Carrier rates of the ancestral Indian W24X mutation in GJB2 in the general Gypsy population and individual subisolates

Mutations in the GJB2 gene are the most common cause of autosomal recessive nonsyndromic hearing loss and occur in approximately 20% of all cases of prelingual deafness. Previous studies of Roma/Gypsies in Slovakia, the Czech Republic, and Spain have shown that W24X, the most common GJB2 mutation in India, is also the prevalent molecular defect in the Gypsy population. The reported W24X frequencies vary broadly from 23% to 93% of Gypsy mutant alleles, likely reflecting local founder effects, drift, and differential admixture in the subisolates of this genetically structured population. Our goal was to provide more representative data on W24X carrier rates in European Gypsies, which can inform individual diagnostic investigations and public health initiatives across countries. Mutation testing in 603 control subjects of Gypsy ethnicity, representing 8 traditional subisolates in southeastern Europe and 4 additional European regions revealed that W24X is spread across subisolates, as expected for an ancestral founder mutation. While variation between subisolates does exist, the average carrier rates, overall and in the major linguistic/migrational categories of Balkan Gypsies, Vlax Roma, and west European Gypsies, are consistently in the 4%-5% range. The results place W24X among the three most common founder mutations in the Gypsies, and classify them as one of the high-risk populations for prelingual deafness. Higher demands on language acquisition in this bilingual population, together with poorer quality of health care compared to autochthonous Europeans, make the consequences of congenital deafness even more damaging than is usually the case. Neonatal screening for W24X among Gypsies would be a justified and cost-effective public health intervention.     

Removal of microcystin-LR by strains of metabolically active probiotic bacteria

The ability of specific strains of probiotic bacteria to remove the cyanobacterial peptide toxin microcystin-LR from aqueous solutions was assessed. Lactobacillus rhamnosus strains GG and LC-705, Bifidobacterium longum 46, Bifidobacterium lactis 420 and Bifidobacterium lactis Bb12 were shown to be the most effective in toxin removal among 11 tested strains. The highest removal percentage of microcystin-LR was 58.1%, observed with B. lactis Bb12 (toxin concentration 100 microg L(-1), 10(10) CFU mL(-1), 37 degrees C, 24 h). Freshly cultured bacteria were shown to be more efficient in microcystin removal than lyophilized or nonviable bacteria. Removal of microcystin-LR was shown to be dependent on both temperature and bacterial concentration. It is concluded that some of the tested strains have good potential in removing microcystins from aqueous solutions.     

Endogenous retroviral insertion in Cryge in the mouse No3 cataract mutant

No3 (nuclear opacity 3) is a novel congenital nuclear cataract in mice. Microsatellite mapping placed the No3 locus on chromosome 1 between D1Mit480 (32cM) and D1Mit7 (41cM), a region containing seven crystallin genes; Cryba2 and the Cryga-Crygf cluster. Although polymorphic variants were observed, no candidate mutations were found for six of the genes. However, DNA walking identified a murine endogenous retrovirus (IAPLTR1: ERVK) insertion in exon 3 of Cryge, disrupting the coding sequence for gammaE-crystallin. Recombinant protein for the mutant gammaE was completely insoluble. The No3 cataract is mild compared with the effects of similar mutations of gammaE. Quantitative RT-PCR showed that gammaE/F mRNA levels are reduced in No3, suggesting that the relatively mild phenotype results from suppression of gammaE levels due to ERVK insertion. However, the severity of cataract is also strain dependent suggesting that genetic background modifiers also play a role in the development of opacity.     

Regulation of membrane fusion in synaptic excitation-secretion coupling: speed and accuracy matter

Unlike most other secretory processes, neurotransmitter release at chemical synapses is extremely fast, tightly regulated, spatially restricted, and dynamically adjustable at the same time. In this review, we focus on recent discoveries of molecular and cell biological processes that determine how fusion competence of vesicles is achieved and controlled in order to suit the specific requirements of synaptic transmitter release with respect to speed and spatial selectivity.     

Homeostatic regulation of eye-specific responses in visual cortex during ocular dominance plasticity

Experience-dependent plasticity is crucial for the precise formation of neuronal connections during development. It is generally thought to depend on Hebbian forms of synaptic plasticity. In addition, neurons possess other, homeostatic means of compensating for changes in sensory input, but their role in cortical plasticity is unclear. We used two-photon calcium imaging to investigate whether homeostatic response regulation contributes to changes of eye-specific responsiveness after monocular deprivation (MD) in mouse visual cortex. Short MD durations decreased deprived-eye responses in neurons with binocular input. Longer MD periods strengthened open-eye responses, and surprisingly, also increased deprived-eye responses in neurons devoid of open-eye input. These bidirectional response adjustments effectively preserved the net visual drive for each neuron. Our finding that deprived-eye responses were either weaker or stronger after MD, depending on the amount of open-eye input a cell received, argues for both Hebbian and homeostatic mechanisms regulating neuronal responsiveness during experience-dependent plasticity.     

Stomatal conductance in mature deciduous forest trees exposed to elevated CO<Subscript>2</Subscript>

Stomatal conductance (g _s) of mature trees exposed to elevated CO₂ concentrations was examined in a diverse deciduous forest stand in NW Switzerland. Measurements of g _s were carried out on upper canopy foliage before noon, over four growing seasons, including an exceptionally dry summer (2003). Across all species reductions in stomatal conductance were smaller than 25% most likely around 10%, with much variation among species and trees. Given the large heterogeneity in light conditions within a tree crown, this signal was not statistically significant, but the responses within species were surprisingly consistent throughout the study period. Except during a severe drought, stomatal conductance was always lower in trees of Carpinus betulus exposed to elevated CO₂ compared to Carpinus trees in ambient air, but the difference was only statistically significant on 2 out of 15 days. In contrast, stomatal responses in Fagus sylvatica and Quercus petraea varied around zero with no consistent trend in relation to CO₂ treatment. During the 2003 drought in the third treatment year, the CO₂ effect became reversed in Carpinus, resulting in higher g _s in trees exposed to elevated CO₂ compared to control trees, most likely due to better water supply because of the previous soil water savings. This was supported by less negative predawn leaf water potential in CO₂ enriched Carpinus trees, indicating an improved water status. These findings illustrate (1) smaller than expected CO₂-effects on stomata of mature deciduous forest trees, and (2) the possibility of soil moisture feedback on canopy water relations under elevated CO₂.     

Compartmentalised expression of <Emphasis Type="Italic">Delta-like 1</Emphasis> in epithelial somites is required for the formation of intervertebral joints

Background  

Expression of the mouse Delta-like 1 (Dll1) gene in the presomitic mesoderm and in the caudal halves of somites of the developing embryo is required for the formation of epithelial somites and for the maintenance of caudal somite identity, respectively. The rostro-caudal polarity of somites is initiated early on within the presomitic mesoderm in nascent somites. Here we have investigated the requirement of restricted Dll1 expression in caudal somite compartments for the maintenance of rostro-caudal somite polarity and the morphogenesis of the axial skeleton. We did this by overexpressing a functional copy of the Dll1 gene throughout the paraxial mesoderm, in particular in anterior somite compartments, during somitogenesis in transgenic mice.     

Mutation in the Scyl1 gene encoding amino-terminal kinase-like protein causes a recessive form of spinocerebellar neurodegeneration

Here, we show that the murine neurodegenerative disease mdf (autosomal recessive mouse mutant 'muscle deficient') is caused by a loss-of-function mutation in Scyl1, disrupting the expression of N-terminal kinase-like protein, an evolutionarily conserved putative component of the nucleocytoplasmic transport machinery. Scyl1 is prominently expressed in neurons, and enriched at central nervous system synapses and neuromuscular junctions. We show that the pathology of mdf comprises cerebellar atrophy, Purkinje cell loss and optic nerve atrophy, and therefore defines a new animal model for neurodegenerative diseases with cerebellar involvement in humans.     

The tRNA methyltransferase Dnmt2 is required for accurate polypeptide synthesis during haematopoiesis

The Dnmt2 enzyme utilizes the catalytic mechanism of eukaryotic DNA methyltransferases to methylate several tRNAs at cytosine 38. Dnmt2 mutant mice, flies, and plants were reported to be viable and fertile, and the biological function of Dnmt2 has remained elusive. Here, we show that endochondral ossification is delayed in newborn Dnmt2‐deficient mice, which is accompanied by a reduction of the haematopoietic stem and progenitor cell population and a cell‐autonomous defect in their differentiation. RNA bisulfite sequencing revealed that Dnmt2 methylates C38 of tRNA Asp^GTC, Gly^GCC, and Val^AAC, thus preventing tRNA fragmentation. Proteomic analyses from primary bone marrow cells uncovered systematic differences in protein expression that are due to specific codon mistranslation by tRNAs lacking Dnmt2‐dependent methylation. Our observations demonstrate that Dnmt2 plays an important role in haematopoiesis and define a novel function of C38 tRNA methylation in the discrimination of near‐cognate codons, thereby ensuring accurate polypeptide synthesis.