Imaging mouse embryonic cardiovascular development

The LPS-inactivating enzyme acyloxyacyl hydrolase protects the brain from experimental stroke

Blood-brain-barrier (BBB) disruption is a pathological hallmark of ischemic stroke, and inflammation occurring at the BBB contributes to the pathogenesis of ischemic brain injury. Lipopolysaccharide (LPS), a cell wall component of Gram-negative bacteria, is elevated in patients with acute stroke. The activity of LPS is controlled by acyloxyacyl hydrolase (AOAH), a host enzyme that deacylates LPS to inactivated forms. However, whether AOAH influences the pathogenesis of ischemic stroke remain elusive. We performed in vivo experiments to explore the role and mechanism of AOAH on neutrophil extravasation, BBB disruption, and brain infarction. We found that AOAH was upregulated in neutrophils in peri-infarct areas from mice with transient focal cerebral ischemia. AOAH deficiency increased neutrophil extravasation into the brain parenchyma and proinflammatory cytokine production, broke down the BBB and worsened stroke outcomes in mice. These effects require Toll-like receptor 4 (TLR4) because absence of TLR4 or pharmacologic inhibition of TLR4 signaling prevented the exacerbated inflammation and BBB damage in Aoah-/- mice after ischemic stroke. Importantly, neutrophil depletion or inhibition of neutrophil trafficking by blocking LFA-1 integrin dramatically reduced stroke-induced BBB breakdown in Aoah-/- mice. Furthermore, virus-mediated overexpression of AOAH induced a substantial decrease in neutrophil recruitment that was accompanied by reducing BBB damage and stroke volumes. Our findings show the importance of AOAH in regulating neutrophil-dependent BBB breakdown and cerebral infarction. Consequently, strategies that modulate AOAH may be a new therapeutic approach for treatment of ischemic stroke.

Analysis of Mid- to Late-Gestation Phenotypes in Mice

Mid- to late gestation is characterized by tissue differentiation, maturation, organogenesis, and growth, and many mutant genes have detrimental effects during this phase of development. The outcome may be lethal before birth or may be compatible with life but result in birth defects. Some of the common causes of death during late gestation are hematopoietic defects, cardiovascular problems, and placental insufficiency. Many morphological abnormalities, lethal or not, can be investigated with gross and histological analyses or by visualization of the developing skeleton. Molecular characterization of mutant phenotypes, guided by the expression pattern of the mutant gene, can reveal disruptions in gene expression patterns of known developmental genes. Cell proliferation and cell death assays will reveal disruptions in cellular dynamics. Various modalities of 3D imaging of intact embryos can provide volumetric information about mutant phenotypes.

Mouse embryo phenotyping with optical coherence tomography

With the explosion of gene editing tools in recent years, there has been a much greater demand for mouse embryo phenotyping, and traditional methods such as histology and histochemistry experienced a methodological renaissance as they became the principal tools for phenotyping. However, it is important to explore alternative phenotyping options to maximize time and resources and implement volumetric structural analysis for enhanced investigation of phenotypes. Cardiovascular phenotyping, in particular, is important to perform in vivo due to the dramatic structural and functional changes that occur in heart development over relatively short periods of time. Optical coherence tomography (OCT) is one of the most exciting advanced imaging techniques emerging within the field of developmental biology, and this review provides a summary of how it is currently being implemented in mouse embryo investigations and phenotyping. This review aims to provide an understanding of the approaches used in optical coherence tomography and how they can be applied in embryology and developmental biology, with the overall aim of bridging the gap between biology and technology.

Vertebrate embryos as tools for anti-angiogenic drug screening and function

The development of new angiogenic inhibitors highlights a need for robust screening assays that adequately capture the complexity of vessel formation, and allow for the quantitative evaluation of the teratogenicity of new anti-angiogenic agents. This review discusses the use of screening assays in vertebrate embryos, specifically focusing upon chicken and zebrafish embryos, for the detection of anti-angiogenic agents.

Four-dimensional live imaging of hemodynamics in mammalian embryonic heart with Doppler optical coherence tomography

Hemodynamic analysis of the mouse embryonic heart is essential for understanding the functional aspects of early cardiogenesis and advancing the research in congenital heart defects. However, high-resolution imaging of cardiac hemodynamics in mammalian models remains challenging, primarily due to the dynamic nature and deep location of the embryonic heart. Here we report four-dimensional micro-scale imaging of blood flow in the early mouse embryonic heart, enabling time-resolved measurement and analysis of flow velocity throughout the heart tube. Our method uses Doppler optical coherence tomography in live mouse embryo culture, and employs a post-processing synchronization approach to reconstruct three-dimensional data over time at a 100 Hz volume rate. Experiments were performed on live mouse embryos at embryonic day 9.0. Our results show blood flow dynamics inside the beating heart, with the capability for quantitative flow velocity assessment in the primitive atrium, atrioventricular and bulboventricular regions, and bulbus cordis. Combined cardiodynamic and hemodynamic analysis indicates this functional imaging method can be utilized to further investigate the mechanical relationship between blood flow dynamics and cardiac wall movement, bringing new possibilities to study biomechanics in early mammalian cardiogenesis. Four-dimensional live hemodynamic imaging of the mouse embryonic heart at embryonic day 9.0 using Doppler optical coherence tomography, showing directional blood flows in the sinus venosus, primitive atrium, atrioventricular region and vitelline vein.

Cardiovascular Imaging in Mice

The mouse is the mammalian model of choice for investigating cardiovascular biology, given our ability to manipulate it by genetic, pharmacologic, mechanical, and environmental means. Imaging is an important approach to phenotyping both function and structure of cardiac and vascular components. This review details commonly used imaging approaches, with a focus on echocardiography and magnetic resonance imaging and brief overviews of other imaging modalities. We also briefly outline emerging imaging approaches but caution that reliability and validity data may be lacking.

Optical coherence tomography guided microinjections in live mouse embryos: high-resolution targeted manipulation for mouse embryonic research

The ability to conduct highly localized delivery of contrast agents, viral vectors, therapeutic or pharmacological agents, and signaling molecules or dyes to live mammalian embryos is greatly desired to enable a variety of studies in the field of developmental biology, such as investigating the molecular regulation of cardiovascular morphogenesis. To meet such a demand, we introduce, for the first time, the concept of employing optical coherence tomography (OCT)-guide microinjections in live mouse embryos, which provides precisely targeted manipulation with spatial resolution at the micrometer scale. The feasibility demonstration is performed with experimental studies on cultured live mouse embryos at E8.5 and E9.5. Additionally, we investigate the OCT-guided microinjection of gold–silica nanoshells to the yolk sac vasculature of live cultured mouse embryos at the stage when the heart just starts to beat, as a potential approach for dynamic assessment of cardiovascular form and function before the onset of blood cell circulation. Also, the capability of OCT to quantitatively monitor and measure injection volume is presented. Our results indicate that OCT-guided microinjection could be a useful tool for mouse embryonic research.

Optical coherence tomography guided microinjections in live mouse embryos: high-resolution targeted manipulation for mouse embryonic research

The ability to conduct highly localized delivery of contrast agents, viral vectors, therapeutic or pharmacological agents, and signaling molecules or dyes to live mammalian embryos is greatly desired to enable a variety of studies in the field of developmental biology, such as investigating the molecular regulation of cardiovascular morphogenesis. To meet such a demand, we introduce, for the first time, the concept of employing optical coherence tomography (OCT)-guide microinjections in live mouse embryos, which provides precisely targeted manipulation with spatial resolution at the micrometer scale. The feasibility demonstration is performed with experimental studies on cultured live mouse embryos at E8.5 and E9.5. Additionally, we investigate the OCT-guided microinjection of gold–silica nanoshells to the yolk sac vasculature of live cultured mouse embryos at the stage when the heart just starts to beat, as a potential approach for dynamic assessment of cardiovascular form and function before the onset of blood cell circulation. Also, the capability of OCT to quantitatively monitor and measure injection volume is presented. Our results indicate that OCT-guided microinjection could be a useful tool for mouse embryonic research.

Live confocal microscopy of the developing mouse embryonic yolk sac vasculature

Understanding of mouse embryonic development is an invaluable resource for our interpretation of human embryology. Traditional imaging approaches such as immunofluorescence and in situ hybridization are excellent methods for characterizing gene expression and morphology but lack the ability to reveal the dynamic morphogenesis. Furthermore, mammalian embryonic development occurs in utero, which bars our ability to visualize development in dynamics. With the use of live confocal microscopy, vital fluorescent reporters, and embryo culture methods, we can observe cell migration, proliferation, differentiation, and cell-cell interaction in live developing wild-type and mutant embryos. In this chapter, we will discuss how confocal microscopy can be used to visualize the developing vasculature and hemodynamics of the mouse embryonic yolk sac. We will describe fluorescent protein reporter mouse models allowing to image yolk sac vessel development and blood flow, live embryo culture approaches, and confocal time-lapse imaging methods to study vascular morphology and hemodynamics in early embryos.

Quantitative approaches to uncover physical mechanisms of tissue morphogenesis

Morphogenesis, the creation of tissue and organ architecture, is a series of complex and dynamic processes driven by genetic programs, microenvironmental cues, and intercellular interactions. Elucidating the physical mechanisms that generate tissue form is key to understanding development, disease, and the strategies needed for regenerative therapies. Advancements in imaging technologies, genetic recombination techniques, laser ablation, and microfabricated tissue models have enabled quantitative descriptions of the cellular motions and tissue deformations and stresses with unprecedented temporal and spatial resolution. Using these data synergistically with increasingly more sophisticated physical, mathematical, and computational models will unveil the physical mechanisms that drive morphogenesis.

Live imaging of mouse embryos

The development of the mouse embryo is a dynamic process that requires the spatial and temporal coordination of multiple cell types as they migrate, proliferate, undergo apoptosis, and differentiate to form complex structures. However, the confined nature of embryos as they develop in utero limits our ability to observe these morphogenetic events in vivo. Previous work has used fixed samples and histological methods such as immunofluorescence or in situ hybridization to address expression or localization of a gene of interest within a developmental time line. However, such methods do not allow us to follow the complex, dynamic movements of individual cells as the embryo develops. Genetic manipulation methods now allow us to label virtually any cell type or protein of interest fluorescently, providing powerful insights into morphogenetic events at cellular and subcellular resolutions. The development of ex vivo embryo culture methods combined with high-resolution imaging now provides a strong platform for observing morphogenetic events as they occur within the developing embryo. In this article, we discuss the advantages of live embryo imaging for observing dynamic morphogenetic events in vivo.