Diffusion MR microscopy of cortical development in the mouse embryo

Cortical development in the mouse embryo involves complex changes in the microstructure of the telencephalic wall, which are challenging to examine using three-dimensional (3D) imaging techniques. In this study, high-resolution 3D diffusion magnetic resonance (dMR) microscopy of the embryonic mouse cortex is presented. Using diffusion-weighted gradient- and spin-echo based acquisition, dMR microimaging data were acquired from fixed mouse embryos at 7 developmental stages from embryonic day (E)12.5 to E18.5. The dMR imaging (dMRI) contrasts revealed microscopic structural detail in the mouse telencephalic wall, allowing delineation of transient zones in the developing cortex based on their unique diffusion signatures. With the high-resolution 3D data of the mouse embryo, we were able to visualize the complex microstructure of embryonic cerebral tissue and to resolve its regional and temporal evolution during cortical formation. Furthermore, averaged dMRI contrasts generated via deformable registration revealed distinct spatial and temporal gradients of anisotropy variation across the developing embryonic cortical plate and the ventricular zone. The findings of this study demonstrate the potential of 3D dMRI to resolve the complex microstructure of the embryonic mouse cortex, and will be important for investigations of corticogenesis and its disruption in embryonic mouse models

Mutations in DCC cause isolated agenesis of the corpus callosum with incomplete penetrance

Brain malformations involving the corpus callosum are common in children with developmental disabilities. We identified DCC mutations in four families and five sporadic individuals with isolated agenesis of the corpus callosum (ACC) without intellectual disability. DCC mutations result in variable dominant phenotypes with decreased penetrance, including mirror movements and ACC associated with a favorable developmental prognosis. Possible phenotypic modifiers include the type and location of mutation and the sex of the individual

Evolution and development of interhemispheric connections in the vertebrate forebrain

Axonal connections between the left and right sides of the brain are crucial for bilateral integration of lateralized sensory, motor, and associative functions. Throughout vertebrate species, forebrain commissures share a conserved developmental plan, a similar position relative to each other within the brain and similar patterns of connectivity. However, major events in the evolution of the vertebrate brain, such as the expansion of the telencephalon in tetrapods and the origin of the six-layered isocortex in mammals, resulted in the emergence and diversification of new commissural routes. These new interhemispheric connections include the pallial commissure, which appeared in the ancestors of tetrapods and connects the left and right sides of the medial pallium (hippocampus in mammals), and the corpus callosum, which is exclusive to eutherian (placental) mammals and connects both isocortical hemispheres. A comparative analysis of commissural systems in vertebrates reveals that the emergence of new commissural routes may have involved co-option of developmental mechanisms and anatomical substrates of preexistent commissural pathways. One of the embryonic regions of interest for studying these processes is the commissural plate, a portion of the early telencephalic midline that provides molecular specification and a cellular scaffold for the development of commissural axons. Further investigations into these embryonic processes in carefully selected species will provide insights not only into the mechanisms driving commissural evolution, but also regarding more general biological problems such as the role of developmental plasticity in evolutionary change

Investigating early formation of the cerebral cortex by in utero electroporation: Methods and protocols

Cortical development requires a strict balance between neuronal proliferation, differentiation, and cellular migration within restricted developmental stages. The precise spatiotemporal gene manipulation used in developmental studies can be achieved by in vitro or ex vivo experiments or by the generation of transgenic animals. However, these approaches have significant limitations when trying to investigate the origin and molecular regulation of early cortical neurons. In utero electroporation (IUE) is an informative cell labeling technique that provides the ability to label neural progenitor cells and their progeny in vivo with promoter-specific reporter constructs as well as to induce or repress gene expression in a spatially and temporally specific manner. Technical improvements of this method have allowed the targeting of multiple neural cell types, as well as the precise transfection of subpopulations of neurons at increasingly earlier embryonic stages. Furthermore, neuronal projection studies and the use of multiple electroporations in the same embryo have made it possible to examine processes occurring at different developmental stages and/or cortical areas and link their anatomy to their function. In this chapter, we present the latest advances of the in utero electroporation technique for the study of early formation of the cerebral cortex, together with a description of the necessary tools

Natural killer cell engineering – a new hope for cancer immunotherapy

Natural killer (NK) cells are an important component of the innate immune system, particularly for metastasis immunosurveillance. They can rapidly recognize and kill transformed cells without the requirement of specific neo-antigen recognition. Their effector functions are modulated by a range of stimulatory and inhibitory surface receptors that regulate their cellular activation, differentiation and homeostasis. However, cancer cells can evade NK cell detection by receptor interaction or secretion of soluble immunosuppressant molecules. Therefore, genetic reprogramming of these immune suppressing or activating receptors of NK cells is a promising strategy to augment NK cell tumoricidal functions. In this review, we highlight the current clinical trials of chimeric antigen receptor (CAR) engineered NK cells with redirected antigen specificity to eliminate hematological cancers and solid tumors. New alternative strategies that are advancing NK cell engineering for cancer treatment are also outlined. Lastly, different NK cell transgenesis approaches are reviewed and compared, and we discuss how these methods can be employed to maximize their anti-tumor effector functions

Astroglial-mediated remodeling of the interhemispheric midline during telencephalic development is exclusive to eutherian mammals

The corpus callosum forms the major interhemispheric connection in the human brain and is unique to eutherian (or placental) mammals. The developmental events associated with the evolutionary emergence of this structure, however, remain poorly understood. A key step in callosal formation is the prior remodeling of the interhemispheric fissure by embryonic astroglial cells, which then subsequently act as a permissive substrate for callosal axons, enabling them to cross the interhemispheric midline. However, whether astroglial-mediated interhemispheric remodeling is unique to eutherian mammals, and thus possibly associated with the phylogenetic origin of the corpus callosum, or instead is a general feature of mammalian brain development, is not yet known. To investigate this, we performed a comparative analysis of interhemispheric remodeling in eutherian and non-eutherian mammals, whose lineages branched off before the evolution of the corpus callosum. Whole brain MRI analyses revealed that the interhemispheric fissure is retained into adulthood in marsupials and monotremes, in contrast to eutherians (mice), in which the fissure is significantly remodeled throughout development. Histological analyses further demonstrated that, while midline astroglia are present in developing marsupials, these cells do not intercalate with one another through the intervening interhemispheric fissure, as they do in developing mice. Thus, developing marsupials do not undergo astroglial-mediated interhemispheric remodeling. As remodeling of the interhemispheric fissure is essential for the subsequent formation of the corpus callosum in eutherians, our data highlight the role of astroglial-mediated interhemispheric remodeling in the evolutionary origin of the corpus callosum

Formation of functional areas in the cerebral cortex is disrupted in a mouse model of autism spectrum disorder

Background: Autism spectrum disorders (ASD) are a group of poorly understood behavioural disorders, which have increased in prevalence in the past two decades. Animal models offer the opportunity to understand the biological basis of these disorders. Studies comparing different mouse strains have identified the inbred BTBR T + tf/J (BTBR) strain as a mouse model of ASD based on its anti-social and repetitive behaviours. Adult BTBR mice have complete agenesis of the corpus callosum, reduced cortical thickness and changes in early neurogenesis. However, little is known about the development or ultimate organisation of cortical areas devoted to specific sensory and motor functions in these mice that may also contribute to their behavioural phenotype

Astroglial-Mediated Remodeling of the Interhemispheric Midline Is Required for the Formation of the Corpus Callosum.

The corpus callosum is the major axon tract that connects and integrates neural activity between the two cerebral hemispheres. Although ∼1:4,000 children are born with developmental absence of the corpus callosum, the primary etiology of this condition remains unknown. Here, we demonstrate that midline crossing of callosal axons is dependent upon the prior remodeling and degradation of the intervening interhemispheric fissure. This remodeling event is initiated by astroglia on either side of the interhemispheric fissure, which intercalate with one another and degrade the intervening leptomeninges. Callosal axons then preferentially extend over these specialized astroglial cells to cross the midline. A key regulatory step in interhemispheric remodeling is the differentiation of these astroglia from radial glia, which is initiated by Fgf8 signaling to downstream Nfi transcription factors. Crucially, our findings from human neuroimaging studies reveal that developmental defects in interhemispheric remodeling are likely to be a primary etiology underlying human callosal agenesis

Astroglial-Mediated Remodeling of the Interhemispheric Midline Is Required for the Formation of the Corpus Callosum

The corpus callosum is the major axon tract that connects and integrates neural activity between the two cerebral hemispheres. Although ∼1:4,000 children are born with developmental absence of the corpus callosum, the primary etiology of this condition remains unknown. Here, we demonstrate that midline crossing of callosal axons is dependent upon the prior remodeling and degradation of the intervening interhemispheric fissure. This remodeling event is initiated by astroglia on either side of the interhemispheric fissure, which intercalate with one another and degrade the intervening leptomeninges. Callosal axons then preferentially extend over these specialized astroglial cells to cross the midline. A key regulatory step in interhemispheric remodeling is the differentiation of these astroglia from radial glia, which is initiated by Fgf8 signaling to downstream Nfi transcription factors. Crucially, our findings from human neuroimaging studies reveal that developmental defects in interhemispheric remodeling are likely to be a primary etiology underlying human callosal agenesis