Agyria — pachygyria and Miller-Dieker syndrome: clinical,genetic and chromosome studies

Summary Twelve cases of lissencephaly are reported. A high resolution chromosome study was performed on each in order to detect small chromosomal anomalies, undetectable with routine techniques. Only one case was shown to have an unbalanced karyotype with a microdeletion of the short arm of chromosome 17(del 17p). This child also had symptoms of the Miller-Dieker syndrome, consisting of lissencephaly, characteristic facies, pre- and post-natal growth retardation and other birth defects. As proposed by Dobyns, it seems justifiable to classify lissencephalies into four different groups, according to other clinical manifestations and results of chromosome studies.     

Inverted neurons in agyria

Summary An anatomoclinical observation of agyria is reported. The karyotype revealed a partial deletion of the short arm of chromosome 17. The etiology of agyria is reviewed in the light of this chromosomal abnormality. In addition we describe the peculiar pattern of neurons in the cortex: Golgi stain demonstrated many inverted pyramidal cells in the superficial part of the cortical layer. The mechanism of this abnormality is discussed.     

Quantitative trait loci involved in the reproductive success of a parasitoid wasp

Dissecting the genetic basis of intraspecific variations in life history traits is essential to understand their evolution, notably for potential biocontrol agents. Such variations are observed in the endoparasitoid Cotesia typhae (Hymenoptera: Braconidae), specialized on the pest Sesamia nonagrioides (Lepidoptera: Noctuidae). Previously, we identified two strains of C. typhae that differed significantly for life history traits on an allopatric host population. To investigate the genetic basis underlying these phenotypic differences, we used a quantitative trait locus (QTL) approach based on restriction site‐associated DNA markers. The characteristic of C. typhae reproduction allowed us generating sisters sharing almost the same genetic content, named clonal sibship. Crosses between individuals from the two strains were performed to generate F2 and F8 recombinant CSS. The genotypes of 181 clonal sibships were determined as well as the phenotypes of the corresponding 4,000 females. Informative markers were then used to build a high‐quality genetic map. These 465 markers spanned a total length of 1,300 cM and were organized in 10 linkage groups which corresponded to the number of C. typhae chromosomes. Three QTLs were detected for parasitism success and two for offspring number, while none were identified for sex ratio. The QTLs explained, respectively, 27.7% and 24.5% of the phenotypic variation observed. The gene content of the genomic intervals was investigated based on the genome of C. congregata and revealed 67 interesting candidates, as potentially involved in the studied traits, including components of the venom and of the symbiotic virus (bracovirus) shown to be necessary for parasitism success in related wasps.     

Functional expression of murine V2R pheromone receptors involves selective association with the M10 and M1 families of MHC class Ib molecules

The vomeronasal organ (VNO) of the mouse has two neuronal compartments expressing distinct families of pheromone receptors, the V1Rs and the V2Rs. We report here that two families of major histocompatibility complex (MHC) class Ib molecules, the M10 and the M1 families, show restricted expression in V2R-expressing neurons. Our data suggest that neurons expressing a given V2R specifically co-express one or a few members of the M10 family. Biochemical and immunocytochemical analysis demonstrates that in VNO sensory dendrites M10s belong to large multi-molecular complexes that include pheromone receptors and beta2-microglobulin (beta2m). In cultured cells, M10s appear to function as escort molecules in transport of V2Rs to the cell surface. Accordingly, beta2m-deficient mice exhibit mislocalization of V2Rs in the VNO and a specific defect in male-male aggressive behavior. The functional characterization of M10 highlights an unexpected role for MHC molecules in pheromone detection by mammalian VNO neurons.     

Mutations in QARS,Encoding Glutaminyl-tRNA Synthetase,Cause Progressive Microcephaly,Cerebral-Cerebellar Atrophy,and Intractable Seizures

Progressive microcephaly is a heterogeneous condition with causes including mutations in genes encoding regulators of neuronal survival. Here, we report the identification of mutations in QARS (encoding glutaminyl-tRNA synthetase [QARS]) as the causative variants in two unrelated families affected by progressive microcephaly, severe seizures in infancy, atrophy of the cerebral cortex and cerebellar vermis, and mild atrophy of the cerebellar hemispheres. Whole-exome sequencing of individuals from each family independently identified compound-heterozygous mutations in QARS as the only candidate causative variants. QARS was highly expressed in the developing fetal human cerebral cortex in many cell types. The four QARS mutations altered highly conserved amino acids, and the aminoacylation activity of QARS was significantly impaired in mutant cell lines. Variants p.Gly45Val and p.Tyr57His were located in the N-terminal domain required for QARS interaction with proteins in the multisynthetase complex and potentially with glutamine tRNA, and recombinant QARS proteins bearing either substitution showed an over 10-fold reduction in aminoacylation activity. Conversely, variants p.Arg403Trp and p.Arg515Trp, each occurring in a different family, were located in the catalytic core and completely disrupted QARS aminoacylation activity in vitro. Furthermore, p.Arg403Trp and p.Arg515Trp rendered QARS less soluble, and p.Arg403Trp disrupted QARS-RARS (arginyl-tRNA synthetase 1) interaction. In zebrafish, homozygous qars loss of function caused decreased brain and eye size and extensive cell death in the brain. Our results highlight the importance of QARS during brain development and that epilepsy due to impairment of QARS activity is unusually severe in comparison to other aminoacyl-tRNA synthetase disorders.     

Superresolution imaging of chemical synapses in the brain

Determination of the molecular architecture of synapses requires nanoscopic image resolution and specific molecular recognition, a task that has so far defied many conventional imaging approaches. Here, we present a superresolution fluorescence imaging method to visualize the molecular architecture of synapses in the brain. Using multicolor, three-dimensional stochastic optical reconstruction microscopy, the distributions of synaptic proteins can be measured with nanometer precision. Furthermore, the wide-field, volumetric imaging method enables high-throughput, quantitative analysis of a large number of synapses from different brain regions. To demonstrate the capabilities of this approach, we have determined the organization of?ten protein components of the presynaptic active?zone and the postsynaptic density. Variations?in synapse morphology, neurotransmitter receptor composition, and receptor distribution were observed both among synapses and across different?brain regions. Combination with optogenetics further?allowed molecular events associated with synaptic plasticity to be resolved at the single-synapse level.