Hein Duhamel

NXF5, a novel member of the nuclear RNA export factor family, is lost in a male patient with a syndromic form of mental retardation

BACKGROUND Although X-linked mental retardation (XLMR) affects 2%-3% of the human population, little is known about the underlying molecular mechanisms. Recent interest in this topic led to the identification of several genes for which mutations result in the disturbance of cognitive development. RESULTS We identified a novel gene that is interrupted by an inv(X)(p21.1;q22) in a male patient with a syndromic form of mental retardation. Molecular analysis of both breakpoint regions did not reveal an interrupted gene on Xp, but identified a novel nuclear RNA export factor (NXF) gene cluster, Xcen-NXF5-NXF2-NXF4-NXF3-Xqter, in which NXF5 is split by the breakpoint, leading to its functional nullisomy. The predicted NXF5 protein shows high similarity with the central part of the presumed mRNA nuclear export factor TAP/NXF1. Functional analysis of NXF5 demonstrates binding to RNA as well as to the RNA nuclear export-associated protein p15/NXT. In contrast to TAP/NXF1, overexpression studies localized NXF5 in the form of granules in the cell body and neurites of mature hippocampal neurons, suggesting a role in mRNA transport. The two newly identified mouse nxf homologs, nxf-a and nxf-b, which also map on X, show highest mRNA levels in the brain. CONCLUSIONS A novel member of the nuclear RNA export factor family is absent in a male patient with a syndromic form of mental retardation. Although we did not find direct evidence for the involvement of NXF5 in MR, the gene could be involved in development, possibly through a process in mRNA metabolism in neurons.

Multiple small accessory marker chromosomes from different centromeric origin in a moderately mentally retarded male

Abstract. The occurrence of more than two small accessory chromosomes (SACs) in a single individual is extremely rare. Here, we characterize six SACs found in the cells of two different tissues of a moderately mentally retarded male. Microdissection combined with regular FISH demonstrates that the SACs are ring chromosomes derived from the centromeres of different chromosomes. The SACs are often associated with the centromeres of other chromosomes. Immunofluorescence with an anti-CENP-C antibody demonstrates that the SACs contain an active centromere. A possible mechanism by which the SACs originated and their clinical relevance are discussed.

A physical map of the chromosome 12 centromere

While current sequencing efforts consider the detection of alpha satellite repeats as logical end points for map construction, detailed maps of most pericentromeric regions are lacking to confirm this hypothesis. Here we identify the different alpha satellite families present at the pericentromeric region of chromosome 12. The order, size and location of these repeats is established using radiation hybrid analysis, pulsed field gel analysis and FISH and the maps are integrated with current sequence information. For the different classes of alpha satellites present at the chromosome 12 centromere the paralogs in the human genome were mapped by FISH. Unique sequences flanking the alpha satellite repeats were identified, some of which are not represented in the current draft sequence. This mapping effort localises the different alpha satellite repeats within the pericentromeric region and anchors them in the current maps. The novel sequences identified may serve as the end point for the ongoing sequencing efforts.

SSCP: a tool for contig building of duplicated genomic regions

Center for Human Genetics, Flanders Interuniversity Institute for Biotechnology, University of Leuven, Leuven, Belgium▼High-resolution physical maps are constructed by thegeneration of a contiguous set of overlapping YAC, BAC,PAC or cosmid clones representing a genomic region ofinterest. This is usually achieved by STS-content mappingand fingerprinting of the clones. If there are many STSsthen screening a genomic library can isolate a contiguousset of clones directly.Although chromosome walking has been highly success-ful for most genomic regions, it is not successful when theregion of interest is not unique in the genome. When STSsderived from such a region are used as a probe to screena genomic library, they will identify clones containing in-serts derived from different genomic regions. This results in‘branching’ of the contig during contig construction. Notsurprisingly, the gaps in the present-day human genomicmapsareinpreciselytheregionsofthehumangenomethatcontain duplications or regions with low-copy-number re-peats.Thepericentromericregionsaretheparadigmforthis(Ref. 1–4).Different observations can point to ‘branching’ of acontig:1. the number of clones isolated with an STS exceeds thegenomic representation in the library;2. neither of the two insert ends of a newly isolated clonemap back to the parent clone;3. more than one hybridization signal is detected whenthe STS is used as a probe for Southern blot or fluores-cent