Apical assemblies of intermediate filament‐like protein FilP are highly dynamic and affect polar growth determinant DivIVA in Streptomyces venezuelae

Streptomyces spp. grow as branching hyphae, building the cell wall in restricted zones at hyphal tips. The organization of this mode of polar growth involves three coiled‐coil proteins: DivIVA and Scy, which form apical protein complexes referred to as polarisomes; and the intermediate filament‐like protein FilP, which influences cell shape and interacts with both Scy and DivIVA. Here, we use live cell imaging of Streptomyces venezuelae to clarify the subcellular localization and dynamics of FilP and its effect on hyphal morphology. By monitoring a FilP‐mCherry fusion protein, we show that FilP accumulates in gradient‐like zones behind the hyphal tips. The apical gradient pattern of FilP localization is dependent on hyphal tip extension and immediately dissipates upon growth arrest. Fluorescence recovery after photobleaching experiments show that FilP gradients are dynamic and subject to subunit exchange during vegetative growth. Further, the localization of FilP at hyphal tips is not directly dependent on scy, even though the strongly perturbed morphology of most scy mutant hyphae is associated with mislocalization of FilP. Finally, we find that filP has an effect on the size and position of the foci of key polar growth determinant DivIVA. This effect likely contributes to the phenotype of filP mutants.     

Specific amino acid substitutions in β strand S2 of FtsZ cause spiraling septation and impair assembly cooperativity in Streptomyces spp.

Bacterial cell division is orchestrated by the Z ring, which is formed by single‐stranded treadmilling protofilaments of FtsZ. In Streptomyces, during sporulation, multiple Z rings are assembled and lead to formation of septa that divide a filamentous hyphal cell into tens of prespore compartments. We describe here mutant alleles of ftsZ in Streptomyces coelicolor and Streptomyces venezuelae that perturb cell division in such a way that constriction is initiated along irregular spiral‐shaped paths rather than as regular septa perpendicular to the cell length axis. This conspicuous phenotype is caused by amino acid substitutions F37I and F37R in β strand S2 of FtsZ. The F37I mutation leads, instead of regular Z rings, to formation of relatively stable spiral‐shaped FtsZ structures that are capable of initiating cell constriction. Further, we show that the F37 mutations affect the polymerization properties and impair the cooperativity of FtsZ assembly in vitro. The results suggest that specific residues in β strand S2 of FtsZ affect the conformational switch in FtsZ that underlies assembly cooperativity and enable treadmilling of protofilaments, and that these features are required for formation of regular Z rings. However, the data also indicate FtsZ‐directed cell constriction is not dependent on assembly cooperativity.     

Interaction Effects of Social Isolation and Peripheral Work Position on Risk of Disability Pension: A Prospective Study of Swedish Women and Men

Purpose

The study examines various combinations of levels of social isolation in private life and peripheral work position as predictors of disability pension (DP). A second aim was to test the potential interaction effects (above additivity) of social isolation and peripheral work position on the future risk of DP, and to provide results for men and women by age.

Method

The study was based on a sample of 45567 women and men from the Swedish population who had been interviewed between 1992 and 2007. Further information on DP and diagnoses was obtained from the Swedish Social Insurance Agency’s database (1993–2011). The studied predictors were related to DP using Cox’s proportional hazard regression. The analyses were stratified on sex and age (20–39 years, 40–64 years), with control for selected confounders.

Results

Increased risks of DP were found for most combinations of social isolation and peripheral work position in all strata. The hazard ratios (HRs) for joint exposure to high degree of social isolation and a peripheral work position were particularly strong among men aged 20–39 (HR 5.70; CI 95% 3.74–8.69) and women aged 20–39 (HR 4.07; CI 2.99–5.56). An interaction effect from combined exposure was found for women in both age groups as well as a tendency in the same direction among young men. However, after confounder control the effects did not reach significance.

Conclusions

Individuals who were socially isolated and in a peripheral work position had an increased risk of future DP. The fact that an interaction effect was found among women indicates that a combination of social isolation and peripheral work position may reinforce adverse health effects. There was no evidence that a peripheral work position can be compensated by a high degree of social intergration in private life.     

Changes in the functional features of macrophyte communities and driving factors across a 70-year period

Hydrobiologia - Functional homogenisation occurs across many areas and organism groups, thereby seriously affecting biodiversity loss and ecosystem functioning. In this study, we examined how...     

Inactivation of Pmel alters melanosome shape but has only a subtle effect on visible pigmentation

PMEL is an amyloidogenic protein that appears to be exclusively expressed in pigment cells and forms intralumenal fibrils within early stage melanosomes upon which eumelanins deposit in later stages. PMEL is well conserved among vertebrates, and allelic variants in several species are associated with reduced levels of eumelanin in epidermal tissues. However, in most of these cases it is not clear whether the allelic variants reflect gain-of-function or loss-of-function, and no complete PMEL loss-of-function has been reported in a mammal. Here, we have created a mouse line in which the Pmel gene has been inactivated (Pmel ^−/−). These mice are fully viable, fertile, and display no obvious developmental defects. Melanosomes within Pmel ^−/− melanocytes are spherical in contrast to the oblong shape present in wild-type animals. This feature was documented in primary cultures of skin-derived melanocytes as well as in retinal pigment epithelium cells and in uveal melanocytes. Inactivation of Pmel has only a mild effect on the coat color phenotype in four different genetic backgrounds, with the clearest effect in mice also carrying the brown/Tyrp1 mutation. This phenotype, which is similar to that observed with the spontaneous silver mutation in mice, strongly suggests that other previously described alleles in vertebrates with more striking effects on pigmentation are dominant-negative mutations. Despite a mild effect on visible pigmentation, inactivation of Pmel led to a substantial reduction in eumelanin content in hair, which demonstrates that PMEL has a critical role for maintaining efficient epidermal pigmentation.     

Correlation between the ripple phase and stripe domains in membranes

We investigate the relationship between stripe domains and the ripple phase in membranes. These have previously been observed separately without being linked explicitly. Past results have demonstrated that solid and ripple phases exhibit rich textural patterns related to the orientational order of tilted lipids and the orientation of ripple corrugations. Here we reveal a highly complex network pattern of ripple and solid domains in DLPC, DPPC bilayers with structures covering length scales from 10 nm to 100 μm. Using spincoated double supported membranes we investigate domains by correlated AFM and fluorescence microscopy. Cooling experiments demonstrate the mode of nucleation and growth of stripe domains enriched in the fluorescent probe. Concurrent AFM imaging reveals that these stripe domains have a one-to-one correspondence with a rippled morphology running parallel to the stripe direction. Both thin and thick stripe domains are observed having ripple periods of 13.5±0.2 nm and 27.4±0.6 nm respectively. These are equivalent to previously observed asymmetric/equilibrium and symmetric/metastable ripple phases, respectively. Thin stripes grow from small solid domains and grow predominantly in length with a speed of ~3 times that of the thick stripes. Thick stripes grow by templating on the sides of thinner stripes or can emerge directly from the fluid phase. Bending and branching angles of stripes are in accordance with an underlying six fold lattice. We discuss mechanisms for the nucleation and growth of ripples and discuss a generic phase diagram that may partly rationalize the coexistence of metastable and stable phases.     

Repeated exposure of the developing rat brain to magnetic resonance imaging did not affect neurogenesis, cell death or memory function

The effect of magnetic fields on the brain is a matter of debate. The objective of this study was to investigate whether repeated exposure to strong magnetic fields, such as during magnetic resonance imaging (MRI), could elicit changes in the developing rat brain. Embryonic day 15 (E15) and postnatal day 14 (P14) rats were exposed to MRI using a 7.05 T MR system. The animals were anesthetized and exposed for 35 min per day for 4 successive days. Control animals were anesthetized but no MRI was performed. Body temperature was maintained at 37 °C. BrdU was injected after each session (50 mg/kg). One month later, cell proliferation, neurogenesis and astrogenesis in the dentate gyrus were evaluated, revealing no effects of MRI, neither in the E15, nor in the P14 group. DNA damage in the dentate gyrus in the P14 group was evaluated on P18, 1 day after the last session, using TUNEL staining. There was no difference in the number of TUNEL-positive cells after MRI compared with controls, neither in mature neurons, nor in newborn progenitors (BrdU/TUNEL double-labeled cells). Novel object recognition was performed to assess memory function 1 month after MRI. There was no difference in the recognition index observed after MRI compared with the control rats, neither for the E15, nor for the P14 group. In conclusion, repeated exposure to MRI did not appear to affect neurogenesis, cell death or memory function in rats, neither in late gestation (E15–E18) nor in young postnatal (P14–P17) rats.     

LRRC3B gene is frequently epigenetically inactivated in several epithelial malignancies and inhibits cell growth and replication

Chromosome 3 specific NotI microarrays containing 180 NotI linking clones associated with 188 genes were hybridized to NotI representation probes prepared using matched tumor/normal samples from major epithelial cancers: breast (47 pairs), lung (40 pairs) cervical (43 pairs), kidney (34 pairs of clear cell renal cell carcinoma), colon (24 pairs), ovarian (25 pairs) and prostate (18 pairs). In all tested primary tumors (compared to normal controls) methylation and/or deletions was found. For the first time we showed that the gene LRRC3B was frequently methylated and/or deleted in breast carcinoma - 32% of samples, cervical - 35%, lung - 40%, renal - 35%, ovarian - 28%, colon - 33% and prostate cancer - 44%. To check these results bisulfite sequencing using cloned PCR products with representative two breast, one cervical, two renal, two ovarian and two colon cancer samples was performed. In all cases methylation was confirmed. Expression analysis using RT-qPCR showed that LRRC3B is strongly down-regulated at the latest stages of RCC and ovarian cancers. In addition we showed that LRRC3B exhibit strong cell growth inhibiting activity (more than 95%) in colony formation experiments in vitro in KRC/Y renal cell carcinoma line. All these data suggest that LRRC3B gene could be involved in the process of carcinogenesis as a tumor suppressor gene.