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The development of single-cell RNA sequencing enabled the high throughput characterization of cell populations with unprecedented detail. Yet, it failed in capturing the spatial localization of individual cells. Overcoming this, different spatial profiling methods have been developed in recent years, with in situ sequencing (ISS) being among the most powerful solutions ISS is a targeted spatially-resolved transcriptomics method designed to detect the expression of hundreds of genes in situ in a single experiment. For this, ISS employs padlock probes, a type of oligonucleotide designed to specifically hybridize on the targeted regions, with rolling circle amplification and a combinatorial detection of the transcripts imaged. Due to its throughput and resolution, ISS is seen as a useful tool to create high content molecular maps of tissues, being of special use for building spatial atlases. However, due to its recent development, it’s still unclear how this should be done. The work presented in this thesis explores ISS as a tool for building large spatially-resolved atlases of cell types. In paper I, we compare the performance of cDNA-based ISS with the High Sensitivity Library Preparation Kit, developed by CARTANA AB. We identify this product to be fivefold more sensitive than cDNA-based ISS due to its improved chemistry. In addition, we show that this increased sensitivity enhances the analytical capabilities of the resulting data. In paper II, we build a topographic atlas of the developmental human lung. We identify 83 different cell types and states, including a novel type of GHRL-positive neuroendocrine cell. We further elucidate the developmental origin multiple populations, defining their location in situ and predicting potential interactions. In paper III, we create a topographic atlas of the adult human lung. We combine multiple spatial transcriptomic technologies to generate spatial maps of the populations found in the adult lung. We decipher regional

With the emergence of high throughput single cell techniques, the understanding of the molecular and cellular diversity of mammalian organs have rapidly increased. In order to understand the spatial organization of this diversity, single cell data is often integrated with spatial data to create probabilistic cell maps. However, targeted cell typing approaches relying on existing single cell data achieve incomplete and biased maps that could mask the true diversity present in a tissue slide. Here we applied a de novo technique to spatially resolve and characterize cellular diversity of in situ sequencing data during human heart development. We obtained and made accessible well defined spatial cell-type maps of fetal hearts from 4.5 to 9 post conception weeks, not biased by probabilistic cell typing approaches. With our analysis, we could characterize previously unreported molecular diversity within cardiomyocytes and epicardial cells and identified their characteristic expression signatures, comparing them with specific subpopulations found in single cell RNA sequencing datasets. We further characterized the differentiation trajectories of epicardial cells, identifying a clear spatial component on it. All in all, our study provides a novel technique for conducting de novo spatial-temporal analyses in developmental tissue samples and a useful resource for online exploration of cell-type differentiation during heart development at sub-cellular image resolution.

Visualization of the transcriptome in situ has proven to be a valuable tool in exploring single-cell RNA-sequencing data, providing an additional spatial dimension to investigate multiplexed gene expression, cell types, disease architecture or even data driven discoveries. In situ sequencing (ISS) method based on padlock probes and rolling circle amplification has been used to spatially resolve gene transcripts in tissue sections of various origins. Here, we describe the next iteration of ISS, HybISS, hybridization-based in situ sequencing. Modifications in probe design allows for a new barcoding system via sequence-by-hybridization chemistry for improved spatial detection of RNA transcripts. Due to the amplification of probes, amplicons can be visualized with standard epifluorescence microscopes for high-throughput efficiency and the new sequencing chemistry removes limitations bound by sequence-by-ligation chemistry of ISS. HybISS design allows for increased flexibility and multiplexing, increased signal-to-noise, all without compromising throughput efficiency of imaging large fields of view. Moreover, the current protocol is demonstrated to work on human brain tissue samples, a source that has proven to be difficult to work with image-based spatial analysis techniques. Overall, HybISS technology works as a targeted amplification detection method for improved spatial transcriptomic visualization, and importantly, with an ease of implementation.

The respiratory system, encompassing the lungs, trachea, and vasculature, is essential for terrestrial life. Although recent research has illuminated aspects of lung development, such as cell lineage origins and their molecular drivers, much of our knowledge is still based on animal models, or is deduced from transcriptome analyses. In this study, conducted within the Human Developmental Cell Atlas (HDCA) initiative, we describe the spatiotemporal organization of lung during the first trimester of human gestation in situ and at protein level. We used high-parametric tissue imaging on human lung samples, aged 6 to 13 post-conception weeks, using a 30-plex antibody panel. Our approach yielded over 2 million individual lung cells across five developmental timepoints, with an in-depth analysis of nearly 1 million cells. We present a spatially resolved cell type composition of the developing human lung, with a particular emphasis on their proliferative states, spatial arrangement traits, and their temporal evolution throughout lung development. We also offer new insights into the emerging patterns of immune cells during lung development. To the best of our knowledge, this study is the most extensive protein-level examination of the developing human lung. The generated dataset is a valuable resource for further research into the developmental roots of human respiratory health and disease., QC 20240411

Heart development relies on a topologically defined interplay between a diverse array of cardiac cells. We finely curated spatial and single-cell measurements with subcellular imaging-based transcriptomics validation to explore spatial dynamics during early human cardiogenesis. Analyzing almost 80,000 individual cells and 70,000 spatially barcoded tissue regions between the 5.5th and 14th postconceptional weeks, we identified 31 coarse- and 72 fine-grained cell states and mapped them to highly resolved cardiac cellular niches. We provide novel insight into the development of the cardiac pacemaker-conduction system, heart valves, and atrial septum, and decipher heterogeneity of the hitherto elusive cardiac fibroblast population. Furthermore, we describe the formation of cardiac autonomic innervation and present the first spatial account of chromaffin cells in the fetal human heart. In summary, our study delineates the cellular and molecular landscape of the developing heart’s architecture, offering links to genetic causes of heart disease., QC 20240411

Multiplexed spatial profiling of mRNAs has recently gained traction as a tool to explore the cellular diversity and the architecture of tissues. We propose a sensitive, open-source, simple and flexible method for the generation of in-situ expression maps of hundreds of genes. We exploit direct ligation of padlock probes on mRNAs, coupled with rolling circle amplification and hybridization-based in situ combinatorial barcoding, to achieve high detection efficiency, high throughput and large multiplexing. We validate the method across a number of species, and show its use in combination with orthogonal methods such as antibody staining, highlighting its potential value for developmental and tissue biology studies. Finally, we provide an end-to-end computational workflow that covers the steps of probe design, image processing, data extraction, cell segmentation, clustering and annotation of cell types. By enabling easier access to high-throughput spatially resolved transcriptomics, we hope to encourage a diversity of applications and the exploration of a wide range of biological questions.

Heart development relies on a topologically defined interplay between a diverse array of cardiac cells. We finely curated spatial and single-cell measurements with subcellular imaging-based transcriptomics validation to explore spatial dynamics during early human cardiogenesis. Analyzing almost 80,000 individual cells and 70,000 spatially barcoded tissue regions between the 5.5th and 14th postconceptional weeks, we identified 31 coarse- and 72 fine-grained cell states and mapped them to highly resolved cardiac cellular niches. We provide novel insight into the development of the cardiac pacemaker-conduction system, heart valves, and atrial septum, and decipher heterogeneity of the hitherto elusive cardiac fibroblast population. Furthermore, we describe the formation of cardiac autonomic innervation and present the first spatial account of chromaffin cells in the fetal human heart. In summary, our study delineates the cellular and molecular landscape of the developing heart’s architecture, offering links to genetic causes of heart disease., QC 20240411

The respiratory system, encompassing the lungs, trachea, and vasculature, is essential for terrestrial life. Although recent research has illuminated aspects of lung development, such as cell lineage origins and their molecular drivers, much of our knowledge is still based on animal models, or is deduced from transcriptome analyses. In this study, conducted within the Human Developmental Cell Atlas (HDCA) initiative, we describe the spatiotemporal organization of lung during the first trimester of human gestation in situ and at protein level. We used high-parametric tissue imaging on human lung samples, aged 6 to 13 post-conception weeks, using a 30-plex antibody panel. Our approach yielded over 2 million individual lung cells across five developmental timepoints, with an in-depth analysis of nearly 1 million cells. We present a spatially resolved cell type composition of the developing human lung, with a particular emphasis on their proliferative states, spatial arrangement traits, and their temporal evolution throughout lung development. We also offer new insights into the emerging patterns of immune cells during lung development. To the best of our knowledge, this study is the most extensive protein-level examination of the developing human lung. The generated dataset is a valuable resource for further research into the developmental roots of human respiratory health and disease., QC 20240411

The respiratory system, encompassing the lungs, trachea, and vasculature, is essential for terrestrial life. Although recent research has illuminated aspects of lung development, such as cell lineage origins and their molecular drivers, much of our knowledge is still based on animal models, or is deduced from transcriptome analyses. In this study, conducted within the Human Developmental Cell Atlas (HDCA) initiative, we describe the spatiotemporal organization of lung during the first trimester of human gestation in situ and at protein level. We used high-parametric tissue imaging on human lung samples, aged 6 to 13 post-conception weeks, using a 30-plex antibody panel. Our approach yielded over 2 million individual lung cells across five developmental timepoints, with an in-depth analysis of nearly 1 million cells. We present a spatially resolved cell type composition of the developing human lung, with a particular emphasis on their proliferative states, spatial arrangement traits, and their temporal evolution throughout lung development. We also offer new insights into the emerging patterns of immune cells during lung development. To the best of our knowledge, this study is the most extensive protein-level examination of the developing human lung. The generated dataset is a valuable resource for further research into the developmental roots of human respiratory health and disease., QC 20240411

Heart development relies on a topologically defined interplay between a diverse array of cardiac cells. We finely curated spatial and single-cell measurements with subcellular imaging-based transcriptomics validation to explore spatial dynamics during early human cardiogenesis. Analyzing almost 80,000 individual cells and 70,000 spatially barcoded tissue regions between the 5.5th and 14th postconceptional weeks, we identified 31 coarse- and 72 fine-grained cell states and mapped them to highly resolved cardiac cellular niches. We provide novel insight into the development of the cardiac pacemaker-conduction system, heart valves, and atrial septum, and decipher heterogeneity of the hitherto elusive cardiac fibroblast population. Furthermore, we describe the formation of cardiac autonomic innervation and present the first spatial account of chromaffin cells in the fetal human heart. In summary, our study delineates the cellular and molecular landscape of the developing heart’s architecture, offering links to genetic causes of heart disease., QC 20240411

Heart development relies on a topologically defined interplay between a diverse array of cardiac cells. We finely curated spatial and single-cell measurements with subcellular imaging-based transcriptomics validation to explore spatial dynamics during early human cardiogenesis. Analyzing almost 80,000 individual cells and 70,000 spatially barcoded tissue regions between the 5.5th and 14th postconceptional weeks, we identified 31 coarse- and 72 fine-grained cell states and mapped them to highly resolved cardiac cellular niches. We provide novel insight into the development of the cardiac pacemaker-conduction system, heart valves, and atrial septum, and decipher heterogeneity of the hitherto elusive cardiac fibroblast population. Furthermore, we describe the formation of cardiac autonomic innervation and present the first spatial account of chromaffin cells in the fetal human heart. In summary, our study delineates the cellular and molecular landscape of the developing heart’s architecture, offering links to genetic causes of heart disease., QC 20240411

The respiratory system, encompassing the lungs, trachea, and vasculature, is essential for terrestrial life. Although recent research has illuminated aspects of lung development, such as cell lineage origins and their molecular drivers, much of our knowledge is still based on animal models, or is deduced from transcriptome analyses. In this study, conducted within the Human Developmental Cell Atlas (HDCA) initiative, we describe the spatiotemporal organization of lung during the first trimester of human gestation in situ and at protein level. We used high-parametric tissue imaging on human lung samples, aged 6 to 13 post-conception weeks, using a 30-plex antibody panel. Our approach yielded over 2 million individual lung cells across five developmental timepoints, with an in-depth analysis of nearly 1 million cells. We present a spatially resolved cell type composition of the developing human lung, with a particular emphasis on their proliferative states, spatial arrangement traits, and their temporal evolution throughout lung development. We also offer new insights into the emerging patterns of immune cells during lung development. To the best of our knowledge, this study is the most extensive protein-level examination of the developing human lung. The generated dataset is a valuable resource for further research into the developmental roots of human respiratory health and disease., QC 20240411