Embryology

Impact of Intrauterine Insults on Fetal and Postnatal Cerebellar Development in Humans and Rodents

Many children suffer from neurodevelopmental aberrations that have long-term effects. To understand the consequences of pathological processes during particular periods in neurodevelopment, one has to understand the differences in the developmental timelines of brain regions. The cerebellum is one of the first brain structures to differentiate during development but one of the last to achieve maturity. This relatively long period of development underscores its vulnerability to detrimental environmental exposures throughout gestation. Moreover, as postnatal functionality of the cerebellum is multifaceted, enveloping sensorimotor, cognitive, and emotional domains, prenatal disruptions in cerebellar development can result in a large variety of neurological and mental health disorders. Here, we review major intrauterine insults that affect cerebellar development in both humans and rodents, ranging from abuse of toxic chemical agents, such as alcohol, nicotine, cannabis, and opioids, to stress, malnutrition, and infections. Understanding these pathological mechanisms in the context of the different stages of cerebellar development in humans and rodents can help us to identify critical and vulnerable periods and thereby prevent the risk of associated prenatal and early postnatal damage that can lead to lifelong neurological and cognitive disabilities. The aim of the review is to raise awareness and to provide information for obstetricians and other healthcare professionals to eventually design strategies for preventing or rescuing related neurodevelopmental disorders.

Anomalies of Midbrain/Hindbrain Development and Related Disabilities: Pontocerebellar Hypoplasia, Congenital Disorders of Glycosylation, and Cerebellar Hemisphere Hypoplasia

Recent progress in developmental biology, molecular genetics, and neuroimaging has enabled a more profound comprehension of developmental disorders affecting the embryonic midbrain and hindbrain, which manifest clinically. The purpose of this review is to describe anomalies of the midbrain/hindbrain such as pontocerebellar hypoplasia (PCH), congenital disorders of glycosylation (CDG), cerebellar hemisphere hypoplasia. PCH is a group of disorders that is both clinically and genetically diverse. These disorders are identified by the hypoplasia and degeneration of the cerebellum and ventral pons. A total of 18 distinct clinical subtypes of PCH, each linked to pathogenic variants in 19 different genes, have been documented, like mutations in TSEN54 (coding a subunit of tRNA splicing endonucleases complex) and TBC1D23 which display moderate-to-severe intellectual disability (ID) and microcephaly. CDG represent a set of inherited conditions marked by impaired glycosylation of proteins and lipids. The most prevalent subtype among CDG is PMM2-CDG, inherited in a recessive manner, causing reduced activity of phosphomannomutase. Its phenotype varies from mild to severe, involving the central nervous system and affecting many other organs as well. Patients who are severely affected also exhibit visceral symptoms alongside severe ID and other neurological manifestations. Cerebellar hypoplasia (CH) is characterized by a cerebellum of diminished volume while maintaining its shape. CH exhibits a diverse range of neuroradiologic features, etiologies, clinical characteristics, and neurodevelopmental involvement. Cerebello–oculo–facio–genital syndrome is linked to a recessive MAB21L1 mutation. Jubert's syndrome, associated with a rare autosomal recessive mutation, is identified on magnetic resonance imaging by cerebellar worm hypoplasia and midbrain malformations. The rhombencephalosynapsis, characterized by vermian agenesis or hypogenesis with the fusion of the cerebellar hemispheres, emerges during embryogenesis. It can manifest alone or in conjunction with other and/or extracerebral abnormalities.

Convolutional Neural Network for Fully Automated Cerebellar Volumetry in Children in Comparison to Manual Segmentation and Developmental Trajectory of Cerebellar Volumes

The purpose of this study was to develop a fully automated and reliable volumetry of the cerebellum of children during infancy and childhood using deep learning algorithms in comparison to manual segmentation. In addition, the clinical usefulness of measuring the cerebellar volume is shown. One hundred patients (0 to 16.3 years old) without infratentorial signal abnormalities on conventional MRI were retrospectively selected from our pool of pediatric MRI examinations. Based on a routinely acquired 3D T1-weighted magnetization prepared rapid gradient echo (MPRAGE) sequence, the cerebella were manually segmented using ITK-SNAP. The data set of all 100 cases was divided into four splits (four-fold cross-validation) to train the network (NN) to delineate the boundaries of the cerebellum. First, the accuracy of the newly created neural network was compared with the manual segmentation. Secondly, age-related volume changes were investigated. Our trained NN achieved an excellent Spearman correlation coefficient of 0.99, a Dice Coefficient of 95.0 ± 2.1%, and an intersection over union (IoU) of 90.6 ± 3.8%. Cerebellar volume increased continuously with age, showing an exponentially rapid growth within the first year of life. Using a convolutional neural network, it was possible to achieve reliable, fully automated cerebellar volume measurements in childhood and infancy, even when based on a relatively small cohort. In this preliminary study, age-dependent cerebellar volume changes could be acquired.

Pleiotrophin and the Expression of Its Receptors during Development of the Human Cerebellar Cortex

During embryonic and fetal development, the cerebellum undergoes several histological changes that require a specific microenvironment. Pleiotrophin (PTN) has been related to cerebral and cerebellar cortex ontogenesis in different species. PTN signaling includes PTPRZ1, ALK, and NRP-1 receptors, which are implicated in cell differentiation, migration, and proliferation. However, its involvement in human cerebellar development has not been described so far. Therefore, we investigated whether PTN and its receptors were expressed in the human cerebellar cortex during fetal and early neonatal development. The expression profile of PTN and its receptors was analyzed using an immunohistochemical method. PTN, PTPRZ1, and NRP-1 were expressed from week 17 to the postnatal stage, with variable expression among granule cell precursors, glial cells, and Purkinje cells. ALK was only expressed during week 31. These results suggest that, in the fetal and neonatal human cerebellum, PTN is involved in cell communication through granule cell precursors, Bergmann glia, and Purkinje cells via PTPRZ1, NRP-1, and ALK signaling. This communication could be involved in cell proliferation and cellular migration. Overall, the present study represents the first characterization of PTN, PTPRZ1, ALK, and NRP-1 expression in human tissues, suggesting their involvement in cerebellar cortex development.

High quality mapping of chromatin at or near the nuclear lamina from small numbers of cells reveals cell cycle and developmental changes of chromatin at the nuclear periphery

The chromatin associated with the nuclear lamina (NL) is referred to as lamina-associated domains (LADs). Here, we present an adaptation of the tyramide-signal amplification sequencing (TSA-seq) protocol, which we call chromatin pull down-based TSA-seq (cTSA-seq), that can be used to map chromatin regions at or near the NL from as little as 50 000 cells. The cTSA-seq mapped regions are composed of previously defined LADs and smaller chromatin regions that fall within the Hi-C defined B-compartment containing nuclear peripheral heterochromatin. We used cTSA-seq to map chromatin at or near the assembling NL in cultured cells progressing through early G1. cTSA-seq revealed that the distal ends of chromosomes are near or at the reassembling NL during early G1, a feature similar to those found in senescent cells. We expand the use of cTSA-seq to the mapping of chromatin at or near the NL from fixed-frozen mouse cerebellar tissue sections. This mapping reveals a general conservation of NL-associated chromatin and identifies global and local changes during cerebellar development. The cTSA-seq method reported here is useful for analyzing chromatin at or near the NL from small numbers of cells derived from both in vitro and in vivo sources.

A rare additional lobe of cerebellum, projecting from its superior surface

Human cerebellum plays a vital role in motor coordination, regulation of muscle tone and maintaining the equilibrium of the body. It seldom shows anatomical/morphological variations. Herein, we report the presence of a small additional lobe projecting out on the superior surface of the right cerebellar hemisphere in the para-vermal area in an adult male cadaver. There was a notch on the tentorial surface of the occipital lobe of the right cerebral hemisphere, corresponding to the additional lobe of cerebellum. The additional lobe was histologically normal, with no evidence of any tumour cells. Knowledge of this variation is of importance to radiologists, neuroanatomists and neurosurgeons.

Human organoids in basic research and clinical applications

Organoids are three-dimensional (3D) miniature structures cultured in vitro produced from either human pluripotent stem cells (hPSCs) or adult stem cells (AdSCs) derived from healthy individuals or patients that recapitulate the cellular heterogeneity, structure, and functions of human organs. The advent of human 3D organoid systems is now possible to allow remarkably detailed observation of stem cell morphogens, maintenance and differentiation resemble primary tissues, enhancing the potential to study both human physiology and developmental stage. As they are similar to their original organs and carry human genetic information, organoids derived from patient hold great promise for biomedical research and preclinical drug testing and is currently used for personalized, regenerative medicine, gene repair and transplantation therapy. In recent decades, researchers have succeeded in generating various types of organoids mimicking in vivo organs. Herein, we provide an update on current in vitro differentiation technologies of brain, retinal, kidney, liver, lung, gastrointestinal, cardiac, vascularized and multi-lineage organoids, discuss the differences between PSC- and AdSC-derived organoids, summarize the potential applications of stem cell-derived organoids systems in the laboratory and clinic, and outline the current challenges for the application of organoids, which would deepen the understanding of mechanisms of human development and enhance further utility of organoids in basic research and clinical studies.

Role of engrailed homeobox 2 (EN2) gene in the development of the cerebellum and effects of its altered and ectopic expressions

Background

Morphological organization, folial pattern formation and establishment of the neural circuitry within the cerebellum are the important events taking place during the development of the cerebellum. Expression of engrailed homeobox 2 (EN2) gene plays an essential role in taking place of these events in the developing cerebellum.

Main body

A search was performed by following the PRISMA guidelines to review the role of the EN2 gene in the development of the cerebellum. Human and animal in vivo and in vitro studies showed that expression of the EN2 gene maintains the normal development of the cerebellum, morphological organization, cerebellar foliation, fissure formation, establishment of the afferent topography, molecular pattern formation and patterned gene expression in the developing cerebellum. Altered expression of the EN2 gene changes the morphology and folial pattern of the cerebellum, whereas its activation rescues these defects. EN2 gene polymorphism is reported as a susceptible cause for autism spectrum disorder (ASD). Ectopic expression of EN2 gene may result cancer and it also may play anti-oncogenic role depending on the organ of its expression.

Conclusion

Expression of the EN2 gene is essential for the normal development of the cerebellum. Its altered expression results deformed cerebellum, polymorphysm is associated with autism and ectopic expression may results cancer.

Networking of the Human Cerebellum: From Anatomo-Functional Development to Neurosurgical Implications

In the past, the cerebellum was considered to be substantially involved in sensory-motor coordination. However, a growing number of neuroanatomical, neuroimaging, clinical and lesion studies have now provided converging evidence on the implication of the cerebellum in a variety of cognitive, affective, social, and behavioral processes as well. These findings suggest a complex anatomo-functional organization of the cerebellum, involving a dense network of cortical territories and reciprocal connections with many supra-tentorial association areas. The final architecture of cerebellar networks results from a complex, highly protracted, and continuous development from childhood to adulthood, leading to integration between short-distance connections and long-range extra-cerebellar circuits. In this review, we summarize the current evidence on the anatomo-functional organization of the cerebellar connectome. We will focus on the maturation process of afferent and efferent neuronal circuitry, and the involvement of these networks in different aspects of neurocognitive processing. The final section will be devoted to identifying possible implications of this knowledge in neurosurgical practice, especially in the case of posterior fossa tumor resection, and to discuss reliable strategies to improve the quality of approaches while reducing postsurgical morbidity.

Posterior Fossa Venous Drainage

This paper aims to make simple the evaluation of the main veins related to the brainstem and cerebellum. Posterior fossa venous drainage is best understood in context with its three main collectors: superior: toward the Vein of Galen; posterior: toward the torcular complex; and anterior: toward the superior petrosal sinus. A fourth possible drainage path, often harder to distinguish, is directed toward the inferior petrosal sinus. Veins of these four systems are frequently connected to one another. Despite traditionally being considered less regular than its arterial disposition, posterior fossa venous anatomy follows specific patterns that are easy to identify. The three more representative veins of each venous confluent have been selected, to help in recognizing them angiographically. Since pial large veins are primarily located over the surface of the encephalon, most related anatomical structures can be confidently identified. This is of special interest when angiographic 2D or 3D studies are evaluated and provide fundamental assistance in locating precise structures. To better aid in understanding venous disposition, an overview of embryologic and fetal development is also discussed.

Cerebellum and Prematurity: A Complex Interplay Between Disruptive and Dysmaturational Events

The cerebellum plays a critical regulatory role in motor coordination, cognition, behavior, language, memory, and learning, hence overseeing a multiplicity of functions. Cerebellar development begins during early embryonic development, lasting until the first postnatal years. Particularly, the greatest increase of its volume occurs during the third trimester of pregnancy, which represents a critical period for cerebellar maturation. Preterm birth and all the related prenatal and perinatal contingencies may determine both dysmaturative and lesional events, potentially involving the developing cerebellum, and contributing to the constellation of the neuropsychiatric outcomes with several implications in setting-up clinical follow-up and early intervention.

A Focus on the Cerebellum: From Embryogenesis to an Age-Related Clinical Perspective

The cerebellum and its functional multiplicity and heterogeneity have been objects of curiosity and interest since ancient times, giving rise to the urge to reveal its complexity. Since the first hypothesis of cerebellar mere role in motor tuning and coordination, much more has been continuously discovered about the cerebellum’s circuitry and functioning throughout centuries, leading to the currently accepted knowledge of its prominent involvement in cognitive, social, and behavioral areas. Particularly in childhood, the cerebellum may subserve several age-dependent functions, which might be compromised in several Central Nervous System pathologies. Overall, cerebellar damage may produce numerous signs and symptoms and determine a wide variety of neuropsychiatric impairments already during the evolutive age. Therefore, an early assessment in children would be desirable to address a prompt diagnosis and a proper intervention since the first months of life. Here we provide an overview of the cerebellum, retracing its morphology, histogenesis, and physiological functions, and finally outlining its involvement in typical and atypical development and the age-dependent patterns of cerebellar dysfunctions.

Intrauterine growth restriction compromises cerebellar development by affecting radial migration of granule cells via the JamC/Pard3a molecular pathway

Intrauterine growth restriction (IUGR) affects ~10% of human pregnancies, results in infants born small for gestational age (SGA), and is associated with motor and cognitive deficits. Human studies suggest that some deficits in SGA patients originate in the cerebellum, a major motor-coordination and cognitive center, but the underlying mechanisms remain unknown. To identify the cerebellar developmental program affected by IUGR, we analyzed the pig as a translational animal model in which some fetuses spontaneously develop IUGR due to early-onset chronic placental insufficiency. Similar to humans, SGA pigs revealed small cerebella, which contained fewer mature granule cells (GCs) in the internal granule cell layer (IGL). Surprisingly, newborn SGA pigs had increased proliferation of GC precursors in the external granule cell layer (EGL), which was associated with an increased density of Purkinje cells, known to non-autonomously promote the proliferation of GCs. However, the GCs of SGA pigs did not properly initiate exit from the EGL to IGL, which was associated with a decreased density of guiding Bergmann glial fibers, reduced expression of pro-migratory genes Pard3a, JamC and Sema6a, and increased apoptosis. While proliferation spontaneously normalized during postnatal development, accumulation of pre-migratory GCs and apoptosis in the EGL were long-lasting consequences of IUGR. Using organotypic cerebellar slice cultures, we showed that normalizing expression of Pard3a and JamC, which operate in the same molecular pathway in GCs, was sufficient to rescue both migratory and, at a later time point, apoptotic defects of IUGR. Thus, a decreased exit of GCs from the EGL, due to disrupted Pard3a/JamC radial migration initiation pathway, is a major mechanism of IUGR-related cerebellar pathology.

Location and Size of Preterm Cerebellar Hemorrhage and Childhood Development

OBJECTIVE

To examine the association between cerebellar hemorrhage (CBH) size and location and preschool-age neurodevelopment in very preterm neonates.

METHODS

Preterm magnetic resonance images of 221 very preterm neonates (median gestational age = 27.9 weeks) were manually segmented for CBH quantification and location. Neurodevelopmental assessments at chronological age 4.5 years included motor (Movement Assessment Battery for Children, 2nd Edition [MABC-2]), visuomotor integration (Beery-Buktenica Developmental Test of Visual-Motor Integration, 6th Edition), cognitive (Wechsler Primary and Preschool Scale of Intelligence, 3rd Edition), and behavioral (Child Behavior Checklist) outcomes. Multivariable linear regression models examined the association between CBH size and 4.5-year outcomes accounting for sex, gestational age, and supratentorial injury. Probabilistic maps assessed CBH location and likelihood of a lesion to predict adverse outcome.

RESULTS

Thirty-six neonates had CBH: 14 (6%) with only punctate CBH and 22 (10%) with ≥1 larger CBH. CBH occurred mostly in the inferior aspect of the posterior lobes. CBH total volume was independently associated with MABC-2 motor scores at 4.5 years (β = -0.095, 95% confidence interval = -0.184 to -0.005), with a standardized β coefficient (-0.16) that was similar to that of white matter injury volume (standardized β = -0.22). CBH size was similarly associated with visuomotor integration and externalizing behavior but not cognition. Voxelwise odds ratio and lesion-symptom maps demonstrated that CBH extending more deeply into the cerebellum predicted adverse motor, visuomotor, and behavioral outcomes.

INTERPRETATION

CBH size and location on preterm magnetic resonance imaging were associated with reduced preschool motor and visuomotor function and more externalizing behavior independent of supratentorial brain injury in a dose-dependent fashion. The volumetric quantification and localization of CBH, even when punctate, may allow opportunity to improve motor and behavioral outcomes by providing targeted intervention. ANN NEUROL 2020;88:1095-1108.

Placental Pathology Findings and the Risk of Intraventricular and Cerebellar Hemorrhage in Preterm Neonates

Placental pathology as a predisposing factor to intraventricular hemorrhage remains a matter of debate, and its contribution to cerebellar hemorrhage development is still largely unexplored. Our study aimed to assess placental and perinatal risk factors for intraventricular and cerebellar hemorrhages in preterm infants. This retrospective cohort study included very low-birth weight infants born at the Gaslini Children's Hospital between January 2012 and October 2016 who underwent brain magnetic resonance with susceptibility-weighted imaging at term-equivalent age and whose placenta was analyzed according to the Amsterdam Placental Workshop Group Consensus Statement. Of the 286 neonates included, 68 (23.8%) had intraventricular hemorrhage (all grades) and 48 (16.8%) had a cerebellar hemorrhage (all grades). After correction for gestational age, chorioamnionitis involving the maternal side of the placenta was found to be an independent risk factor for developing intraventricular hemorrhage, whereas there was no association between maternal and fetal inflammatory response and cerebellar hemorrhage. Among perinatal factors, we found that intraventricular hemorrhage was significantly associated with cerebellar hemorrhage (odds ratio [OR], 8.14), mechanical ventilation within the first 72 h (OR, 2.67), and patent ductus arteriosus requiring treatment (OR, 2.6), whereas cesarean section emerged as a protective factor (OR, 0.26). Inotropic support within 72 h after birth (OR, 5.24) and intraventricular hemorrhage (OR, 6.38) were independent risk factors for cerebellar hemorrhage, whereas higher gestational age was a protective factor (OR, 0.76). Assessing placental pathology may help in understanding mechanisms leading to intraventricular hemorrhage, although its possible role in predicting cerebellar bleeding needs further evaluation.

Effects of Phosphatidylserine Source of Docosahexaenoic Acid on Cerebellar Development in Preterm Pigs

Preterm birth, a major contributor to infant mortality and morbidity, impairs development of the cerebellum, the brain region involved in cognitive processing and motor function. Previously, we showed that at term-equivalent age, preterm pigs that received formula supplemented with docosahexaenoic acid (DHA) esterified to phosphatidylserine (PS) had cerebellar weights similar to those of newborn term pigs and were heavier than control preterm pigs. However, whether PS-DHA promotes the development of specific cerebellar cell populations or enhances key developmental processes remains unknown. Here we investigated the effects of the PS-DHA on development of the cerebellum in preterm pigs delivered via caesarean section and reared for ten days on a milk replacer with either PS-DHA (experimental group) or sunflower oil (control group). Upon necropsy, key cerebellar populations were analyzed using immunohistochemistry. Consumption of PS-DHA was associated with the expansion of undifferentiated granule cell precursors and increased proliferation in the external granule cell layer (EGL). Preterm pigs that received PS-DHA also had significantly fewer apoptotic cells in the internal granule cell layer (IGL) that contains differentiated granule neurons. PS-DHA did not affect the number of differentiating granule cells in the inner EGL, thickness of the inner EGL, density of Purkinje cells, or Bergmann glial fibers, or diameter of Purkinje cells. Thus, PS-DHA may support cerebellar development in preterm subjects by enhancing proliferation of granule cells, a process specifically inhibited by preterm birth, and increasing the survival of granule cells in the IGL. These findings suggest that PS-DHA is a promising candidate for clinical studies directed at enhancing brain development.

Deconstructing cerebellar development cell by cell

The cerebellum is a pivotal centre for the integration and processing of motor and sensory information. Its extended development into the postnatal period makes this structure vulnerable to a variety of pathologies, including neoplasia. These properties have prompted intensive investigations that reveal not only developmental mechanisms in common with other regions of the neuraxis but also unique strategies to generate neuronal diversity. How the phenotypically distinct cell types of the cerebellum emerge rests on understanding how gene expression differences arise in a spatially and temporally coordinated manner from initially homogeneous cell populations. Increasingly sophisticated fate mapping approaches, culminating in genetic-induced fate mapping, have furthered the understanding of lineage relationships between early- versus later-born cells. Tracing the developmental histories of cells in this way coupled with analysis of gene expression patterns has provided insight into the developmental genetic programmes that instruct cellular heterogeneity. A limitation to date has been the bulk analysis of cells, which blurs lineage relationships and obscures gene expression differences between cells that underpin the cellular taxonomy of the cerebellum. This review emphasises recent discoveries, focusing mainly on single-cell sequencing in mouse and parallel human studies that elucidate neural progenitor developmental trajectories with unprecedented resolution. Complementary functional studies of neural repair after cerebellar injury are challenging assumptions about the stability of postnatal cellular identities. The result is a wealth of new information about the developmental mechanisms that generate cerebellar neural diversity, with implications for human evolution.

The developing brain by trimester

Transient anatomical entities play a role in the maturation of brain regions and early functional fetal networks. At the postmenstrual age of 7 weeks, major subdivisions of the brain are visible. At the end of the embryonic period, the cortical plate covers the neopallium. The choroid plexus develops in concert with it, and the dorsal thalamus covers about half the diencephalic third ventricle surface. In addition to the fourth ventricle neuroepithelium the rhombic lips are an active neuroepithelial production site. Early reciprocal connections between the thalamus and cortex are present. The corticospinal tract has reached the pyramidal decussation, and the arteries forming the mature circle of Willis are seen. Moreover, the superior sagittal sinus has formed, and at the rostral neuropore the massa commissuralis is growing. At the viable preterm age of around 24 weeks PMA, white matter tracts are in full development. Asymmetric progenitor division permits production of neurons, subventricular zone precursors, and glial cells. Myelin is present in the ventral spinal quadrant, cuneate fascicle, and spinal motor fibers. The neopallial mantle has been separated into transient layers (stratified transitional fields) between the neuroepithelium and the cortical plate. The subplate plays an important role in organizing the structuring of the cortical plate. Commissural tracts have shaped the corpus callosum, early primary gyri are present, and opercularization has started caudally, forming the lateral fissure. Thalamic and striatal nuclei have formed, although GABAergic neurons continue to migrate into the thalamus from the corpus gangliothalamicum. Near-term PMA cerebral sublobulation is active. Between 24 and 32 weeks, primary sulci develop. Myelin is present in the superior cerebellar peduncle, rubrospinal tract, and inferior olive. Germinal matrix disappears from the telencephalon, except for the GABAergic frontal cortical subventricular neuroepithelium.