Tissue morphology influences the temporal program of human cerebral organoids
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ABSTRACT: Organs are the ensemble of different cell types in a complex architectural milieu. It is well-known that progression through fate decisions sets up the complex cellular makeup and architecture of an organ, but how that same architecture may impact on cell fate is less clear. We sought to examine this by taking advantage of the unique capabilities of organoids as a tractable in vitro model to interrogate how fate and form interact during organ development. Screening methodological variations encountered in the literature revealed that common protocol adjustments, such as small molecule patterning and exposure to exogenous extracellular matrix, impacted various aspects of morphology, from macro structure to tissue architecture. We demonstrated that overall morphology is a predictor of tissue architecture and that perturbing morphology results in changes in cytoarchitecture. Vice-versa, perturbing cytoarchitecture by mechanically redistributing cells in a random spatial conformation resulted in a simplified overall morphology. We next examined the impact of these morphological perturbations on cell fate through integrated snRNA-seq and spatial transcriptomics within the phenotypic landscape. Regardless of the specific protocol, organoids with more complex morphology better mimicked in vivo human fetal brain development than organoids with simplified morphology. Further, organoids with perturbed tissue architecture profiled with scRNA-seq over a time course experiment displayed aberrant temporal progression in cell fate, with cells being intermingled in both space and time. Finally, imparting a simplified morphology through physical encapsulation led to disrupted tissue cytoarchitecture and a similar abnormal temporal progression. These data not only point to the importance of tissue morphology in organoid fidelity compared to in vivo, but also demonstrate that cells require proper spatial coordinates in order to undergo the proper temporal trajectory of events.
Project description:This project used snRNA-seq and Molecular Cartography (single cell spatial transcriptomics) to investigate the relation between morphology and molecular identity in human brain organoids.
Project description:<p>Human brain organoids are emerging models to study human brain development and pathology as they recapitulate the development and characteristics of major neural cell types, and enable manipulation through an <em>in vitro</em> system. Over the past decade, with the advent of spatial technologies, mass spectrometry imaging (MSI) has become a prominent tool for metabolic microscopy, providing label-free, non-targeted molecular and spatial distribution information of the metabolites within tissue, including lipids. This technology has never been used for studies of brain organoids and here, we set out to develop a standardized protocol for preparation and mass spectrometry imaging of human brain organoids. We present an optimized and validated sample preparation protocol, including sample fixation, optimal embedding solution, homogenous deposition of matrices, data acquisition and processing to maximize the molecular information derived from mass spectrometry imaging. We focus on lipids in organoids, as they play critical roles during cellular and brain development. Using high spatial and mass resolution in positive- and negative-ion modes, we detected 260 lipids in the organoids. Seven of them were uniquely localized within the neurogenic niches or rosettes as confirmed by histology, suggesting their importance for neuroprogenitor proliferation. We observed a particularly striking distribution of ceramide-phosphoethanolamine CerPE 36:1; O2 restricted within rosettes and of phosphatidyl-ethanolamine PE 38:3, which was distributed throughout the organoid tissue but not in rosettes. This suggests that ceramide in this particular lipid species might be important for neuroprogenitor biology, while its removal may be important for terminal differentiation of their progeny. Overall, our study establishes the first optimized experimental pipeline and data processing strategy for mass spectrometry imaging of human brain organoids, allowing direct comparison of lipid signal intensities and distributions in these tissues. Further, our data shed new light on the complex processes that govern brain development by identifying specific lipid signatures that may play a role in metabolic cell fate trajectories. mass spectrometry imaging thus has great potential in advancing our understanding of early brain development as well as disease modeling and drug discovery.</p>
Project description:Spatial transcriptomics (ST) is an innovative technology that holds tremendous potential for transforming the field of tissue biology research. By simultaneously capturing multiple types of spatial data, including gene expression values, spatial distance information, and tissue morphology, ST enables a comprehensive understanding of biological samples. However, the effective integration of these diverse data types remains a challenge. In this study, we present stLearn, a collection of three computational-statistical algorithms specifically designed to exploit the combined power of gene expression, spatial distance, and tissue morphology data. Our aim is to unlock novel insights into tissue maintenance, development, and disease. The first algorithm, known as pseudo-time-space (PSTS), employs a spatial-graph-based approach to uncover the spatial relationships between cells' transcriptional states in dynamic tissue contexts. To demonstrate the effectiveness of stLearn, we utilize traumatic brain injury datasets to investigate the spatio-temporal dynamics of microglia activation. By applying the PSTS algorithm to a well-established mouse model of acquired brain injury, we successfully reconstruct the spatial trajectory of microglia activation following insult, thereby validating this key component of stLearn.
Project description:Cell fate transition is a spatiotemporal process, however, previous work has largely neglected the spatial dimension. Incorporating space and time into models of cell fate transition would be a key step toward characterizing how interactions among neighboring cells, local niche factors, and cell migration contribute to tissue development. Here, we developed topological velocity inference (TopoVelo), a computational tool to infer spatial and temporal dynamics of cell fate transition from spatial transcriptomic data. We show that TopoVelo significantly improves the accuracy and spatial coherence of inferred cell ordering compared to previous methods. TopoVelo also reveals spatial cell state dependencies of ligand-receptor genes, spatial signatures of mouse neural tubes, and patterns of early differentiation in 3D cell culture.
Project description:Positional patterning during human brain development is orchestrated through highly coordinated interplays of locally produced inductive signals. While animal models have elucidated general signaling pathways during early neurodevelopment, individual morphogens' effects underlying the proper human brain regionalization remain unclear. Current technologies are limited in generating stable, well-confined gradients in neural organoids for robust regionalization. Here, we report a Matrigel-free passive diffusion-based morphogen gradient generator (PdMG) that reliably established a steep exogenous spatial morphogen gradient in human neural organoids. We further established dorsal-ventral forebrain, rostral-caudal fore-midbrain, and rostral-caudal fore-mid/hindbrain/spinal cord patterning by applying Sonic hedgehog/ WNT-inhibitor, WNT, and retinoic acid gradients, respectively. Spatial transcriptomics analysis revealed robust regionalization in early-stage patterned organoids, as well as active neurogenesis and GABAergic interneuron migrations in late-stage patterned organoids. Together, this study provides a framework for modeling the spatial-temporal morphogen dynamics that regulate key cell fate specifications and axis formations using patterned neural organoid models.
Project description:Knowledge of cell signaling pathways that drive human neural crest differentiation into craniofacial chondrocytes is incomplete, yet essential for using stem cells to regenerate craniomaxillofacial structures. To accelerate translational progress, we developed a differentiation protocol that generated self-organizing craniofacial cartilage organoids from human embryonic stem cell-derived neural crest stem cells. Histological staining of cartilage organoids revealed tissue architecture and staining typical of elastic cartilage. Protein and post-translational modification (PTM) mass spectrometry and snRNASeq data showed that chondrocyte organoids expressed robust levels of cartilage extracellular matrix (ECM) components: many collagens, aggrecan, perlecan, proteoglycans, and elastic fibers. We identified two populations of chondroprogenitor cells, mesenchyme cells and nascent chondrocytes and the growth factors involved in paracrine signaling between them. We show that ECM components secreted by chondrocytes not only create a structurally resilient matrix that defines cartilage, but also play a pivotal autocrine cell signaling role to determine chondrocyte fate.
Project description:The vertebrate neural tube generates a large diversity of molecularly and functionally distinct neurons and glia from a small progenitor pool. While the role of spatial patterning in organising cell fate specification has been extensively studied, temporal patterning, which controls the timing of cell type generation, is equally important. Here we define a global temporal programme in the spinal cord. This governs cell fate choices by regulating chromatin accessibility in neural progenitors. Perturbation of this cis-regulatory programme affects sequential transitions in spinal cord progenitors and the identity of progeny. The temporal programme operates in parallel to spatial patterning, ensuring the timely availability of regulatory elements for spatial determinants to direct cell-type specific gene expression. These findings identify a chronotopic spatiotemporal integration strategy in which a global temporal chromatin programme determines the output of a spatial gene regulatory network resulting in the temporally and spatially ordered allocation of cell type identity.
Project description:The vertebrate neural tube generates a large diversity of molecularly and functionally distinct neurons and glia from a small progenitor pool. While the role of spatial patterning in organising cell fate specification has been extensively studied, temporal patterning, which controls the timing of cell type generation, is equally important. Here we define a global temporal programme in the spinal cord. This governs cell fate choices by regulating chromatin accessibility in neural progenitors. Perturbation of this cis-regulatory programme affects sequential transitions in spinal cord progenitors and the identity of progeny. The temporal programme operates in parallel to spatial patterning, ensuring the timely availability of regulatory elements for spatial determinants to direct cell-type specific gene expression. These findings identify a chronotopic spatiotemporal integration strategy in which a global temporal chromatin programme determines the output of a spatial gene regulatory network resulting in the temporally and spatially ordered allocation of cell type identity.
Project description:The vertebrate neural tube generates a large diversity of molecularly and functionally distinct neurons and glia from a small progenitor pool. While the role of spatial patterning in organising cell fate specification has been extensively studied, temporal patterning, which controls the timing of cell type generation, is equally important. Here we define a global temporal programme in the spinal cord. This governs cell fate choices by regulating chromatin accessibility in neural progenitors. Perturbation of this cis-regulatory programme affects sequential transitions in spinal cord progenitors and the identity of progeny. The temporal programme operates in parallel to spatial patterning, ensuring the timely availability of regulatory elements for spatial determinants to direct cell-type specific gene expression. These findings identify a chronotopic spatiotemporal integration strategy in which a global temporal chromatin programme determines the output of a spatial gene regulatory network resulting in the temporally and spatially ordered allocation of cell type identity.