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Collective cell migration, where cells move as a cohesive unit, is a vital process underlying morphogenesis and cancer metastasis. Thanks to recent advances in imaging and modelling, we are beginning to understand the intricate relationship between a cell and its microenvironment and how this shapes cell polarity, metabolism and modes of migration. The use of biophysical and mathematical models offers a fresh perspective on how cells migrate collectively, either flowing in a fluid-like state or transitioning to more static states. Continuing to unite researchers in biology, physics and mathematics will enable us to decode more complex biological behaviours that underly collective cell migration; only then can we understand how this coordinated movement of cells influences the formation and organisation of tissues and directs the spread of metastatic cancer. In this Perspective, we highlight exciting discoveries, emerging themes and common challenges that have arisen in recent years, and possibleways forward to bridge the gaps in our current understanding of collective cell migration. [ABSTRACT FROM AUTHOR]

The vertebrate brain and spinal cord arise from a common precursor, the neural tube, which forms very early during embryonic development. To shape the forming neural tube, changes in cellular architecture must be tightly co-ordinated in space and time. Live imaging of different animal models has provided valuable insights into the cellular dynamics driving neural tube formation. The most well-characterised morphogenetic processes underlying this transformation are convergent extension and apical constriction, which elongate and bend the neural plate. Recent work has focused on understanding how these two processes are spatiotemporally integrated from the tissue- to the subcellular scale. Various mechanisms of neural tube closure have also been visualised, yielding a growing understanding of how cellular movements, junctional remodelling and interactions with the extracellular matrix promote fusion and zippering of the neural tube. Additionally, live imaging has also now revealed a mechanical role for apoptosis in neural plate bending, and how cell intercalation forms the lumen of the secondary neural tube. Here, we highlight the latest research on the cellular dynamics underlying neural tube formation and provide some perspectives for the future. [ABSTRACT FROM AUTHOR]

Probing dynamic processes occurring within the cell nucleus at the quantitative level has long been a challenge in mammalian biology. Advances in bioimaging techniques over the past decade have enabled us to directly visualize nuclear processes in situ with unprecedented spatial and temporal resolution and single-molecule sensitivity. Here, using transcription as our primary focus, we survey recent imaging studies that specifically emphasize the quantitative understanding of nuclear dynamics in both time and space. These analyses not only inform on previously hidden physical parameters and mechanistic details, but also reveal a hierarchical organizational landscape for coordinating a wide range of transcriptional processes shared by mammalian systems of varying complexity, from single cells to whole embryos. [ABSTRACT FROM AUTHOR]

Compaction of the preimplantation embryo is the earliest morphogenetic process essential for mammalian development, yet it remains unclear how round cells elongate to form a compacted embryo. Here, using live mouse embryo imaging, we demonstrate that cells extend long E-cadherin-dependent filopodia on to neighbouring cells, which control the cell shape changes necessary for compaction. We found that filopodia extension is tightly coordinated with cell elongation, whereas retraction occurs before cells become round again before dividing. Laser-based ablations revealed that filopodia are required to maintain elongated cell shapes. Moreover, molecular disruption of the filopodia components E-cadherin, α- and β-catenin, F-actin and myosin-X prevents cells from elongating and compacting the embryo. Finally, we show that early filopodia formation triggered by overexpressing myosin-X is sufficient to induce premature compaction. Our findings establish a role for filopodia during preimplantation embryonic development and provide an in vivo context to investigate the biological functions of filopodia in mammals. [ABSTRACT FROM AUTHOR]

Here, we report the generation of a transgenic Lifeact-EGFP quail line for the investigation of actin organization and dynamics during morphogenesis in vivo. This transgenic avian line allows for the high-resolution visualization of actin structures within the living embryo, from the subcellular filaments that guide cell shape to the supracellular assemblies that coordinate movements across tissues. The unique suitability of avian embryos to live imaging facilitates the investigation of previously intractable processes during embryogenesis. Using high-resolution live imaging approaches, we present the dynamic behaviors and morphologies of cellular protrusions in different tissue contexts. Furthermore, through the integration of live imaging with computational segmentation, we visualize cells undergoing apical constriction and large-scale actin structures such as multicellular rosettes within the neuroepithelium. These findings not only enhance our understanding of tissue morphogenesis but also demonstrate the utility of the Lifeact-EGFP transgenic quail as a new model system for live in vivo investigations of the actin cytoskeleton. [ABSTRACT FROM AUTHOR]

The neural crest generates numerous cell types, but conflicting results leave developmental origins unresolved. Here using somatic mosaic variants as cellular barcodes, we infer embryonic clonal dynamics of trunk neural crest, focusing on the sensory and sympathetic ganglia. From three independent adult neurotypical human donors, we identified 1,278 mosaic variants using deep whole-genome sequencing, then profiled allelic fractions in 187 anatomically dissected ganglia. We found a massive rostrocaudal spread of progenitor clones specific to sensory or sympathetic ganglia, which unlike in the brain, showed robust bilateral distributions. Computational modeling suggested neural crest progenitor fate specification preceded delamination from neural tube. Single-cell multiomic analysis suggested both neurons and glia contributed to the rostrocaudal clonal organization. CRISPR barcoding in mice and live imaging in quail embryos confirmed these clonal dynamics across multiple somite levels. Our findings reveal an evolutionarily conserved clonal spread of cells populating peripheral neural ganglia.

Cells migrating through complex three-dimensional environments experience considerable physical challenges, including tensile stress and compression. To move, cells need to resist these forces while also squeezing the large nucleus through confined spaces. This requires highly coordinated cortical contractility. Microtubules can both resist compressive forces and sequester key actomyosin regulators to ensure appropriate activation of contractile forces. Yet, how these two roles are integrated to achieve nuclear transmigration in three dimensions is largely unknown. Here, we demonstrate that compression triggers reinforcement of a dedicated microtubule structure at the rear of the nucleus by the mechanoresponsive recruitment of cytoplasmic linker-associated proteins, which dynamically strengthens and repairs the lattice. These reinforced microtubules form the mechanostat: an adaptive feedback mechanism that allows the cell to both withstand compressive force and spatiotemporally organize contractility signalling pathways. The microtubule mechanostat facilitates nuclear positioning and coordinates force production to enable the cell to pass through constrictions. Disruption of the mechanostat imbalances cortical contractility, stalling migration and ultimately resulting in catastrophic cell rupture. Our findings reveal a role for microtubules as cellular sensors that detect and respond to compressive forces, enabling movement and ensuring survival in mechanically demanding environments., (© 2024. The Author(s), under exclusive licence to Springer Nature Limited.)

Our understanding of how the first mammalian cell lineages arise has been shaped largely by studies of the preimplantation mouse embryo. Painstaking work over many decades has begun to reveal how a single totipotent cell is transformed into a multilayered structure representing the foundations of the body plan. Here, we review how the first lineage decision is initiated by epigenetic regulation but consolidated by the integration of morphological features and transcription factor activity. The establishment of pluripotent and multipotent stem cell lines has enabled deeper analysis of molecular and epigenetic regulation of cell fate decisions. The capability to assemble these stem cells into artificial embryos is an exciting new avenue of research that offers a long-awaited window into cell fate specification in the human embryo. Together, these approaches are poised to profoundly increase our understanding of how the first lineage decisions are made during mammalian embryonic development., (Copyright © 2020 Cold Spring Harbor Laboratory Press; all rights reserved.)

Probing transcription factor (TF)-DNA interactions remains challenging in complex in vivo systems such as mammalian embryos, especially when TF copy numbers and fluorescence background are high. To address this difficulty, fluorescence correlation spectroscopy (FCS) can be combined with the use of photoactivatable fluorescent proteins to achieve selective photoactivation of a subset of tagged TF molecules. This approach, termed paFCS, enables FCS measurements within single cell nuclei inside live embryos, and obtains autocorrelation data of a quality previously only attainable in simpler in vitro cell culture systems. Here, we present a protocol demonstrating the applicability of paFCS in developing mouse embryos by outlining its implementation on a commercial laser-scanning microscope. We also provide procedures for optimizing the photoactivation and acquisition parameters and determining key parameters describing TF-DNA binding. The entire procedure can be performed within ∼2 d (excluding embryo culture time), although the acquisition of each paFCS data set takes only ∼10 min. This protocol can be used to noninvasively reveal cell-to-cell variation in TF dynamics, as well as critical, fate-predicting changes over the course of early embryonic development.

We introduce a molecular toolbox for manipulation of neuronal gene expression in vivo. The toolbox includes promoters, ion channels, optogenetic tools, fluorescent proteins, and intronic artificial microRNAs. The components are easily assembled into adeno-associated virus (AAV) or lentivirus vectors using recombination cloning. We demonstrate assembly of toolbox components into lentivirus and AAV vectors and use these vectors for in vivo expression of inwardly rectifying potassium channels (Kir2.1, Kir3.1, and Kir3.2) and an artificial microRNA targeted against the ion channel HCN1 (HCN1 miRNA). We show that AAV assembled to express HCN1 miRNA produces efficacious and specific in vivo knockdown of HCN1 channels. Comparison of in vivo viral transduction using HCN1 miRNA with mice containing a germ line deletion of HCN1 reveals similar physiological phenotypes in cerebellar Purkinje cells. The easy assembly and re-usability of the toolbox components, together with the ability to up- or down-regulate neuronal gene expression in vivo, may be useful for applications in many areas of neuroscience.

Effective treatment of neurodegenerative disease is one of the major challenges facing biomedical research. These disorders, which include Alzheimer's, Huntington's and Parkinson's diseases - as well as the rarer prion diseases - constitute an ever-increasing burden in the developed world, socially, medically and economically. The key barrier to effective therapy is that they present clinically when neuronal loss is advanced, and irreversible. Current treatments are almost all directed at modifying symptoms; few address underlying pathogenic mechanisms and are inevitably delivered too late to rescue dying neurons. In the field of prion diseases, however, insights into the molecular basis and the temporal evolution of prion neurotoxicity are increasing. Recent work in mice leads to new hope for the treatment of these disorders, and potentially for rescuing neurodegeneration more broadly. Using lentivirally mediated RNA interference (RNAi) against native prion protein (PrP), White et al report the first intervention resulting in neuronal rescue, prevention of symptoms and increased survival in mice with established prion disease. Central to the effectiveness of this strategy are both the target and the timing of the intervention: the treatment prevents the formation of the neurotoxic prion agent at a point when diseased neurons can still be saved from death. This review introduces the basic concepts of prion pathogenesis, emerging insights into mechanisms of prion neurotoxicity and the rationale for targeting endogenous prion protein (PrP) in prion therapeutics. It describes the discovery of a window of reversibility of early neuronal damage in prion disease and how together these advances led to the subsequent development of the strategy using RNAi based therapy for these disorders. It discusses the use and relevance of this approach more broadly in neurodegeneration.