Neural tube closure: cellular, molecular and biomechanical mechanisms

Canonical Wnt pathway modulation is required to correctly execute multiple independent cellular dynamic programs during cranial neural tube closure

Defects in cranial neural tube closure are among the most common and deleterious human structural birth defects. Correct cranial closure requires the coordination of multiple cell dynamic programs including cell proliferation and cell shape change. Mutations that impact Wnt signaling, including loss of the pathway co-receptor LRP6, lead to defects in cranial neural tube closure, but the cellular dynamics under control of the Wnt pathway during this critical morphogenetic process remain unclear. Here, we use mice mutant for LRP6 to examine the consequences of conditional and global reduction in Wnt signaling and mutants with conditional inactivation of APC to examine the consequences of pathway hyperactivation. Strikingly, we find that regulated Wnt signaling is required for two independent events during cranial neural tube closure. First, global reduction of Wnt leads to a surprising hyperplasia of the cranial neural folds driven by excessive cell proliferation at early pre-elevation stages, with the increased tissue volume creating a mechanical blockade to efficient closure despite normal apical constriction and cell polarization at later stages. Conversely, conditional hyperactivation of the pathway at later elevation stages prevents correct actin organization, blocking apical constriction and neural fold elevation without impacting tissue scaling. Together these data reveal that Wnt signaling levels must be modulated to restrict proliferation at early stages and promote apical constriction at later elevation stages to drive efficient closure of the cranial neural tube.

Human organoids potentially boost research into environmental factors of neural tube defects

Human neural tube closure occurs during the third to fourth gestational week, often before people realize they are pregnant. Ethical issues limit collection of embryonic human neural tube tissue. However, the development of human neural tube organoids is beginning to empower the study of neural tube closure and neural tube defects. A previous review summarized human neural tube organoid models which are grown on top of or embedded in Matrigel or Hydrogel. Recent advances in human neural tube organoid models through micropatterned or microfluidic methods recapitulate diverse and complex neural tube features. In this review, our goal is to summarize these human iPSC-derived advanced organoid models. Moreover, these organoid models provide the possibility of testing how environmental factors influence the process of neural tube closure. Focusing on folic acid supplementation which can reduce the prevalence of neural tube defects, we review experimental evidence for three molecular mechanisms of folic acid function. Our perspective is to boost research on the impacts of environmental factors on reducing the risk of neural tube defects by utilizing human neural tube organoid models.

Cell signaling facilitates apical constriction by basolaterally recruiting Arp2/3 via Rac and WAVE

Apical constriction is a critical cell shape change that drives cell internalization and tissue bending. How precisely localized actomyosin regulators drive apical constriction remains poorly understood. Caenorhabditis elegans gastrulation provides a valuable model to address this question. The Arp2/3 complex is essential in C. elegans gastrulation. To understand how Arp2/3 is locally regulated, we imaged embryos with endogenously tagged Arp2/3 and its nucleation-promoting factors (NPFs). The three NPFs-WAVE, WASP, and WASH-controlled Arp2/3 localization at distinct subcellular locations. We exploited this finding to study distinct populations of Arp2/3 and found that only WAVE depletion caused penetrant gastrulation defects. WAVE localized basolaterally with Arp2/3 and controlled F-actin levels near cell-cell contacts. WAVE and Arp2/3 localization depended on CED-10/Rac. Establishing ectopic cell contacts recruited WAVE and Arp2/3, identifying the contact as a symmetry-breaking cue for localization of these proteins. These results suggest that cell-cell signaling via Rac activates WAVE and Arp2/3 basolaterally and that basolateral Arp2/3 makes an important contribution to apical constriction.

IFITM2 Modulates Endocytosis Maintaining Neural Stem Cells in Developing Neocortex

Brain development is orchestrated by a complex interplay of genetic and environmental signals, with endocytosis serving as a pivotal process in integrating extracellular cues. However, the specific role of endocytosis in neurogenesis remains unclear. We uncover a critical function of the interferon-induced transmembrane protein, IFITM2, essential for endocytic processes in radial glial cells (RGCs). IFITM2 is highly expressed near the ventricular surface in the developing brain. Loss of IFITM2 impairs endosome formation and disrupts RGC maintenance. Mechanistically, we confirmed that the YXXø endocytic motif on IFITM2 is essential for its subcellular localization, with mutations in this motif reducing endocytic vesicles. Additionally, the K82 and K87 residues of IFITM2 interact with phosphoinositides to promote endocytic vesicle formation. Polarized localization of phosphatidylinositol 3,4-bisphosphate (PI(3,4)P2) on the ventricular side suggests its role in vesicle formation. IFITM2 deficiency also leads to reduced phosphorylation of AKT and GSK3β. These findings highlight the essential role of IFITM2 in regulating endocytosis in RGCs, which is critical for maintaining neural stem cells and proper brain development, offering new insights into the connection between cellular signaling and neurogenesis in both mouse and human models.

Spinal Cord Organoids from Human Amniotic Fluid iPSC Recapitulate the Diversity of Cell Phenotypes During Fetal Neural Tube Morphogenesis

Myelomeningocele (MMC) is a severe form of spina bifida associated with substantial neurologic morbidity. In vitro modeling systems of human spinal cord development may help to elucidate the underlying pathophysiology of the MMC spinal cord. To that end, we developed spinal cord organoids (SCO), defined as self-organized, three-dimensional clusters of spinal tissue, that were derived from human amniotic fluid-induced pluripotent stem cells. Here, we used a variety of analyses, including immunofluorescent and single-cell transcriptomic approaches, to characterize SCOs from healthy and MMC fetuses. Organoids contained a diverse range of neural and mesodermal phenotypes when cultured for up to 130 days in vitro. Multielectrode arrays revealed functional activity with evidence of emerging neuronal networks. Fetal spina bifida environment modeling was successfully established by culturing SCOs in second- and third-trimester amniotic fluid for 3 weeks. Taken together, we show that functional SCOs can recapitulate the cellular identity of the fetal spinal cord and represent a novel research platform to study the interplay between cellular, biochemical, and mechanical cues during human MMC neural tube morphogenesis.

Characterization of a novel GRHL2 mutation reveals molecular mechanisms underlying autosomal dominant hearing loss (DFNA28): insights from structural and functional studies

The GRHL2 gene, encoding the Grainyhead-like 2 transcription factor, is essential for various biological processes. While GRHL2 has a complex role in cancer biology, its genetic variants have been also implicated in different forms of hearing loss (HL), including autosomal dominant non-syndromic hearing loss (DFNA28). Here, we report a novel c.1061C>T, p.(Ala354Val) mutation within the DNA binding domain (DBD) of GRHL2 that was identified in a three-generation HL family using a targeted multi-gene panel covering 237 HL-related genes. Unlike the previously reported DFNA28-causing variants that result in protein truncation, the impact of the p.(Ala354Val) missense change cannot be attributed to GRHL2 transcript level or composition, but to an alteration in protein function. Molecular dynamics simulations revealed destabilization of the p.(Ala354Val) mutant GRHL2 dimer interface and an altered DNA binding dynamics, leading to chaotic interaction patterns despite increased binding affinity to DNA. Functional assays demonstrated that the p.(Ala354Val) mutation and other DFNA28-related mutations in the DBD lead to loss of GRHL2 transcriptional transactivation activity, while the p.(Arg537Profs*11) mutation in the dimerization domain results in a gain-of-function effect. The findings indicate that both GRHL2 haploinsufficiency and gain-of-function contribute to HL and underscore the complex regulatory role of GRHL2 in maintaining proper function of the auditory system. Our study emphasizes the need to consider structural and functional aspects of gene variants to better understand their pathogenic potential. As GRHL2 is involved in a multitude of cellular processes, the data gathered here can be also applicable to other conditions.

Cell extrusion drives neural crest cell delamination

Neural crest cells (NCC) comprise a heterogeneous population of cells with variable potency that contribute to nearly every tissue and organ throughout the body. Considered unique to vertebrates, NCC are transiently generated within the dorsolateral region of the neural plate or neural tube during neurulation. Their delamination and migration are crucial for embryo development as NCC differentiation is influenced by their final resting locations. Previous work in avian and aquatic species revealed that NCC delaminate via an epithelial-mesenchymal transition (EMT), which transforms these progenitor cells from static polarized epithelial cells into migratory mesenchymal cells with fluid front and back polarity. However, the cellular and molecular mechanisms facilitating NCC delamination in mammals are poorly understood. Through time-lapse imaging of NCC delamination in mouse embryos, we identified a subset of cells that exit the neuroepithelium as isolated round cells, which then halt for a short period prior to acquiring the mesenchymal migratory morphology classically associated with delaminating NCC. High-magnification imaging and protein localization analyses of the cytoskeleton, together with measurements of pressure and tension of delaminating NCC and neighboring neuroepithelial cells, revealed that round NCC are extruded from the neuroepithelium prior to completion of EMT. Furthermore, cranial NCC are extruded through activation of the mechanosensitive ion channel, PIEZO1. Our results support a model in which cell density, pressure, and tension in the neuroepithelium result in activation of the live cell extrusion pathway and delamination of a subpopulation of NCC in parallel with EMT, which has implications for cell delamination in development and disease.

Protective Effect of myo-Inositol Against Decitabine-Induced Neural Tube Defects in Embryonic Zebrafish

Neural tube defects (NTDs) are severe congenital anomalies affecting 1-2 infants per 1000 births, and are influenced by genetic and environmental factors, with DNA hypomethylation and methylation cycle suppression being key causes. In our earlier investigation, decitabine (DCT) caused multiple NTDs in embryonic zebrafish, supporting this hypothesis. Recent research has emphasized the importance of myo-inositol (MI) in embryonic development and its efficacy in reducing the risk of neural tube defects, even in cases resistant to folate. We aimed to examine the effect of MI on DCT-induced NTDs in an embryonic zebrafish model. The embryos were exposed to 1 mM DCT alone, 50 µM MI with 1 mM DCT, 100 µM MI with 1 mM DCT, and a control group for comparison. The development, hatching, mortality rates, neural tube malformations, and neural tube patterning of developing embryos were monitored and recorded. Exposure to MI significantly reduced the incidence of NTDs in developing embryos. At concentrations of 50 µM and 100 µM, MI provided 35% and 30% protection against DCT-induced neural tube malformation, respectively. Multiple NTDs were significantly reduced in the MI groups, with 1 mM DCT causing 95% defects, 50 µM MI with 1 mM DCT causing 50%, and 100 µM MI with 1 mM DCT causing 55% defects. The DCT-induced hatching delay was also reversed by MI treatment. Alizarin red staining and histopathological observations supported these observations. In the context of neural tube development, the protective effects of MI against DCT-induced NTDs could be attributed to its potential role in epigenetic regulation, which may influence genetic expression.

The Mechanics of Building Functional Organs

Organ morphogenesis is multifaceted, multiscale, and fundamentally a robust process. Despite the complex and dynamic nature of embryonic development, organs are built with reproducible size, shape, and function, allowing them to support organismal growth and life. This striking reproducibility of tissue form exists because morphogenesis is not entirely hardwired. Instead, it is an emergent product of mechanochemical information flow, operating across spatial and temporal scales-from local cellular deformations to organ-scale form and function, and back. In this review, we address the mechanical basis of organ morphogenesis, as understood by observations and experiments in living embryos. To this end, we discuss how mechanical information controls the emergence of a highly conserved set of structural motifs that shape organ architectures across the animal kingdom: folds and loops, tubes and lumens, buds, branches, and networks. Moving forward, we advocate for a holistic conceptual framework for the study of organ morphogenesis, which rests on an interdisciplinary toolkit and brings the embryo center stage.

Fundamental origins of neural tube defects with a basis in genetics and nutrition

Neural tube defects (NTDs) are leading congenital malformations. Its global prevalence is one in 1000 pregnancies and it has high morbidity and mortality. It has multiple risk factors like genetic errors and environmental stressors like maternal malnutrition and in utero exposure to pollutants like chemicals. The genetic program determines neural tube development based on timely expression of many genes involved in developmental signaling pathways like BMP, PCP and SHH. BMP expression defines ectoderm. SOX represses BMP in ectoderm and convertes to the neuroectoderm. Subsequently, PCP molecules define the tissue patterning for convergent-extension, a critical step in neural tube genesis. Further, SHH sets spatial patterning of the neural tube. Nutrients are the essential major environmental input for embryogenesis. But it may also carry risk factors. Malnutrition, especially folate deficiency, during embryogenesis is a major cause for NTDs. Folate is integral in the One Carbon metabolic pathway. Its deficiency and error in the pathway are implicated in NTDs. Folate supplementation alone is insufficient to prevent NTDs. Thus, a comprehensive understanding of the various risk factors is necessary to strategize reduction of NTDs. We review the current knowledge of various risk factors, like genetic, metabolic, nutritional, and drugs causing NTDs and discuss the steps required to identify them in the early embryogenesis to avoid NTDs.

An analysis of contractile and protrusive cell behaviors at the superficial surface of the zebrafish neural plate

BACKGROUND

The forces underlying convergence and internalization of the teleost neural plate remain unknown. To help understand this morphogenesis, we analyzed collective and individual cell behaviors at the superficial surface of the neural plate as internalization begins to form the neural keel in the hindbrain region of the zebrafish embryo.

RESULTS

Convergence to the midline is not accompanied by anteroposterior elongation at this stage, and it is characterized by oscillatory contractile behaviors at the superficial surface of the neural plate, a punctate distribution of Cdh2 and medially polarized actin-rich protrusions at the surface of the neural plate. We also characterize the intimate relationship and dynamic protrusive cell behaviors between the surfaces of the motile neural plate and the stationary overlying non-neural enveloping layer.

CONCLUSIONS

Superficial neural plate cells are coupled by a punctate distribution of Cdh2-rich adhesions. At this surface, cells tug on neighbors using oscillatory contractions. Oscillatory contractions accompany convergence and shrinkage of the cells' superficial surface for internalization during keeling. Some shrinkage for internalization occurs without oscillations. The deep surface of the overlying non-neural enveloping layer is in contact with the superficial surface of the neural plate, suggesting that it may constrain the neural plate movements of convergence and internalization.

The dynamics of tubulogenesis in development and disease

Tubes are crucial for the function of many organs in animals given their fundamental roles in transporting and exchanging substances to maintain homeostasis within an organism. Therefore, the development and maintenance of these tube-like structures within organs is a vital process. Tubes can form in diverse ways, and advances in our understanding of the molecular and cellular mechanisms underpinning these different modes of tubulogenesis have significant impacts in many biological contexts, including development and disease. This Review discusses recent progress in understanding developmental mechanisms underlying tube formation.

Clipping spline: interactive, dynamic 4D volume clipping and analysis based on thin plate spline

Methods for seeing inside volumetric images are increasingly important with the rapid advancements in 3D and 4D (3D + time) biomedical imaging techniques. Here, we report a novel volume clipping method and its open-source implementation which enables unprecedented 4D visualization and analysis of embryonic mouse heart development with data from optical coherence tomography (OCT). Clipping a volume to extract information inside has long been a vital approach in biomedical image analysis; however, it is challenging to make a dynamic non-planar cutaway view that is simultaneously smooth, adjustable, efficient to compute, easy to control, and interactive in real time. We addressed this challenge by applying the thin plate spline (TPS) to create a new way of volume clipping, called the clipping spline. Specifically, the clipping spline produces a cutaway view by generating a binary mask based on the unique TPS surface that intersects with a set of 3D control points while having minimal curvature. We implemented this method in an open-source platform where the clipping spline can be interactively controlled for real-time, adjustable, and dynamic cutaway views into a volume. We also developed an algorithm that automatically connects and interpolates different sets of control points over time, providing 4D volume clipping. In addition to characterizing the clipping spline, we demonstrate its application by revealing a series of never-before-seen dynamics and processes of embryonic mouse heart development based on OCT data. We also show a TPS-based method for tracking the embryonic myocardium with control points over two timescales (heartbeat and development). Our results indicate that the clipping spline promises to be broadly used in volumetric biomedical image visualization and analysis, especially by the OCT community.

ApoM maintains cellular homeostasis between mitophagy and apoptosis by affecting the stability of Nnt mRNA through the Zic3-ApoM-Elavl2-Nnt axis during neural tube closure

Research on the aetiology of neural tube defects (NTDs) has made progress in recent years. However, the molecular mechanism of apolipoproteins underlying NTDs development remains unclear. This study aimed to investigate the function of apolipoprotein M (ApoM) in the pathogenesis of NTDs and its underlying mechanisms. We demonstrated that ApoM expression was reduced in the spinal cord samples of rat models and human fetuses with NTDs respectively. Specifically, lack of ApoM resulted in reduced cytosolic localization of Elavl2 and caused Nnt mRNA degradation, which further led to impaired cell homeostasis by suppressing PINK1-PRKN-mediated mitophagy and promoting apoptosis and subsequent NTDs formation. Moreover, Zic3 directly interacted with the promoter of ApoM and activated its transcription. Lastly, intra-amniotic delivery of adenoviral recombinant Zic3 or ApoM could promote mitophagy and alleviate apoptosis in spinal cords of NTDs. Collectively, these findings highlight the important role of the Zic3-ApoM-Elavl2-Nnt axis in cellular homeostasis during neural tube development, thereby revealing an intracellular molecular regulatory mechanism of ApoM, providing a mechanistic basis for understanding embryonic neural development, and offering experimental evidence for potential therapeutic targets for NTDs.

Vesicular glutamate release is necessary for neural tube formation

The brain and spinal cord originate from a neural tube that is preceded by a flat structure known as the neural plate during early embryogenesis. In humans, failure of the neural plate to convert into a tube by the fourth week of pregnancy leads to neural tube defects (NTDs), birth defects with serious neurological consequences. The signaling mechanisms governing the process of neural tube morphogenesis are unclear. Here we show that in Xenopus laevis embryos, neural plate cells release glutamate during neural plate folding in a Ca 2+ and vesicular glutamate transporter-1 (VGluT1)-dependent manner. Vesicular release of glutamate elicits Ca 2+ transients in neural plate cells that correlate with activation of Erk1/2. Knocking down or out VGluT1 leads to NTDs through increased expression of Sox2, neural stem cell transcription factor, and neural plate cell proliferation. Exposure during early pregnancy to neuroactive drugs that disrupt these signaling mechanisms might increase the risk of NTDs in offspring.

Small molecule valproic acid enhances ventral patterning of human neural tube organoids by regulating Wnt and Shh signalling

Valproic acid (VPA), a clinically approved small molecule, has been reported to activate Wnt signalling that is critical for dorsal-ventral (DV) patterning of neural tube. However, little is known about the impact of VPA on DV patterning process. Here, we show that even though VPA has a negative impact on the early formation of human neural tube organoids (hNTOs), it significantly enhances the efficiency of ventrally patterned hNTOs, when VPA is added during the entire differentiation process. RNA sequencing and RT-qPCR analysis demonstrates VPA activates endogenous Wnt signalling in hNTOs. Surprisingly, transcriptome analysis also identifies upregulation of genes for degradation of GLI2 and GLI3 proteins, whose truncated fragment are transcriptional repressors of Shh signalling. The Western-blot analysis confirms the increase of GLI3R proteins after VPA treatment. Thus, VPA might enhance ventral patterning of hNTOs through both activating Wnt, which can antagonise Shh signalling by inducing GLI3 expression, and/or inhibiting Shh signalling by inducing GLI protein degradation. We further obtain results to show that VPA still increases patterning efficiency of hNTOs with a weak influence on their early formation when the initiation time of VPA is delayed and its duration is reduced. Taken together, this study demonstrates that VPA enhances the generation of more reproducible hNTOs with ventral patterning, opening the avenues for the applications of hNTOs in developmental biology and regenerative medicine.

The DNA demethylase TET1 modifies the impact of maternal folic acid status on embryonic brain development

Folic acid (FA) is well known to prevent neural tube defects (NTDs), but we do not know why many human NTD cases still remain refractory to FA supplementation. Here, we investigate how the DNA demethylase TET1 interacts with maternal FA status to regulate mouse embryonic brain development. We determined that cranial NTDs display higher penetrance in non-inbred than in inbred Tet1-/- embryos and are resistant to FA supplementation across strains. Maternal diets that are either too rich or deficient in FA are linked to an increased incidence of cranial deformities in wild type and Tet1+/- offspring and to altered DNA hypermethylation in Tet1-/- embryos, primarily at neurodevelopmental loci. Excess FA in Tet1-/- embryos results in phospholipid metabolite loss and reduced expression of multiple membrane solute carriers, including a FA transporter gene that exhibits increased promoter DNA methylation and thereby mimics FA deficiency. Moreover, FA deficiency reveals that Tet1 haploinsufficiency can contribute to DNA hypermethylation and susceptibility to NTDs. Overall, our study suggests that epigenetic dysregulation may underlie NTD development despite FA supplementation.

A computational dynamic systems model for in silico prediction of neural tube closure defects

Neural tube closure is a critical morphogenetic event during early vertebrate development. This complex process is susceptible to perturbation by genetic errors and chemical disruption, which can induce severe neural tube defects (NTDs) such as spina bifida. We built a computational agent-based model (ABM) of neural tube development based on the known biology of morphogenetic signals and cellular biomechanics underlying neural fold elevation, bending and fusion. The computer model functionalizes cell signals and responses to render a dynamic representation of neural tube closure. Perturbations in the control network can then be introduced synthetically or from biological data to yield quantitative simulation and probabilistic prediction of NTDs by incidence and degree of defect. Translational applications of the model include mechanistic understanding of how singular or combinatorial alterations in gene-environmental interactions and animal-free assessment of developmental toxicity for an important human birth defect (spina bifida) and potentially other neurological problems linked to development of the brain and spinal cord.

Spinal neural tube formation and tail development in human embryos

Primary and secondary neurulation - processes that form the spinal cord - are incompletely understood in humans, largely due to the challenge of accessing neurulation-stage embryos (3-7 weeks post-conception). Here, we describe findings from 108 human embryos, spanning Carnegie stages (CS) 10-18. Primary neurulation is completed at the posterior neuropore with neural plate bending that is similar, but not identical, to the mouse. Secondary neurulation proceeds from CS13 with formation of a single lumen as in mouse, not coalescence of multiple lumens as in chick. There is no evidence of a 'transition zone' from primary to secondary neurulation. Secondary neural tube 'splitting' occurs in 60% of proximal human tail regions. A somite is formed every 7 hr in human, compared with 2 hr in mice and a 5 hr 'segmentation clock' in human organoids. Termination of axial elongation occurs after down-regulation of WNT3A and FGF8 in the CS15 embryonic tailbud, with a 'burst' of apoptosis that may remove neuro-mesodermal progenitors. Hence, the main differences between human and mouse/rat spinal neurulation relate to timing. Investigators are now attempting to recapitulate neurulation events in stem cell-derived organoids, and our results provide 'normative data' for interpretation of such research findings.

SLMAP3 is essential for neurulation through mechanisms involving cytoskeletal elements, ABP, and PCP

SLMAP3 is a tail-anchored membrane protein that targets subcellular organelles and is believed to regulate Hippo signaling. The global loss of SLMAP3 causes late embryonic lethality in mice, with some embryos exhibiting neural tube defects such as craniorachischisis. We show here that SLMAP3 -/- embryos display reduced length and increased width of neural plates, signifying arrested convergent extension. The expression of planar cell polarity (PCP) components Dvl2/3 and the activity of the downstream targets ROCK2, cofilin, and JNK1/2 were dysregulated in SLMAP3 -/- E12.5 brains. Furthermore, the cytoskeletal proteins (γ-tubulin, actin, and nestin) and apical components (PKCζ and ZO-1) were mislocalized in neural tubes of SLMAP3 -/- embryos, with a subsequent decrease in colocalization of PCP proteins (Fzd6 and pDvl2). However, no changes in PCP or cytoskeleton proteins were found in cultured neuroepithelial cells depleted of SLMAP3, suggesting an essential requirement for SLMAP3 for these processes in vivo for neurulation. The loss of SLMAP3 had no impact on Hippo signaling in SLMAP3 -/- embryos, brains, and neural tubes. Proteomic analysis revealed SLMAP3 in an interactome with cytoskeletal components, including nestin, tropomyosin 4, intermediate filaments, plectin, the PCP protein SCRIB, and STRIPAK members in embryonic brains. These results reveal a crucial role of SLMAP3 in neural tube development by regulating the cytoskeleton organization and PCP pathway.

Self-organized cell patterning via mechanical feedback in hindbrain neuropore morphogenesis

Cell patterning is essential for organized tissue development, enabling precise geometric arrangement of cells, body axis establishment and developmental timing. Here we investigate the role of physical forces and mechanical cues in organizing and maintaining cell morphological patterns during hindbrain neuropore closure, a critical morphogenetic event in vertebrate development. Through live-imaging in mouse embryos and cell-based biophysical modeling, we demonstrate that active cell crawling and actomyosin purse-string contraction at the neuropore border are insufficient to account for the observed cellular arrangements in space and time. Instead, mechanosensitive feedback between cellular stress, shape, and nematic alignment is required to establish and maintain cell morphological patterns and their spatial order. This feedback-driven model generates persistent shape memory in cells, stalls cell rearrangements, and promotes local tissue solidification to preserve the spatial organization during the closure process. We validate this model experimentally, establishing the critical role of mechanical feedback in guiding tissue-level morphogenesis through active, force-driven patterning.

Myo-Inositol and Its Derivatives: Their Roles in the Challenges of Infertility

Myo-inositol (MYO) and D-chiro-inositol (DCI) are the two most significant isomeric forms of inositol, playing a critical role in intracellular signaling. MYO is the most abundant form of inositol in nature; DCI is produced from MYO through epimerization by an insulin-dependent enzyme. Recently, it has been demonstrated that inositol may influence oocyte maturation and improve intracellular Ca2+ oscillation in the oocytes, and it has been proposed as a potential intervention for restoring spontaneous ovulation. The MYO concentration in human follicular fluid is considered a bioindicator of oocyte quality. In the ovary, DCI modulates the activity of aromatase, thus regulating androgen synthesis. Under physiological conditions, the MYO/DCI ratio is maintained at 40:1 in plasma. In women with PCOS, the MYO/DCI ratio is lowered to 0:2:1, contributing to elevated androgen production. By regulating FSH signaling, MYO administration increases the number of high-quality embryos available for transfer in poor responder patients. Finally, by acting downstream to insulin signaling, inositol administration during pregnancy may represent a novel strategy for counteracting gestational diabetes. These findings show that diet supplementation with inositol may be a promising strategy to address female infertility and sustain a healthy pregnancy.

Effect and mechanism of Jinkui Shenqi Pill on preventing neural tube defects in mice based on network pharmacology

ETHNOPHARMACOLOGICAL RELEVANCE

jinkui Shenqi Pill (JSP) is a classic traditional Chinese medicine used to treat "Kidney Yang Deficiency" disease. Previous studies indicate a protective effect of JSP on apoptosis in mouse neurons.

AIM OF THE STUDY

This research, combining network pharmacology with in vivo experiments, explores the mechanism of JSP in preventing neural tube defects (NTDs) in mice.

MATERIALS AND METHODS

Network pharmacology analyzed JSP components and targets, identifying common genes with NTDs and exploring potential pathways. Molecular docking assessed interactions between key JSP components and pathway proteins. In an all-trans retinoic acid (atRA)-induced NTDs mouse model, histopathological changes were observed using HE staining, neuronal apoptosis was detected using TUNEL, and Western Blot assessed changes in the PI3K/AKT signaling pathway and apoptosis-related proteins.

RESULTS

Different concentrations of JSP led to varying degrees of reduction in the occurrence of neural tube defects in mouse embryos, with the highest dose showing the most significant decrease. Furthermore, it showed a better reduction in NTDs rates compared to folic acid (FA). Network pharmacology constructed a Drug-Active Ingredient-Gene Target network, suggesting key active ingredients such as Quercetin, Wogonin, Beta-Sitosterol, Kaempferol, and Stigmasterol, possibly acting on the PI3K/Akt signaling pathway. Molecular docking confirmed stable binding structures. Western Blot analysis demonstrated increased expression of p-PI3K, p-Akt, p-Akt1, p-Akt2, p-Akt3, downregulation of cleaved caspase-3 and Bax, and upregulation of Bcl-2, indicating prevention of NTDs through anti-apoptotic effects.

CONCLUSION

We have identified an effective dosage of JSP for preventing NTDs, revealing its potential by activating the PI3K/Akt signaling pathway and inhibiting cell apoptosis in atRA-induced mouse embryonic NTDs.

Quantifying mechanical forces during vertebrate morphogenesis

Morphogenesis requires embryonic cells to generate forces and perform mechanical work to shape their tissues. Incorrect functioning of these force fields can lead to congenital malformations. Understanding these dynamic processes requires the quantification and profiling of three-dimensional mechanics during evolving vertebrate morphogenesis. Here we describe elastic spring-like force sensors with micrometre-level resolution, fabricated by intravital three-dimensional bioprinting directly in the closing neural tubes of growing chicken embryos. Integration of calibrated sensor read-outs with computational mechanical modelling allows direct quantification of the forces and work performed by the embryonic tissues. As they displace towards the embryonic midline, the two halves of the closing neural tube reach a compression of over a hundred nano-newtons during neural fold apposition. Pharmacological inhibition of Rho-associated kinase to decrease the pro-closure force shows the existence of active anti-closure forces, which progressively widen the neural tube and must be overcome to achieve neural tube closure. Overall, our approach and findings highlight the intricate interplay between mechanical forces and tissue morphogenesis.

Neural Tube Organoids: A Novel System to Study Developmental Timing

The neural tube (NT) is a transient structure formed during embryogenesis which develops into the brain and spinal cord. While mouse models have been commonly used in place of human embryos to study NT development, species-specific differences limit their applicability. One major difference is developmental timing, with NT formation from the neural plate in 16 days in humans compared to 4 days in mice, as well as differences in the time taken to form neuronal subtypes and complete neurogenesis. Neural tube organoids (NTOs) represent a new way to study NT development in vitro. While mouse and human NTOs have been shown to recapitulate the major developmental events of NT formation; it is unknown whether species-specific developmental timing, also termed allochrony, is also recapitulated. This review summarises current research using both mouse and human NTOs and compares developmental timing events in order to assess if allochrony is maintained in organoids.

Linking planar polarity signalling to actomyosin contractility during vertebrate neurulation

Actomyosin contractility represents an ancient feature of eukaryotic cells participating in many developmental and homeostasis events, including tissue morphogenesis, muscle contraction and cell migration, with dysregulation implicated in various pathological conditions, such as cancer. At the molecular level, actomyosin comprises actin bundles and myosin motor proteins that are sensitive to posttranslational modifications like phosphorylation. While the molecular components of actomyosin are well understood, the coordination of contractility by extracellular and intracellular signals, particularly from cellular signalling pathways, remains incompletely elucidated. This study focuses on WNT/planar cell polarity (PCP) signalling, previously associated with actomyosin contractility during vertebrate neurulation. Our investigation reveals that the main cytoplasmic PCP proteins, Prickle and Dishevelled, interact with key actomyosin components such as myosin light chain 9 (MLC9), leading to its phosphorylation and localized activation. Using proteomics and microscopy approaches, we demonstrate that both PCP proteins actively control actomyosin contractility through Rap1 small GTPases in relevant in vitro and in vivo models. These findings unveil a novel mechanism of how PCP signalling regulates actomyosin contractility through MLC9 and Rap1 that is relevant to vertebrate neurulation.

Pharmacological Inhibition of the Spliceosome SF3b Complex by Pladienolide-B Elicits Craniofacial Developmental Defects in Mouse and Zebrafish

BACKGROUND

Mutations in genes encoding spliceosome components result in craniofacial structural defects in humans, referred to as spliceosomopathies. The SF3b complex is a crucial unit of the spliceosome, but model organisms generated through genetic modification of the complex do not perfectly mimic the phenotype of spliceosomopathies. Since the phenotypes are suggested to be determined by the extent of spliceosome dysfunction, an alternative experimental system that can seamlessly control SF3b function is needed.

METHODS

To establish another experimental system for model organisms elucidating relationship between spliceosome function and human diseases, we administered Pladienolide-B (PB), a SF3b complex inhibitor, to mouse and zebrafish embryos and assessed resulting phenotypes.

RESULTS

PB-treated mouse embryos exhibited neural tube defect and exencephaly, accompanied by apoptosis and reduced cell proliferation in the neural tube, but normal structure in the midface and jaw. PB administration to heterozygous knockout mice of Sf3b4, a gene coding for a SF3b component, influenced the formation of cranial neural crest cells (CNCCs). Despite challenges in continuous PB administration and a high death rate in mice, PB was stably administered to zebrafish embryos, resulting in prolonged survival. Brain, cranial nerve, retina, midface, and jaw development were affected, mimicking spliceosomopathy phenotypes. Additionally, alterations in cell proliferation, cell death, and migration of CNCCs were detected.

CONCLUSIONS

We demonstrated that zebrafish treated with PB exhibited phenotypes similar to those observed in human spliceosomopathies. This experimental system may serve as a valuable research tool for understanding spliceosome function and human diseases.

Cell signaling facilitates apical constriction by basolaterally recruiting Arp2/3 via Rac and WAVE

Apical constriction is a critical cell shape change that bends tissues. How precisely-localized actomyosin regulators drive apical constriction remains poorly understood. C. elegans gastrulation provides a valuable model to address this question. The Arp2/3 complex is essential in C. elegans gastrulation. To understand how Arp2/3 is locally regulated, we imaged embryos with endogenously-tagged Arp2/3 and its nucleation-promoting factors (NPFs). The three NPFs - WAVE, WASP, and WASH - colocalized with Arp2/3 and controlled Arp2/3 localization at distinct subcellular locations. We exploited this finding to study distinct populations of Arp2/3 and found that only WAVE depletion caused penetrant gastrulation defects. WAVE localized basolaterally with Arp2/3 at cell-cell contacts, dependent on CED-10/Rac. Establishing ectopic cell contacts recruited WAVE and Arp2/3, identifying contact as a symmetry-breaking cue for localization of these proteins. These results suggest that cell-cell signaling via Rac activates WAVE and Arp2/3 basolaterally, and that basolateral Arp2/3 is important for apical constriction.

Adelola Adeyole (1935-2021): Early descriptor of congenital dermoid or epidermoid inclusion cyst over the anterior fontanelle and below the galea aponeurotica

The author wished to detail the life and contributions of Dr. Adelola Adeloye, MBBS, MS, FWCS, FRCS, FACS, FRCP, in hope to pay homage to this giant in Global Neurosurgery. Dr. Adelola Adeloye was born on July 18, 1935 in Illesa, Osun State, present-day South-West Nigeria. The Adeloye-Odeku disease is an eponym for a congenital dermoid or epidermoid inclusion cyst (CDIC/CEDIC) over the anterior fontanelle and below the galea aponeurotica. In 1971, Adeloye and Odeku first described these cysts in 18 Nigerian patients. While overall rare and predominantly noted in children, the Adeloye-Odeku disease has been found to impact adults too. In terms of rarity, CDICs make up 0.1-0.5% of cranial tumors and 0.2% of inclusion cysts. CDICs can be distinguished from CEDICs through histopathology as dermoid cysts may contain hair follicles, sweat, sebaceous glands, and teeth, whereas CEDICs usually are only composed of keratinized debris and epidermal tissue. Assumed first to be an African cyst, cases of the Adeloye-Odeku disease were subsequently reported in other ethnic populations: Turkish, Czechs, Slovaks, Chinese, Japanese, Canadians, Saudi Arabians, Indians, Caucasians, Bangladeshis, Spaniards, and Brazilians.

Brain development and bioenergetic changes

Bioenergetics describe the biochemical processes responsible for energy supply in organisms. When these changes become dysregulated in brain development, multiple neurodevelopmental diseases can occur, implicating bioenergetics as key regulators of neural development. Historically, the discovery of disease processes affecting individual stages of brain development has revealed critical roles that bioenergetics play in generating the nervous system. Bioenergetic-dependent neurodevelopmental disorders include neural tube closure defects, microcephaly, intellectual disability, autism spectrum disorders, epilepsy, mTORopathies, and oncogenic processes. Developmental timing and cell-type specificity of these changes determine the long-term effects of bioenergetic disease mechanisms on brain form and function. Here, we discuss key metabolic regulators of neural progenitor specification, neuronal differentiation (neurogenesis), and gliogenesis. In general, transitions between glycolysis and oxidative phosphorylation are regulated in early brain development and in oncogenesis, and reactive oxygen species (ROS) and mitochondrial maturity play key roles later in differentiation. We also discuss how bioenergetics interface with the developmental regulation of other key neural elements, including the cerebrospinal fluid brain environment. While questions remain about the interplay between bioenergetics and brain development, this review integrates the current state of known key intersections between these processes in health and disease.

Self-organizing models of human trunk organogenesis recapitulate spinal cord and spine co-morphogenesis

Integrated in vitro models of human organogenesis are needed to elucidate the multi-systemic events underlying development and disease. Here we report the generation of human trunk-like structures that model the co-morphogenesis, patterning and differentiation of the human spine and spinal cord. We identified differentiation conditions for human pluripotent stem cells favoring the formation of an embryo-like extending antero-posterior (AP) axis. Single-cell and spatial transcriptomics show that somitic and spinal cord differentiation trajectories organize along this axis and can self-assemble into a neural tube surrounded by somites upon extracellular matrix addition. Morphogenesis is coupled with AP patterning mechanisms, which results, at later stages of organogenesis, in in vivo-like arrays of neural subtypes along a neural tube surrounded by spine and muscle progenitors contacted by neuronal projections. This integrated system of trunk development indicates that in vivo-like multi-tissue co-morphogenesis and topographic organization of terminal cell types can be achieved in human organoids, opening windows for the development of more complex models of organogenesis.

Epigenetic regulation by TET1 in gene-environmental interactions influencing susceptibility to congenital malformations

The etiology of neural tube defects (NTDs) involves complex gene-environmental interactions. Folic acid (FA) prevents NTDs, but the mechanisms remain poorly understood and at least 30% of human NTDs resist the beneficial effects of FA supplementation. Here, we identify the DNA demethylase TET1 as a nexus of folate-dependent one-carbon metabolism and genetic risk factors post-neural tube closure. We determine that cranial NTDs in Tet1 -/- embryos occur at two to three times higher penetrance in genetically heterogeneous than in homogeneous genetic backgrounds, suggesting a strong impact of genetic modifiers on phenotypic expression. Quantitative trait locus mapping identified a strong NTD risk locus in the 129S6 strain, which harbors missense and modifier variants at genes implicated in intracellular endocytic trafficking and developmental signaling. NTDs across Tet1 -/- strains are resistant to FA supplementation. However, both excess and depleted maternal FA diets modify the impact of Tet1 loss on offspring DNA methylation primarily at neurodevelopmental loci. FA deficiency reveals susceptibility to NTD and other structural brain defects due to haploinsufficiency of Tet1. In contrast, excess FA in Tet1 -/- embryos drives promoter DNA hypermethylation and reduced expression of multiple membrane solute transporters, including a FA transporter, accompanied by loss of phospholipid metabolites. Overall, our study unravels interactions between modified maternal FA status, Tet1 gene dosage and genetic backgrounds that impact neurotransmitter functions, cellular methylation and individual susceptibilities to congenital malformations, further implicating that epigenetic dysregulation may underlie NTDs resistant to FA supplementation.

Maternal Smoking during Pregnancy and its effects on Neural Tube Defects

Objectives

Maternal smoking is a potent teratogen among congenital malformations, however its role in the development of Neural Tube Defects (NTDs) is still unclear. In this systematic review, we intend to further investigate the interaction of smoking during pregnancy and the incidence of NTDs.

Materials & Methods

This article was written according to PRISMA criteria from February 2015 and August 2022. After examining the four stages of PRISMA criteria, we selected clinical articles. These articles were selected from PubMed, Scopus and Google scholar (for results follow-up) databases. We gathered NTDs effect and types, smoking type and habit of parents, from neonates.

Results

Eventually, 8 articles were included by two separated authors, Smoking was associated with an increase NTDs in the population of pregnant mothers and also among children whose fathers smoked. The main side effects that were considered to be the cause of NTDs besides smoking were alcohol and BMI (18.5-24.9). Smoking also affects the level of folic acid as a substance with an essential role that affects the closure of the neural tube. folic acid available to infants changing along with the level of other blood elements such as zinc, that necessary prevent for NTDs condition.

Conclusion

Parental smoking can be considered as one of the strong teratogens in the occurrence of NTDs. Smoking, whether active or passive by the mother, or by the father, is associated with the occurrence of NTDs, In order to reduce the prevalence this disorder, we advise pregnant mothers and neonate's fathers to quit smoking.

The non-mitotic role of HMMR in regulating the localization of TPX2 and the dynamics of microtubules in neurons

A functional nervous system is built upon the proper morphogenesis of neurons to establish the intricate connection between them. The microtubule cytoskeleton is known to play various essential roles in this morphogenetic process. While many microtubule-associated proteins (MAPs) have been demonstrated to participate in neuronal morphogenesis, the function of many more remains to be determined. This study focuses on a MAP called HMMR in mice, which was originally identified as a hyaluronan binding protein and later found to possess microtubule and centrosome binding capacity. HMMR exhibits high abundance on neuronal microtubules and altering the level of HMMR significantly affects the morphology of neurons. Instead of confining to the centrosome(s) like cells in mitosis, HMMR localizes to microtubules along axons and dendrites. Furthermore, transiently expressing HMMR enhances the stability of neuronal microtubules and increases the formation frequency of growing microtubules along the neurites. HMMR regulates the microtubule localization of a non-centrosomal microtubule nucleator TPX2 along the neurite, offering an explanation for how HMMR contributes to the promotion of growing microtubules. This study sheds light on how cells utilize proteins involved in mitosis for non-mitotic functions.

Up-regulation of miR-10a-5p expression inhibits the proliferation and differentiation of neural stem cells by targeting Chl1

Neural tube defects (NTDs) are characterized by the failure of neural tube closure during embryogenesis and are considered the most common and severe central nervous system anomalies during early development. Recent microRNA (miRNA) expression profiling studies have revealed that the dysregulation of several miRNAs plays an important role in retinoic acid (RA)-induced NTDs. However, the molecular functions of these miRNAs in NTDs remain largely unidentified. Here, we show that miR-10a-5p is significantly upregulated in RA-induced NTDs and results in reduced cell growth due to cell cycle arrest and dysregulation of cell differentiation. Moreover, the cell adhesion molecule L1-like ( Chl1) is identified as a direct target of miR-10a-5p in neural stem cells (NSCs) in vitro, and its expression is reduced in RA-induced NTDs. siRNA-mediated knockdown of intracellular Chl1 affects cell proliferation and differentiation similar to those of miR-10a-5p overexpression, which further leads to the inhibition of the expressions of downstream ERK1/2 MAPK signaling pathway proteins. These cellular responses are abrogated by either increased expression of the direct target of miR-10a-5p ( Chl1) or an ERK agonist such as honokiol. Overall, our study demonstrates that miR-10a-5p plays a major role in the process of NSC growth and differentiation by directly targeting Chl1, which in turn induces the downregulation of the ERK1/2 cascade, suggesting that miR-10a-5p and Chl1 are critical for NTD formation in the development of embryos.

Vangl-dependent mesenchymal thinning shapes the distal lung during murine sacculation

The planar cell polarity (PCP) complex is speculated to function in murine lung development, where branching morphogenesis generates an epithelial tree whose distal tips expand dramatically during sacculation. Here, we show that PCP is dispensable in the airway epithelium for sacculation. Rather, we find a Celsr1-independent role for the PCP component Vangl in the pulmonary mesenchyme: loss of Vangl1/2 inhibits mesenchymal thinning and expansion of the saccular epithelium. Further, loss of mesenchymal Wnt5a mimics sacculation defects observed in Vangl2-mutant lungs, implicating mesenchymal Wnt5a/Vangl signaling as a key regulator of late lung morphogenesis. A computational model predicts that sacculation requires a fluid mesenchymal compartment. Lineage-tracing and cell-shape analyses are consistent with the mesenchyme acting as a fluid tissue, suggesting that loss of Vangl1/2 impacts the ability of mesenchymal cells to exchange neighbors. Our data thus identify an explicit function for Vangl and the pulmonary mesenchyme in actively shaping the saccular epithelium.

Optical coherence tomography-guided Brillouin microscopy highlights regional tissue stiffness differences during anterior neural tube closure in the Mthfd1l murine mutant

Neurulation is a highly synchronized biomechanical process leading to the formation of the brain and spinal cord, and its failure leads to neural tube defects (NTDs). Although we are rapidly learning the genetic mechanisms underlying NTDs, the biomechanical aspects are largely unknown. To understand the correlation between NTDs and tissue stiffness during neural tube closure (NTC), we imaged an NTD murine model using optical coherence tomography (OCT), Brillouin microscopy and confocal fluorescence microscopy. Here, we associate structural information from OCT with local stiffness from the Brillouin signal of embryos undergoing neurulation. The stiffness of neuroepithelial tissues in Mthfd1l null embryos was significantly lower than that of wild-type embryos. Additionally, exogenous formate supplementation improved tissue stiffness and gross embryonic morphology in nullizygous and heterozygous embryos. Our results demonstrate the significance of proper tissue stiffness in normal NTC and pave the way for future studies on the mechanobiology of normal and abnormal embryonic development.

Research Progress on the Mechanism of the SFRP-Mediated Wnt Signalling Pathway Involved in Bone Metabolism in Osteoporosis

Osteoporosis (OP) is a metabolic bone disease linked to an elevated fracture risk, primarily stemming from disruptions in bone metabolism. Present clinical treatments for OP merely alleviate symptoms. Hence, there exists a pressing need to identify novel targets for the clinical treatment of OP. Research indicates that the Wnt signalling pathway is modulated by serum-secreted frizzled-related protein 5 (SFRP5), potentially serving as a pivotal regulator in bone metabolism disorders. Moreover, studies confirm elevated SFRP5 expression in OP, with SFRP5 overexpression leading to the downregulation of Wnt and β-catenin proteins in the Wnt signalling pathway, as well as the expression of osteogenesis-related marker molecules such as RUNX2, ALP, and OPN. Conversely, the opposite has been reported when SFRP5 is knocked out, suggesting that SFRP5 may be a key factor involved in the regulation of bone metabolism via the Wnt signalling axis. However, the molecular mechanisms underlying the action of SFRP5-induced OP have yet to be comprehensively elucidated. This review focusses on the molecular structure and function of SFRP5 and the potential molecular mechanisms of the SFRP5-mediated Wnt signalling pathway involved in bone metabolism in OP, providing reasonable evidence for the targeted therapy of SFRP5 for the prevention and treatment of OP.

Planar Cell Polarity Signaling: Coordinated Crosstalk for Cell Orientation

The planar cell polarity (PCP) system is essential for positioning cells in 3D networks to establish the proper morphogenesis, structure, and function of organs during embryonic development. The PCP system uses inter- and intracellular feedback interactions between components of the core PCP, characterized by coordinated planar polarization and asymmetric distribution of cell populations inside the cells. PCP signaling connects the anterior-posterior to left-right embryonic plane polarity through the polarization of cilia in the Kupffer's vesicle/node in vertebrates. Experimental investigations on various genetic ablation-based models demonstrated the functions of PCP in planar polarization and associated genetic disorders. This review paper aims to provide a comprehensive overview of PCP signaling history, core components of the PCP signaling pathway, molecular mechanisms underlying PCP signaling, interactions with other signaling pathways, and the role of PCP in organ and embryonic development. Moreover, we will delve into the negative feedback regulation of PCP to maintain polarity, human genetic disorders associated with PCP defects, as well as challenges associated with PCP.

Exploring research hotspots and future directions in neural tube defects field by bibliometric and bioinformatics analysis

Background

Neural tube defects (NTDs) is the most common birth defect of the central nervous system (CNS) which causes the death of almost 88,000 people every year around the world. Much efforts have been made to investigate the reasons that contribute to NTD and explore new ways to for prevention. We trawl the past decade (2013-2022) published records in order to get a worldwide view about NTDs research field.

Methods

7,437 records about NTDs were retrieved from the Web of Science (WOS) database. Tools such as shell scripts, VOSviewer, SCImago Graphica, CiteSpace and PubTator were used for data analysis and visualization.

Results

Over the past decade, the number of publications has maintained an upward trend, except for 2022. The United States is the country with the highest number of publications and also with the closest collaboration with other countries. Baylor College of Medicine has the closest collaboration with other institutions worldwide and also was the most prolific institution. In the field of NTDs, research focuses on molecular mechanisms such as genes and signaling pathways related to folate metabolism, neurogenic diseases caused by neural tube closure disorders such as myelomeningocele and spina bifida, and prevention and treatment such as folate supplementation and surgical procedures. Most NTDs related genes are related to development, cell projection parts, and molecular binding. These genes are mainly concentrated in cancer, Wnt, MAPK, PI3K-Akt and other signaling pathways. The distribution of NTDs related SNPs on chromosomes 1, 3, 5, 11, 14, and 17 are relatively concentrated, which may be associated with high-risk of NTDs.

Conclusion

Bibliometric analysis of the literature on NTDs field provided the current status, hotspots and future directions to some extant. Further bioinformatics analysis expanded our understanding of NTDs-related genes function and revealed some important SNP clusters and loci. This study provided some guidance for further studies. More extensive cooperation and further research are needed to overcome the ongoing challenge in pathogenesis, prevention and treatment of NTDs.

The Critical Role of the Shroom Family Proteins in Morphogenesis, Organogenesis and Disease

The Shroom (Shrm) family of actin-binding proteins has a unique and highly conserved Apx/Shrm Domain 2 (ASD2) motif. Shroom protein directs the subcellular localization of Rho-associated kinase (ROCK), which remodels the actomyosin cytoskeleton and changes cellular morphology via its ability to phosphorylate and activate non-muscle myosin II. Therefore, the Shrm-ROCK complex is critical for the cellular shape and the development of many tissues, including the neural tube, eye, intestines, heart, and vasculature system. Importantly, the structure and expression of Shrm proteins are also associated with neural tube defects, chronic kidney disease, metastasis of carcinoma, and X-link mental retardation. Therefore, a better understanding of Shrm-mediated signaling transduction pathways is essential for the development of new therapeutic strategies to minimize damage resulting in abnormal Shrm proteins. This paper provides a comprehensive overview of the various Shrm proteins and their roles in morphogenesis and disease.

Pcgf5: An important regulatory factor in early embryonic neural induction

Polycomb group RING finger (PCGF) proteins, a crucial subunits of the Polycomb complex, plays an important role in regulating gene expression, embryonic development, and cell fate determination. In our research, we investigated Pcgf5, one of the six PCGF homologs, and its impact on the differentiation of P19 cells into neural stem cells. Our findings revealed that knockdown of Pcgf5 resulted in a significant decrease in the expression levels of the neuronal markers Sox2, Zfp521, and Pax6, while the expression levels of the pluripotent markers Oct4 and Nanog increased. Conversely, Pcgf5 overexpression upregulated the expression of Sox2 and Pax6, while downregulating the expression of Oct4 and Nanog. Additionally, our analysis revealed that Pcgf5 suppresses Wnt3 expression via the activation of Notch1/Hes1, and ultimately governs the differentiation fate of neural stem cells. To further validate our findings, we conducted in vivo experiments in zebrafish. We found that knockdown of pcgf5a using morpholino resulted in the downregulated expression of neurodevelopmental genes such as sox2, sox3, and foxg1 in zebrafish embryos. Consequently, these changes led to neurodevelopmental defects. In conclusion, our study highlights the important role of Pcgf5 in neural induction and the determination of neural cell fate.

Loss of SHROOM3 affects neuroepithelial cell shape through regulating cytoskeleton proteins in cynomolgus monkey organoids

Neural tube defects (NTDs) are severe congenital neurodevelopmental disorders arising from incomplete neural tube closure. Although folate supplementation has been shown to mitigate the incidence of NTDs, some cases, often attributable to genetic factors, remain unpreventable. The SHROOM3 gene has been implicated in NTD cases that are unresponsive to folate supplementation; at present, however, the underlying mechanism remains unclear. Neural tube morphogenesis is a complex process involving the folding of the planar epithelium of the neural plate. To determine the role of SHROOM3 in early developmental morphogenesis, we established a neuroepithelial organoid culture system derived from cynomolgus monkeys to closely mimic the in vivo neural plate phase. Loss of SHROOM3 resulted in shorter neuroepithelial cells and smaller nuclei. These morphological changes were attributed to the insufficient recruitment of cytoskeletal proteins, namely fibrous actin (F-actin), myosin II, and phospho-myosin light chain (PMLC), to the apical side of the neuroepithelial cells. Notably, these defects were not rescued by folate supplementation. RNA sequencing revealed that differentially expressed genes were enriched in biological processes associated with cellular and organ morphogenesis. In summary, we established an authentic in vitro system to study NTDs and identified a novel mechanism for NTDs that are unresponsive to folate supplementation.

Cell extrusion - a novel mechanism driving neural crest cell delamination

Neural crest cells (NCC) comprise a heterogeneous population of cells with variable potency, that contribute to nearly every tissue and organ system throughout the body. Considered unique to vertebrates, NCC are transiently generated within the dorsolateral region of the neural plate or neural tube, during neurulation. Their delamination and migration are crucial events in embryo development as the differentiation of NCC is heavily influenced by their final resting locations. Previous work in avian and aquatic species has shown that NCC delaminate via an epithelial-mesenchymal transition (EMT), which transforms these stem and progenitor cells from static polarized epithelial cells into migratory mesenchymal cells with fluid front and back polarity. However, the cellular and molecular drivers facilitating NCC delamination in mammals are poorly understood. We performed live timelapse imaging of NCC delamination in mouse embryos and discovered a group of cells that exit the neuroepithelium as isolated round cells, which then halt for a short period prior to acquiring the mesenchymal migratory morphology classically associated with most delaminating NCC. High magnification imaging and protein localization analyses of the cytoskeleton, together with measurements of pressure and tension of delaminating NCC and neighboring neuroepithelial cells, revealed these round NCC are extruded from the neuroepithelium prior to completion of EMT. Furthermore, we demonstrate that cranial NCC are extruded through activation of the mechanosensitive ion channel, PIEZO1, a key regulator of the live cell extrusion pathway, revealing a new role for PIEZO1 in neural crest cell development. Our results elucidating the cellular and molecular dynamics orchestrating NCC delamination support a model in which high pressure and tension in the neuroepithelium results in activation of the live cell extrusion pathway and delamination of a subpopulation of NCC in parallel with EMT. This model has broad implications for our understanding of cell delamination in development and disease.

Claudin-3 in the non-neural ectoderm is essential for neural fold fusion in chicken embryos

The neural tube, the embryonic precursor to the brain and spinal cord, begins as a flat sheet of epithelial cells, divided into non-neural and neural ectoderm. Proper neural tube closure requires that the edges of the neural ectoderm, the neural folds, to elevate upwards and fuse along the dorsal midline of the embryo. We have previously shown that members of the claudin protein family are required for the early phases of chick neural tube closure. Claudins are transmembrane proteins, localized in apical tight junctions within epithelial cells where they are essential for regulation of paracellular permeability, strongly involved in apical-basal polarity, cell-cell adhesion, and bridging the tight junction to cytoplasmic proteins. Here we explored the role of Claudin-3 (Cldn3), which is specifically expressed in the non-neural ectoderm. We discovered that depletion of Cldn3 causes folic acid-insensitive primarily spinal neural tube defects due to a failure in neural fold fusion. Apical cell surface morphology of Cldn3-depleted non-neural ectodermal cells exhibited increased membrane blebbing and smaller apical surfaces. Although apical-basal polarity was retained, we observed altered Par3 and Pals1 protein localization patterns within the apical domain of the non-neural ectodermal cells in Cldn3-depleted embryos. Furthermore, F-actin signal was reduced at apical junctions. Our data presents a model of spina bifida, and the role that Cldn3 is playing in regulating essential apical cell processes in the non-neural ectoderm required for neural fold fusion.

TIAM-1 regulates polarized protrusions during dorsal intercalation in the Caenorhabditis elegans embryo through both its GEF and N-terminal domains

Mediolateral cell intercalation is a morphogenetic strategy used throughout animal development to reshape tissues. Dorsal intercalation in the Caenorhabditis elegans embryo involves the mediolateral intercalation of two rows of dorsal epidermal cells to create a single row that straddles the dorsal midline, and thus is a simple model to study cell intercalation. Polarized protrusive activity during dorsal intercalation requires the C. elegans Rac and RhoG orthologs CED-10 and MIG-2, but how these GTPases are regulated during intercalation has not been thoroughly investigated. In this study, we characterized the role of the Rac-specific guanine nucleotide exchange factor (GEF) TIAM-1 in regulating actin-based protrusive dynamics during dorsal intercalation. We found that TIAM-1 can promote formation of the main medial lamellipodial protrusion extended by intercalating cells through its canonical GEF function, whereas its N-terminal domains function to negatively regulate the generation of ectopic filiform protrusions around the periphery of intercalating cells. We also show that the guidance receptor UNC-5 inhibits these ectopic filiform protrusions in dorsal epidermal cells and that this effect is in part mediated via TIAM-1. These results expand the network of proteins that regulate basolateral protrusive activity during directed rearrangement of epithelial cells in animal embryos.

The Phylotypic Brain of Vertebrates, from Neural Tube Closure to Brain Diversification

BACKGROUND

The phylotypic or intermediate stages are thought to be the most evolutionary conserved stages throughout embryonic development. The contrast with divergent early and later stages derived from the concept of the evo-devo hourglass model. Nonetheless, this developmental constraint has been studied as a whole embryo process, not at organ level. In this review, we explore brain development to assess the existence of an equivalent brain developmental hourglass. In the specific case of vertebrates, we propose to split the brain developmental stages into: (1) Early: Neurulation, when the neural tube arises after gastrulation. (2) Intermediate: Brain patterning and segmentation, when the neuromere identities are established. (3) Late: Neurogenesis and maturation, the stages when the neurons acquire their functionality. Moreover, we extend this analysis to other chordates brain development to unravel the evolutionary origin of this evo-devo constraint.

SUMMARY

Based on the existing literature, we hypothesise that a major conservation of the phylotypic brain might be due to the pleiotropy of the inductive regulatory networks, which are predominantly expressed at this stage. In turn, earlier stages such as neurulation are rather mechanical processes, whose regulatory networks seem to adapt to environment or maternal geometries. The later stages are also controlled by inductive regulatory networks, but their effector genes are mostly tissue-specific and functional, allowing diverse developmental programs to generate current brain diversity. Nonetheless, all stages of the hourglass are highly interconnected: divergent neurulation must have a vertebrate shared end product to reproduce the vertebrate phylotypic brain, and the boundaries and transcription factor code established during the highly conserved patterning will set the bauplan for the specialised and diversified adult brain.

KEY MESSAGES

The vertebrate brain is conserved at phylotypic stages, but the highly conserved mechanisms that occur during these brain mid-development stages (Inducing Regulatory Networks) are also present during other stages. Oppositely, other processes as cell interactions and functional neuronal genes are more diverse and majoritarian in early and late stages of development, respectively. These phenomena create an hourglass of transcriptomic diversity during embryonic development and evolution, with a really conserved bottleneck that set the bauplan for the adult brain around the phylotypic stage.

A mechanical wave travels along a genetic guide to drive the formation of an epithelial furrow during Drosophila gastrulation

Epithelial furrowing is a fundamental morphogenetic process during gastrulation, neurulation, and body shaping. A furrow often results from a fold that propagates along a line. How fold formation and propagation are controlled and driven is poorly understood. To shed light on this, we study the formation of the cephalic furrow, a fold that runs along the embryo dorsal-ventral axis during Drosophila gastrulation and the developmental role of which is still unknown. We provide evidence of its function and show that epithelial furrowing is initiated by a group of cells. This cellular cluster works as a pacemaker, triggering a bidirectional morphogenetic wave powered by actomyosin contractions and sustained by de novo medial apex-to-apex cell adhesion. The pacemaker's Cartesian position is under the crossed control of the anterior-posterior and dorsal-ventral gene patterning systems. Thus, furrow formation is driven by a mechanical trigger wave that travels under the control of a multidimensional genetic guide.

Intrasellar Dermoid Cyst: Case Report of a Rare Lesion and Systematic Literature Review Comparing Intrasellar, Suprasellar, and Parasellar Locations

OBJECTIVE

Intracranial dermoid cyst (DC) is a rare benign, slow-growing lesion, most commonly arising along the midline. They can occur in the supratentorial compartment, very rarely involve the sellar region and only exceptionally are intrasellar. The aim of our study is to address the challenges in the diagnosis and management of sellar DCs.

METHODS

We performed a systematic review of sellar DCs, in keeping with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines, and described an intrasellar DC in a 32-year-old female who presented with bilateral blurring vision.

RESULTS

The review identified 4 intrasellar, 29 suprasellar, and 28 parasellar cases. Intrasellar DCs more likely present with progressive visual impairment and pituitary hormone dysfunctions during the fifth decade of life. Suprasellar and parasellar DCs are typically diagnosed during the third decade of life because of diplopia, ptosis, trigeminal hypoaesthesia/para-esthesia or cyst's rupture. Sellar DCs are typically hypodense on computed tomography scans and contain calcifications. Magnetic resonance imaging features include T1 hyperintensity, T2 heterogeneous intensity, no restriction on diffusion-weighted images, and no contrast enhancement. Surgery is the treatment of choice. Gross total resection is achieved in 60% of intrasellar and 61.9% of suprasellar and parasellar DCs. Early postoperative complications are reported in 40.0%, 16.7%, and 23.8% of intrasellar, suprasellar, and parasellar DCs, respectively.

CONCLUSIONS

Intrasellar DCs are rare lesions typically diagnosed later than suprasellar and parasellar DCs due to their different clinical presentations. However, they should be considered in the differential diagnosis of cystic lesions of the sella, including epidermoid cysts, craniopharyngiomas, Rathke's cleft cysts, and teratomas.

Engineering the Physical Microenvironment into Neural Organoids for Neurogenesis and Neurodevelopment

Understanding the signals from the physical microenvironment is critical for deciphering the processes of neurogenesis and neurodevelopment. The discovery of how surrounding physical signals shape human developing neurons is hindered by the bottleneck of conventional cell culture and animal models. Notwithstanding neural organoids provide a promising platform for recapitulating human neurogenesis and neurodevelopment, building neuronal physical microenvironment that accurately mimics the native neurophysical features is largely ignored in current organoid technologies. Here, it is discussed how the physical microenvironment modulates critical events during the periods of neurogenesis and neurodevelopment, such as neural stem cell fates, neural tube closure, neuronal migration, axonal guidance, optic cup formation, and cortical folding. Although animal models are widely used to investigate the impacts of physical factors on neurodevelopment and neuropathy, the important roles of human stem cell-derived neural organoids in this field are particularly highlighted. Considering the great promise of human organoids, building neural organoid microenvironments with mechanical forces, electrophysiological microsystems, and light manipulation will help to fully understand the physical cues in neurodevelopmental processes. Neural organoids combined with cutting-edge techniques, such as advanced atomic force microscopes, microrobots, and structural color biomaterials might promote the development of neural organoid-based research and neuroscience.