Epigenetic and transcriptional regulation of cortico-ponto-cerebellar circuit formation

The precerebellar system constitutes an array of nuclei located in the mammalian hindbrain and conveys movement and balance information from the cortex, spinal cord and periphery to the cerebellum (Sotelo, 2004). Within this system, the pontine nuclei (PN), including pontine gray and reticulotegmental nuclei, mostly relay cortical information (Schwarz and Thier, 1999). During the processing through the cortex, PN and cerebellum, continuous maps of sensorimotor information are transformed into a complex fractured map (Leergaard et al., 2006). To date, however, there is a paucity of knowledge on the molecular and cellular mechanisms organizing this complex circuitry. Previous work suggests an intrinsic topographic organization, according to rostro-caudal progenitor origin, that is maintained during migration and nucleation of the PN (Di Meglio et al., 2013). As a result, one of the hallmarks of the PN topography is a well-defined population of Hox paralogous group 5 (PG5) expressing neurons in the posterior part of the PN. However, the molecular mechanisms governing the spatial expression pattern of Hox PG5 genes in the PN and their functional impact on circuit formation remain largely unknown. The first part of this thesis focuses on the molecular mechanisms of Hox PG5 induction in the precerebellar system. We find that the precise spatio-temporal expression pattern of Hox PG5 genes rely on the integration of environmental signaling and the resulting modifications of the epigenetic landscape. Unlike transcripts of more anterior Hox genes, expression of Hox PG5 genes is entirely excluded from progenitors in the rhombic lip (RL) and only induced in a subset of postmitotic neurons. Mapping and manipulation of signaling pathways show that the restriction of Hox PG5 induction to the ventrally located (i.e. posterior RL-derived) postmitotic pontine neuron subsets is due to an interplay between retinoic acid (RA) and Wnt environmental signaling. Assessment of histone profiles at Hox loci indicate that the induction of Hox PG5 genes through RA is tightly linked to a depletion of the histone mark H3K27me3. However, conditional inactivation of Ezh2, a member of the polycomb repressive complex 2 responsible for setting the H3K27me3 mark (Margueron and Reinberg, 2011), does not result in a de-repression of Hox PG5 genes in the progenitor domain. In contrast, removal of H3K27me3 in Ezh2 depleted PN neurons leads to an ectopic induction of Hox PG5 in rostral PN neuron subsets of the migratory stream showing an enhanced response to RA (Di Meglio et al., 2013). Moreover, high levels of RA-induced Hox PG5 expression in postmitotic PN neurons require Jmjd3, one of the enzymes known to catalyze the removal of methyl groups at H3K27 (Agger et al., 2007; De Santa et al., 2007). We show that Jmjd3 is physically present at RA responsive elements in proximity to the Hoxa5 promoter supporting the direct involvement of Jmjd3 in Hox PG5 induction. Thus, a central function of H3K27me3 regulation during late stages of precerebellar development is the establishment of a threshold for RA mediated activation of Hox PG5 genes to allow for diversification of PN neurons. Finally, we show how the integration of environmental signaling on the epigenetic level results in distinct changes of the three dimensional (3D) organization of chromatin at Hox PG5 loci in vivo. Together, the late specification of PN neurons employs a sophisticated sequence of interactions between signaling pathways such as RA and Wnt, and histone modifying enzymes like Ezh2 and Jmjd3. The second part of the thesis addresses the functional significance of Hox PG5 genes in sub-circuit formation of PN neurons. Using multiple conditional overexpression strategies, we show that the expression of Hoxa5 is sufficient to shape the input-output relationship of PN neurons. Hoxa5 expressing neurons migrate into a posterior position in the PN and induce a distinct transcriptional program specific for topographic circuit formation. Together, this indicates a crucial role of Hoxa5 in the specification of the positional identity of PN subsets. We further describe a genetically identified Hox PG5 negative PN subset that primarily projects to the paraflocculus, a lobule in the cerebellum heavily concerned with visually related tasks. Conditional overexpression of Hoxa5 in this PN subset leads to the ectopic targeting of several other lobes in the cerebellum concerned with processing of somatosensory information. This matches with the input connectivity of the PN that has been shown to be antero-posteriorly patterned, such that visual/medioposterior projections target the anterior, Hox PG5 negative, and somatosensory projections target the posterior, Hox PG5 positive part of the PN (Di Meglio et al., 2013; Leergaard and Bjaalie, 2007). Consequently, Hoxa5 overexpressing PN neurons are largely devoid of input from the visual cortex and primarily engage in a somatosensory hindlimb specific circuitry. One single Hox gene is thus sufficient to position neurons in the posterior aspects of the PN, change their transcriptional program and rearrange both, output connectivity to the cerebellum and input connectivity from the cortex. These findings extend the function of Hox genes to orchestrating topographic circuit formation in the PN. Further, the presented results point towards an involvement of Hox genes in the longstanding problem of fracturing of the somatosensory map that is realized between the cortex and the cerebellum

Renormalization of the Minimal Supersymmetric Standard Model

The renormalization of the Minimal Supersymmetric Standard Model (MSSM) is presented. We describe symmetry identities that constitute a framework in which the MSSM is completely characterized and renormalizability can be proven. Furthermore, we discuss applications of this framework for the determination of symmetry-restoring counterterms, the gauge dependence of tan(beta) and the derivation of non-renormalization theorems.Comment: Talk given by D.S. at the RADCOR/Loops and Legs in Quantum Field Theory 2002, September 8--13, Kloster Banz, Germany. 5 pages. Layout improve

Microscopic Softening Mechanisms of an Ionic Liquid Additive in an Electrically Conductive Carbon-Silicone Composite

The microstructural changes caused by the addition of the ionic liquid (IL) 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide to polydimethylsiloxane (PDMS) elastomer composites filled with carbon black (CB) are analyzed to explain the electrical, mechanical, rheological, and optical properties of IL-containing precursors and composites. Swelling experiments and optical analysis indicate a limited solubility of the IL in the PDMS matrix that reduces the cross-linking density of PDMS both globally and locally, which reduces the Young's moduli of the composites. A rheological analysis of the precursor mixture shows that the IL reduces the strength of carbon–carbon and carbon–PDMS interactions, thus lowering the filler–matrix coupling and increasing the elongation at break. Electromechanical testing reveals a combination of reversible and irreversible piezoresistive responses that is consistent with the presence of IL at microscopic carbon–carbon interfaces, where it enables re-established electrical connections after stress release but reduces the absolute conductivity

Immobilized Ru‐Pincer Complexes for Continuous Gas‐Phase Low‐Temperature Methanol Reforming‐Improving the Activity by a Second Ru‐Complex and Variation of Hydroxide Additives

Ru-pincer complexes were immobilized as supported liquid phase (SLP) materials to allow the methanol reforming reaction as continuous gas phase process. Under reaction conditions, the liquid phase forms from the hydroxide coating. Several hydroxides were screened and CsOH showed highest activity compared to the standard KOH coating. The well-known Ru-pincer complex carbonylchlorohydrido [bis(2-di-i-propylphosphinoethyl)amine]ruthenium(II) is limited in catalyzing the final step of the methanol reforming. Addition of a second complex, having a methylated backbone in the pincer-ligand, could overcome these limitations. Significant enhancement of the overall catalytic activity was observed

Self-assembly of gold nanoparticles at the oil-vapor interface: from mono- to multilayers

Alkylthiol-coated gold nanoparticles spontaneously segregate from dispersion in toluene to the toluene-vapor interface. We show that surface tension drops during segregation with a rate that depends on particle concentration. Mono- and multilayers of particles form depending on particle concentration, time, and temperature. X-ray reflectometry indicates fast monolayer formation and slow multilayer formation. A model that combines diffusion-limited segregation driven by surface energy and heterogeneous agglomeration driven by dispersive van der Waals particle interactions is proposed to describe film formation

Prevalence of findings compatible with carotid artery calcifications on dental panoramic radiographs

Cerebrovascular accidents are responsible for killing or disabling more than half a million Americans every year. They are the third leading cause of death in this country. In Germany, the annual stroke incidence reaches 182 cases per 100,000 inhabitants. Stroke there is the fourth leading cause of death. There is a need of finding cost-effective means of decreasing stroke mortality and morbidity. Instruments for early diagnosis are of great humanitarian and economic importance. All possible clinical findings should be taken into account. It is not the demand of this study to present the panoramic radiograph as a screening test method for early diagnosis of atherosclerosis. The aim is to show the potential of this radiograph used in everyday clinical dental practice by the prevalence of radiopaque findings in the carotid region. This study included panoramic dental radiographs of 2,557 patients older than 30years of age. Fifty-nine percent of the patients were women and 41% were men. The radiographs were adjudged for signs compatible with carotid arterial calcifications appearing as a radiopaque nodular mass adjacent to the cervical vertebrae at or below the intervertebral space C3-4. Of all these radiographs, 4.8% showed radiopaque findings compatible with atherosclerotic lesions. The proportion of women reached 64.8% and that of men reached 35.2%. In accordance to recent literature, the results of this study show that about 5% of the patients show radiological findings compatible with carotid arterial calcifications. Some of these patients at risk for a cerebrovascular accident may be identified in the dentist's office by appropriate review of the panoramic dental radiograph. The suspicion of carotid artery calcifications demands an impetuous referral to an appropriate practitioner who can assist in the control of risk factors and if necessary arrange surgical removal of the carotid arterial plaque. So, the dentist should be aware of this problem and able to make a contribution to stroke preventio

Clinical retention force development of double crowns

This study deals with the development of the retentive forces of double crowns intraorally measured. Twenty-five combined fixed-removable prostheses with a total of 84 double crowns were included in the study. The intraoral measurement was performed at 72 defined measuring points directly adjacent to the double crowns of the dentures. The measurement was performed 4-6weeks (baseline), 6months (recall 1), and 18months (recall 2) after the insertion of the restoration. A specifically designed measuring device was used. The median values for the single measuring points reached 4.705N at the baseline, 5.190N after 6months, and 3.740N after 18months. The measured values were analyzed according to differences between the median retention forces at the three defined points in time. The statistical analysis of the median values showed no statistical difference for the retention force change after 6months but for the decrease until the second recall (Mann-Whitney test). The retention force per denture was calculated by a summation of the single measuring points. At the baseline, 12.9N was reached. The forces did only decrease slightly and were not statistically significant. The results indicate that retention force values of double crowns, measured intraorally at the patient, do not relevantly change clinically within the first 1.5years. Within the limitations of this study, it can be stated that wear does not influence the retentive forces of double crowns within the first 18months. After this period the retention force should be still sufficient for denture retentio

Prevention of internal bacterial colonization of dental implants: A comparative longitudinal observational study.

OBJECTIVES Previous studies have indicated a progressive internal bacterial colonization of implants and possible implications for peri-implant bone loss. The aim of this study was to evaluate a decontamination protocol, two disinfectants, and a sealant for their ability to prevent such a colonization. MATERIALS AND METHODS Bacterial samples were harvested from the peri-implant sulcus (external) and following abutment removal from the implant cavity (internal) during routine supportive peri-implant care in 30 edentulous patients 2 years after they had obtained two implants. In a split-mouth design, implants were randomly assigned to receive either internal decontamination alone (10% H2 O2 , brush) or additional placement of either sealant (GS), disinfectant agent (CHX-varnish) or disinfectant gel (1% CHX-gel), in the internal cavity before remounting of abutment/suprastructure. Twelve months later, internal and external sampling was repeated. Total bacterial counts (TBCs) were determined using real-time PCR in a total of 240 samples (eight per patient). RESULTS Total bacterial counts in the internal cavity significantly reduced overall treatment modalities 1 year after the treatments (4.0 [2.3-6.9]-fold reduction; p = .000). No significant differences between the four treatment types were found (p = .348). Comparison of internal and external sampling points revealed significant correlation (R2  = .366; p = .000) with systematically higher TBC counts in external samples. CONCLUSIONS Within the limitations of the present study, it can be concluded that the use of disinfectant agents or a sealant did not show an additional benefit in the prevention of internal bacterial colonization of implants compared to a decontamination protocol alone