Synaptotagmin perturbs the structure of phospholipid bilayers

Synaptotagmin I (syt), an integral protein of the synaptic vesicle membrane, is believed to act as a Ca2+ sensor for neuronal exocytosis. Syt's cytoplasmic domain consists largely of two C2 domains, C2A and C2B. In response to Ca2+ binding, the C2 domains interact with membranes, becoming partially embedded in the lipid bilayer. We have imaged syt C2AB in association with lipid bilayers under fluid, using AFM. As expected, binding of C2AB to bilayers required both an anionic phospholipid [phosphatidylserine (PS)] and Ca2+. C2AB associated with bilayers in the form of aggregates of varying stoichiometries, and aggregate size increased with an increase in PS content. Repeated scanning of bilayers revealed that as C2AB dissociated it left behind residual indentations in the bilayer. The mean depth of these identations was 1.81 nm, indicating that they did not span the bilayer. Individual C2 domains (C2A and C2B) also formed aggregates and produced bilayer indentations. Binding of C2AB to bilayers and the formation of indentations were significantly compromised by mutations that interfere with binding of Ca2+ to syt or reduce the positive charge on the surface of C2B. We propose that bilayer perturbation by syt might be significant with respect to its ability to promote membrane fusion.     

Mitochondrial and nuclear DNA damage induced by sulphur mustard in keratinocytes.

The extent and role of mitochondrial DNA damage in the mechanism of action of sulphur mustard (SM) is poorly understood. In this study, a combination of quantitative polymerase chain reaction and Southern hybridization was used to determine the levels of both total DNA adducts and DNA interstrand crosslinks in genomic and mitochondrial DNA isolated from normal human epidermal keratinocytes exposed to SM. The formation of both types of lesions occurred simultaneously in nuclear and mitochondrial DNA, however, SM produced significantly higher levels of both total adducts and crosslinks in genomic DNA than mitochondrial DNA. The total lesion frequency was 0.45 lesions/kb per 100 microM SM in the DHFR gene and 0.12 lesions/kb per 100 microM SM in the mitochondrial segment. Interstrand crosslinks occurred at a frequency of 0.28 crosslinks/10 kb per 100 microM SM in the DHFR gene and 0.05 crosslinks/10 kb per 100 microM SM in the mitochondrial segment. DNA interstrand crosslinks are thought to be the critical lesion produced by similar bi-functional alkylating agents. However, the levels of DNA cross-linking revealed in this study show that even at vesicating doses of SM mitochondrial DNA is still largely free of cross-links and the predominant form of DNA damage contributing to cell death occurs in the nucleus.     

Genetic differentiation and relationship of the dipodidsAllactaga andJaculus (Mammalia, Rodentia) in Egypt based on protein variation

Genetic differentiation among 14 populations representing all Egyptian dipodid (jerboa) species and subspecies was examined at 25 structural loci and interspecific relationships are discussed. Of the 25 loci, only 3 were monomorphic, with the same allele fixed in all taxa, 9 loci were monomorphic, but demonstrated intertaxon variation, and only 13 loci were polymorphic. The overall mean number of alleles per locus (A) was 1.23 ± 0.02 and the average percentage of polymorphic loci per taxon (P) was 23%. The overall mean of observed heterozygosity (H _o) was found significantly higher than that of expected heterozygosity (He); the overall means per taxon were 0.25 ± 0.017 and 0.085 ± 0.007. Mean levels of genetic identity (I) were 0.970 ± 0.003 among geographic populations, 0.718 ± 0.022 between subspecies, 0.590 ± 0.030 between congeneric species, and 0.368 ± 0.020 between genera. Phenetic analysis of genetic distance matrix produced a phenogram indicating a close association ofJaculus orientalis Erxleben, 1777 toJaculus jaculus (Linnaeus, 1758), particularly to its subspeciesJaculus jaculus butleri (Thomas, 1922), and indicating a distinct affinity between these latter two species andAllactaga tetradactyla (Lichtenstein, 1823). Estimates of genetic divergence demonstrated that J. orientalis appears to have shared a more recent common ancestor withJ. jaculus thanA. tetradactyla. Divergence of these species would have occurred by Miocene (ca 9.6 to 18.7 million years ago). The pattern of relationships of the dipodid species indicated in this study was closely consistent with the hypotheses derived from morphological and chromosomal data.     

Impaired recruitment of bone-marrow-derived endothelial and hematopoietic precursor cells blocks tumor angiogenesis and growth.

The role of bone marrow (BM)-derived precursor cells in tumor angiogenesis is not known. We demonstrate here that tumor angiogenesis is associated with recruitment of hematopoietic and circulating endothelial precursor cells (CEPs). We used the angiogenic defective, tumor resistant Id-mutant mice to show that transplantation of wild-type BM or vascular endothelial growth factor (VEGF)-mobilized stem cells restore tumor angiogenesis and growth. We detected donor-derived CEPs throughout the neovessels of tumors and Matrigel-plugs in an Id1+/-Id3-/- host, which were associated with VEGF-receptor-1-positive (VEGFR1+) myeloid cells. The angiogenic defect in Id-mutant mice was due to impaired VEGF-driven mobilization of VEGFR2+ CEPs and impaired proliferation and incorporation of VEGFR1+ cells. Although targeting of either VEGFR1 or VEGFR2 alone partially blocks the growth of tumors, inhibition of both VEGFR1 and VEGFR2 was necessary to completely ablate tumor growth. These data demonstrate that recruitment of VEGF-responsive BM-derived precursors is necessary and sufficient for tumor angiogenesis and suggest new clinical strategies to block tumor growth.     

Human β-Synuclein Rendered Fibrillogenic by Designed Mutations

Filamentous inclusions made of α-synuclein are found in nerve cells and glial cells in a number of human neurodegenerative diseases, including Parkinson disease, dementia with Lewy bodies, and multiple system atrophy. The assembly and spreading of these inclusions are likely to play an important role in the etiology of common dementias and movement disorders. Both α-synuclein and the homologous β-synuclein are abundantly expressed in the central nervous system; however, β-synuclein is not present in the pathological inclusions. Previously, we observed a poor correlation between filament formation and the presence of residues 73–83 of α-synuclein, which are absent in β-synuclein. Instead, filament formation correlated with the mean β-sheet propensity, charge, and hydrophilicity of the protein (global physicochemical properties) and β-strand contiguity calculated by a simple algorithm of sliding averages (local physicochemical property). In the present study, we rendered β-synuclein fibrillogenic via one set of point mutations engineered to enhance global properties and a second set engineered to enhance predominantly β-strand contiguity. Our findings show that the intrinsic physicochemical properties of synucleins influence their fibrillogenic propensity via two distinct but overlapping modalities. The implications for filament formation and the pathogenesis of neurodegenerative diseases are discussed.     

The Modulatory Effect of Metabotropic Glutamate Receptor Type-1α on Spike-Wave Discharges in WAG/Rij Rats

Modulatory function of metabotropic glutamate type 1 (mGlu1) receptors plays a crucial role in the pathophysiology of some neurological disorders, including schizophrenia and epilepsy. In this study, the expression of mGlu1α receptors in the thalamic nuclei was assessed during development of absence seizures in the WAG/Rij rats, a valid genetic animal model of absence epilepsy. In addition, the effect of pharmacological modulation of mGlu1α receptors in the laterodorsal (LD) nucleus of the thalamus on the characteristic features of bioelectrical brain activities in the WAG/Rij rats was assessed. The expression of mGlu1α receptors in the LD was assessed in four experimental groups of both WAG/Rij and Wistar rats with 2 and 6 months of age. Agonist and antagonist of mGlu1α receptors were infused in LD in the six months old WAG/Rij (epileptic) rats. The protein level of mGlu1α receptors in the thalamus of the 6-month-old WAG/Rij rats was lower than non-epileptic animals. In addition, the distribution of mGlu1α receptors in different thalamic nuclei was lower in the 6-month-old WAG/Rij compared to age-matched Wistar rats. The gene expression of mGlu1α receptor was also significantly lower in 6-month-old WAG/Rij rats in the LD compared to other animal groups. The microinjection of mGlu1α receptors agonist and antagonist in the LD reduced the duration of spike-wave discharges (SWDs) and increased the amplitude and duration of SWDs, respectively, in 6-month-old WAG/Rij rats. The alterations of mGlu1α receptors expression in the thalamus of epileptic WAG/Rij rats as well as its modulatory effects in the generation of SWDs suggest the potential of mGlu1 receptors as a therapeutic target in absence epilepsy.     

State-of-the-Art Review of Biocementation by Microbially Induced Calcite Precipitation (MICP) for Soil Stabilization

Biocementation is a recently developed new branch in geotechnical engineering that deals with the application of microbiological activity to improve the engineering properties of soils. One of the most commonly adopted processes to achieve soil biocementation is through microbially induced calcite precipitation (MICP). This technique utilizes the metabolic pathways of bacteria to form calcite (CaCO₃) that binds the soil particles together, leading to increased soil strength and stiffness. This paper presents a review of the use of MICP for soil improvement and discusses the treatment process including the primary components involved and major affecting factors. Envisioned applications, potential advantages and limitations of MICP for soil improvement are also presented and discussed. Finally, the primary challenges that lay ahead for the future research (i.e. treatment optimization, upscaling for in situ implementation and self-healing of biotreated soils) are briefly discussed.