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The Hedgehog (Hh) pathway plays a crucial role in embryonic development, acting both as a morphogenic signal that organizes tissue formation and a potent mitogenic signal driving cell proliferation. Dysregulated Hh signaling leads to various developmental defects in the brain. This article aims to review the roles of Hh signaling in the development of the neocortex in the mammalian brain, focusing on its regulation of neural progenitor proliferation and neuronal production. The review will summarize studies on genetic mouse models that have targeted different components of the Hh pathway, such as the ligand Shh, the receptor Ptch1, the GPCR-like transducer Smo, the intracellular transducer Sufu, and the three Gli transcription factors. As key insights into the Hh signaling transduction mechanism were obtained from mouse models displaying neural tube defects, this review will also cover some studies on Hh signaling in neural tube development. The results from these genetic mouse models suggest an intriguing hypothesis that elevated Hh signaling may play a role in the gyrification of the brain in certain species. Additionally, the distinctive production of GABAergic interneurons in the dorsal cortex in the human brain may also be linked to the extension of Hh signaling from the ventral to the dorsal brain region. Overall, these results suggest key roles of Hh signaling as both a morphogenic and mitogenic signal during the forebrain development and imply the potential involvement of Hh signaling in the evolutionary expansion of the neocortex.

Mutations in the IER3IP1 (Immediate Early Response-3 Interacting Protein 1) gene can give rise to MEDS1 (Microcephaly with Simplified Gyral Pattern, Epilepsy, and Permanent Neonatal Diabetes Syndrome-1), a severe condition leading to early childhood mortality. The small endoplasmic reticulum (ER)-membrane protein IER3IP1 plays a non-essential role in ER-Golgi transport. Here, we employed secretome and cell-surface proteomics to demonstrate that the absence of IER3IP1 results in the mistrafficking of proteins crucial for neuronal development and survival, including FGFR3, UNC5B and SEMA4D. This phenomenon correlates with the distension of ER membranes and increased lysosomal activity. Notably, the trafficking of cargo receptor ERGIC53 and KDEL-receptor 2 are compromised, with the latter leading to the anomalous secretion of ER-localized chaperones. Our investigation extended to in-utero knock-down of Ier3ip1 in mouse embryo brains, revealing a morphological phenotype in newborn neurons. In summary, our findings provide insights into how the loss or mutation of a 10 kDa small ER-membrane protein can cause a fatal syndrome. [ABSTRACT FROM AUTHOR]

Entosis, a form of cell cannibalism, is a newly discovered pathogenic mechanism leading to the development of small brains, termed microcephaly, in which P53 activation was found to play a major role. Microcephaly with entosis, found in Pals1 mutant mice, displays P53 activation that promotes entosis and apoptotic cell death. This previously unappreciated pathogenic mechanism represents a novel cellular dynamic in dividing cortical progenitors which is responsible for cell loss. To date, various recent models of microcephaly have bolstered the importance of P53 activation in cell death leading to microcephaly. P53 activation caused by mitotic delay or DNA damage manifests apoptotic cell death which can be suppressed by P53 removal in these animal models. Such genetic studies attest P53 activation as quality control meant to eliminate genomically unfit cells with minimal involvement in the actual function of microcephaly associated genes. In this review, we summarize the known role of P53 activation in a variety of microcephaly models and introduce a novel mechanism wherein entotic cell cannibalism in neural progenitors is triggered by P53 activation. [ABSTRACT FROM AUTHOR]

DDX3X syndrome is a neurodevelopmental disorder accounting for up to 3% of cases of intellectual disability (ID) and affecting primarily females. Individuals diagnosed with DDX3X syndrome can also present with behavioral challenges, motor delays and movement disorders, epilepsy, and congenital malformations. DDX3X syndrome is caused by mutations in the X‐linked gene DDX3X, which encodes a DEAD‐box RNA helicase with critical roles in RNA metabolism, including mRNA translation. Emerging discoveries from animal models are unveiling a fundamental role of DDX3X in neuronal differentiation and development, especially in the neocortex. Here, we review the current knowledge of genetic and neurobiological mechanisms underlying DDX3X syndrome and their relationship with clinical phenotypes. [ABSTRACT FROM AUTHOR]

Since the beautiful images of Santiago Ramón y Cajal provided a first glimpse into the immense diversity and complexity of cell types found in the cerebral cortex, neuroscience has been challenged and inspired to understand how these diverse cells are generated and how they interact with each other to orchestrate the development of this remarkable tissue. Some fundamental questions drive the field's quest to understand cortical development: what are the mechanistic principles that govern the emergence of neuronal diversity? How do extrinsic and intrinsic signals integrate with physical forces and activity to shape cell identity? How do the diverse populations of neurons and glia influence each other during development to guarantee proper integration and function? The advent of powerful new technologies to profile and perturb cortical development at unprecedented resolution and across a variety of modalities has offered a new opportunity to integrate past knowledge with brand new data. Here, we review some of this progress using cortical excitatory projection neurons as a system to draw out general principles of cell diversification and the role of cell-cell interactions during cortical development. In this review, Di Bella et al. provide a comprehensive overview of our current understanding of the multifactorial mechanisms that govern cellular diversification in the cerebral cortex, from cell-intrinsic processes to intercellular interactions. Advancing this knowledge is pivotal to deciphering the logic defining cortical development and how it goes awry in neurodevelopmental disease. [ABSTRACT FROM AUTHOR]

Introduction: γ-Aminobutyric acid (GABA) type A receptors (GABAARs) are ligand-gated Cl-channels that mediate the bulk of inhibitory neurotransmission in the mature CNS and are targets of many drugs. During cortical development, GABAAR-mediated signals are significantly modulated by changing subunit composition and expression of Cl-transporters as part of developmental processes and early network activity. To date, this developmental evolution has remained understudied, particularly at the level of cortical layer-specific changes. In this study, we characterized the expression of nine major GABAAR subunits and K-Cl transporter 2 (KCC2) in mouse somatosensory cortex from embryonic development to postweaning maturity. Methods: We evaluated expression of α1-5, β2-3, γ2, and δ GABAAR subunits using immunohistochemistry and Western blot techniques, and expression of KCC2 using immunohistochemistry in cortices from E13.5 to P25 mice. Results: We found that embryonic cortex expresses mainly α3, α5, β3, and γ2, while expression of α1, α2, α4, β2, δ, and KCC2 begins at later points in development; however, many patterns of nuanced expression can be found in specific lamina, cortical regions, and cells and structures. Discussion: While the general pattern of expression of each subunit and KCC2 is similar to previous studies, we found a number of unique temporal, regional, and laminar patterns that were previously unknown. These findings provide much needed knowledge of the intricate developmental evolution in GABAAR composition and KCC2 expression to accommodate developmental signals that transition to mature neurotransmission. [ABSTRACT FROM AUTHOR]

Background: Stimulant medication is commonly prescribed as treatment for attention-deficit/hyperactivity disorder (ADHD). While we previously found that short-term stimulant-treatment influences apparent cortical thickness development in an age-dependent manner, it remains unknown whether these effects persist throughout development into adulthood. Purpose: Investigate the long-term age-dependent effects of stimulant medication use on apparent cortical thickness development in adolescents and adults previously diagnosed with ADHD. Methods: This prospective study included the baseline and 4-year follow-up assessment of the "effects of Psychotropic drugs On the Developing brain-MPH" ("ePOD-MPH") project, conducted between June-1-2011 and December-28-2019. The analyses were pre-registered (https://doi.org/10.17605/OSF.IO/32BHF). T1-weighted MR scans were obtained from male adolescents and adults, and cortical thickness was estimated for predefined regions of interest (ROIs) using Freesurfer. We determined medication use and assessed symptoms of ADHD, anxiety, and depression at both time points. Linear mixed models were constructed to assess main effects and interactions of stimulant medication use, time, and age group on regional apparent cortical thickness. Results: A total of 32 male adolescents (aged mean ± SD, 11.2 ± 0.9 years at baseline) and 24 men (aged mean ± SD, 29.9 ± 5.0 years at baseline) were included that previously participated in the ePOD-MPH project. We found no evidence for long-term effects of stimulant medication use on ROI apparent cortical thickness. As expected, we did find age-by-time interaction effects in all ROIs (left prefrontal ROI: P=.002, right medial and posterior ROIs: P<.001), reflecting reductions in apparent cortical thickness in adolescents. Additionally, ADHD symptom severity (adolescents: P<.001, adults: P=.001) and anxiety symptoms (adolescents: P=0.03) were reduced, and more improvement of ADHD symptoms was associated with higher medication use in adults (P=0.001). Conclusion: We found no evidence for long-term effects of stimulant-treatment for ADHD on apparent cortical thickness development in adolescents and adults. The identified age-dependent differences in apparent cortical thickness development are consistent with existing literature on typical cortical development. [ABSTRACT FROM AUTHOR]

In utero infection and maternal inflammation can adversely impact fetal brain development. Maternal systemic illness, even in the absence of direct fetal brain infection, is associated with an increased risk of neuropsychiatric disorders in affected offspring. The cell types mediating the fetal brain response to maternal inflammation are largely unknown, hindering the development of novel treatment strategies. Here, we show that microglia, the resident phagocytes of the brain, highly express receptors for relevant pathogens and cytokines throughout embryonic development. Using a rodent maternal immune activation (MIA) model in which polyinosinic: polycytidylic acid is injected into pregnant mice, we demonstrate long-lasting transcriptional changes in fetal microglia that persist into postnatal life. We find that MIA induces widespread gene expression changes in neuronal and non-neuronal cells; importantly, these responses are abolished by selective genetic deletion of microglia, indicating that microglia are required for the transcriptional response of other cortical cell types to MIA. These findings demonstrate that microglia play a crucial durable role in the fetal response to maternal inflammation, and should be explored as potential therapeutic cell targets. [ABSTRACT FROM AUTHOR]

Background: Recent studies have shown that prenatal BPA exposure altered the transcriptome profiles of autism-related genes in the offspring's hippocampus, disrupting hippocampal neuritogenesis and causing male-specific deficits in learning. However, the sex differences in the effects of prenatal BPA exposure on the developing prefrontal cortex, which is another brain region highly implicated in autism spectrum disorder (ASD), have not been investigated. Methods: We obtained transcriptome data from RNA sequencing analysis of the prefrontal cortex of male and female rat pups prenatally exposed to BPA or control and reanalyzed. BPA-responsive genes associated with cortical development and social behaviors were selected for confirmation by qRT-PCR analysis. Neuritogenesis of primary cells from the prefrontal cortex of pups prenatally exposed to BPA or control was examined. The social behaviors of the pups were assessed using the two-trial and three-chamber tests. The male-specific impact of the downregulation of a selected BPA-responsive gene (i.e., Sema5a) on cortical development in vivo was interrogated using siRNA-mediated knockdown by an in utero electroporation technique. Results: Genes disrupted by prenatal BPA exposure were associated with ASD and showed sex-specific dysregulation. Sema5a and Slc9a9, which were involved in neuritogenesis and social behaviors, were downregulated only in males, while Anxa2 and Junb, which were also linked to neuritogenesis and social behaviors, were suppressed only in females. Neuritogenesis was increased in males and showed a strong inverse correlation with Sema5a and Slc9a9 expression levels, whereas, in the females, neuritogenesis was decreased and correlated with Anxa2 and Junb levels. The siRNA-mediated knockdown of Sema5a in males also impaired cortical development in utero. Consistent with Anxa2 and Junb downregulations, deficits in social novelty were observed only in female offspring but not in males. Conclusion: This is the first study to show that prenatal BPA exposure dysregulated the expression of ASD-related genes and functions, including cortical neuritogenesis and development and social behaviors, in a sex-dependent manner. Our findings suggest that, besides the hippocampus, BPA could also exert its adverse effects through sex-specific molecular mechanisms in the offspring's prefrontal cortex, which in turn would lead to sex differences in ASD-related neuropathology and clinical manifestations, which deserves further investigation. Highlights: Prenatal BPA exposure altered the transcriptome-interactome profiles of ASD-related genes in the offspring's prefrontal cortex in a sex-specific pattern. Primary prefrontal cortical neurons isolated from male pups prenatally exposed to BPA exhibited increased neuritogenesis, while that was decreased in the cells from female pups. Deficits in social novelty were observed only in female pups prenatally exposed to BPA but not in males. Sema5a and Slc9a9 were reduced and showed an inverse correlation with neuritogenesis only in male pups exposed to BPA but not in females, suggesting that these genes may negatively regulate neuritogenesis in a male-specific manner. Anxa2 and Junb were suppressed and showed a correlation with impaired social novelty behavior only in female pups exposed to BPA but not in males, suggesting that these genes are involved in BPA-mediated social impairment in females only. siRNA-mediated knockdown of Sema5a in male embryos increased neuronal migration in the developing cortex. [ABSTRACT FROM AUTHOR]

The mammalian brain, especially the cerebral cortex, has evolved to increase in size and complexity. The proper development of the cerebral cortex requires the coordination of several events, such as differentiation and migration, that are essential for forming a precise six-layered structure. We have previously reported that Cdk5-mediated phosphorylation of JIP1 at T205 modulates axonal outgrowth. However, the spatiotemporal expression patterns and functions of these three genes (Cdk5, Cdk5r1 or p35, and Mapk8ip1 or JIP1) in distinct cell types during cortical development remain unclear. In this study, we analyzed single-cell RNA-sequencing data of mouse embryonic cortex and discovered that Cdk5, p35, and JIP1 are dynamically expressed in intermediate progenitors (IPs). Pseudotime analysis revealed that the expression of these three genes was concomitantly upregulated in IPs during neuronal migration and differentiation. By manipulating the expression of JIP1 and phospho-mimetic JIP1 using in utero electroporation, we showed that phosphorylated JIP1 at T205 affected the temporal migration of neurons. [ABSTRACT FROM AUTHOR]

A theoretical account of development in mesocortical anatomy is derived from the free energy principle, operating in a neural field with both Hebbian and anti-Hebbian neural plasticity. An elementary structural unit is proposed, in which synaptic connections at mesoscale are arranged in paired patterns with mirror symmetry. Exchanges of synaptic flux in each pattern form coupled spatial eigenmodes, and the line of mirror reflection between the paired patterns operates as a Markov blanket, so that prediction errors in exchanges between the pairs are minimized. The theoretical analysis is then compared to the outcomes from a biological model of neocortical development, in which neuron precursors are selected by apoptosis for cell body and synaptic connections maximizing synchrony and also minimizing axonal length. It is shown that this model results in patterns of connection with the anticipated mirror symmetries, at micro-, meso- and inter-arial scales, among lateral connections, and in cortical depth. This explains the spatial organization and functional significance of neuron response preferences, and is compatible with the structural form of both columnar and noncolumnar cortex. Multi-way interactions of mirrored representations can provide a preliminary anatomically realistic model of cortical information processing. [ABSTRACT FROM AUTHOR]

In a recent study, Ziak et al. employed precise sparse labeling and spatiotemporally controlled genetic manipulations to uncover novel regulators of axon branching of layer 2/3 mouse callosal projection neurons. The authors elucidated a cell-autonomous signaling pathway wherein glycogen synthase kinase 3β (GSK3β) phosphorylation of microtubule-associated protein 1B (MAP1B) restricts interstitial axon branching by modulating microtubule (MT) tyrosination status. [ABSTRACT FROM AUTHOR]

The cerebral cortex contains billions of neurons, and their disorganization or misspecification leads to neurodevelopmental disorders. Understanding how the plethora of projection neuron subtypes are generated by cortical neural stem cells (NSCs) is a major challenge. Here, we focused on elucidating the transcriptional landscape of murine embryonic NSCs, basal progenitors (BPs), and newborn neurons (NBNs) throughout cortical development. We uncover dynamic shifts in transcriptional space over time and heterogeneity within each progenitor population. We identified signature hallmarks of NSC, BP, and NBN clusters and predict active transcriptional nodes and networks that contribute to neural fate specification. We find that the expression of receptors, ligands, and downstream pathway components is highly dynamic over time and throughout the lineage implying differential responsiveness to signals. Thus, we provide an expansive compendium of gene expression during cortical development that will be an invaluable resource for studying neural developmental processes and neurodevelopmental disorders.

The development of the neocortex involves an interplay between neural cells and the vasculature. However, little is known about this interplay at the ultrastructural level. To gain a 3D insight into the ultrastructure of the developing neocortex, we have analyzed the embryonic mouse neocortex by serial block-face scanning electron microscopy (SBF-SEM). In this study, we report a first set of findings that focus on the interaction of blood vessels, notably endothelial tip cells (ETCs), and the neural cells in this tissue. A key observation was that the processes of ETCs, located either in the ventricular zone (VZ) or subventricular zone (SVZ)/intermediate zone (IZ), can enter, traverse the cytoplasm, and even exit via deep plasma membrane invaginations of the host cells, including apical progenitors (APs), basal progenitors (BPs), and newborn neurons. More than half of the ETC processes were found to enter the neural cells. Striking examples of this ETC process “invasion” were (i) protrusions of apical progenitors or newborn basal progenitors into the ventricular lumen that contained an ETC process inside and (ii) ETC process-containing protrusions of neurons that penetrated other neurons. Our observations reveal a — so far unknown — complexity of the ETC–neural cell interaction. [ABSTRACT FROM AUTHOR]

The generation of neurons in the developing neocortex is a major determinant of neocortex size. Crucially, the increase in cortical neuron numbers in the primate lineage, notably in the upper-layer neurons, contributes to increased cognitive abilities. Here, we review major evolutionary changes affecting the apical progenitors in the ventricular zone and focus on the key germinal zone constituting the foundation of neocortical neurogenesis in primates, the outer subventricular zone (OSVZ). We summarize characteristic features of the OSVZ and its key stem cell type, the basal (or outer) radial glia. Next, we concentrate on primate-specific and human-specific genes, expressed in OSVZ-progenitors, the ability of which to amplify these progenitors by targeting the regulation of the cell cycle ultimately underlies the evolutionary increase in upper-layer neurons. Finally, we address likely differences in neocortical development between present-day humans and Neanderthals that are based on humanspecific amino acid substitutions in proteins operating in cortical progenitors. [ABSTRACT FROM AUTHOR]

Simple Summary: The mammalian cerebral cortex is believed to have gained complexity partly because of the abundance of specific cell types, collectively called basal progenitors. If these cells are deficient in the developing brain, it can lead to cortical structure anomalies, which have implications for defective brain function. Certain regulatory molecules have been found to control the production of basal progenitors during brain development. Key amongst them is the Paired Box 6 (Pax6) transcription factor and a chromatin modification mark called histone 3 lysine 9 acetylation (H3K9ac). However, our knowledge of how these regulatory factors interact to drive the generation of basal progenitors is insufficient. In this current work, we found that the enzyme involved in the acetylation of histone 3 at the 9th lysine interacts with Pax6 at the loci of genes critical for the production and amplification of the basal progenitor cell pool. As such, when both factors are decoupled or downregulated, it leads to depletion of the basal progenitor cells, resulting in a reduction in cortical development. The new mechanism identified deepens our understanding of cerebral cortex development and provides potential therapeutic cues for remedying brain abnormalities stemming from basal progenitor cell deficiency. Enrichment of basal progenitors (BPs) in the developing neocortex is a central driver of cortical enlargement. The transcription factor Pax6 is known as an essential regulator in generation of BPs. H3 lysine 9 acetylation (H3K9ac) has emerged as a crucial epigenetic mechanism that activates the gene expression program required for BP pool amplification. In this current work, we applied immunohistochemistry, RNA sequencing, chromatin immunoprecipitation and sequencing, and the yeast two-hybrid assay to reveal that the BP-genic effect of H3 acetylation is dependent on Pax6 functionality in the developing mouse cortex. In the presence of Pax6, increased H3 acetylation caused BP pool expansion, leading to enhanced neurogenesis, which evoked expansion and quasi-convolution of the mouse neocortex. Interestingly, H3 acetylation activation exacerbates the BP depletion and corticogenesis reduction effect of Pax6 ablation in cortex-specific Pax6 mutants. Furthermore, we found that H3K9 acetyltransferase KAT2A/GCN5 interacts with Pax6 and potentiates Pax6-dependent transcriptional activity. This explains a genome-wide lack of H3K9ac, especially in the promoter regions of BP-genic genes, in the Pax6 mutant cortex. Together, these findings reveal a mechanistic coupling of H3 acetylation and Pax6 in orchestrating BP production and cortical expansion through the promotion of a BP gene expression program during cortical development. [ABSTRACT FROM AUTHOR]

Subplate neurons (SpNs) are a heterogeneous neuronal population actively involved in early cortical circuit formation. In rodents, many SpNs survive and form layer 6b. The molecular heterogeneity of SpNs raises the question of whether different subpopulations of SpNs survive through the early postnatal period similarly and whether such diverse SpN populations in the auditory cortex (ACtx) share a common distribution pattern with other sensory systems. To address that, we investigated the expression pattern of multiple specific SpN markers in the ACtx, as well as in the visual (VCtx) and somatosensory (SCtx) cortices as controls, using complexin 3 (Cplx3) antibodies and different SpN‐specific Cre‐driver mice, such as connective tissue growth factor (CTGF), dopamine receptor D1 (Drd1a), and neurexophilin 4 (Nxph4). We focused on two early time windows in auditory development: (1) during the second postnatal week (PNW) before ear‐canal opening and (2) during the third PNW after ear‐canal opening. We compared the expression pattern of different SpN markers in ACtx with VCtx and SCtx. At both examined timepoints, Cplx3 and Nxph4 expressing SpNs form the largest and smallest population in the ACtx, respectively. Similar distribution patterns are observable in the VCtx and SCtx during the second PNW but not during the third PNW, for a higher proportion of Drd1a expressing SpNs is detected in the VCtx and CTGF expressing SpNs in the SCtx. This study suggests that different populations of SpNs might contribute differently to the development of individual sensory circuits. [ABSTRACT FROM AUTHOR]

Lissencephaly is a neurodevelopmental disorder characterized by a loss of brain surface convolutions caused by genetic variants that disrupt neuronal migration. However, the genetic origins of the disorder remain unidentified in nearly one-fifth of people with lissencephaly. Using whole-exome sequencing, we identified a de novo BAIAP2 variant, p.Arg29Trp, in an individual with lissencephaly with a posterior more severe than anterior (P>A) gradient, implicating BAIAP2 as a potential lissencephaly gene. Spatial transcriptome analysis in the developing mouse cortex revealed that Baiap2 is expressed in the cortical plate and intermediate zone in an anterior low to posterior high gradient. We next used in utero electroporation to explore the effects of the Baiap2 variant in the developing mouse cortex. We found that Baiap2 knockdown caused abnormalities in neuronal migration, morphogenesis and differentiation. Expression of the p.Arg29Trp variant failed to rescue themigration defect, suggesting a loss-of-function effect. Mechanistically, the variant interfered with the ability of BAIAP2 to localize to the cell membrane. These results suggest that the functions of BAIAP2 in the cytoskeleton, cell morphogenesis and migration are important for cortical development and for the pathogenesis of lissencephaly in humans. [ABSTRACT FROM AUTHOR]

Introductionγ-Aminobutyric acid (GABA) type A receptors (GABAARs) are ligand-gated Cl-channels that mediate the bulk of inhibitory neurotransmission in the mature CNS and are targets of many drugs. During cortical development, GABAAR-mediated signals are significantly modulated by changing subunit composition and expression of Cl-transporters as part of developmental processes and early network activity. To date, this developmental evolution has remained understudied, particularly at the level of cortical layer-specific changes. In this study, we characterized the expression of nine major GABAAR subunits and K-Cl transporter 2 (KCC2) in mouse somatosensory cortex from embryonic development to postweaning maturity.MethodsWe evaluated expression of α1-5, β2-3, γ2, and δ GABAAR subunits using immunohistochemistry and Western blot techniques, and expression of KCC2 using immunohistochemistry in cortices from E13.5 to P25 mice.ResultsWe found that embryonic cortex expresses mainly α3, α5, β3, and γ2, while expression of α1, α2, α4, β2, δ, and KCC2 begins at later points in development; however, many patterns of nuanced expression can be found in specific lamina, cortical regions, and cells and structures.DiscussionWhile the general pattern of expression of each subunit and KCC2 is similar to previous studies, we found a number of unique temporal, regional, and laminar patterns that were previously unknown. These findings provide much needed knowledge of the intricate developmental evolution in GABAAR composition and KCC2 expression to accommodate developmental signals that transition to mature neurotransmission.

BackgroundStimulant medication is commonly prescribed as treatment for attention-deficit/hyperactivity disorder (ADHD). While we previously found that short-term stimulant-treatment influences apparent cortical thickness development in an age-dependent manner, it remains unknown whether these effects persist throughout development into adulthood.PurposeInvestigate the long-term age-dependent effects of stimulant medication use on apparent cortical thickness development in adolescents and adults previously diagnosed with ADHD.MethodsThis prospective study included the baseline and 4-year follow-up assessment of the “effects of Psychotropic drugs On the Developing brain-MPH” (“ePOD-MPH”) project, conducted between June-1-2011 and December-28-2019. The analyses were pre-registered (https://doi.org/10.17605/OSF.IO/32BHF). T1-weighted MR scans were obtained from male adolescents and adults, and cortical thickness was estimated for predefined regions of interest (ROIs) using Freesurfer. We determined medication use and assessed symptoms of ADHD, anxiety, and depression at both time points. Linear mixed models were constructed to assess main effects and interactions of stimulant medication use, time, and age group on regional apparent cortical thickness.ResultsA total of 32 male adolescents (aged mean ± SD, 11.2 ± 0.9 years at baseline) and 24 men (aged mean ± SD, 29.9 ± 5.0 years at baseline) were included that previously participated in the ePOD-MPH project. We found no evidence for long-term effects of stimulant medication use on ROI apparent cortical thickness. As expected, we did find age-by-time interaction effects in all ROIs (left prefrontal ROI: P=.002, right medial and posterior ROIs: P

Higher cognition in humans, compared to other primates, is often attributed to an increased brain size, especially forebrain cortical surface area. Brain size is determined through highly orchestrated developmental processes, including neural stem cell proliferation, dierentiation, migration, lamination, arborization, and apoptosis. Disruption in these processes often results in either a small (microcephaly) or large (megalencephaly) brain. One of the key mechanisms controlling these developmental processes is the spatial and temporal transcriptional regulation of critical genes. In humans, microcephaly is defined as a condition with a significantly smaller head circumference compared to the average head size of a given age and sex group. A growing number of genes are identified as associated with microcephaly, and among them are those involved in transcriptional regulation. In this review, a subset of genes encoding transcription factors (e.g., homeobox-, basic helix-loop-helix-, forkhead box-, high mobility group box-, and zinc finger domain-containing transcription factors), whose functions are important for cortical development and implicated in microcephaly, are discussed. [ABSTRACT FROM AUTHOR]

Radial neuronal migration is a key neurodevelopmental event for proper cortical laminar organization. The multipolar-to-bipolar transition, a critical step in establishing neuronal polarity during radial migration, occurs in the subplate/intermediate zone (SP/IZ), a distinct region of the embryonic cerebral cortex. It has been known that the extracellular matrix (ECM) molecules are enriched in the SP/IZ. However, the molecular constitution and functions of the ECM formed in this region remain poorly understood. Here, we identified neurocan (NCAN) as a major chondroitin sulfate proteoglycan in the mouse SP/IZ. NCAN binds to both radial glial-cell-derived tenascin-C (TNC) and hyaluronan (HA), a large linear polysaccharide, forming a ternary complex of NCAN, TNC, and HA in the SP/IZ. Developing cortical neurons make contact with the ternary complex during migration. The enzymatic or genetic disruption of the ternary complex impairs radial migration by suppressing the multipolar-to-bipolar transition. Furthermore, both TNC and NCAN promoted the morphological maturation of cortical neurons in vitro. The present results provide evidence for the cooperative role of neuron- and radial glial-cell-derived ECM molecules in cortical development.

The development of the neocortex involves an interplay between neural cells and the vasculature. However, little is known about this interplay at the ultrastructural level. To gain a 3D insight into the ultrastructure of the developing neocortex, we have analyzed the embryonic mouse neocortex by serial block-face scanning electron microscopy (SBF-SEM). In this study, we report a first set of findings that focus on the interaction of blood vessels, notably endothelial tip cells (ETCs), and the neural cells in this tissue. A key observation was that the processes of ETCs, located either in the ventricular zone (VZ) or subventricular zone (SVZ)/intermediate zone (IZ), can enter, traverse the cytoplasm, and even exit via deep plasma membrane invaginations of the host cells, including apical progenitors (APs), basal progenitors (BPs), and newborn neurons. More than half of the ETC processes were found to enter the neural cells. Striking examples of this ETC process “invasion” were (i) protrusions of apical progenitors or newborn basal progenitors into the ventricular lumen that contained an ETC process inside and (ii) ETC process-containing protrusions of neurons that penetrated other neurons. Our observations reveal a — so far unknown — complexity of the ETC–neural cell interaction.

Neurodevelopmental disorders (NDDs) are a collection of diseases with early life onset that often present with developmental delay, cognitive deficits, and behavioral conditions. In some cases, severe outcomes such as brain malformations and intractable epilepsy can occur. The mutations underlying NDDs may be inherited or de novo, can be gain- or loss-of-function, and can affect one or more genes. Recent evidence indicates that brain somatic mutations contribute to several NDDs, in particular malformations of cortical development. While advances in sequencing technologies have enabled the detection of these somatic mutations, the mechanisms by which they alter brain development and function are not well understood due to limited model systems that recapitulate these events. Human brain organoids have emerged as powerful models to study the early developmental events of the human brain. Brain organoids capture the developmental progression of the human brain and contain human-enriched progenitor cell types. Advances in human stem cell and genome engineering provide an opportunity to model NDD-associated somatic mutations in brain organoids. These organoids can be tracked throughout development to understand the impact of somatic mutations on early human brain development and function. In this review, we discuss recent evidence that somatic mutations occur in the developing human brain, that they can lead to NDDs, and discuss how they could be modeled using human brain organoids.

Mutations in the RNA helicase, DDX3X, are a leading cause of Intellectual Disability and present as DDX3X syndrome, a neurodevelopmental disorder associated with cortical malformations and autism. Yet, the cellular and molecular mechanisms by which DDX3X controls cortical development are largely unknown. Here, using a mouse model of Ddx3x loss-of-function we demonstrate that DDX3X directs translational and cell cycle control of neural progenitors, which underlies precise corticogenesis. First, we show brain development is sensitive to Ddx3x dosage; complete Ddx3x loss from neural progenitors causes microcephaly in females, whereas hemizygous males and heterozygous females show reduced neurogenesis without marked microcephaly. In addition, Ddx3x loss is sexually dimorphic, as its paralog, Ddx3y, compensates for Ddx3x in the developing male neocortex. Using live imaging of progenitors, we show that DDX3X promotes neuronal generation by regulating both cell cycle duration and neurogenic divisions. Finally, we use ribosome profiling in vivo to discover the repertoire of translated transcripts in neural progenitors, including those which are DDX3X-dependent and essential for neurogenesis. Our study reveals invaluable new insights into the etiology of DDX3X syndrome, implicating dysregulated progenitor cell cycle dynamics and translation as pathogenic mechanisms.

Human brain development is a complex process, and animal models often have significant limitations. To address this, researchers have developed pluripotent stem cell-derived three-dimensional structures, known as brain-like organoids, to more accurately model early human brain development and disease. To enable more consistent and intuitive reproduction of early brain development, in this study, we incorporated forebrain organoid culture technology into the traditional unguided method of brain organoid culture. This involved embedding organoids in matrigel for only 7 days during the rapid expansion phase of the neural epithelium and then removing them from the matrigel for further cultivation, resulting in a new type of human brain organoid system. This cerebral organoid system replicated the temporospatial characteristics of early human brain development, including neuroepithelium derivation, neural progenitor cell production and maintenance, neuron differentiation and migration, and cortical layer patterning and formation, providing more consistent and reproducible organoids for developmental modeling and toxicology testing. As a proof of concept, we applied the heavy metal cadmium to this newly improved organoid system to test whether it could be used to evaluate the neurotoxicity of environmental toxins. Brain organoids exposed to cadmium for 7 or 14 days manifested severe damage and abnormalities in their neurodevelopmental patterns, including bursts of cortical cell death and premature differentiation. Cadmium exposure caused progressive depletion of neural progenitor cells and loss of organoid integrity, accompanied by compensatory cell proliferation at ectopic locations. The convenience, flexibility, and controllability of this newly developed organoid platform make it a powerful and affordable alternative to animal models for use in neurodevelopmental, neurological, and neurotoxicological studies.

Depth perception emerges from the development of binocular neurons in primary visual cortex. Vision is required for these neurons to acquire their mature responses to visual stimuli. The prevailing view is that vision does not influence binocular circuitry until the onset of the critical period, about a week after eye opening, and that plasticity of visual responses is triggered by increased inhibition. Here, we show that vision is required to form binocular neurons and to improve binocular tuning and matching from eye opening until critical period closure. Enhancing inhibition does not accelerate this process. Vision soon after eye opening improves the tuning properties of binocular neurons by strengthening and sharpening ipsilateral eye cortical responses. This progressively changes the population of neurons in the binocular pool, and this plasticity is sensitive to interocular differences prior to critical period onset. Thus, vision establishes binocular circuitry and guides binocular plasticity from eye opening.

Microglial cells, the innate immune cells of the brain, are derived from yolk sac precursor cells, begin to colonize the telencephalon at the onset of cortical neurogenesis, and occupy specific layers including the telencephalic proliferative zones. Microglia are an intrinsic component of cortical germinal zones, establish extensive contacts with neural precursor cells (NPCs) and developing cortical vessels, and regulate the size of the NPC pool through mechanisms that include phagocytosis. Microglia exhibit notable differences in number and distribution in the prenatal neocortex between rat and old world nonhuman primate telencephalon, suggesting that microglia possess distinct properties across vertebrate species. To begin addressing this subject, we quantified the number of microglia and NPCs in proliferative zones of the fetal human, rhesus monkey, ferret, and rat, and the prehatch chick and turtle telencephalon. We show that the ratio of NPCs to microglia varies significantly across species. Few microglia populate the prehatch chick telencephalon, but the number of microglia approaches that of NPCs in fetal human and nonhuman primate telencephalon. These data demonstrate that microglia are in a position to perform important functions in a number of vertebrate species but more heavily colonize proliferative zones of fetal human and rhesus monkey telencephalon.

The primary objective was to evaluate the effects of fetal sex on fetal cortical development in low-risk pregnancies. Secondary objective was the evaluate the impact of gestational age. This was a secondary analysis of a prospective cross-sectional study on low-risk fetuses undergoing fetal neurosonography between 19 and 34 weeks of gestation. The depth of Sylvian Fissure (SF), Parieto Occipital Fissure (POF) and Calcarine Fissure (CF) were evaluated and related to fetal sex. Neurosonographic variables were normalized for fetal head circumference and expressed as multiple of the median (MoM). A total of 344 fetuses were considered (173 male, 171 female). The baseline characteristic of the two groups were similar except a higher birthweight present in male fetuses (p=0.044). The depth SF (p=0.023) CF (p=0.014) and POF (p=0.046) showed significantly higher values in male fetuses when all the gestational age range was considered. However, when data were controlled for gestational age, these differences resulted significant only after 28 weeks. Differences in cortical development related to gender occur after 28 weeks of gestation with an increase depth of SF, POF and CF in male fetuses. [ABSTRACT FROM AUTHOR]

Hyperactivation of the mechanistic target of rapamycin complex 1 (mTORC1) pathway during neurodevelopment leads to focal cortical malformations associated with intractable seizures. Recent evidence suggests that dysregulated cap-dependent translation downstream of mTORC1 contributes to cytoarchitectural abnormalities and seizure activity. Here, we examined whether reducing capdependent translation by expressing a constitutively active form of the translational repressor, 4E-BP1, downstream of mTORC1 would prevent the development of cortical malformations and seizures. 4E-BP1CA was expressed embryonically either in radial glia (neural progenitor cells) that generate cortical layer 2/3 pyramidal neurons or in migrating neurons destined to layer 2/3 using a conditional expression system. In both conditions, 4E-BP1CA expression reduced mTORC1-induced neuronal hypertrophy and alleviated cortical mislamination, but a subset of ectopic neurons persisted in the deep layers and the white matter. Despite the above improvements, 4E-BP1CA expression in radial glia had no effects on seizure frequency and further exacerbated behavioral seizure severity associated with mTORC1 hyperactivation. In contrast, conditional 4E-BP1CA expression in migratory neurons mitigated the severity of behavioral seizures but the seizure frequency remained unchanged. These findings advise against targeting 4E-BPs by 4E-BP1CA expression during embryonic development for seizure prevention and suggest the presence of a development-dependent role for 4E-BPs in mTORC1-induced epilepsy. [ABSTRACT FROM AUTHOR]

Studying dynamic spatiotemporal patterns of early brain development in macaque monkeys is critical for understanding the cortical organization and evolution in humans, given the phylogenetic closeness between humans and macaques. However, due to huge challenges in the analysis of early brain Magnetic Resonance Imaging (MRI) data typically with extremely low contrast and dynamic imaging appearances, our knowledge of the early macaque cortical development remains scarce. To fill this critical gap, this paper characterizes the early developmental patterns of cortical thickness and surface area in rhesus macaques by leveraging advanced computing tools tailored for early developing brains based on a densely sampled longitudinal dataset with 140 rhesus macaque MRI scans seamlessly covering from birth to 36 mo of age. The average cortical thickness exhibits an inverted U-shaped trajectory with peak thickness at around 4.3 mo of age, which is remarkably in line with the age of peak thickness at 14 mo in humans, considering the around 3:1 age ratio of human to macaque. The total cortical surface area in macaques increases monotonically but with relatively lower expansions than in humans. The spatial distributions of thicker and thinner regions are quite consistent during development, with gyri having a thicker cortex than sulci. By 4 mo of age, over 81% of cortical vertices have reached their peaks in thickness, except for the insula and medial temporal cortices, while most cortical vertices keep expanding in surface area, except for the occipital cortex. These findings provide important insights into early brain development and evolution in primates. [ABSTRACT FROM AUTHOR]

Background: Stress exposure in childhood and adolescence has been linked to reductions in cortical structures and cognitive functioning. However, to date, most of these studies have been cross‐sectional, limiting the ability to make long‐term inferences, given that most cortical structures continue to develop through adolescence. Methods: Here, we used a subset of the IMAGEN population cohort sample (N = 502; assessment ages: 14, 19, and 22 years; mean age: 21.945 years; SD = 0.610) to understand longitudinally the long‐term interrelations between stress, cortical development, and cognitive functioning. To these ends, we first used a latent change score model to examine four bivariate relations – assessing individual differences in change in the relations between adolescent stress exposure and volume, surface area, and cortical thickness of cortical structures, as well as cognitive outcomes. Second, we probed for indirect neurocognitive effects linking stress to cortical brain structures and cognitive functions using rich longitudinal mediation modeling. Results: Latent change score modeling showed that greater baseline adolescence stress at age 14 predicted a small reduction in the right anterior cingulate volume (Std. β = −.327, p =.042, 95% CI [−0.643, −0.012]) and right anterior cingulate surface area (Std. β = −.274, p =.038, 95% CI [−0.533, −0.015]) across ages 14–22. These effects were very modest in nature and became nonsignificant after correcting for multiple comparisons. Our longitudinal analyses found no evidence of indirect effects in the two neurocognitive pathways linking adolescent stress to brain and cognitive outcomes. Conclusion: Findings shed light on the impact of stress on brain reductions, particularly in the prefrontal cortex that have consistently been implicated in the previous cross‐sectional studies. However, the magnitude of effects observed in our study is smaller than that has been reported in past cross‐sectional work. This suggests that the potential impact of stress during adolescence on brain structures may likely be more modest than previously noted. [ABSTRACT FROM AUTHOR]

The mosaic variegated aneuploidy (MVA)-associated gene Budding Uninhibited by Benzimidazole 1B (BUB1B) encodes BUBR1, a core member of the spindle assembly checkpoint complex that ensures kinetochore-spindle attachment for faithful chromosome segregation. BUB1B mutation in humans and its deletion in mice cause microcephaly. In the absence of BubR1 in mice, massive cell death reduces cortical cells during neurogenesis. However, the molecular and cellular mechanisms triggering cell death are unknown. In this study, we performed three-dimensional imaging analysis of mitotic BubR1-deficient neural progenitors in a murine model to show profound chromosomal segregation defects and structural abnormalities. Chromosomal defects and accompanying DNA damage result in P53 activation and apoptotic cell death in BubR1 mutants. To test whether the P53 cell death pathway is responsible for cortical cell loss, we co-deleted Trp53 in BubR1-deficient cortices. Remarkably, we discovered that residual apoptotic cell death remains in double mutants lacking P53, suggesting P53-independent apoptosis. Furthermore, the minimal rescue of cortical size and cortical neuron numbers in double mutant mice suggests the compelling extent of alternative death mechanisms in the absence of P53. This study demonstrates a potential pathogenic mechanism for microcephaly in MVA patients and uncovers the existence of powerful means of eliminating unfit cells even when the P53 death pathway is disabled.

Development is a complex process involving precise regulation. Developmental regulation may vary in tissues and individuals, and is often altered in disorders. Currently, the regulation of developmental timing across neocortical areas and developmental changes in Down syndrome (DS) brains remain unclear. The changes in regulation are often accompanied by changes in the gene expression trajectories, which can be divided into two scenarios: (1) changes of gene expression trajectory shape that reflect changes in cell type composition or altered molecular machinery; (2) temporal shift of gene expression trajectories that indicate different regulation of developmental timing. Therefore, we developed an R package TempShift to separates these two scenarios and demonstrated that TempShift can distinguish temporal shift from different shape (DiffShape) of expression trajectories, and can accurately estimate the time difference between multiple trajectories. We applied TempShift to identify sequential gene expression across 11 neocortical areas, which suggested sequential occurrence of synapse formation and axon guidance, as well as reconstructed interneuron migration pathways within neocortex. Comparison between healthy and DS brains revealed increased microglia, shortened neuronal migration process, and delayed synaptogenesis and myelination in DS. These applications also demonstrate the potential of TempShift in understanding gene expression temporal dynamics during different biological processes. [ABSTRACT FROM AUTHOR]

As the highest center of sensory processing, initiation, and modulation of behavior, the pallium has seen prominent changes during the course of vertebrate evolution, culminating in the emergence of the mammalian isocortex. The processes underlying this remarkable evolution have been a matter of debate for several centuries. Recent studies using modern techniques in a host of vertebrate species are beginning to reveal mechanistic principles underlying pallial evolution from the developmental, connectome, transcriptome and cell type levels. We attempt here to trace and reconstruct the evolution of pallium from an evo-devo perspective, focusing on two phylogenetic extremes in vertebrates – cyclostomes and mammals, while considering data from intercalated species. We conclude that two fundamental processes of evolutionary change – conservation and diversification of cell types, driven by functional demands, are the primary forces dictating the emergence of the diversity of pallial structures and imbibing them with the ability to mediate and control the exceptional variety of motor behaviors across vertebrates. [ABSTRACT FROM AUTHOR]

Microglial cells make extensive contacts with neural precursor cells (NPCs) and affiliate with vasculature in the developing cerebral cortex. But how vasculature contributes to cortical histogenesis is not yet fully understood. To better understand functional roles of developing vasculature in the embryonic rat cerebral cortex, we investigated the temporal and spatial relationships between vessels, microglia, and NPCs in the ventricular zone. Our results show that endothelial cells in developing cortical vessels extend numerous fine processes that directly contact mitotic NPCs and microglia; that these processes protrude from vessel walls and are distinct from tip cell processes; and that microglia, NPCs, and vessels are highly interconnected near the ventricle. These findings demonstrate the complex environment in which NPCs are embedded in cortical proliferative zones and suggest that developing vasculature represents a source of signaling with the potential to broadly influence cortical development. In summary, cortical histogenesis arises from the interplay among NPCs, microglia, and developing vasculature. Thus, factors that impinge on any single component have the potential to change the trajectory of cortical development and increase susceptibility for altered neurodevelopmental outcomes.

Folate is an essential micronutrient required for both cellular proliferation through de novo nucleotide synthesis and epigenetic regulation of gene expression through methylation. This dual requirement places a particular demand on folate availability during pregnancy when both rapid cell generation and programmed differentiation of maternal, extraembryonic, and embryonic/fetal tissues are required. Accordingly, prenatal neurodevelopment is particularly susceptible to folate deficiency, which can predispose to neural tube defects, or when effective transport into the brain is impaired, cerebral folate deficiency. Consequently, adequate folate consumption, in the form of folic acid (FA) fortification and supplement use, is widely recommended and has led to a substantial increase in the amount of FA intake during pregnancy in some populations. Here, we show that either maternal folate deficiency or FA excess in mice results in disruptions in folate metabolism of the offspring, suggesting diversion of the folate cycle from methylation to DNA synthesis. Paradoxically, either intervention causes comparable neurodevelopmental changes by delaying prenatal cerebral cortical neurogenesis in favor of late-born neurons. These cytoarchitectural and biochemical alterations are accompanied by behavioral abnormalities in FA test groups compared with controls. Our findings point to overlooked potential neurodevelopmental risks associated with excessively high levels of prenatal FA intake.

Cerebral cortex projection neurons (PNs) are generated from intermediate progenitors (IPs), which are in turn derived from radial glial progenitors (RGPs). To investigate developmental processes in IPs, we profiled IP transcriptomes in embryonic mouse neocortex, using transgenic Tbr2-GFP mice, cell sorting, and microarrays. These data were used in combination with in situ hybridization to ascertain gene sets specific for IPs, RGPs, PNs, interneurons, and other neural and non-neural cell types. RGP-selective transcripts (n = 419) included molecules for Notch receptor signaling, proliferation, neural stem cell identity, apical junctions, necroptosis, hippo pathway, and NF-κB pathway. RGPs also expressed specific genes for critical interactions with meningeal and vascular cells. In contrast, IP-selective genes (n = 136) encoded molecules for activated Delta ligand presentation, epithelial-mesenchymal transition, core planar cell polarity (PCP), axon genesis, and intrinsic excitability. Interestingly, IPs expressed several "dependence receptors" (Unc5d, Dcc, Ntrk3, and Epha4) that induce apoptosis in the absence of ligand, suggesting a competitive mechanism for IPs and new PNs to detect key environmental cues or die. Overall, our results imply a novel role for IPs in the patterning of neuronal polarization, axon differentiation, and intrinsic excitability prior to mitosis. Significantly, IPs highly express Wnt-PCP, netrin, and semaphorin pathway molecules known to regulate axon polarization in other systems. In sum, IPs not only amplify neurogenesis quantitatively, but also molecularly "prime" new PNs for axogenesis, guidance, and excitability.

Folate is an essential micronutrient required for both cellular proliferation through de novo nucleotide synthesis and epigenetic regulation of gene expression through methylation. This dual requirement places a particular demand on folate availability during pregnancy when both rapid cell generation and programmed differentiation of maternal, extraembryonic, and embryonic/fetal tissues are required. Accordingly, prenatal neurodevelopment is particularly susceptible to folate deficiency, which can predispose to neural tube defects, or when effective transport into the brain is impaired, cerebral folate deficiency. Consequently, adequate folate consumption, in the form of folic acid (FA) fortification and supplement use, is widely recommended and has led to a substantial increase in the amount of FA intake during pregnancy in some populations. Here, we show that either maternal folate deficiency or FA excess in mice results in disruptions in folate metabolism of the offspring, suggesting diversion of the folate cycle from methylation to DNA synthesis. Paradoxically, either intervention causes comparable neurodevelopmental changes by delaying prenatal cerebral cortical neurogenesis in favor of late-born neurons. These cytoarchitectural and biochemical alterations are accompanied by behavioral abnormalities in FA test groups compared with controls. Our findings point to overlooked potential neurodevelopmental risks associated with excessively high levels of prenatal FA intake.

Abstract Background Disruptions of SETBP1 (SET binding protein 1) on 18q12.3 by heterozygous gene deletion or loss-of-function variants cause SETBP1 disorder. Clinical features are frequently associated with moderate to severe intellectual disability, autistic traits and speech and motor delays. Despite the association of SETBP1 with neurodevelopmental disorders, little is known about its role in brain development. Methods Using CRISPR/Cas9 genome editing technology, we generated a SETBP1 deletion model in human embryonic stem cells (hESCs) and examined the effects of SETBP1-deficiency in neural progenitors (NPCs) and neurons derived from these stem cells using a battery of cellular assays, genome-wide transcriptomic profiling and drug-based phenotypic rescue. Results Neural induction occurred efficiently in all SETBP1 deletion models as indicated by uniform transition into neural rosettes. However, SETBP1-deficient NPCs exhibited an extended proliferative window and a decrease in neurogenesis coupled with a deficiency in their ability to acquire ventral forebrain fate. Genome-wide transcriptome profiling and protein biochemical analysis revealed enhanced activation of Wnt/β-catenin signaling in SETBP1 deleted cells. Crucially, treatment of the SETBP1-deficient NPCs with a small molecule Wnt inhibitor XAV939 restored hyper canonical β-catenin activity and restored both cortical and MGE neuronal differentiation. Limitations The current study is based on analysis of isogenic hESC lines with genome-edited SETBP1 deletion and further studies would benefit from the use of patient-derived iPSC lines that may harbor additional genetic risk that aggravate brain pathology of SETBP1 disorder. Conclusions We identified an important role for SETBP1 in controlling forebrain progenitor expansion and neurogenic differentiation. Our study establishes a novel regulatory link between SETBP1 and Wnt/β-catenin signaling during human cortical neurogenesis and provides mechanistic insights into structural abnormalities and potential therapeutic avenues for SETBP1 disorder.

A theoretical account of development in mesocortical anatomy is derived from the free energy principle, operating in a neural field with both Hebbian and anti-Hebbian neural plasticity. An elementary structural unit is proposed, in which synaptic connections at mesoscale are arranged in paired patterns with mirror symmetry. Exchanges of synaptic flux in each pattern form coupled spatial eigenmodes, and the line of mirror reflection between the paired patterns operates as a Markov blanket, so that prediction errors in exchanges between the pairs are minimized. The theoretical analysis is then compared to the outcomes from a biological model of neocortical development, in which neuron precursors are selected by apoptosis for cell body and synaptic connections maximizing synchrony and also minimizing axonal length. It is shown that this model results in patterns of connection with the anticipated mirror symmetries, at micro-, meso- and inter-arial scales, among lateral connections, and in cortical depth. This explains the spatial organization and functional significance of neuron response preferences, and is compatible with the structural form of both columnar and noncolumnar cortex. Multi-way interactions of mirrored representations can provide a preliminary anatomically realistic model of cortical information processing.

Enrichment of basal progenitors (BPs) in the developing neocortex is a central driver of cortical enlargement. The transcription factor Pax6 is known as an essential regulator in generation of BPs. H3 lysine 9 acetylation (H3K9ac) has emerged as a crucial epigenetic mechanism that activates the gene expression program required for BP pool amplification. In this current work, we applied immunohistochemistry, RNA sequencing, chromatin immunoprecipitation and sequencing, and the yeast two-hybrid assay to reveal that the BP-genic effect of H3 acetylation is dependent on Pax6 functionality in the developing mouse cortex. In the presence of Pax6, increased H3 acetylation caused BP pool expansion, leading to enhanced neurogenesis, which evoked expansion and quasi-convolution of the mouse neocortex. Interestingly, H3 acetylation activation exacerbates the BP depletion and corticogenesis reduction effect of Pax6 ablation in cortex-specific Pax6 mutants. Furthermore, we found that H3K9 acetyltransferase KAT2A/GCN5 interacts with Pax6 and potentiates Pax6-dependent transcriptional activity. This explains a genome-wide lack of H3K9ac, especially in the promoter regions of BP-genic genes, in the Pax6 mutant cortex. Together, these findings reveal a mechanistic coupling of H3 acetylation and Pax6 in orchestrating BP production and cortical expansion through the promotion of a BP gene expression program during cortical development.

Hyperactivation of the mechanistic target of rapamycin complex 1 (mTORC1) pathway during neurodevelopment leads to focal cortical malformations associated with intractable seizures. Recent evidence suggests that dysregulated cap-dependent translation downstream of mTORC1 contributes to cytoarchitectural abnormalities and seizure activity. Here, we examined whether reducing cap-dependent translation by expressing a constitutively active form of the translational repressor, 4E-BP1, downstream of mTORC1 would prevent the development of cortical malformations and seizures. 4E-BP1CA was expressed embryonically either in radial glia (neural progenitor cells) that generate cortical layer 2/3 pyramidal neurons or in migrating neurons destined to layer 2/3 using a conditional expression system. In both conditions, 4E-BP1CA expression reduced mTORC1-induced neuronal hypertrophy and alleviated cortical mislamination, but a subset of ectopic neurons persisted in the deep layers and the white matter. Despite the above improvements, 4E-BP1CA expression in radial glia had no effects on seizure frequency and further exacerbated behavioral seizure severity associated with mTORC1 hyperactivation. In contrast, conditional 4E-BP1CA expression in migratory neurons mitigated the severity of behavioral seizures but the seizure frequency remained unchanged. These findings advise against targeting 4E-BPs by 4E-BP1CA expression during embryonic development for seizure prevention and suggest the presence of a development-dependent role for 4E-BPs in mTORC1-induced epilepsy.

The central nervous system contains a myriad of different cell types produced from multipotent neural progenitors. Neural progenitors acquire distinct cell identities depending on their spatial position, but they are also influenced by temporal cues to give rise to different cell populations over time. For instance, the progenitors of the cerebral neocortex generate different populations of excitatory projection neurons following a well-known sequence. The Notch signaling pathway plays crucial roles during this process, but the molecular mechanisms by which Notch impacts progenitor fate decisions have not been fully resolved. Here, we show that Notch signaling is essential for neocortical and hippocampal morphogenesis, and for the development of the corpus callosum and choroid plexus. Our data also indicate that, in the neocortex, Notch controls projection neuron fate determination through the regulation of two microRNA clusters that include let-7, miR-99a/100 and miR-125b. Our findings collectively suggest that balanced Notch signaling is crucial for telencephalic development and that the interplay between Notch and miRNAs is essential for the control of neocortical progenitor behaviors and neuron cell fate decisions. [ABSTRACT FROM AUTHOR]

The development of precise neural circuits in the brain requires spontaneous patterns of neural activity prior to functional maturation. In the rodent cerebral cortex, patchwork and wave patterns of activity develop in somatosensory and visual regions, respectively, and are present at birth. However, whether such activity patterns occur in noneutherian mammals, as well as when and how they arise during development, remain open questions relevant for understanding brain formation in health and disease. Since the onset of patterned cortical activity is challenging to study prenatally in eutherians, here we offer an approach in a minimally invasive manner using marsupial dunnarts, whose cortex forms postnatally. We discovered similar patchwork and travelling waves in the dunnart somatosensory and visual cortices at stage 27 (equivalent to newborn mice) and examined earlier stages of development to determine the onset of these patterns and how they first emerge. We observed that these patterns of activity emerge in a region-specific and sequential manner, becoming evident as early as stage 24 in somatosensory and stage 25 in visual cortices (equivalent to embryonic day 16 and 17, respectively, in mice), as cortical layers establish and thalamic axons innervate the cortex. In addition to sculpting synaptic connections of existing circuits, evolutionarily conserved patterns of neural activity could therefore help regulate other early events in cortical development. [ABSTRACT FROM AUTHOR]