Biology subjects

Copp, A.

Publications and source records attributed to Copp, A..

9 recordsLinked to original sources

bioRxiv2025

Absence of posterior commissure and sub-commissural organ precedes encephalocele development in a new mouse model

Encephalocele is a congenital defect involving herniation of the meninges, with or without brain tissue, outside the skull. Although traditionally considered a neural tube defect (NTD) alongside anencephaly and open spina bifida (myelomeningocele), encephalocele typically shows well-formed brain tissue, and is likely to represent a later-arising, post-neurulation developmental anomaly, with a different pathogenic mechanism from the open NTDs. A detailed understanding of encephalocele pathogenesis requires experimental studies and, recently, we developed a new mouse model in which the genes encoding FGF3, 4 and 15 are over-expressed in the embryonic day (E) 9.5 brain. Encephalocele subsequently develops as a broad forebrain-midbrain swelling, visible from E11.5, that resolves by birth into a focal brain herniation resembling human parieto-occipital encephalocele. A structural analysis of the brain in mutant embryos reveals absence of the posterior commissure and sub-commissural organ, and at later stages the pineal gland. These structures normally develop just rostral to the forebrain-midbrain boundary, and Pax6 immuno-histochemistry demonstrates that this boundary remains intact in the mutant embryos. Histological analysis reveals a more general change in tissue composition of the neural tube roof in the forebrain-midbrain region, with diminished thickness of the neuroepithelium and increased thickness of the overlying layer, including the non-neural ectoderm (future epidermis). We conclude that the posterior commissure and sub-commissural organ, previously implicated in hydrocephalus, may also be fundamental for development of the earlier-arising brain malformation, encephalocele.

developmental biology↗

bioRxiv2025

Chiari II brain malformation is secondary to open spina bifida

Chiari II brain malformation affects 90% of children with open spina bifida. Hindbrain herniation leads to hydrocephalus, together with higher brain anomalies including cerebral cortical defects implicated in learning disability, which affects 20-25% of children with spina bifida. The causal link between Chiari II and spina bifida has long been debated, and we aimed to determine whether Chiari II arises secondary to spina bifida, rather than as a separate effect of shared genetic or non-genetic factor(s). Pax3 gene function was conditionally deleted by Cdx2cre specifically in the lower body of mice, leaving the head genetically intact. Open spina bifida is seen in all Cdx2cre/+; Pax3fl/flfetuses, together with many features of Chiari II in the wild-type brain and skull. These include: hindbrain herniation, callosal and hippocampal hypogenesis, cortical thinning with neuronal heterotopia, a thickened ventricular zone, and posterior skull defects. Hence, the brain and skull defects of Chiari II arise secondary to open spina bifida, with likely disturbance of neurogenesis and neuronal migration early in gestation. The Cdx2cre/+; Pax3fl/fl mouse provides a model for improved understanding of Chiari II pathogenesis.

developmental biology↗

bioRxiv2024

Prenatal glyphosate exposure disrupts the gut-brain axis across several generations in mice.

Glyphosate, a widely used herbicide in North America, has become prevalent in the food supply, raising concerns about potential health impacts. In this exploratory study, male and female F0 mice were exposed to glyphosate through drinking water during mating and gestation. We investigated whether prenatal exposure at dietary-relevant levels (0.01 mg/kg/day, Average American Diet, [AAD]) or the U.S. EPAs acceptable daily intake (1.75 mg/kg/day, [EPA upper limit]) altered gut, metabolic, and behavioral outcomes across two generations in mice with or without genetic susceptibility to colitis (Muc2+/- and Muc2-/-, respectively). Healthy (Muc2+/-) offspring of glyphosate-exposed mice exhibited colonic goblet cell depletion, reduced mucin-2 expression, and pro-inflammatory cytokine profiles in both F1 and F2 generations. These healthy (Muc2+/-) offspring also developed metabolic dysfunction, including impaired glucose tolerance, insulin resistance, and reduced GLP-1 in serum. Behavioral deficits were also observed in healthy (Muc+/-) mice including reduced locomotion and working memory, and these changes were associated with altered microbiome composition and gut-brain mediators. These findings suggest that prenatal glyphosate exposure, even below regulatory thresholds, may disrupt multiple physiological systems across generations, highlighting the need for further research and regulatory consideration.

pharmacology and toxicology↗

bioRxiv2023

AAV-mediated gene therapy in a GLDC-deficient mouse model of Non-Ketotic Hyperglycinemia

Non-Ketotic Hyperglycinemia (NKH) is a rare inborn error of metabolism caused by impaired function of the glycine cleavage system (GCS) and characterised by accumulation of glycine in body fluids and tissues. NKH is an autosomal recessive condition and the majority of affected individuals carry mutations in GLDC (glycine decarboxylase). Current treatments for NKH are not effective or curative. As a monogenic condition with known genetic causation, NKH is potentially amenable to gene therapy. An AAV9-based expression vector was designed to target sites of GCS activity. Using an ubiquitous promoter to drive expression of a GFP reporter, transduction of liver and brain was confirmed following intra-venous and/or intra-cerebroventricular administration to neonatal mice. Using the same capsid and promoter with transgenes to express mouse or human GLDC, vectors were then tested in a GLDC-deficient mice that provide a model of NKH. GLDC-deficient mice exhibited elevated plasma glycine concentration and accumulation of glycine in liver and brain tissues as previously observed. Moreover, the folate profile indicated suppression of folate one carbon metabolism (FOCM) in brain tissue, as found at embryonic stages, and reduced abundance of FOCM metabolites including betaine and choline. Neonatal administration of vector achieved reinstatement of GLDC mRNA and protein expression in GLDC-deficient mice. Treated GLDC-deficient mice showed significant lowering of plasma glycine, confirming functionality of vector expressed protein. AAV9-GLDC treatment also led to lowering of brain tissue glycine, and normalisation of the folate profile indicating restoration of glycine-derived one-carbon supply. These findings support the hypothesis that AAV-mediated gene therapy may offer potential in treatment of NKH.

molecular biology↗

bioRxiv2023

CFL1-dependent dynamicity of surface ectoderm filopodia-like protrusions increases neurulation zippering speed in mice

Epithelial fusion is critical for formation of many embryonic tissues. The developing mammalian spinal cord fuses by zippering, through cell behaviours dependent on F-actin turnover. We propose a caudal-to-rostral sequence of surface ectoderm cell behaviours which drive zippering progression in mice, and test the requirement for the F-actin severing protein CFL1 in this process. Key zipper-advancing behaviours are i. constriction of supracellular actomyosin cables; ii. extension of short-lived (<2 min) filopodial or more persistent lamellipodial protrusions, which we live-image establishing pioneering contacts across the midline; remodelling of iii. cell-cell and iv. cell-ECM adhesions; v. zipper advancement through constriction of leading-edge cell borders. In wildtype embryos CFL1 is enriched at the leading edge of surface ectoderm cells adjacent to the zippering point and localised within some protrusions. Conditional Cfl1 deletion in the surface ectoderm produces more prominent F-actin stress fibres, makes filopodial protrusions excessively stable, diminishes their exploratory movements which may establish nascent contacts, and impairs junctional constriction of cells at the point of fusion. Zippering speed is reduced [~]30% in conditional Cfl1-deleted embryos and [~]30% develop spina bifida. We therefore propose that impaired filopodial dynamicity limits the sequence of cell behaviours driving spinal zippering in mice, predisposing to spina bifida.

developmental biology↗

bioRxiv2022

Synchronisation of apical constriction and cell cycle progression is a conserved behaviour of pseudostratified neuroepithelia informed by their tissue geometry

Neuroepithelial cells balance tissue growth requirement with the morphogenetic imperative of closing the neural tube. They apically constrict to generate mechanical forces which elevate the neural folds, but are thought to apically dilate during mitosis. However, we previously reported that mitotic neuroepithelial cells in the mouse posterior neuropore have smaller apical surfaces than non-mitotic cells. Here, we document progressive apical enrichment of non-muscle myosin-II in mitotic, but not non-mitotic, neuroepithelial cells with smaller apical areas. Live-imaging of the chick posterior neuropore confirms apical constriction synchronised with mitosis, reaching maximal constriction by anaphase, before division and re-dilation. Mitotic apical constriction amplitude is significantly greater than interphase constrictions. To investigate conservation in humans, we characterised early stages of iPSC differentiation through dual SMAD-inhibition to robustly produce pseudostratified neuroepithelia with apically enriched actomyosin. These cultured neuroepithelial cells achieve an equivalent apical area to those in mouse embryos. iPSC-derived neuroepithelial cells have large apical areas in G2 which constrict in M phase and retain this constriction in G1/S. Given that this differentiation method produces anterior neural identities, we studied the anterior neuroepithelium of the elevating mouse mid-brain neural tube. Instead of constricting, mid-brain mitotic neuroepithelial cells have larger apical areas than interphase cells. Tissue geometry differs between the apically convex early midbrain and flat posterior neuropore. Culturing human neuroepithelia on equivalently convex surfaces prevents mitotic apical constriction. Thus, neuroepithelial cells undergo high-amplitude apical constriction synchronised with cell cycle progression but the timing of their constriction if influenced by tissue geometry.

cell biology↗

bioRxiv2020

Hindbrain neuropore tissue geometry determines asymmetric cell-mediated closure dynamics

Gap closure is a common morphogenetic process. In mammals, failure to close the embryonic hindbrain neuropore (HNP) gap causes fatal anencephaly. We observed that surface ectoderm cells surrounding the mouse HNP assemble high-tension actomyosin purse-strings at their leading edge and establish the initial contacts across the embryonic midline. The HNP gap closes asymmetrically, faster from its rostral than caudal extreme, while maintaining an elongated aspect ratio. Cell-based physical modelling identifies two closure mechanisms sufficient to describe tissue-level HNP closure dynamics; purse-string contraction and directional cell crawling. Combining both closure mechanisms hastens gap closure and produces a constant rate of gap shortening. Purse-string contraction reduces, whereas crawling increases gap aspect ratio, and their combination maintains it. Closure rate asymmetry can be explained by embryo tissue geometry, namely a narrower rostral gap apex. At the cellular level, our model predicts highly directional cell migration with a constant rate of cells leaving the HNP rim. These behaviours are reproducibly live-imaged in mouse embryos. Thus, mammalian embryos coordinate cellular and tissue-level mechanics to achieve this critical gap closure event.

biophysics↗

bioRxiv2019

Novel mouse model of encephalocele: post-neurulation origin and relationship to open neural tube defects

Encephalocele is a clinically important birth defect that can lead to severe disability in childhood and beyond. The embryonic pathogenesis of encephalocele is poorly understood and, while usually classified as a neural tube defect, there is conflicting evidence on whether encephalocele results from defective neural tube closure, or is a post-neurulation defect. It is also unclear whether encephalocele can result from the same causative factors as anencephaly and open spina bifida, or whether it is aetiologically distinct. This lack of information results largely from the scarce availability of animal models of encephalocele, particularly ones that resemble the commonest, non-syndromic human defects. Here we report a novel mouse model of occipito-parietal encephalocele, in which the small GTPase Rac1 is conditionally ablated in the (non-neural) surface ectoderm. Most mutant fetuses have open spina bifida, and some also exhibit exencephaly/anencephaly. However, a large proportion of mutant fetuses exhibit encephalocele affecting the occipito-parietal region. The encephalocele phenotype does not result from a defect in neural tube closure, but rather from a later disruption of the surface ectoderm covering the already closed neural tube, allowing the brain to herniate. The neuroepithelium itself shows no down-regulation of Rac1 and appears morphologically normal until late gestation. A large skull defect develops overlying the region of brain herniation. Our work provides a new genetic model of occipito-parietal encephalocele, particularly resembling non-syndromic human cases. While encephalocele has a different, later-arising pathogenesis than open neural tube defects, both can share the same genetic causation.\n\nSUMMARY STATEMENTEncephalocele - a severe brain defect - arises after neural tube closure, but can share a common genetic cause with anencephaly, a defect of neural tube closure.

developmental biology↗

bioRxiv2018

Genetic approaches in mice demonstrate that neuro-mesodermal progenitors express T/Brachyury but not Sox2

Neural tube and somites have long been thought to derive from separate germ layers: the ectoderm and mesoderm. This concept was challenged by the discovery of neuro-mesodermal progenitors, a bi-potent cell population that gives rise to both spinal neural tube and somites. In line with their proposed potency, these cells are considered to co-express the neural marker Sox2 and the mesodermal marker T/Brachyury. We performed genetic lineage tracing in mouse embryos and confirmed that T-expressing cells give rise to both neural tube and mesoderm. Surprisingly, however, Sox2-expressing cell derivatives colonise only the neural tube after embryonic day 8.5. Deletion of Sox2 in T-expressing cells was compatible with an otherwise normal neural tube and paraxial mesoderm. Moreover, Sox2 expression is absent from the chordoneural hinge, where neuro-mesodermal progenitors are located. Our findings demonstrate that neuro-mesodermal progenitors express T but not Sox2, suggesting the need for re-evaluation of the neuro-mesodermal progenitor hypothesis.

developmental biology↗