Mitochondrial ATP synthase alpha-subunit gene amplified in a retinoblastoma cell line maps to chromosome 18

One hit, two hits, three hits, more? Genomic changes in the development of retinoblastoma

The childhood eye cancer retinoblastoma is initiated by the loss of both alleles of the prototypic tumor suppressor gene, RB1. However, a large number of cytogenetic and comparative genomic hybridization (CGH) studies have shown that these M1 and M2 mutational events--although necessary for initiation--are not the only genomic changes in retinoblastoma. Some of these subsequent changes, which we have termed M3 to Mn, are likely crucial for tumor progression not only in retinoblastoma but also in other cancers. Moreover, genes showing genomic change in cancer are more stable markers and, therefore, possible therapeutic targets than genes simply differentially expressed. In this review, we provide the first comprehensive summary of the genomic evidence implicating gain of 1q, 2p, 6p, and 13q, and loss of 16q in retinoblastoma oncogenesis, including karyotype, CGH, and microarray CGH data. We discuss the search for candidate oncogenes and tumor suppressor genes within these regions, including the candidates (KIF14, MDM4, MYCN, E2F3, DEK, CDH11, and others), plus associations between genomic changes and clinical parameters. We also review studies of other regions of the retinoblastoma genome, the epigenetic changes of aberrant methylation of MGMT, RASSF1A, CASP8, and MLH1, and the roles microRNAs might play in this cancer. Although many candidate genes have yet to be functionally validated in retinoblastoma, work in this field lays out a molecular cytogenetic pathway of retinoblastoma development. Candidate cancer genes carry diagnostic, prognostic, and therapeutic implications beyond retinoblastoma.

γδ T cells — innate immune lymphocytes?

It is unclear what the antigen recognition determinants of gammadelta T-cell receptors (TCRs) are. Compared with immunoglobulin and alphabeta TCRs, gammadelta TCRs have the highest potential CDR3 diversity generated by VDJ recombination. However, gammadelta T-cell reactivities seem to segregate with V gene usage, which has been taken to suggest that rearrangement has little role in generating different antigen specificities. During the past year, the CDR3 regions were found to determine the antigen specificities of T10- and T22-reactive gammadelta TCRs, a surface protein complex was identified as a ligand for human phosphoantigen-reactive gammadelta T cells, and the first co-crystal structure of a gammadelta TCR bound to its ligand was reported. These advances warrant a fresh look at gammadelta T-cell antigen recognition.

Relational mapping of MYCN and DDXI in band 2p24 and analysis of amplicon arrays in double minute chromosomes and homogeneously staining regions by use of free chromatin FISH

MYCN amplification has been observed in diverse neuronal tumors including neuroblastoma, retinoblastoma, and small cell carcinoma of the lung, and has been correlated with a poor prognosis in advanced-stage neuroblastomas. Recent studies have shown a co-amplification of DDXI, a DEAD box gene, and MYCN in retinoblastoma and neuroblastoma. DDXI has been mapped to within a megabase of the MYCN gene in band 2p24. In the present study, the relational map of DDXI and MYCN by fluorescence in situ hybridization (FISH) mapping to metaphase cells and extended free chromatin fibers indicated that DDXI is telomeric to MYCN. Dual-color FISH analysis of amplicons within arrays of extended chromatin fibers was performed to examine the physical relationship of MYCN and DDXI within double minute chromosomes (dmins) and homogeneously staining regions (hsrs). No regular reiterated amplicon repeat unit was present in the hsrs, but detailed analysis of the configurations of DDXI and MYCN within each array indicated that multiple rearrangements generated a complex hsr amplicon structure. Similarly, analysis of a cell line bearing dmins showed that a composite amplicon structure involving deletions and/or duplications of MYCN and DDXI is a feature of dmin formation. These data are consistent with a molecular mechanism involving many rearrangements during the evolution of gene amplification, resulting in complex amplicon structures with distinct changes in relative gene copy number and considerable variation in intragenic distances between coamplified genes.