Identification and functional characterization of rare SHANK2 variants in schizophrenia

Recent genetic data on schizophrenia (SCZ) have suggested that proteins of the postsynaptic density of excitatory synapses have a role in its etiology. Mutations in the three SHANK genes encoding for postsynaptic scaffolding proteins have been shown to represent risk factors for autism spectrum disorders and other neurodevelopmental disorders. To address if SHANK2 variants are associated with SCZ, we sequenced SHANK2 in 481 patients and 659 unaffected individuals. We identified a significant increase in the number of rare (minor allele frequency<1%) SHANK2 missense variants in SCZ individuals (6.9%) compared with controls (3.9%, P=0.039). Four out of fifteen non-synonymous variants identified in the SCZ cohort (S610Y, R958S, P1119T and A1731S) were selected for functional analysis. Overexpression and knockdown-rescue experiments were carried out in cultured primary hippocampal neurons with a major focus on the analysis of morphological changes. Furthermore, the effect on actin polymerization in fibroblast cell lines was investigated. All four variants revealed functional impairment to various degrees, as a consequence of alterations in spine volume and clustering at synapses and an overall loss of presynaptic contacts. The A1731S variant was identified in four unrelated SCZ patients (0.83%) but not in any of the sequenced controls and public databases (P=4.6 × 10(-5)). Patients with the A1731S variant share an early prodromal phase with an insidious onset of psychiatric symptoms. A1731S overexpression strongly decreased the SHANK2-Bassoon-positive synapse number and diminished the F/G-actin ratio. Our results strongly suggest a causative role of rare SHANK2 variants in SCZ and underline the contribution of SHANK2 gene mutations in a variety of neuropsychiatric disorders.

A newly discovered bacteriocin produced by Enterococcus faecalis 3915

Different Enterococci, isolated from starters for the production of the traditional Bulgarian yellow cheese 'Kashkaval' were screened for bacteriocin production, and one of them, Enterococcus faecalis 3915 demonstrated bacteriocin activity. In this study, we investigated the growth parameters of the producer strain as well as the production kinetics and preliminary characterisation of the produced bacteriocin named enterocin 3915. For the growth modelling, the logistic model was used, while bacteriocin production was monitored. Experiments on inducibility were conducted, and strain was checked for the presence of plasmids. The peptide was crudely purified by ammonium sulphate precipitation followed by preparative PAGE. The approximate molecular mass was determined electrophoretically, and the activity was visualised by electrophoresis and agar overlay technique. It was found that E. faecalis 3915 produces a bacteriocin with constitutive synthesis and chromosomal localisation of its genetic determinants. The peptide revealed to be relatively heat-stable with a molecular mass of about 6.5 kDa. As E. faecalis 3915 originates from cheese starter it can be classified as generally recognised as safe (GRAS). The inhibitory activity of enterocin 3915 comprises commensals or pathogens, so properties generally accepted as probiotic could be attributed to the producer, and potential application in the dairy industry is not to be excluded.