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The variant surface glycoprotein (VSG) of African trypanosomes plays an essential role in protecting the parasites from host immune factors. These trypanosomes undergo antigenic variation resulting in the expression of a single VSG isoform out of a repertoire of around 2000 genes. The molecular mechanism central to the expression and regulation of the VSG is however not fully understood.
Gene expression in trypanosomes is unusual due to the absence of typical RNA polymerase II promoters and the polycistronic transcription of genes. The regulation of gene expression is therefore mainly post-transcriptional. Regulatory sequences, mostly present in the 3´ UTRs, often serve as key elements in the modulation of the levels of individual mRNAs. In T. brucei VSG genes, a 100 % conserved 16mer motif within the 3´ UTR has been shown to modulate the stability of VSG transcripts and hence their expression. As a stability-associated sequence element, the absence of nucleotide substitutions in the motif is however unusual. It was therefore hypothesised that the motif is involved in other essential roles/processes besides stability of the VSG transcripts.
In this study, it was demonstrated that the 100 % conservation of the 16mer motif is not essential for cell viability or for the maintenance of functional VSG protein levels. It was further shown that the intact motif in the active VSG 3´ UTR is neither required to promote VSG silencing during switching nor is it needed during differentiation from bloodstream forms to procyclic forms. Crosstalk between the VSG and procyclin genes during differentiation to the insect vector stage is also unaffected in cells with a mutated 16mer motif. Ectopic overexpression of a second VSG however requires the intact motif to trigger silencing and exchange of the active VSG, suggesting a role for the motif in transcriptional VSG switching. The 16mer motif therefore plays a dual role in VSG in situ switching and stability of VSG transcripts. The additional role of the 16mer in the essential process of antigenic variation appears to be the driving force for the 100 % conservation of this RNA motif.
A screen aimed at identifying candidate RNA-binding proteins interacting with the 16mer motif, led to the identification of a DExD/H box protein, Hel66. Although the protein did not appear to have a direct link to the 16mer regulation of VSG expression, the DExD/H family of proteins are important players in the process of ribosome biogenesis. This process is relatively understudied in trypanosomes and so this candidate was singled out for detailed characterisation, given that the 16mer story had reached a natural end point. Ribosome biogenesis is a major cellular process in eukaryotes involving ribosomal RNA, ribosomal proteins and several non-ribosomal trans-acting protein factors. The DExD/H box proteins are the most important trans-acting protein factors involved in the biosynthesis of ribosomes. Several DExD/H box proteins have been directly implicated in this process in yeast. In trypanosomes, very few of this family of proteins have been characterised and therefore little is known about the specific roles they play in RNA metabolism. Here, it was shown that Hel66 is involved in rRNA processing during ribosome biogenesis. Hel66 localises to the nucleolus and depleting the protein led to a severe growth defect. Loss of the protein also resulted in a reduced rate of global translation and accumulation of rRNA processing intermediates of both the small and large ribosomal subunits. Hel66 is therefore an essential nucleolar DExD/H protein involved in rRNA processing during ribosome biogenesis. As very few protein factors involved in the processing of rRNAs have been described in trypanosomes, this finding represents an important platform for future investigation of this topic.
The reprogramming of metabolic pathways is a hallmark of cancer: Tumour cells are dependent on the supply with metabolites and building blocks to fulfil their increased need as highly proliferating cells. Especially de novo synthesis pathways are upregulated when the cells of the growing tumours are not able to satisfy the required metabolic levels by uptake from the environment.
De novo synthesis pathways are often under the control of master transcription factors which regulate the gene expression of enzymes involved in the synthesis process. The master regulators for de novo fatty acid synthesis and cholesterogenesis are sterol regulatory element-binding proteins (SREBPs). While SREBP1 preferably controls the expression of enzymes involved in fatty acid synthesis, SREBP2 regulates the transcription of the enzymes of the mevalonate pathway and downstream processes namely cholesterol, isoprenoids and building blocks for ubiquinone synthesis.
SREBP activity is tightly regulated at different levels: The post-translational modification by ubiquitination decreases the stability of active SREBPs. The attachment of K48-linked ubiquitin chains marks the transcription factors for the proteasomal degradation. In tumour cells, high levels of active SREBPs are essential for the upregulation of the respective metabolic pathways. The increased stability and activity of SREBPs were investigated in this thesis.
SREBPs are ubiquitinated by the E3 ligase Fbw7 which leads to the subsequential proteolysis of the transcription factors. The work conducted in this thesis identified the counteracting deubiquitination enzyme USP28 which removes the ubiquitin chains from SREBPs and prevents their proteasomal degradation.
It further revealed that the stabilization of SREBP2 by USP28 plays an important role in the context of squamous cancers. Increased USP28 levels are associated with a poor survival in patients with squamous tumour subtypes. It was shown that reduced USP28 levels in cell lines and in vivo result in a decrease of SREBP2 activity and downregulation of the mevalonate pathway. This manipulation led to reduced proliferation and tumour growth.
A direct comparison of adenocarcinomas and squamous cell carcinomas in lung cancer patients revealed an upregulation of USP28 as well as SREBP2 and its target genes. Targeting the USP28-SREBP2 regulatory axis in squamous cell lines by inhibitors also reduced cell viability and proliferation.
In conclusion, this study reports evidence for the importance of the mevalonate pathway regulated by the USP28-SREBP2 axis in tumour initiation and progression of squamous cancer. The combinatorial inhibitor treatment of USP28 and HMGCR, the rate limiting enzyme of the mevalonate pathway, by statins opens the possibility for a targeted therapeutic treatment of squamous cancer patients.
Highlights
• The GLA variant S126G is not associated with Fabry symptoms in the presented case
• S126G has no effect on α-GAL A activity or Gb3 levels in this patient
• S126G sensory neurons show no electrophysiological abnormalities
Abstract
Fabry disease (FD) is a life-limiting disorder characterized by intracellular globotriaosylceramide (Gb3) accumulations. The underlying α-galactosidase A (α-GAL A) deficiency is caused by variants in the gene GLA. Variants of unknown significance (VUS) are frequently found in GLA and challenge clinical management. Here, we investigated a 49-year old man with cryptogenic lacunar cerebral stroke and the chance finding of the VUS S126G, who was sent to our center for diagnosis and initiation of a costly and life-long FD-specific treatment. We combined clinical examination with in vitro investigations of dermal fibroblasts (HDF), induced pluripotent stem cells (iPSC), and iPSC-derived sensory neurons. We analyzed α-GAL A activity in iPSC, Gb3 accumulation in all three cell types, and action potential firing in sensory neurons. Neurological examination and small nerve fiber assessment was normal except for reduced distal skin innervation. S126G iPSC showed normal α-GAL A activity compared to controls and no Gb3 deposits were found in all three cell types. Baseline electrophysiological characteristics of S126G neurons showed no difference compared to healthy controls as investigated by patch-clamp recordings. We pioneer multi-level cellular characterization of the VUS S126G using three cell types derived from a patient and provide further evidence for the benign nature of S126G in GLA, which is of great importance in the management of such cases in clinical practice.
Immunofluorescence is a common method to localise proteins within their cellular context via fluorophore labelled antibodies and for some applications without alternative. However, some protein targets evade detection due to low protein abundance or accessibility issues. In addition, some imaging methods require a massive reduction in antigen density thus impeding detection of even medium-abundant proteins.Here, we show that the fusion of the target protein to TurboID, a biotin ligase labelling lysine residues in close proximity, and subsequent detection of biotinylation by fluorescent streptavidin offers an “all in one” solution to the above-mentioned restrictions. For a wide range of target proteins tested, the streptavidin signal was significantly stronger than an antibody signal, markedly improving the imaging sensitivity in expansion microscopy and correlative light and electron microscopy, with no loss in resolution. Importantly, proteins within phase-separated regions, such as the central channel of the nuclear pores, the nucleolus or RNA granules, were readily detected with streptavidin, while most antibodies fail to label proteins in these environments. When TurboID is used in tandem with an HA epitope tag, co-probing with streptavidin and anti-HA can be used to map antibody-accessibility to certain cellular regions. As a proof of principle, we mapped antibody access to all trypanosome nuclear pore proteins (NUPs) and found restricted antibody labelling of all FG NUPs of the central channel that are known to be phase-separated, while most non-FG Nups could be labelled. Lastly, we show that streptavidin imaging can resolve dynamic, temporally and spatially distinct sub-complexes and, in specific cases, reveal a history of dynamic protein interaction.In conclusion, streptavidin imaging has major advantages for the detection of lowly abundant or inaccessible proteins and in addition, can provide information on protein interactions and biophysical environment.
The cystine/glutamate antiporter xCT is an important source of cysteine for cancer cells. Once taken up, cystine is reduced to cysteine and serves as a building block for the synthesis of glutathione, which efficiently protects cells from oxidative damage and prevents ferroptosis. As melanomas are particularly exposed to several sources of oxidative stress, we investigated the biological role of cysteine and glutathione supply by xCT in melanoma. xCT activity was abolished by genetic depletion in the Tyr::CreER; Braf\(^{CA}\); Pten\(^{lox/+}\) melanoma model and by acute cystine withdrawal in melanoma cell lines. Both interventions profoundly impacted melanoma glutathione levels, but they were surprisingly well tolerated by murine melanomas in vivo and by most human melanoma cell lines in vitro. RNA sequencing of human melanoma cells revealed a strong adaptive upregulation of NRF2 and ATF4 pathways, which orchestrated the compensatory upregulation of genes involved in antioxidant defence and de novo cysteine biosynthesis. In addition, the joint activation of ATF4 and NRF2 triggered a phenotypic switch characterized by a reduction of differentiation genes and induction of pro-invasive features, which was also observed after erastin treatment or the inhibition of glutathione synthesis. NRF2 alone was capable of inducing the phenotypic switch in a transient manner. Together, our data show that cystine or glutathione levels regulate the phenotypic plasticity of melanoma cells by elevating ATF4 and NRF2.
Proteins fold in water and achieve a clear structure despite a huge parameter space. Inside a (protein) crystal you have everywhere the same symmetries as there is everywhere the same unit cell. We apply this to qubit interactions to do fundamental physics:
We modify cosmological inflation: we replace the big bang by a condensation event in an eternal all-encompassing ocean of free qubits. Rare interactions of qubits in the ocean provide a nucleus or seed for a new universe (domain), as the qubits become decoherent and freeze-out into defined bit ensembles. Next, we replace inflation by a crystallization event triggered by the nucleus of interacting qubits to which rapidly more and more qubits attach (like in everyday crystal growth). The crystal unit cell guarantees same symmetries (and laws of nature) everywhere inside the crystal, no inflation scenario is needed.
Interacting qubits solidify, quantum entropy decreases in the crystal, but increases outside in the ocean. The interacting qubits form a rapidly growing domain where the n**m states become separated ensemble states, rising long-range forces stop ultimately further growth. After this very early modified steps, standard cosmology with the hot fireball model takes over. Our theory agrees well with lack of inflation traces in cosmic background measurements.
Applying the Hurwitz theorem to qubits we prove that initiation of qubit interactions can only be 1,2,4 or 8-dimensional (agrees with E8 symmetry of our universe). Repulsive forces at ultrashort distances result from quantization, long-range forces limit crystal growth. The phase space of the crystal agrees with the standard model of the basic four forces for n quanta. It includes all possible ensemble combinations of their quantum states m, a total of n**m states. We describe a six-bit-ensemble toy model of qubit interaction and the repulsive forces of qubits for ultra-short distances. Neighbor states reach according to transition possibilities (S-matrix) with emergent time from entropic ensemble gradients. However, in our four dimensions there is only one bit overlap to neighbor states left (almost solid, only below Planck´s quantum is liquidity left). The E8 symmetry of heterotic string theory has six curled-up, small dimensions. These keep the qubit crystal together and never expand. We give energy estimates for free qubits vs bound qubits, misplacements in the qubit crystal and entropy increase during qubit crystal formation.
Implications are fundamental answers, e.g. why there is fine-tuning for life-friendliness, why there is string theory with rolled-up dimension and so many free parameters. We explain by cosmological crystallization instead of inflation the early creation of large-scale structure of voids and filaments, supercluster formation, galaxy formation, and the dominance of matter: the unit cell of our crystal universe has a matter handedness avoiding anti-matter. Importantly, crystals come and go in the qubit ocean. This selects for the ability to lay seeds for new crystals, for self-organization and life-friendliness. Vacuum energy gets appropriate low inside the crystal by its qubit binding energy, outside it is 10**20 higher. Scalar fields for color interaction/confinement and gravity could be derived from the qubit-interaction field.
Context
Habitat loss and degradation impose serious threats on biodiversity. However, not all habitats receive the attention commensurate with their ecological importance. Shrub ecotones (successional stages between grasslands and forests) can be highly species-diverse but are often restricted to small areas as prevalent management practices either promote open grassland or forest habitats, threatening the effective conservation of ecotone species.
Objectives
In this study, we assessed the importance of habitat and landscape features of shrub ecotones for the rarely studied true bugs (Heteroptera), a functionally diverse taxon that comprises highly specialized species and broad generalists.
Methods
True bugs were sampled with a beating tray in 118 spatially independent shrub ecotones in a region of 45,000 square kilometers in Germany. In addition to habitat area and landscape context, we used a hedge index to evaluate habitat quality.
Results
Shrub ecotones in open habitats harbored a greater species richness and abundance compared to shaded ones in later seral stages, and species composition differed. Richness and abundance were positively affected by increasing habitat area and quality, whereas an increase in the proportion of semi-natural habitats within 1 km only enhanced richness. While feeding and habitat specialists were more sensitive to habitat area reduction than generalists, this was not the case for weak dispersers and carnivores.
Conclusions
Our findings emphasize the importance of large and high-quality ecotones that form a patchy mosaic of shrubs and herbaceous plants. Such ecotones can benefit both grassland species and species depending on woody plants. Conservation authorities should balance between promoting shrubs and keeping such habitats open to maximize species diversity.
Gastroesophageal junction (GEJ), demarcating the region where the distal esophagus meets with the proximal stomach region, is known for developing pathological conditions, including metaplasia and esophageal adenocarcinoma (EAC). It is essential to understand the mechanisms of developmental stages which lead to EAC since the incidence rate of EAC increased over 7-fold during the past four decades, and the overall five years survival rate is 18.4%. In most cases, patients are diagnosed in the advanced stage without prior symptoms. The main precursor for the development of EAC is a pre-malignant condition called Barrett's esophagus (BE). BE is the metaplastic condition where the multilayered squamous epithelium of the native esophagus is replaced by specialized single-layered columnar epithelium, which shows the molecular characteristics of the gastric as well as intestinal epithelium. The main risk factors for BE development include chronic gastro-esophageal acid reflux disease (GERD), altered microbiota, and altered retinoic acid signaling (RA). The cell of origin of BE is under debate due to a lack of clear evidence demonstrating the process of BE initiation. Here, I investigated how GEJ homeostasis is maintained in healthy tissue by stem cell regulatory morphogens, the role of vitamin A (RA signaling), and how its alteration contributes to BE development.
In the first part of my thesis, I showed the presence of two types of epithelial cells, the squamous type in the esophagus and the columnar type in the stomach region in the GEJ, using single-molecule RNA in situ hybridization (smRNA-ISH) and immunohistochemistry. Employing lineage tracing in the mouse model, I have demonstrated that the esophageal epithelial and stomach epithelial cells derived from two distinct epithelial stem cell lineages in the GEJ. The border between squamous and columnar epithelial cells in the Squamo-columnar junction (SCJ) of GEJ is regulated by opposing Wnt microenvironments. The regeneration of stomach columnar epithelial stem cells is maintained by Wnt activating signal from the stromal compartment while squamous epithelial stem cells of the esophagus are maintained by the Wnt inhibitory signals. I recapitulated the in vivo GEJ epithelial stem cell maintenance by using in vitro epithelial 3D organoid culture model. The growth and propagation of stomach columnar epithelial organoids depend on Wnt growth factors, while squamous epithelial organoids' development needs Wnt-deficient culture conditions.
Further, single-cell RNA sequence (scRNA-seq) analysis of organoid-derived epithelial cells revealed the non-canonical Wnt/ planar cell polarity (PCP) pathway involvement in regulating the squamous epithelial cells. In contrast, columnar stomach epithelial cells are regulated by the canonical Wnt/ beta-catenin and non-canonical Wnt/Ca2+ pathways. My data indicate that the SCJ epithelial cells that merge at the GEJ are regulated by opposing stromal Wnt factors and distinct Wnt pathway signaling in the epithelial cells.
In the second part of the thesis, I investigated the role of Vitamin A-derived bioactive compound RA on esophageal and stomach epithelial stem cells. In vitro treatment of esophageal and stomach, epithelial organoids with RA or its pharmacological inhibitor BMS 493 revealed that each cell type was regulated distinctly. I observed that enhanced RA promoted esophageal stem cell differentiation and loss of stratification, while RA inhibition led to enhanced stemness and regeneration of the esophagus stratified epithelium. As opposed to the esophagus, RA signaling is active in the stomach organoids, and inhibition of RA reduces the growth of stomach organoids. Global transcriptomic data and scRNA-seq data revealed that RA signaling induces dormancy phenotype in the esophageal cells. In contrast, the absence of RA in stomach epithelial cells induces the expression of genes associated with BE. Thus, spatially defined regulation of Wnt and RA signaling at GEJ is critical for healthy homeostasis, and its perturbation leads to disease development.
Chapter I: Introduction
Temperature is a major driver of biodiversity and abundance patterns on our planet, which becomes particularly relevant facing the entanglement of an imminent biodiversity and climate crisis. Climate shapes the composition of species assemblages either directly via abiotic filtering mechanisms or indirectly through alterations in biotic interactions. Insects - integral elements of Earth’s ecosystems - are affected by climatic variation such as warming, yet responses vary among species. While species’ traits, antagonistic biotic interactions, and even species’ microbial mutualists may determine temperature-dependent assembly processes, the lion’s share of these complex relationships remains poorly understood due to methodological constraints. Mountains, recognized as hotspots of diversity and threatened by rapidly changing climatic conditions, can serve as natural experimental settings to study the response of insect assemblages and their trophic interactions to temperature variation, instrumentalizing the high regional heterogeneity of micro- and macroclimate. With this thesis, we aim to enhance our mechanistic understanding of temperature-driven assembly processes within insect communities, exemplified by Orthoptera, that are significant herbivores in temperate mountain grassland ecosystems. Therefore, we combined field surveys of Orthoptera assemblages on grassland sites with molecular tools for foodweb reconstruction, primarily leveraging the elevational gradients offered by the complex topography within the Berchtesgaden Alpine region (Bavaria, Germany) as surrogate for temperature variation (space-for-time substitution approach). In this framework, we studied the effects of temperature variation on (1) species richness, abundance, community composition, and interspecific as well as intraspecific trait patterns, (2) ecological feeding specialisation, and (3) previously neglected links to microbial associates found in the faeces.
Chapter II: Temperature-driven assembly processes
Climate varies at multiple scales. Since microclimate is often overlooked, we assessed effects of local temperature deviations on species and trait compositions of insect communities along macroclimatic temperature gradients in Chapter II. Therefore, we employed joint species distribution modelling to explore how traits drive variation in the climatic niches of Orthoptera species at grassland sites characterized by contrasting micro- and macroclimatic conditions. Our findings revealed two key insights: (1) additive effects of micro- and macroclimate on the diversity, but (2) interactive effects on the abundance of several species, resulting in turnover and indicating that species possess narrower climatic niches than their elevational distributions might imply. This chapter suggests positive effects of warming on Orthoptera, but also highlights that the interplay of macro- and microclimate plays a pivotal role in structuring insect communities. Thus, it underscores the importance of considering both elements when predicting the responses of species to climate change. Additionally, this chapter revealed inter- and intraspecific effects of traits on the niches and distribution of species.
Chapter III: Dietary specialisation along climatic gradients
A crucial trait linked to the position of climatic niches is dietary specialisation. According to the ‘altitudinal niche-breadth hypothesis’, species of high-elevation habitats should be less specialized compared to their low-elevation counterparts. However, empirical evidence on shifts in specialization is scarce for generalist insect herbivores and existing studies often fail to control for the phylogeny and abundance of interaction partners. In Chapter III, we used a combination of field observations and amplicon sequencing to reconstruct dietary relationships between Orthoptera and plants along an extensive temperature gradient. We did not find close but flexible links between individual grasshopper and plant taxa in space. While interaction network specialisation increased with temperature, the corrected dietary specialisation pattern peaked at intermediate elevations on assemblage level. These nuanced findings demonstrate that (1) resource availability, (2) phylogenetic relationships, and (3) climate can affect empirical foodwebs intra- and interspecifically and, hence, the dietary specialisation of herbivorous insects. In this context, we discuss that the underlying mechanisms involved in shaping the specialisation of herbivore assemblages may switch along temperature clines.
Chapter IV: Links between faecal microbe communities, feeding habits, and climate
Since gut microbes affect the fitness and digestion of insects, studying their diversity could provide novel insights into specialisation patterns. However, their association with insect hosts that differ in feeding habits and specialisation has never been investigated along elevational climatic gradients. In Chapter IV, we utilized the dietary information gathered in Chapter III to characterize links between insects with distinct feeding behaviour and the microbial communities present in their faeces, using amplicon sequencing. Both, feeding and climate affected the bacterial communities. However, the large overlap of microbes at site level suggests that common bacteria are acquired from the shared feeding environment, such as the plants consumed by the insects. These findings emphasize the influence of a broader environmental context on the composition of insect gut microbial communities.
Chapter V: Discussion & Conclusions
Cumulatively, the sections of this dissertation provide support for the hypothesis that climatic conditions play a role in shaping plant–herbivore systems. The detected variation of taxonomic and functional compositions contributes to our understanding of assembly processes and resulting diversity patterns within Orthoptera communities, shedding light on the mechanisms that structure their trophic interactions in diverse climates. The combined results presented suggest that a warmer climate could foster an increase of Orthoptera species richness in Central European semi-natural grasslands, also because the weak links observed between insect herbivores and plants are unlikely to limit decoupled range shifts. However, the restructuring of Orthoptera communities in response to warmer temperatures depends on species' traits such as moisture preferences or phenology. Notably, we were able to demonstrate a crucial role of microclimate for many species, partly unravelling narrower climatic niches than their elevational ranges suggest. We found evidence that not only Orthoptera community composition, specialisation, and traits varied along elevational gradients, but even microbial communities in the faeces of Orthoptera changed, which is a novel finding. This complex restructuring and reassembly of communities, coupled with the nonlinear specialisation of trophic interactions and a high diversity of associated bacteria, emphasize our currently incomplete comprehension of how ecosystems will develop under future climatic conditions, demanding caution in making simplified predictions for biodiversity change under climate warming. Since these predictions may benefit from including biotic interactions and both, micro- and macroclimate based on our findings, conservation authorities and practitioners must not neglect improving microclimatic conditions to ensure local survival of a diverse set of threatened and demanding species. In this context, mountains can play a pivotal role for biodiversity conservation since these offer heterogeneous microclimatic conditions in proximity that can be utilized by species with distinct niches.
The unicellular pathogen Trypanosoma brucei is the causative agent of African
trypanosomiasis, an endemic disease prevalent in sub-Saharan Africa. Trypanosoma brucei alternates between a mammalian host and the tsetse fly vector. The extracellular parasite survives in the mammalian bloodstream by periodically exchanging their ˈvariant surface glycoproteinˈ (VSG) coat to evade the host immune response. This antigenic variation is achieved through monoallelic expression of one VSG variant from subtelomeric ˈbloodstream
form expression sitesˈ (BES) at a given timepoint. During the differentiation from the bloodstream form (BSF) to the procyclic form (PCF) in the tsetse fly midgut, the stage specific surface protein is transcriptionally silenced and replaced by procyclins. Due to their subtelomeric localization on the chromosomes, VSG transcription and silencing is partly regulated by homologues of the mammalian telomere complex such as TbTRF, TbTIF2 and TbRAP1 as well as by ˈtelomere-associated proteinsˈ (TelAPs) like TelAP1. To gain more insights into transcription regulation of VSG genes, the identification and characterization of other TelAPs is critical and has not yet been achieved. In a previous study, two biochemical approaches were used to identify other novel TelAPs. By using ˈco-immunoprecipitationˈ (co-IP) to enrich possible interaction partners of TbTRF and by affinity chromatography using telomeric repeat oligonucleotides, a listing of TelAP candidates has been conducted. With this approach TelAP1 was identified as a novel component of the telomere complex, involved in the kinetics of transcriptional BES silencing during BSF to PCF differentiation. To gain further insights into the telomere complex composition, other previously enriched proteins were characterized through a screening process using RNA interference to deplete potential candidates. VSG expression profile changes and overall proteomic changes after depletion were analyzed by mass spectrometry. With this method, one can gain insights into the functions of the proteins and their involvement in VSG expression site regulation. To validate the interaction of proteins enriched by co-IP with TbTRF and TelAP1 and to identify novel interaction proteins, I performed reciprocal affinity purifications of the four most promising candidates (TelAP2, TelAP3, PPL2 and PolIE) and additionally confirmed colocalization of two candidates with TbTRF via immunofluorescence (TelAP2, TelAP3). TelAP3 colocalizes with TbTRF and potentially interacts with TbTRF, TbTIF2, TelAP1 and TelAP2, as well as with two translesion polymerases PPL2 and PolIE in BSF. PPL2 and PolIE seem to be in close contact to each other at the telomeric ends and fulfill different roles as only PolIE is involved in VSG regulation while PPL2 is not. TelAP2 was previously characterized to be associated with telomeres by partially colocalizing with TbTRF and cells show a VSG derepression phenotype when the protein was depleted. Here I show that TelAP2 interacts with the telomere-binding proteins TbTRF and TbTIF2 as well as with the telomere-associated protein TelAP1 in BSF and that TelAP2 depletion results in a loss of TelAP1 colocalization with TbTRF in BSF.
In conclusion, this study demonstrates that characterizing potential TelAPs is effective in gaining insights into the telomeric complex's composition and its role in VSG regulation in Trypanosoma brucei. Understanding these interactions could potentially lead to new therapeutic targets for combatting African trypanosomiasis.