FisB Mediated Membrane Fission during Sporulation in Bacillus Subtilis

Membrane fusion and fission are important to all forms of life as they are required for processes such as cellular division, intracellular trafficking, and synaptic vesicle recycling. While membrane fission is extensively studied in eukaryotes, little is known about bacterial membrane fission even though it is required for every cell cycle. Membrane fission also occurs during sporulation. When nutrients are scarce, certain bacteria (e.g. Bacillus subtilis) are able to sporulate, thereby creating resistant endospores that can withstand harsh environmental conditions, such as radiation and drought, for hundreds of years. The first step of sporulation is asymmetric cell division which generates a larger mother cell and a smaller forespore. The mother cell then engulfs the forespore in a process similar to phagocytosis. When engulfment is complete, the leading membrane edge forms a small pore or membrane neck. Membrane fission of this neck connecting the engulfment membrane to the rest of the mother cell membrane, releases the forespore into the mother cell’s cytoplasm. Our lab and collaborators had previously identified that fission protein B (FisB) is required for this membrane fission step. The mother cell nurtures the forespore and once it is mature, lysis of the mother cell releases the spore into the environment. FisB is expressed shortly after asymmetric division and the only dedicated membrane fission machinery described for bacteria so far. It forms small, mobile clusters during engulfment and a large immobile cluster at the engulfment pole where membrane fission occurs. FisB is predicted to have a small N-terminal cytoplasmic domain, one transmembrane domain, and a larger extracellular domain (FisB(ECD)) which binds the phospholipid cardiolipin (CL). CL is a negatively charged lipid with spontaneous, negative curvature and is implicated in membrane fusion and fission reactions. However, the physiological significance of these findings was not clear. Overall, the aims of my thesis were to determine (1) how FisB localizes to the fission site and (2) the mechanism by which it mediates fission. First, we tested if FisB is recruited to the fission site by interaction with another protein, a specific lipid domain, or by membrane curvature. We were unable to identify a protein that interacts with FisB and found that FisB localization and membrane fission do not depend on membrane microdomains of CL or phosphatidylethanolamine (PE), another lipid that previously had been implicated in membrane fission and fusion. Additionally, our results suggest that FisB does not sense or induce membrane curvature, thus localization to the highly curved membrane fission site must rely on a separate mechanism. However, by using mutagenesis, we found that FisB self-oligomerization and binding to acidic lipids is required for targeting of FisB to the fission site. Next, we characterized interactions of FisB(ECD) with artificial membranes and found that FisB(ECD) forms an extended stable network on GUV membranes which is so stable that it persists even when the lipids are subsequently removed with detergent. Moreover, we found that FisB(ECD) bridges membranes of small liposomes and GUVs. Finally, we noticed a strong correlation between forespore inflation during sporulation and membrane fission. We found that forespores of cells that have undergone fission are inflated, while spores of pre-fission cells are not, even if engulfment appears complete. DNA translocation from the mother cell into the forespore by the protein SpoIIIE leads to forespore inflation and requires membrane flow from the peripheral mother cell membrane through the membrane neck into the engulfment membrane. We hypothesize that by forming a stable network in the membrane neck when engulfment is complete, FisB opposes lipid flow, leading to increased stress in the neck and ultimately membrane fission. Future work will test this hypothesis rigorously. Altogether, our results suggest that FisB localizes to the fission site by relying largely on FisB-FisB and FisB-lipid interactions. Since the larger portion of FisB faces into the extracellular space, the membrane geometry at the end of engulfment allows for FisB molecules to interact in trans. Therefore, we propose that a FisB cluster gets trapped in the membrane neck by interacting with other FisB molecules and/or the membrane in trans across the neck. Thus, FisB exploits the high curvature geometry of the membrane fission site without relying on an intrinsic membrane curvature sensing mechanism. Our results also suggest that membrane fission and forespore inflation are linked. We suggest that FisB accumulation in the membrane neck resists membrane flow leading to friction between the FisB network and the membrane which when high enough can lead to membrane fission

Sturing in de Wmo-praktijk:op weg naar nieuwe sturingsmodellen in de Wmo

De uitvoering van de Wet maatschappelijke ondersteuning (Wmo) ligt bij de gemeente. Deze heeft veel vrijheid om het beleid naar eigen inzicht in te richten. Wél moet de gemeente uitvoering geven aan de doeleinden van de wet, zoals die door de rijksoverheid zijn vastgesteld: de maatschappelijke doelen die zijn gericht op meer zelfredzaamheid en participatie van (kwetsbare) burgers en de bestuurlijke doelen, die onder andere zijn gericht op een betere afstemming en samenhang in de beleidsvorming en de uitvoering van het beleid. Daarbij nodigt de Wmo gemeenten nadrukkelijk uit burgers en maatschappelijke organisaties bij de voorbereiding van het beleid te betrekken. Dit vergt van gemeenten een vorm van sturing die burgers en instellingen actief betrekt bij de beleidsvorming en de beleidsuitvoering. Vier Wmo-werkplaatsen – Groningen-Drenthe, Nijmegen, Twente en Utrecht – hebben in de afgelopen jaren onderzoek gedaan naar de wijze waarop gemeenten projecten op het terrein van de Wmo aansturen. Daarbij ging het om zaken als de manier waarop gemeenten sturen (van bovenaf of meer ruimte voor burgers en instellingen), samenhang en samenwerking en natuurlijk de vraag of het lukt om te sturen volgens de filosofie van de Wmo. Dit boek is een neerslag van de vier onderzoeken van de genoemde werkplaatsen

Are Newly Discovered HI High Velocity Clouds Minihalos in the Local Group?

A set of HI sources extracted from the north Galactic polar region by the ongoing ALFALFA survey has properties that are consistent with the interpretation that they are associated with isolated minihalos in the outskirts of the Local Group (LG). Unlike objects detected by previous surveys, such as the Compact High Velocity Clouds of Braun & Burton (1999), the HI clouds found by ALFALFA do not violate any structural requirements or halo scaling laws of the LambdaCDM structure paradigm, nor would they have been detected by extant HI surveys of nearby galaxy groups other than the LG. At a distance of d Mpc, their HI masses range between $5 x 10^4 d^2 and 10^6 d^2 solar and their HI radii between <0.4d and 1.6 d kpc. If they are parts of gravitationally bound halos, the total masses would be on order of 10^8--10^9 solar, their baryonic content would be signifcantly smaller than the cosmic fraction of 0.16 and present in a ionized gas phase of mass well exceeding that of the neutral phase. This study does not however prove that the minihalo interpretation is unique. Among possible alternatives would be that the clouds are shreds of the Leading Arm of the Magellanic Stream.Comment: 4 pages, 3 figures, 1 table; to appear Ap.J. Letter

Eenzaam ben je niet alleen:samen werken aan een nieuwe blik op eenzaamheid en sociaal isolement

Eenzaamheid en sociaal isolement treft mensen van alle leeftijden en uit alle lagen van de samenleving. Hoewel er in Nederland verschillende instrumenten in gebruik zijn, ontbreekt een integrale benadering voor het oppakken van deze problematiek samen met de persoon. De meeste handvatten richten zich op signaleren en slechts een enkele op het bespreekbaar maken van de problemen. De Wmo-werkplaatsen wilden daarom een werkwijze ontwikkelen die zich richt op de verschillende fases van de aanpak van eenzaamheid en sociaal isolement. Met behulp van dit werkboek kunnen professionals en vrijwilligers elkaar helpen bij de ondersteuning van mensen die hiermee kampen. Het werkboek focust op het (leren) luisteren naar de persoon en vervolgens het samen bepalen van volgende stappen. Door nauw aan te sluiten bij de persoon is de kans op effect van de persoonlijk vormgegeven interventie het grootst. Het boek biedt werkvormen om vanuit wat de persoon zelf kan en wil, zo mogelijk samen met het sociale netwerk, tot actie te komen. Professionals en vrijwilligers worden hiermee in verschillende fases ondersteund om al doende de persoon tot eigen inzichten, bevindingen en acties te begeleiden

Triangulations, order polytopes, and generalized snake posets

This work regards the order polytopes arising from the class of generalized snake posets and their posets of meet-irreducible elements. Among generalized snake posets of the same rank, we characterize those whose order polytopes have minimal and maximal volume. We give a combinatorial characterization of the circuits in these order polytopes and then conclude that every regular triangulation is unimodular. For a generalized snake word, we count the number of flips for the canonical triangulation of these order polytopes. We determine that the flip graph of the order polytope of the poset whose lattice of filters comes from a ladder is the Cayley graph of a symmetric group. Lastly, we introduce an operation on triangulations called twists and prove that twists preserve regular triangulations.Comment: 39 pages, 26 figures, comments welcomed

Relationships between lead biomarkers and diurnal salivary cortisol indices in pregnant women from Mexico City: a cross-sectional study

Background: Lead (Pb) exposure during pregnancy may increase the risk of adverse maternal, infant, or childhood health outcomes by interfering with hypothalamic-pituitary-adrenal-axis function. We examined relationships between maternal blood or bone Pb concentrations and features of diurnal cortisol profiles in 936 pregnant women from Mexico City. Methods: From 2007–11 we recruited women from hospitals/clinics affiliated with the Mexican Social Security System. Pb was measured in blood (BPb) during the second trimester and in mothers’ tibia and patella 1-month postpartum. We characterized maternal HPA-axis function using 10 timed salivary cortisol measurements collected over 2-days (mean: 19.7, range: 14–35 weeks gestation). We used linear mixed models to examine the relationship between Pb biomarkers and cortisol area under the curve (AUC), awakening response (CAR), and diurnal slope. Results: After adjustment for confounders, women in the highest quintile of BPb concentrations had a reduced CAR (Ratio: −13%; Confidence Interval [CI]: −24, 1, p-value for trend < 0.05) compared to women in the lowest quintile. Tibia/patella Pb concentrations were not associated with CAR, but diurnal cortisol slopes were suggestively flatter among women in the highest patella Pb quantile compared to women in the lowest quantile (Ratio: 14%; CI: −2, 33). BPb and bone Pb concentrations were not associated with cortisol AUC. Conclusions: Concurrent blood Pb levels were associated with cortisol awakening response in these pregnant women and this might explain adverse health outcomes associated with Pb. Further research is needed to confirm these results and determine if other environmental chemicals disrupt hypothalamic-pituitary-adrenal-axis function during pregnancy

Effect of Support Supervision on Maternal and Newborn Health Services and Practices in Rural Eastern Uganda

Background: Support supervision is one of the strategies used to check the quality of services provided at health facilities. From 2013 to 2015, Makerere University School of Public Health strengthened support supervision in the district of Kibuku, Kamuli and Pallisa in Eastern Uganda to improve the quality of maternal and newborn services. Objective: This article assesses quality improvements in maternal and newborn care services and practices during this period. Methods: District management teams were trained for two days on how to conduct the supportive supervision. Teams were then allocated particular facilities, which they consistently visited every quarter. During each visit, teams scored the performance of each facility based on checklists; feedback and corrective actions were implemented. Support supervision focused on maternal health services, newborn care services, human resources, laboratory services, availability of Information, education and communication materials and infrastructure. Support supervision reports and checklists from a total of 28 health facilities, each with at least three support supervision visits, were analyzed for this study and 20 key-informant interviews conducted. Results: There was noticeable improvement in maternal and newborn services. For instance, across the first, second and third quarters, availability of parenteral oxytocin increased from 57% to 75% and then to 82%. Removal of retained products increased from 14% to 50% to 54%, respectively. There was perceived improvement in the use of standards and guidelines for emergency obstetric care and quality of care provided. Qualitatively, three themes were identified that promote the success of supportive supervision: changes in the support supervision style, changes in the adherence to clinical standards and guidelines, and multi-stakeholder engagement. Conclusion: Support supervision helped district health managers to identify and address maternal and newborn service-delivery gaps. However, issues beyond the jurisdiction of district health managers and facility managers may require additional interventions beyond supportive supervision.DFI