Spatial mapping of juxtacrine axo-glial interactions identifies novel molecules in peripheral myelination.

Cell-cell interactions promote juxtacrine signals in specific subcellular domains, which are difficult to capture in the complexity of the nervous system. For example, contact between axons and Schwann cells triggers signals required for radial sorting and myelination. Failure in this interaction causes dysmyelination and axonal degeneration. Despite its importance, few molecules at the axo-glial surface are known. To identify novel molecules in axo-glial interactions, we modified the 'pseudopodia' sub-fractionation system and isolated the projections that glia extend when they receive juxtacrine signals from axons. By proteomics we identified the signalling networks present at the glial-leading edge, and novel proteins, including members of the Prohibitin family. Glial-specific deletion of Prohibitin-2 in mice impairs axo-glial interactions and myelination. We thus validate a novel method to model morphogenesis and juxtacrine signalling, provide insights into the molecular organization of the axo-glial contact, and identify a novel class of molecules in myelination.

Detection of t(4;14)(p16.3;q32) chromosomal translocation in multiple myeloma by reverse transcription-polymerase chain reaction analysis of IGH-MMSET fusion transcripts.

We and others have recently identified a novel recurring t(4;14)(p16.3; q32) translocation in multiple myeloma (MM) that leads to an apparent deregulation of the FGFR3 and WHSC1/MMSET genes. Because the presence of IGH-MMSET hybrid transcripts has been found in MM cell lines with t(4;14), they may represent a specific tumor-associated marker in MM. In this study, we developed a reverse transcription-PCR (RTPCR) assay for detecting chimeric transcripts from all of the 4p16.3 breakpoints identified thus far, and we used it to investigate a representative panel of 53 MM patients and 16 patients with monoclonal gammopathy of uncertain significance; in addition, t(4;14) was investigated in all of the MM patients by means of two-color fluorescence in situ hybridization. IGH-MMSET transcripts were found in 11 of the 53 (20%) MM cases and 1 of 16 (6%) cases of monoclonal gammopathy of uncertain significance. There was complete concordance between the RT-PCR and fluorescence in situ hybridization analyses of the MM cases. The results of this study indicate that RT-PCR is a sensitive and reliable method of detecting t(4;14) and suggest that it may be useful for monitoring the disease in a significant proportion of patients.

Molecular analysis of 11q13 breakpoints in multiple myeloma.

The t(11;14)(q13;q32) chromosomal translocation, which is the hallmark of mantle cell lymphoma (MCL), is found in approximately 30% of multiple myeloma (MM) tumors with a 14q32 translocation. Although the overexpression of cyclin D1 has been found to be correlated with MM cell lines carrying the t(11;14), rearrangements of the BCL-1/cyclin D1 regions frequently involved in MCL rarely occur in MM cell lines or primary tumors. To test whether specific 11q13 breakpoint clusters may occur in MM, we investigated a representative panel of primary tumors by means of Southern blot analysis using probes derived from MM-associated 11q13 breakpoints. To this end, we first cloned the breakpoints and respective germ-line regions from a primary tumor and the U266 cell line, as well as the germ-line region from the KMS-12 cell line. DNA from 50 primary tumors was tested using a large panel of probes, but a rearrangement was detected in only one case using the KMS-12 breakpoint probe. Our results confirm previous findings that the 11q13 breakpoints in MM are scattered throughout the 11q13 region encompassing the cyclin D1 gene, thus suggesting the absence of 11q13 breakpoint clusters in MM.

A mammalian homologue of the Drosophila retinal degeneration B gene: implications for the evolution of phototransduction mechanisms.

Comparative analysis of homologous genes in distantly related species provides important insights into the evolution of complex physiological processes. The Drosophila retinal degeneration B (rdgB) gene encodes a protein involved in phototransduction in the fly. We have isolated a human gene, DRES9, and its murine homologue (Dres9), which show a high degree of similarity to the Drosophila rdgB gene. RNA in situ hybridization studies performed on mouse-embryo tissue sections at various developmental stages revealed that Dres9 is expressed at very high levels in the neural retina and in the central nervous system (CNS), similar to its Drosophila counterpart. The high level of sequence conservation and similarities in the expression patterns of rdgB and DRES9 during development in Drosophila and mammals indicate that Dres9 is the orthologue of RdgB, and strongly suggest a possible functional conservation of these proteins during evolution. DRES9 encodes a phosphatidylinositol-transfer protein, suggesting that phosphatidylinositol may have a role as an intracellular messenger in vertebrate phototransduction. The identification of this gene and the study of its expression pattern in mammals will help shed new light on the evolution of vision mechanisms and suggest DRES9 as a candidate gene for human retinopathies.