Single-cell multiomics provides comprehensive insights into gene regulatory networks, cellular diversity, and temporal dynamics. Here, we introduce nanoSPLITS (nanodroplet SPlitting for Linked-multimodal Investigations of Trace Samples), an integrated platform that enables global profiling of the transcriptome and proteome from same single cells via RNA sequencing and mass spectrometry-based proteomics, respectively. Benchmarking of nanoSPLITS demonstrates high measurement precision with deep proteomic and transcriptomic profiling of single-cells. We apply nanoSPLITS to cyclin-dependent kinase 1 inhibited cells and found phospho-signaling events could be quantified alongside global protein and mRNA measurements, providing insights into cell cycle regulation. We extend nanoSPLITS to primary cells isolated from human pancreatic islets, introducing an efficient approach for facile identification of unknown cell types and their protein markers by mapping transcriptomic data to existing large-scale single-cell RNA sequencing reference databases. Accordingly, we establish nanoSPLITS as a multiomic technology incorporating global proteomics and anticipate the approach will be critical to furthering our understanding of biological systems.

The origins of wound myofibroblasts and scar tissue remains unclear, but it is assumed to involve conversion of adipocytes into myofibroblasts. Here, we directly explore the potential plasticity of adipocytes and fibroblasts after skin injury. Using genetic lineage tracing and live imaging in explants and in wounded animals, we observe that injury induces a transient migratory state in adipocytes with vastly distinct cell migration patterns and behaviours from fibroblasts. Furthermore, migratory adipocytes, do not contribute to scar formation and remain non-fibrogenic in vitro, in vivo and upon transplantation into wounds in animals. Using single-cell and bulk transcriptomics we confirm that wound adipocytes do not convert into fibrogenic myofibroblasts. In summary, the injury-induced migratory adipocytes remain lineage-restricted and do not converge or reprogram into a fibrosing phenotype. These findings broadly impact basic and translational strategies in the regenerative medicine field, including clinical interventions for wound repair, diabetes, and fibrotic pathologies.

The U2AF Homology Motif Kinase 1 (UHMK1) is the only kinase that contains the U2AF homology motif (UHM), a common protein interaction domain among splicing factors. Through this motif, UHMK1 interacts with the splicing factors SF1 and SF3B1, known to participate in the 3’ splice site recognition during the early steps of spliceosome assembly. Although UHMK1 phosphorylates these splicing factors in vitro , the involvement of UHMK1 in RNA processing has not previously been demonstrated. Here, we identify novel putative substrates of this kinase and evaluate UHMK1 contribution to overall gene expression and splicing, by integrating global phosphoproteomics, RNA-seq, and bioinformatics approaches. Upon UHMK1 modulation, 163 unique phosphosites were differentially phosphorylated in 117 proteins, of which 106 are novel potential substrates of this kinase. Gene Ontology (GO) analysis showed enrichment of terms previously associated with UHMK1 function, such as mRNA splicing, cell cycle, cell division and microtubule organization. The majority of the annotated RNA-related proteins are components of the spliceosome, but are also involved in several steps of gene expression. Comprehensive analysis of splicing showed that UHMK1 affected over 200 alternative splicing events. Moreover, splicing reporter assay further supported UHMK1 function on splicing. Overall, RNA-seq data demonstrated that UHMK1 knockdown had a minor impact on gene expression and pointed to UHMK1 function in epithelial-mesenchymal transition. Finally, the functional assays demonstrated that UHMK1 modulation affects proliferation, colony formation, and migration of the cells. Taken together, our data implicate UHMK1 as a splicing regulatory kinase, connecting protein regulation through phosphorylation and gene expression in key cellular processes.

Activating colony-stimulating factor-3 receptor gene (CSF3R) mutations are recurrent in acute myeloid leukemia (AML) with t(8;21) translocation. However, the nature of oncogenic collaboration between alterations of CSF3R and the t(8;21) associated RUNX1-RUNX1T1 fusion remains unclear. In CD34+ hematopoietic stem and progenitor cells from healthy donors, double oncogene expression led to a clonal advantage, increased self-renewal potential, and blast-like morphology and distinct immunophenotype. Gene expression profiling revealed hedgehog signaling as a potential mechanism, with upregulation of GLI2 constituting a putative pharmacological target. Both primary hematopoietic cells and the t(8;21) positive AML cell line SKNO-1 showed increased sensitivity to the GLI inhibitor GANT61 when expressing CSF3R T618I. Our findings suggest that during leukemogenesis, the RUNX1-RUNXT1 fusion and CSF3R mutation act in a synergistic manner to alter hedgehog signaling, which can be exploited therapeutically.

Acute myeloid leukemia (AML) patients suffer dismal prognosis upon treatment resistance. To study functional heterogeneity of resistance, we generated serially transplantable patient-derived xenograft (PDX) models from one patient with AML and twelve clones thereof, each derived from a single stem cell, as proven by genetic barcoding. Transcriptome and exome sequencing segregated clones according to their origin from relapse one or two. Undetectable for sequencing, multiplex fluorochrome-guided competitive in vivo treatment trials identified a subset of relapse two clones as uniquely resistant to cytarabine treatment. Transcriptional and proteomic profiles obtained from resistant PDX clones and refractory AML patients defined a 16-gene score that was predictive of clinical outcome in a large independent patient cohort. Thus, we identified novel genes related to cytarabine resistance and provide proof of concept that intra-tumor heterogeneity reflects inter-tumor heterogeneity in AML.

Plasmacytoid and conventional dendritic cells (pDC and cDC) are generated from progenitor cells in the bone marrow and commitment to pDCs or cDC subtypes may occur in earlier and later progenitor stages. Cells within the CD11c+MHCII-/loSiglec-H+CCR9lo DC precursor fraction of the mouse bone marrow generate both pDCs and cDCs. Here we investigate the heterogeneity and commitment of subsets in this compartment by single-cell transcriptomics and high-dimensional flow cytometry combined with cell fate analysis: Within the CD11c+MHCII-/loSiglec-H+CCR9lo DC precursor pool cells expressing high levels of Ly6D and lacking expression of transcription factor Zbtb46 contain CCR9loB220hi immediate pDC precursors and CCR9loB220lo (lo-lo) cells which still generate pDCs and cDCs in vitro and in vivo under steady state conditions. cDC-primed cells within the Ly6DhiZbtb46- lo-lo precursors rapidly upregulate Zbtb46 and pass through a Zbtb46+Ly6D+ intermediate stage before acquiring cDC phenotype after cell division. Type I IFN stimulation limits cDC and promotes pDC output from this precursor fraction by arresting cDC-primed cells in the Zbtb46+Ly6D+ stage preventing their expansion and differentiation into cDCs. Modulation of pDC versus cDC output from precursors by external factors may allow for adaptation of DC subset composition at later differentiation stages.

Cost-efficient library generation by early barcoding has been central in propelling single-cell RNA sequencing. Here, we optimize and validate prime-seq, an early barcoding bulk RNA-seq method. We show that it performs equivalently to TruSeq, a standard bulk RNA-seq method, but is fourfold more cost-efficient due to almost 50-fold cheaper library costs. We also validate a direct RNA isolation step, show that intronic reads are derived from RNA, and compare cost-efficiencies of available protocols. We conclude that prime-seq is currently one of the best options to set up an early barcoding bulk RNA-seq protocol from which many labs would profit.

The cytokine receptor colony stimulating factor 3 (CSF3R) controls differentiation, proliferation and function of granulocytes as well as mobilization of hematopoietic stem cells upon activation via G-CSF. An oncogenic role of CSF3R mutations has been mainly described in chronic neutrophilic leukemia (CNL) and, more rarely, in atypical chronic myeloid leukemia and pediatric acute myeloid leukemia (AML) (Maxson et al., 2013, N Engl J Med; Maxson et al.,2016, Blood).

Comparing the molecular and cellular properties among primates is crucial to better understand human evolution and biology. However, it is difficult or ethically impossible to collect matched tissues from many primates, especially during development. An alternative is to model different cell types and their development using induced pluripotent stem cells (iPSCs). These can be generated from many tissue sources, but non-invasive sampling would decisively broaden the spectrum of non-human primates that can be investigated. Here, we report the generation of primate iPSCs from urine samples. We first validate and optimize the procedure using human urine samples and show that suspension- Sendai Virus transduction of reprogramming factors into urinary cells efficiently generates integration-free iPSCs, which maintain their pluripotency under feeder-free culture conditions. We demonstrate that this method is also applicable to gorilla and orangutan urinary cells isolated from a non-sterile zoo floor. We characterize the urinary cells, iPSCs and derived neural progenitor cells using karyotyping, immunohistochemistry, differentiation assays and RNA-sequencing. We show that the urine-derived human iPSCs are indistinguishable from well characterized PBMC-derived human iPSCs and that the gorilla and orangutan iPSCs are well comparable to the human iPSCs. In summary, this study introduces a novel and efficient approach to non-invasively generate iPSCs from primate urine. This will extend the zoo of species available for a comparative approach to molecular and cellular phenotypes.

High-throughput sequencing describes multiple alterations in individual tumors, but their functional relevance is often unclear. Clinic-close, individualized molecular model systems are required for functional validation and to identify therapeutic targets of high significance for each patient. Here, we establish a Cre-ERT2-loxP (causes recombination, estrogen receptor mutant T2, locus of X-over P1) based inducible RNAi- (ribonucleic acid interference) mediated gene silencing system in patient-derived xenograft (PDX) models of acute leukemias in vivo. Mimicking anti-cancer therapy in patients, gene inhibition is initiated in mice harboring orthotopic tumors. In fluorochrome guided, competitive in vivo trials, silencing of the apoptosis regulator MCL1 (myeloid cell leukemia sequence 1) correlates to pharmacological MCL1 inhibition in patients´ tumors, demonstrating the ability of the method to detect therapeutic vulnerabilities. The technique identifies a major tumor-maintaining potency of the MLL-AF4 (mixed lineage leukemia, ALL1-fused gene from chromosome 4) fusion, restricted to samples carrying the translocation. DUX4 (double homeobox 4) plays an essential role in patients' leukemias carrying the recently described DUX4-IGH (immunoglobulin heavy chain) translocation, while the downstream mediator DDIT4L (DNA-damage-inducible transcript 4 like) is identified as therapeutic vulnerability. By individualizing functional genomics in established tumors in vivo, our technique decisively complements the value chain of precision oncology. Being broadly applicable to tumors of all kinds, it will considerably reinforce personalizing anti-cancer treatment in the future.

Bulk and single cell RNA sequencing have revolutionized biomedical research and empower researchers to quantify the global gene expression of populations and single cells to further understand the development, manifestation and the treatment of diseases like cancer. Acute myeloid leukemia (AML), a cancer of the myeloid line of blood cells, could benefit from these technologies as relapse and mortality rates remain high despite the extensive research conducted over several decades. This is partly because AML is a heterogeneous disease, differing substantially between patients and hence requiring more fine-grained classifications and specialised treatment strategies, for example by incorporating expression profiles. In addition, single cell RNA sequencing (scRNA-seq) can resolve genetic and epigenetic subclonal structures within a patient to improve understanding and treatment of AML. However, improving and adapting RNA-seq technologies is still often necessary to efficiently and reliably obtain expression profiles, especially from small or suboptimally processed samples. To this end, we developed a bulk RNA-seq protocol, which copes with the major challenges of limited sample quantities, different sample types, throughput and costs and subsequently applied this method to further understand the subclonal structures in AML. We were able to characterize a plastic cell state of AML cells that is defined by increased stemness and dormancy and could influence treatment outcome and relapse. For this, we isolated non-dividing AML cells based on a proliferation-sensitive dye from patient derived xenograft (PDX) models of two AML patients. We found that these cells have low levels of cell cycle genes confirming dormancy, and additionally had similar expression patterns to previously described dormant minimal residual disease (MRD) cells in lymphoblastic leukemia (ALL). This included high expression levels of cell adhesion molecules, potentially reflecting the persistence of dormant AML and ALL cells in the hematopoietic niche. Lastly, we could show that resting and cycling AML cells can transition between these two states, indicating that dormancy might be a general property of AML cells and not depend on particular genetic subclones. In a second project, we optimized a single cell RNA-seq technology. We used a systematic approach to evaluate experimental conditions of SCRB-seq, a powerful and efficient scRNA-seq method. Focussing on reverse transcription, arguably the most important and inefficient reaction, , we used a standardized human RNA (UHRR) and systematically tested nine different RT enzymes, several reaction enhancers and primer compositions to increase sensitivity. We found that Maxima H- showed the highest sensitivity and that molecular crowding using poylethylene glycol (PEG) could increase the efficiency of the reaction significantly. Together with several smaller changes in the workflow, primer design and PCR conditions, we developed mcSCRB-seq (molecular crowding SCRB-seq). We verified the 2.5x increase in sensitivity using mES cells in a side by side test between SCRB-seq and mcSCRB-seq, and further found mcSCRB-seq to be amongst the most sensitive methods using artificial RNA spike in molecules (ERCCS). Lastly, since method comparisons between studies suffer from missing accuracy due to batch effects and external factors, we participated in a complex scRNA-seq benchmark study aiming to provide a fair comparison between methods concerning sensitivity, accuracy and applicability for building expression atlases. In contrast to before, we found that in this particular setting, mcSCRB-seq did not perform well and identified fields for further improvement. In conclusion, my work described in this thesis not only contributes towards a deeper understanding of the emergence and progression of AML but also towards the development of experimental bulk and single-cell RNA sequencing methods, improving their widespread application to biomedical problems such as leukemia.

T follicular helper (Tfh) cells are crucial for the establishment of germinal centers (GCs) and potent antibody responses. Nevertheless, the T cell-intrinsic factors that are required for the maintenance of already-established Tfh cells and GCs remain largely unknown. Here, we use temporally guided gene ablation in CD4(+) T cells to dissect the contributions of the Tfh-associated chemokine receptor CXCR5 and the transcription factor Bcl6. Induced ablation of Cxcr5 has minor effects on the function of established Tfh cells, and Cxcr5-ablated cells still exhibit most of the features of CXCR5(+) Tfh cells. In contrast, continued Bcl6 expression is critical to maintain the GC Tfh cell phenotype and also the GC reaction. Importantly, Bcl6 ablation during acute viral infection results in the transdifferentiation of established Tfh into Th1 cells, thus highlighting the plasticity of Tfh cells. These findings have implications for strategies that boost or restrain Tfh cells and GCs in health and disease.

Resistance against chemotherapy remains a major obstacle in treating patients with acute myeloid leukemia (AML). Novel therapeutic concepts are especially desired to target and eliminate resistant AML stem cells. Here we show that AML stem cells harbor the plasticity to switch from a low-cycling, chemotherapy resistant state into an actively proliferating state associated with treatment response. We used patient-derived xenograft (PDX) cells from patients with high risk or relapsed AML, which were lentivirally transduced for marker expression, stained with the proliferation-sensitive dye Carboxyfluorescein succinimidyl ester (CFSE), and re-transplanted into next-recipient mice. A rare subpopulation of AML cells displayed reduced proliferation in vivo , associated with increased treatment resistance. The proportion of AML cells with stem cell potential was identical in both, the highly and lowly proliferative sub-fraction. In re-transplantation experiments, proliferation behavior proved reversible, and AML stem cells were able to switch between a high and low proliferation state. Our data indicate that AML stem cells display functional plasticity in vivo , which might be exploited for therapeutic purposes, to prevent AML relapse and ultimately improve the prognosis of patients with AML.

ZBTB7A is frequently mutated in acute myeloid leukemia (AML) with t(8;21) translocation. However, the oncogenic collaboration between mutated ZBTB7A and the RUNX1–RUNX1T1 fusion gene in AML t(8;21) remains unclear. Here, we investigate the role of ZBTB7A and its mutations in the context of normal and malignant hematopoiesis. We demonstrate that clinically relevant ZBTB7A mutations in AML t(8;21) lead to loss of function and result in perturbed myeloid differentiation with block of the granulocytic lineage in favor of monocytic commitment. In addition, loss of ZBTB7A increases glycolysis and hence sensitizes leukemic blasts to metabolic inhibition with 2-deoxy-d-glucose. We observed that ectopic expression of wild-type ZBTB7A prevents RUNX1-RUNX1T1-mediated clonal expansion of human CD34+ cells, whereas the outgrowth of progenitors is enabled by ZBTB7A mutation. Finally, ZBTB7A expression in t(8;21) cells lead to a cell cycle arrest that could be mimicked by inhibition of glycolysis. Our findings suggest that loss of ZBTB7A may facilitate the onset of AML t(8;21), and that RUNX1-RUNX1T1-rearranged leukemia might be treated with glycolytic inhibitors.

Single-cell RNA sequencing (scRNA-seq) is the leading technique for charting the molecular properties of individual cells. The latest methods are scalable to thousands of cells, enabling in-depth characterization of sample composition without prior knowledge. However, there are important differences between scRNA-seq techniques, and it remains unclear which are the most suitable protocols for drawing cell atlases of tissues, organs and organisms. We have generated benchmark datasets to systematically evaluate techniques in terms of their power to comprehensively describe cell types and states. We performed a multi-center study comparing 13 commonly used single-cell and single-nucleus RNA-seq protocols using a highly heterogeneous reference sample resource. Comparative and integrative analysis at cell type and state level revealed marked differences in protocol performance, highlighting a series of key features for cell atlas projects. These should be considered when defining guidelines and standards for international consortia, such as the Human Cell Atlas project.