White matter fiber microstructure is associated with prior hospitalizations rather than acute symptomatology in major depressive disorder.

BACKGROUND: Eighty percent of all patients suffering from major depressive disorder (MDD) relapse at least once in their lifetime. Thus, understanding the neurobiological underpinnings of the course of MDD is of utmost importance. A detrimental course of illness in MDD was most consistently associated with superior longitudinal fasciculus (SLF) fiber integrity. As similar associations were, however, found between SLF fiber integrity and acute symptomatology, this study attempts to disentangle associations attributed to current depression from long-term course of illness. METHODS: A total of 531 patients suffering from acute (N = 250) or remitted (N = 281) MDD from the FOR2107-cohort were analyzed in this cross-sectional study using tract-based spatial statistics for diffusion tensor imaging. First, the effects of disease state (acute v. remitted), current symptom severity (BDI-score) and course of illness (number of hospitalizations) on fractional anisotropy (FA), mean diffusivity (MD), radial diffusivity (RD), and axial diffusivity were analyzed separately. Second, disease state and BDI-scores were analyzed in conjunction with the number of hospitalizations to disentangle their effects. RESULTS: Disease state (pFWE < 0.042) and number of hospitalizations (pFWE< 0.032) were associated with decreased FA and increased MD and RD in the bilateral SLF. A trend was found for the BDI-score (pFWE > 0.067). When analyzed simultaneously only the effect of course of illness remained significant (pFWE < 0.040) mapping to the right SLF. CONCLUSIONS: Decreased FA and increased MD and RD values in the SLF are associated with more hospitalizations when controlling for current psychopathology. SLF fiber integrity could reflect cumulative illness burden at a neurobiological level and should be targeted in future longitudinal analyses.

High-resolution genomic analysis suggests the absence of recurrent genomic alterations other than SMARCB1 aberrations in atypical teratoid/rhabdoid tumors.

Atypical teratoid/rhabdoid tumor (AT/RT) is a rare malignant pediatric brain tumor characterized by genetic alterations affecting the SMARCB1 (hSNF5/INI1) locus in chromosome band 22q11.2. To identify potential additional genetic alterations, high-resolution genome-wide analysis was performed using a molecular inversion probe single-nucleotide polymorphism (MIP SNP) assay (Affymetrix OncoScan formalin-fixed paraffin-embedded express) on DNA isolated from 18 formalin-fixed paraffin-embedded archival samples. Alterations affecting the SMARCB1 locus could be demonstrated by MIP SNP in 15 out of 16 evaluable cases (94%). These comprised five tumors with homozygous deletions, six tumors with heterozygous deletions, and four tumors with copy number neutral loss of heterozygosity (LOH) involving chromosome band 22q11.2. Remarkably, MIB SNP analysis did not yield any further recurrent chromosomal gains, losses, or copy neutral LOH. On MIP SNP screening for somatic mutations, the presence of a SMARCB1 mutation (c.472C>T p.R158X) was confirmed, but no recurrent mutations of other cancer relevant genes could be identified. Results of fluorescence in situ hybridization, multiplex ligation-dependent probe amplification, and SMARCB1 sequencing were highly congruent with that of the MIP SNP assay. In conclusion, these data further suggest the absence of recurrent genomic alterations other than SMARCB1 in AT/RT.

Claudin-2 pore function requires an intramolecular disulfide bond between two conserved extracellular cysteines.

Claudins constitute a family of tight junction transmembrane proteins whose first extracellular loop (ECL1) determines the paracellular permeability and ion selectivity in epithelia. There are two cysteines in the ECL1 that are conserved among all claudins. We hypothesized that these extracellular cysteines are linked by an intramolecular disulfide bond that is necessary for correct pore folding and function. To test this, we mutated C54 and C64 in claudin-2, either individually or together to alanine or serine, and generated stable Madin-Darby canine kidney (MDCK) I Tet-off cell lines. Immunoblotting showed a higher molecular mass band in the mutants with a single cysteine mutation, consistent with a claudin-2 dimer, suggesting that the two conserved cysteines normally form an intramolecular disulfide bond in wild-type claudin-2. By immunofluorescent staining, the alanine mutants were mislocalized intracellularly, while the serine mutants were expressed at the tight junction. Thus dimerization of both C54A and C64A did not require tight junction expression, suggesting that C54 and C64 are located near an intermolecular interface involved in cis-interaction. The conductance and Na(+) permeability of the serine mutants were markedly lower than the wild type, but there was no difference between the single mutants and the double mutant. We conclude that the disulfide bond between the conserved extracellular cysteines in claudin-2 is necessary for pore formation, probably by stabilizing the ECL1 fold, but is not required for correct protein trafficking. We further speculate that this role is generalizable to other claudin family members.

Identification of genes involved in the biology of atypical teratoid/rhabdoid tumours using Drosophila melanogaster.

Atypical teratoid/rhabdoid tumours (AT/RT) are malignant brain tumours. Unlike most other human brain tumours, AT/RT are characterized by inactivation of one single gene, SMARCB1. SMARCB1 is a member of the evolutionarily conserved SWI/SNF chromatin remodelling complex, which has an important role in the control of cell differentiation and proliferation. Little is known, however, about the pathways involved in the oncogenic effects of SMARCB1 inactivation, which might also represent targets for treatment. Here we report a comprehensive genetic screen in the fruit fly that revealed several genes not yet associated with loss of snr1, the Drosophila homologue of SMARCB1. We confirm the functional role of identified genes (including merlin, kibra and expanded, known to regulate hippo signalling pathway activity) in human rhabdoid tumour cell lines and AT/RT tumour samples. These results demonstrate that fly models can be employed for the identification of clinically relevant pathways in human cancer.