangements were found in both cell lines, including three more reciprocal translocations in cell line H292 [t(1;16), t(6;8)x2] and three other reciprocal translocations in cell line H3118 [t(1;7), t(3;15), and t(7;15)]. A review of the literature of other reported cases of mucoepidermoid carcinomas analyzed with standard G-banding techniques, as well as distinct benign salivary gland tumors, such as pleomorphic adenomas and Warthin tumor, confirmed the presence of a karyotype dominated by reciprocal translocations. Four chromosomal bands were involved in chromosomal translocations in both cell lines: 1q32, 5p15, 7q22, and 15q22. Fluorescence in situ hybridization studies showed that the breakpoints in these four bands were often within a few megabases of each other. The involvement of similar chromosomal bands in breakpoints in these two cell lines suggests that these regions may be predisposed or selected for chromosomal rearrangements in this tumor type. The presence of multiple reciprocal translocations in both benign and malignant salivary gland tumors may also suggest a particular mechanism within mucous or serous glands mediating chromosomal rearrangements.

t(11;19)(q21;p13) translocation in mucoepidermoid carcinoma creates a novel fusion product that disrupts a Notch signaling pathway

Truncation of Notch1 has been shown to cause a subtype of acute leukemia, and activation of Notch4 has been associated with mammary and salivary gland carcinomas of mice. Here we identify a new mechanism for disrupting Notch signaling in human tumorigenesis, characterized by altered function of a new ortholog of the Drosophila melanogaster Notch co-activator molecule Mastermind. We cloned the t(11;19) translocation that underlies the most common type of human malignant salivary gland tumor. This rearrangement fuses exon 1 from a novel gene of unknown function at 19p13, termed mucoepidermoid carcinoma translocated 1 (MECT1), with exons 2-5 of a novel member of the Mastermind-like gene family (MAML2) at 11q21 (ref. 3). Similar to D. melanogaster Mastermind and MAML1 (refs. 4,5), full-length MAML2 functioned as a CSL (CBF-1, suppressor of hairless and Lag-1)-dependent transcriptional co-activator for ligand-stimulated Notch. In contrast, MECT1-MAML2 activated transcription of the Notch target gene HES1 independently of both Notch ligand and CSL binding sites. MECT1-MAML2 induced foci formation in RK3E epithelial cells, confirming a biological effect for the fusion product. These data suggest a new mechanism to disrupt the function of a Notch co-activator in a common type of malignant salivary gland tumor.

Advances in the detection of chromosomal aberrations using spectral karyotyping

Spectral karyotyping (SKY) is a powerful 24-color, whole chromosome-painting assay allowing the visualization of each chromosome in one experiment. Subtle karyotype rearrangements can be detected easily so that small translocations lead to a transition from one color to another at the chromosomal breakpoint region. SKY has enabled the elucidation of several examples of hidden or "cryptic" structural aberrations that may otherwise have been left undetected by classical cytogenetic methods. Furthermore, the chromosomal origins of abnormalities once designated "marker chromosomes" can now be determined rather than left unidentified. SKY analysis of cancer cytogenetics samples provides a much more detailed description of the highly abnormal karyotypes that characterize advanced tumors and cancer cell lines. In addition, SKY significantly adds to the power of clinical cytogenetic analysis of constitutional chromosomal aberrations by facilitating the identification of subtle structural rearrangements that may contain aneuploidy with potential pathological consequences.

Chromosome arm-specific multicolor FISH

Several systems for 24-color fluorescence in situ hybridization (FISH) have been developed and applied to karyotyping and detection of chromosomal abnormalities. We have developed a 42-color multicolor FISH (mFISH) technique (armFISH), which permits the detection of chromosomal aberrations at the resolution of chromosome arms. The armFISH uses a commercially available mFISH reagent kit (24XCyte, MetaSystems GmbH) supplemented with a set of differentially labeled chromosome arm-specific painting probes (arm-kit, comprising either p- or q-arms of all human chromosomes, except the p-arm of the acrocentric- and Y chromosomes). The mFISH-probe cocktail and the arm-kit are combined and hybridized together to metaphase chromosomes. The armFISH is analyzed in two steps; first, the conventional mFISH image analysis is performed, followed by the arm-kit analysis to reveal the chromosome arms involved. The examples demonstrate the utility of armFISH in defining chromosomal rearrangements of human cancers.