Emergence of complexity in hierarchically organized chiral particles

The structural complexity of composite biomaterials and biomineralized particles arises from the hierarchical ordering of inorganic building blocks over multiple scales. Although empirical observations of complex nanoassemblies are abundant, the physicochemical mechanisms leading to their geometrical complexity are still puzzling, especially for nonuniformly sized components. We report the self-assembly of hierarchically organized particles (HOPs) from polydisperse gold thiolate nanoplatelets with cysteine surface ligands. Graph theory methods indicate that these HOPs, which feature twisted spikes and other morphologies, display higher complexity than their biological counterparts. Their intricate organization emerges from competing chirality-dependent assembly restrictions that render assembly pathways primarily dependent on nanoparticle symmetry rather than size. These findings and HOP phase diagrams open a pathway to a large family of colloids with complex architectures and unusual chiroptical and chemical properties

N to Δ\Delta transition amplitudes from QCD sum rules

We present a calculation of the N to $\Delta$ electromagnetic transition amplitudes using the method of QCD sum rules. A complete set of QCD sum rules are derived for the entire family of transitions from the baryon octet to decuplet. They are analyzed in conjunction with the corresponding mass sum rules using a Monte-Carlo-based analysis procedure. The performance of each of the sum rules is examined using the criteria of OPE convergence and ground-state dominance, along with the role of the transitions in intermediate states. Individual contributions from the u, d and s quarks are isolated and their implications in the underlying dynamics are explored. Valid sum rules are identified and their predictions are obtained. The results are compared with experiment and other calculations.Comment: 18 pages, 8 figures, 7 tables. Updated references and Fig. 7 and Fig.

Exploring therapeutic vulnerabilities in tumours with GLI1 oncogene activation

Deregulation of oncogene expression is one of the main drivers in tumorigenesis. Genetic alterations, such as gene amplification and structural variation, or epigenetic mechanisms based on the chemical modification of DNA or histones, facilitate the activation of proto-oncogenes that convey growth and survival advantages to the cells. Previously, our group identified focal amplification of the chromosome arm 12q in 14 of 60 glioblastoma patients (23.3 %) of which 4 patients harboured fusion genes with the oncogene GLI Family Zinc Finger 1 (GLI1). In this study, I investigated the frequency and structure of GLI1 fusion genes, mechanisms of GLI1 transcriptional activation, GLI1-dependent tumour cell phenotype, and the potential value of GLI1 as a therapeutic target in precision-oncology in glioblastoma and liposarcoma. Initially, I identified GLI1 fusion genes linked with focal amplification on chromosome arm 12q in three independent glioblastoma cohorts (HIPO016, HIPO043, and TCGA-GB). GLI1 fusion genes were associated with high expression of GLI1 and its target genes, such as HHIP, PTCH1, and FOXS1. The boundary of the 12q amplification region often coincided with the GLI1 locus, presumably causing the breakage within the gene and the formation of fusion transcripts. The analysis of sarcoma tumours of the NCT MASTER study revealed high GLI1 expression in subtypes of osteosarcoma and soft tissue sarcoma. In addition, GLI1 fusion genes were found in liposarcoma and leiomyosarcoma. Furthermore, the disruption of a CTCF binding site upstream of the GLI1 locus upregulated the RNA expression of GLI1 and its target genes and increased cell proliferation. These data suggest that fusion-related genetic and epigenetic mechanisms regulate GLI1 expression. To explore its oncogenic function, I conducted phenotypic assays with and without GLI1 suppression and observed a reduction in tumour cell proliferation, anchorage-independent growth and increased apoptosis upon shRNA depletion or inhibition with the GLI1 inhibitor GlaB. The downregulation of several DNA repair pathways upon GLI1 depletion suggested that patients with aberrant GLI1 expression might benefit from combined GLI1 and DNA repair inhibitor therapy. To address this question, I performed a pre-clinical drug combination screen of GLI1 and DNA repair/cell cycle checkpoint inhibitors in glioblastoma and liposarcoma cell lines. In the primary screen, I tested inhibitors individually to identify effective and selective drugs of which the most promising candidates were tested in combination in the subsequent secondary screen. Both glioblastoma and liposarcoma showed high sensitivities to the SHH inhibitor JK184 and the GLI1 inhibitor GlaB. Synergistic effects were observed when GLI1 inhibitors were combined with inhibitors of the ATR/CHK1 axis, i.e., the CHK1 inhibitor LY2606368 or the ATR inhibitor Berzosertib. The independent validation of the screening results in cellular assays showed an increased effect of the combination treatment compared to the single agents on short- and long-term tumour cell proliferation. I furthermore confirmed the reduction in tumour growth upon treatment with GlaB and LY2606368 in a glioblastoma cerebral organoid model. In conclusion, these data suggest that concurrent targeting of the SHH/GLI1 and ATR/CHK1 axes provides a possible precision-therapy approach for tumours with high GLI1 expression

The role of MYT1L in the aetiology of neurodevelopmental disorders

Neurodevelopmental disorders (NDDs) represent a huge global health burden. However, the aetiology of most psychiatric disorders remains enigmatic, making it very difficult to find adequate treatment options. While many transcription factors are associated with mental disorders, MYT1L stands out as one of very few life-long-expressed and neuronspecific transcriptional regulators. MYT1L mutations are closely linked to various neurodevelopmental disorders, like autism spectrum disorder and schizophrenia. In this work, I used embryonic stem cell-derived human neurons and mice to study how MYT1L regulates brain development, whether mutations are sufficient to cause mental disease and, if so, whether there is potential for therapeutic intervention. I found that MYT1L deficiency caused upregulation of its target genes, including members of the WNT and NOTCH signalling pathways. This resulted in neurodevelopmental delays that could be partially rescued by chemical pathway inhibition. MYT1L-deficient mice also presented with abnormal brain morphology and behavioural deficits. I found that MYT1L loss caused upregulation of non-neuronal genes, including the main cardiac sodium channel SCN5A, which might explain the unexpected neuronal network hyperactivity observed in mouse and human neurons. Supporting this hypothesis, I was able to normalise electrophysiological hyperactivity by Myt1l overexpression and Scn5a knockdown. Excitingly, the FDA-approved sodium channel blocker lamotrigine rescued electrophysiological abnormalities in vitro and behavioural deficits in vivo. The findings in this study show an important role of MYT1L as a transcriptional repressor not only during development but also after neurogenesis. Failure to silence non-neuronal gene expression in neurons might represent a novel mechanism that, at least in part, can contribute to NDD aetiology. The rescue of MYT1L deficiency-associated phenotypes in post-mitotic cells and adult mice opens up the possibility of therapeutic intervention for patients with MYT1L syndrome, including later in life

Tetratricopeptide 39C (TTC39C) Is Upregulated During Skeletal Muscle Atrophy and is Necessary for Muscle Cell Differentiation

Ttc39c has been identified as a novel gene in skeletal muscle that is upregulated in response to neurogenic atrophy in mice. Quantitative PCR and Western blot analysis confirmed that Ttc39c is expressed in both proliferating and differentiated muscle cells. Furthermore, comparison of Ttc39c expression in undifferentiated and differentiated C2C12 cells demonstrated that Ttc39c levels peak in early differentiation, but decreases as cells become fully differentiated myotubes. The transcriptional regulation of Ttc39c was examined by cloning promoter fragments of the gene and fusing it with the SEAP reporter gene. The Ttc39c reporter gene constructs were transfected into muscle cells and confirmed to have significant transcriptional activity in cultured muscle cells and were also found to be transcriptionally repressed in response to ectopic expression of myogenic regulatory factors (MRF). Furthermore, conserved E-box elements in the proximal promoter region were identified, mutated, and analyzed for their role in the transcriptional regulation of Ttc39c expression. Mutation of the conserved E-box sequences reduced the activity of the Ttc39c reporter gene, suggesting that these elements are potentially necessary for full Ttc39c expression. To determine the sub-cellular location of Ttc39c in muscle cells, the Ttc39c cDNA was fused with the green fluorescent protein (GFP), expressed in muscle cells, and visualized by confocal microscopy revealing that Tct39c is localized to the cytoplasm of proliferating myoblasts and differentiating myotubes. Furthermore, Ttc39c appears to localize to the microtubule network and differentiating muscle cells developed elongated primary cilia in response to Ttc39c ectopic expression. Additionally, Ttc39c overexpression resulted in impaired muscle cell differentiation, attenuated Hedgehog and MAP Kinase signaling, and increased expression of IFT144, a component of the intraflagellar transport complex A involved in retrograde movement in primary cilia. Interestingly, Ttc39c knockdown also resulted in abrogated muscle cell differentiation and impaired Hedgehog and MAP Kinase signaling, but did not affect IFT144 expression levels. These results suggest that muscle cell differentiation is sensitive to aberrant Ttc39c expression, that Ttc39c is necessary for proper muscle cell differentiation, and that Ttc39c may participate in retrograde transport of the primary cilia of developing muscle cells

The developing brain and pediatric brain cancer:in the context of genomic integrity, replication stress and DNA damage

During the early development of the embryo, brain development also begins. Because this must occur in a relatively short period of time, the cells experience a lot of stress due to the high speed of cell division. This can lead to mistakes in the DNA, which can lead to mutations. This can eventually develop into (brain) cancer. In this thesis, brain development and two different childhood brain cancers, medulloblastoma and high-grade glioma, are discussed. Medulloblastoma is a cancer that originates in the small brain, the cerebellum. High-grade gliomas can arise in different locations in the biggest part of the brain, the cerebrum. This depends on which mutation it contains. It is thought that these mutations and location in the brain are due to the point in the developmental phase that the brain was in when errors in the DNA developed, with certain phases perhaps more resistant to these errors than others. In addition, this thesis looks at the relationship of healthy cells during brain development and cancer formation by investigating the response to cell division stress and DNA damage of healthy cells. Here, too, cells from different developmental phases of the brain are examined and compared, and the difference in response between cells with and without a certain mutation in these mechanisms is examined. With the research in this thesis we try to gain moreknowledge about why these cancers behave in a certain way and develop

Myc inhibition impairs autophagosome formation

Autophagy, a major clearance route for most long-lived proteins and organelles, has long been implicated in cancer development. Myc is a proto-oncogene often found to be deregulated in many cancers, and thus presents as an attractive target for design of cancer therapy. Therefore, understanding the relationship between anti-Myc strategies and autophagy will be important for development of effective therapy. Here we show that Myc depletion inhibits autophagosome formation and impairs clearance of autophagy substrates. Myc suppression has an inhibitory effect on autophagy via reduction of JNK1 and Bcl2 phosphorylation. Additionally, the decrease in JNK1 phosphorylation observed with Myc knockdown is associated with a reduction in ROS production. Our data suggest that targeting Myc in cancer therapy might have the additional benefit of inhibiting autophagy in the case of therapy resistance associated with chemotherapy-induced autophagy

Self-organisation of anisometric particles : statistical theory of shape, confinement and external-field effects

Colloidal particles dispersed in a uid exhibit rich and unusual behaviour, in par- ticular if the particles are strongly anisometric, i.e., highly elongated or very at. Fluid dispersions containing anisometric colloids are, apart from being interesting in their own right, relevant to the industrial production and processing of nanocompos- ites, high-performance ??bers, gels and so on. Their unusual properties result from strongly anisotropic interactions that, amongst others, give rise to the buildup of temporal, system-spanning networks of particles as well as various liquid-crystalline states even at quite low concentrations below one volume per cent. By invoking microscopic and mesoscopic statistical theories, we investigate in this thesis aspects of both network formation and liquid crystallinity as they present themselves on a macroscopic scale. We ??nd that both are strongly a??ected by the particle shape. Our work on network formation focuses on the critical concentration where the in??nite network forms, and the properties of the clusters at concentrations just below and above this. We investigate how particle shape, variation in the dimensions, externally applied ??elds, and so on impact upon them. Our calculations, based on so-called connectedness-percolation theory, are inspired by observations of strong variations in the emergence of electrical conduction in composites containing carbon nanotubes and graphene. We make plausible that this is caused by the formulation of the nanocomposite on the one hand and the processing conditions on the other. Our predictions agree favourably with experimental data on polymeric composites containing graphene of known size distribution, and con??rm that the presence of very few, very elongated or very at particles dictate the critical loading. Our calculations also predict that at higher particle concentrations, the particle network breaks down due to a competition with a transition to the uniaxial, ne- matic liquid-crystalline phase. This phase presents itself initially in the form of droplets that eventually coalesce to become a macroscopic uid. Properties of both we investigate at the level of Frank-Oseen-Rapini-Papoular theory to describe the competition between elastic and surfaces forces. These determine the interfacial shape and spatial structure of the uniaxial symmetry axis. We predict that under conditions of isotropic-nematic phase co-existence, the capillary rise of a macroscopic nematic uid up a vertical solid wall produces a non-monotonic isotropic-nematic uid interface. Our theory allows us to extract from capillary-rise experiments on dispersions of plate-like clay particles estimates for the surface tension and the an- choring strength of the nematic symmetry axis to the interface. Observations on droplets of the same (gibbsite) clay particles, which have a nega- tive diamagnetic susceptibility and prefer perpendicular anchoring of the symmetry axis to the isotropic-nematic uid interface, have shown that their internal structure and shape depend strongly on their size and on the strength of an externally applied magnetic ??eld that aligns them. Our calculations show that the transitions between spherical and elongated droplets, and between di??erent kinds of internal organisation of the symmetry axis, are sharp, i.e., resemble phase transitions. By comparing our theory to shape and internal-structure measurements, we have been able to extract values for an elastic constant, the surface tension and anchoring strength. We ??nd that whether or not the droplets elongate under the presence of a magnetic ??eld, depends only on the ratio of the anchoring strength and surface tension

Advances and Novel Treatment Options in Metastatic Melanoma

The book presents several studies reporting advances on melanoma pathogenesis, diagnosis and therapy. It represents a milestone on the state of the art, updated at 2021, and also presents the current knowledge on the future developments in melanoma field