Epimutation of the telomeric imprinting center region on chromosome 11p15 in Silver-Russell syndrome

Silver-Russell syndrome (SRS, OMIM 180860) is a congenital disorder characterized by severe intrauterine and postnatal growth retardation, dysmorphic facial features and body asymmetry. SRS is genetically heterogenous with maternal uniparental disomy with respect to chromosome 7 occurring in approximately 10% of affected individuals. Given the crucial role of the 11p15 imprinted region in the control of fetal growth, we hypothesized that dysregulation of genes at 11p15 might be involved in syndromic intrauterine growth retardation. We identified an epimutation (demethylation) in the telomeric imprinting center region ICR1 of the 11p15 region in several individuals with clinically typical SRS. This epigenetic defect is associated with, and probably responsible for, relaxation of imprinting and biallelic expression of H19 and downregulation of IGF2. These findings provide new insight into the pathogenesis of SRS and strongly suggest that the 11p15 imprinted region, in addition to those of 7p11.2-p13 and 7q31-qter, is involved in SRS.     

Disruption of Bardet-Biedl syndrome ciliary proteins perturbs planar cell polarity in vertebrates

The evolutionarily conserved planar cell polarity (PCP) pathway (or noncanonical Wnt pathway) drives several important cellular processes, including epithelial cell polarization, cell migration and mitotic spindle orientation. In vertebrates, PCP genes have a vital role in polarized convergent extension movements during gastrulation and neurulation. Here we show that mice with mutations in genes involved in Bardet-Biedl syndrome (BBS), a disorder associated with ciliary dysfunction, share phenotypes with PCP mutants including open eyelids, neural tube defects and disrupted cochlear stereociliary bundles. Furthermore, we identify genetic interactions between BBS genes and a PCP gene in both mouse (Ltap, also called Vangl2) and zebrafish (vangl2). In zebrafish, the augmented phenotype results from enhanced defective convergent extension movements. We also show that Vangl2 localizes to the basal body and axoneme of ciliated cells, a pattern reminiscent of that of the BBS proteins. These data suggest that cilia are intrinsically involved in PCP processes.     

Probing carrier dynamics in nanostructures by picosecond cathodoluminescence

Picosecond and femtosecond spectroscopy allow the detailed study of carrier dynamics in nanostructured materials. In such experiments, a laser pulse normally excites several nanostructures at once. However, spectroscopic information may also be acquired using pulses from an electron beam in a modern electron microscope, exploiting a phenomenon called cathodoluminescence. This approach offers several advantages. The multimode imaging capabilities of the electron microscope enable the correlation of optical properties (via cathodoluminescence) with surface morphology (secondary electron mode) at the nanometre scale. The broad energy range of the electrons can excite wide-bandgap materials, such as diamond- or gallium-nitride-based structures that are not easily excited by conventional optical means. But perhaps most intriguingly, the small beam can probe a single selected nanostructure. Here we apply an original time-resolved cathodoluminescence set-up to describe carrier dynamics within single gallium-arsenide-based pyramidal nanostructures with a time resolution of 10 picoseconds and a spatial resolution of 50 nanometres. The behaviour of such charge carriers could be useful for evaluating elementary components in quantum computers, optical quantum gates or single photon sources for quantum cryptography.