A tridimensional atlas of the developing human head.

The evolution and development of the head have long captivated researchers due to the crucial role of the head as the gateway for sensory stimuli and the intricate structural complexity of the head. Although significant progress has been made in understanding head development in various vertebrate species, our knowledge of early human head ontogeny remains limited. Here, we used advanced whole-mount immunostaining and 3D imaging techniques to generate a comprehensive 3D cellular atlas of human head embryogenesis. We present detailed developmental series of diverse head tissues and cell types, including muscles, vasculature, cartilage, peripheral nerves, and exocrine glands. These datasets, accessible through a dedicated web interface, provide insights into human embryogenesis. We offer perspectives on the branching morphogenesis of human exocrine glands and unknown features of the development of neurovascular and skeletomuscular structures. These insights into human embryology have important implications for understanding craniofacial defects and neurological disorders and advancing diagnostic and therapeutic strategies.

Tridimensional Visualization and Analysis of Early Human Development.

Generating a precise cellular and molecular cartography of the human embryo is essential to our understanding of the mechanisms of organogenesis in normal and pathological conditions. Here, we have combined whole-mount immunostaining, 3DISCO clearing, and light-sheet imaging to start building a 3D cellular map of the human development during the first trimester of gestation. We provide high-resolution 3D images of the developing peripheral nervous, muscular, vascular, cardiopulmonary, and urogenital systems. We found that the adult-like pattern of skin innervation is established before the end of the first trimester, showing important intra- and inter-individual variations in nerve branches. We also present evidence for a differential vascularization of the male and female genital tracts concomitant with sex determination. This work paves the way for a cellular and molecular reference atlas of human cells, which will be of paramount importance to understanding human development in health and disease. PAPERCLIP.

Fetal dental panorama on three-dimensional ultrasound imaging of cleft lip and palate and other facial anomalies.

OBJECTIVES: Craniofacial deformities have a high psychosocial impact. The aim of this paper is to improve obstetric ultrasonography and prenatal detection of facial anomalies by providing a new fetal dental panorama. MATERIAL AND METHODS: The present study describes a new modality to visualize the fetal tooth germs and an easy step-by-step diagnostic approach. Image acquisition was performed between 23 and 32 weeks of gestation using a Voluson E10 GE ultrasound machine with an RM6C transducer (GE Medical Systems, Zipf, Austria). Reconstruction was performed using Omniview from the axial image. Volume contrast imaging (VCI) was used with a thickness of 20 mm, and a render mode that combined "Rx mode" and "surface texture." RESULTS: The resulting imaging allows a more precise visualization of the fetal dental arch and can be obtained between 14 and 28 weeks of gestation. The presence of dental anomalies can be a clue for the diagnosis of various congenital defects, in particular conditions with a shortage of other physical abnormalities, such as ectodermal dysplasia and Binder syndrome. CONCLUSIONS: The creation of a precise fetal dental panorama allows an improved detection of facial deformities. CLINICAL RELEVANCE: With the current paper, we want to increase prenatal diagnostics facial anomalies, and help to establish a tailored multidisciplinary treatment plan. This paper should be of interest to readers who are currently treating patients with craniofacial malformations and readers who are performing diagnostic prenatal sonography.

Respective contribution of the cephalic neural crest and mesoderm to SIX1-expressing head territories in the avian embryo.

BACKGROUND: Vertebrate head development depends on a series of interactions between many cell populations of distinct embryological origins. Cranial mesenchymal tissues have a dual embryonic source: - the neural crest (NC), which generates most of craniofacial skeleton, dermis, pericytes, fat cells, and tenocytes; and - the mesoderm, which yields muscles, blood vessel endothelia and some posterior cranial bones. The molecular players that orchestrate co-development of cephalic NC and mesodermal cells to properly construct the head of vertebrates remain poorly understood. In this regard, Six1 gene, a vertebrate homolog of Drosophila Sine Oculis, is known to be required for development of ear, nose, tongue and cranial skeleton. However, the embryonic origin and fate of Six1-expressing cells have remained unclear. In this work, we addressed these issues in the avian embryo model by using quail-chick chimeras, cephalic NC cultures and immunostaining for SIX1. RESULTS: Our data show that, at early NC migration stages, SIX1 is expressed by mesodermal cells but excluded from the NC cells (NCC). Then, SIX1 becomes widely expressed in NCC that colonize the pre-otic mesenchyme. In contrast, in the branchial arches (BAs), SIX1 is present only in mesodermal cells that give rise to jaw muscles. At later developmental stages, the distribution of SIX1-expressing cells in mesoderm-derived tissues is consistent with a possible role of this factor in the myogenic program of all types of head muscles, including pharyngeal, extraocular and tongue muscles. In NC derivatives, SIX1 is notably expressed in perichondrium and chondrocytes of the nasal septum and in the sclera, although other facial cartilages such as Meckel's were negative at the stages considered. Moreover, in cephalic NC cultures, chondrocytes and myofibroblasts, not the neural and melanocytic cells express SIX1. CONCLUSION: The present results point to a dynamic tissue-specific expression of SIX1 in a variety of cephalic NC- and mesoderm-derived cell types and tissues, opening the way for further analysis of Six1 function in the coordinated development of these two cellular populations during vertebrate head formation.

Prenatal diagnosis of Pierre Robin Sequence: accuracy and ability to predict phenotype and functional severity.

OBJECTIVE: To assess the outcome of fetuses who had sonographic features suggestive of Pierre Robin Sequence (PRS). METHOD: All prenatal ultrasounds that mentioned 'posterior cleft palate', or 'micro or retrognathia' or 'PRS' over 13 and 20 years, respectively, at two obstetrical centers were reviewed. Medical records for children with isolated PRS monitored over 20 years at a PRS referral center for prenatal anomalies and the severity of neonatal feeding and respiratory functional disorders were utilized for comparison. RESULTS: From a prenatal ultrasound database of 166 000 cases, 157 had one or more of the sonographic signs suggestive of PRS and had follow-up available. Of them, 33 (21%) had confirmed PRS, 9 (6%) were normal and 115 (73%) had chromosomal aberrations, associated malformations or neurological anomalies. Visualization of a posterior cleft palate in addition to retro-micrognathia had a positive predictive value of 100% for PRS. The distribution of functional severity grades was similar in cases suspected prenatally as in 238 cases of PRS followed in the referral center in Necker Hospital. CONCLUSION: Only a minority of cases of fetal retrognathia have complete PRS; the majority have other severe conditions. Prenatal prediction of functional severity of isolated PRS is not possible.

Two Cases of Cleft Lip and Other Congenital Anomalies in Wild Chimpanzees Living in Kibale National Park, Uganda.

DESIGN: Observations of wild chimpanzees ( Pan troglodytes schweinfurthii) were conducted in Kibale National Park, Uganda, at the sites of Sebitoli and Ngogo. RESULTS: We report the first two cases of cleft lip in wild chimpanzees. Additionally, some other chimpanzees in the Sebitoli community show facial dysplasia and congenital anomalies, such as patches of depigmented hairs and limb defects. CONCLUSIONS: Cleft lip has been documented in several species of nonhuman primates, but much remains unknown about the occurrence of cleft lip and cleft palate in great apes, probably because such malformations are rare, wild apes are difficult to monitor and observe, and severe cases associated with cleft palates render suckling impossible and lead to early death of infants. The genetic basis of such defects in great apes warrants investigation, as does the possibility that environmental toxins contribute to their etiology in Kibale in ways that could affect humans as well.

Dlx5 and Dlx6 expression in the anterior neural fold is essential for patterning the dorsal nasal capsule.

Morphogenesis of the vertebrate facial skeleton depends upon inductive interactions between cephalic neural crest cells (CNCCs) and cephalic epithelia. The nasal capsule is a CNCC-derived cartilaginous structure comprising a ventral midline bar (mesethmoid) overlaid by a dorsal capsule (ectethmoid). Although Shh signalling from the anterior-most region of the endoderm (EZ-I) patterns the mesethmoid, the cues involved in ectethmoid induction are still undefined. Here, we show that ectethmoid formation depends upon Dlx5 and Dlx6 expression in a restricted ectodermal territory of the anterior neural folds, which we name NF-ZA. In both chick and mouse neurulas, Dlx5 and Dlx6 expression is mostly restricted to NF-ZA. Simultaneous Dlx5 and Dlx6 inactivation in the mouse precludes ectethmoid formation, while the mesethmoid is still present. Consistently, siRNA-mediated downregulation of Dlx5 and Dlx6 in the cephalic region of the early avian neurula specifically prevents ectethmoid formation, whereas other CNCC-derived structures, including the mesethmoid, are not affected. Similarly, NF-ZA surgical removal in chick neurulas averts ectethmoid development, whereas grafting a supernumerary NF-ZA results in an ectopic ectethmoid. Simultaneous ablation or grafting of both NF-ZA and EZ-I result, respectively, in the absence or duplication of both dorsal and ventral nasal capsule components. The present work shows that early ectodermal and endodermal signals instruct different contingents of CNCCs to form the ectethmoid and the mesethmoid, which then assemble to form a complete nasal capsule.

Facial dysplasia in wild chimpanzees.

At least 10% of the Sebitoli chimpanzee community of the Kibale National Park (Uganda) present a characteristic facial phenotype with flattened nose, reduced nostrils, and concave mid-face. Affected individuals do not present skin lesions, and also young infants are affected. We suggest, therefore, a congenital origin of this defect.

The neural crest is a powerful regulator of pre-otic brain development.

The role of the neural crest (NC) in the construction of the vertebrate head was demonstrated when cell tracing techniques became available to follow the cells exiting from the cephalic neural folds in embryos of various vertebrate species. Experiments carried out in the avian embryo, using the quail/chick chimera system, were critical in showing that the entire facial skeleton and most of the skull (except for he occipital region) were derived from the NC domain of the posterior diencephalon, mesencephalon and rhombomeres 1 and 2 (r1, r2). This region of the NC was designated FSNC (for Facial Skeletogenic NC). One characteristic of this part of the head including the neural anlage is that it remains free of expression of the homeotic genes of the Hox-clusters. In an attempt to see whether this rostral Hox-negative domain of the NC has a specific role in the development of the skeleton, we have surgically removed it in chick embryos at 5-6 somite stages (5-6 ss). The operated embryos showed a complete absence of facial and skull cartilages and bones showing that the Hox expressing domain of the NC caudally located to the excision did not regenerate to replace the anterior NC. In addition to the deficit in skeletal structures, the operated embryos exhibited severe brain defects resulting in anencephaly. Experiments described here have shown that the neural crest cells regulate the amount of Fgf8 produced by the two brain organizers, the Anterior Neural Ridge (ANR) and the isthmus. This regulation is exerted via the secretion of anti-BMP signaling molecules (e.g. Gremlin and Noggin), which decrease BMP production hence enhancing the amount of Fgf8 synthesized in the ANR (also called "Prosencephalic organizer") and the isthmus. In addition to its role in building up the face and skull, the NC is therefore an important signaling center for brain development.

Developmental outcome in Pierre Robin sequence: a longitudinal and prospective study of a consecutive series of severe phenotypes.

Pierre Robin sequence (PRS) is a congenital condition with a heterogeneous and imprecise developmental prognosis. We conducted a longitudinal prospective study analyzing the long-term developmental outcome of a consecutive series of 39 children with PRS who had an a priori good prognosis (isolated PRS or PRS associated with a Stickler syndrome) but severe neonatal disorders (respiratory and feeding difficulties). Psychomotor and cognitive levels, speech, and eating behavior were assessed at 15 months of age and 3 and 6 years of age; 24 of the oldest children were interviewed at age 11 or 12 years. Results were analyzed by diagnosis, extent of respiratory and feeding disorders, and treatment modalities. Cognitive scores were within normal ranges and increased over time, from 90.5 at 15 months of age to 109.1 at 6 years. The 24 oldest children were enrolled in the appropriate junior high school grade at the normal age. For children 15 months of age, language scores were below the average, as were scores for vocabulary at 3 years for half of the patients. At 6 years, children's speech showed persistent rhinolalia, which was mild (47%), moderate (11%), or major (11%). At 15 months of age, 74% of the children had satisfactory eating behavior, and 15% had serious difficulties. At 3 and 6 years, 18% and 6% of the children, respectively, had eating problems. Treatment modalities had no significant effect on long-term outcome. Global developmental quotient scores were lower but not significantly for children with an associated Stickler syndrome than those with isolated PRS. Children with isolated PRS showed good prognosis.

Jaw muscularization requires Dlx expression by cranial neural crest cells.

The origin of active predation in vertebrates is associated with the rise of three major, uniquely derived developmental characteristics of the head: (i) migratory cranial neural crest cells (CNCCs) giving rise to most skeletal skull elements; (ii) expression of Dlx genes by CNCCs in the Hox-free first pharyngeal arch (PA1); and (iii) muscularization of PA1 derivatives. Here we show that these three innovations are tightly linked. Expression of Dlx genes by CNCCs is not only necessary for head skeletogenesis, but also for the determination, differentiation, and patterning of cephalic myogenic mesoderm leading to masticatory muscle formation. In particular, inactivation of Dlx5 and Dlx6 in the mouse results in loss of jaw muscles. As Dlx5/6 are not expressed by the myogenic mesoderm, our findings imply an instructive role for Dlx5/6-positive CNCCs in muscle formation. The defect in muscularization does not result from the loss of mandibular identity observed in Dlx5/6(-/-) mice because masticatory muscles are still present in EdnRA(-/-) mutants, which display a similar jaw transformation. The genesis of jaws and their muscularization should therefore be seen as an integrated Dlx-dependent developmental process at the origin of the vertebrate head. The role of Dlx genes in defining gnathostome jaw identity could, therefore, be secondary to a more primitive function in the genesis of the oral skeletomuscular system.

Evolving maps in craniofacial development.

The shaping of the vertebrate head results from highly dynamic integrated processes involving the growth and exchange of signals between the ectoderm, the endoderm, the mesoderm and Cephalic Neural Crest Cells (CNCCs). During embryonic development, these tissues change their shape and relative position rapidly and come transiently in contact with each other. Molecular signals exchanged in restricted regions of tissue interaction are crucial in providing positional identity to the mesenchymes which will form the different skeletal and muscular components of the head. Slight spatio-temporal modifications of these signalling maps can result in profound changes in craniofacial development and might have contributed to the evolution of facial diversity. Abnormal signalling patterns could also be at the origin of congenital craniofacial malformations. This review brings into perspective recent work on spatial and temporal aspects of facial morphogenesis with particular focus on the molecular mechanisms of jaw specification.

Masticatory muscle defects in hemifacial microsomia: a new embryological concept.

First arch syndromes correspond to a wide spectrum of human latero-facial congenital anomalies affecting cranial neural crest cells (CNCCs) derivatives of the first pharyngeal arch (PA1). The abnormal traits display variable quantitative expression and are often unilateral. Mandibular skeletal defects are invariably accompanied by hypoplasia or agenesis of masticatory muscles, but no explanation has been proposed for this association. Indeed, during embryonic development, CNCCs give only rise to skeletal components of the head while muscles derive from cephalic myogenic mesodermal cells (CMMCs). Recent studies on animal models have shown that communication between CNCCs and CMMCs is essential for the development of masticatory muscles: genetic lesions affecting only CNCCs can prevent muscularization of the jaws. To evaluate the involvement of CNCC/CMMC interactions in human craniofacial development, we performed a quantitative analysis of masticatory muscle and mandibular bone volumes on craniofacial CT-scans from 8 children, ages 3 months to 16 years, affected by hemifacial microsomia. We found that: (1) in seven patients the masseter muscle is absent in the affected side; (2) the absence of masseter is correlated neither with the age of the patients nor with the volume and shape of the affected ramus; and (3) in all cases the pterygoid and the temporal muscles are either reduced or absent. Our findings suggest that an early developmental event is the origin of the muscular defects in these patients. We propose that the hypoplasia or agenesis of masticatory muscles derives from a defect in the CNCCs/CMMCs communication during early embryonic development.

[To eat, to breath, to cry, to speak, to sing, the zoological language epopee]. / Manger, respirer, crier, parler, chanter : l'épopée zoologique du langage.

The language emergence during the last one million years is the success of the use of oral nutritive and breathing functional organs, which existed several hundred million years ago. But two new neurogenomic innovations were also necessary: The genesis of pneumo-laryngo-glossal Broca praxic area, associated to FOXP2 gene, and the brain connectome. The last one has connected, thanks to its network, the Broca area to these two vital functions, feeding orality and respiration, by using their motor pyramidal and cortico-nuclear ways already constituted. These connections have given the language its efficiency of sonor laryngeal emission and oral articulation. The baby cry precedes from 18 months the language beginning, and is produced by the same motor neurologic connectomic organization that future language. To eat, to breath, and to cry, to speak, to sing constitute a neuro-functional and temporal filiation of Evolution since the first early vertebrates. To eat, then to breath, then to cry have constituted the language founding parentage.

TITLE: Manger, respirer, crier, parler, chanter : l'épopée zoologique du langage. ABSTRACT: L'émergence du langage doit son succès à des circonstances favorables de l'Évolution : la genèse neurogénomique du centre moteur frontal pneumo-laryngo-bucco-lingual de Broca, associée au gène FOXP2 ; l'utilisation, pour la production du langage, de la neuro-fonctionnalité des organes de la respiration et de l'oralité nutritionnelle, efficiente depuis des millions d'années ; et le connectome, la connexion des voies motrices pyramidales et cortico-nucléaires de l'encéphale. Celles-ci, en raccordant le centre de Broca aux effecteurs neuromusculaires de la ventilation et de l'oralité nutritionnelle, ont assuré au langage sa production sonore laryngée et son articulation, qui ont succédé aux cris du nourrisson, ce protolangage. Manger, puis respirer et crier ont constitué une filiation fondatrice du futur langage.

Quality of life and phonatory and morphological outcomes in cognitively unimpaired adolescents with Pierre Robin sequence: a cross-sectional study of 72 patients.

BACKGROUND: Pierre Robin sequence (PRS) is a heterogeneous condition involving retro(micro)gnathia, glossoptosis and upper airway obstruction, very often with posterior cleft palate. Patients with PRS, either isolated or associated with Stickler syndrome have good intellectual prognosis. Nevertheless, the quality of life in adolescence and the phonatory and morphological outcomes are rarely analysed. We assessed the phonatory and morphological outcomes of 72 cognitively unimpaired adolescents with PRS, studied their oral (COHIP-SF19), vocal (VHI-9i) and generic quality of life (QoL; KIDSCREEN-52), and searched for determinants of these outcomes. RESULTS: Two-thirds of our adolescents retained low or moderate phonation difficulties, but risk factors were not identified. For 14%, morphological results were considered disharmonious, with no link to neonatal retrognathia severity. Only one vs two-stage surgery seemed to affect final aesthetic results. The oral QoL of these adolescents was comparable to that of control patients and was significantly better than that of children with other craniofacial malformations (COHIP-SF19 = 17.5, 15.4 and 25.7, respectively). The oral QoL of the adolescents with non-isolated PRS was significantly worse (COHIP-SF19 = 24.2) than that of control patients and close to that of children with other craniofacial malformations. The vocal QoL of the adolescents (mean [SD] VHI-9i = 7.5 [5.4]) was better than that of patients with other voice pathologies and better when phonation was good. The generic QoL of the adolescents was satisfactory but slightly lower than that of controls, especially in dimensions concerning physical well-being, relationships and autonomy. QoL results were lower for adolescents with non-isolated than isolated PRS. Only non-isolated PRS and low oral QoL affected generic QoL. CONCLUSION: Morphological or phonatory impairments remain non-rare in adolescents with PRS but do not seem to be directly responsible for altered QoL. These adolescents, especially those with non-isolated PRS, show self-confidence and social-relation fragility. We must focus on long-term functional and psychological results for PRS patients and improve therapy protocols and follow-up, notably those affecting the oral aspects of the disease.

Spatio-temporal dynamics of gene expression of the Edn1-Dlx5/6 pathway during development of the lower jaw.

The morphogenesis of the vertebrate skull results from highly dynamic integrated processes involving the exchange of signals between the ectoderm, the endoderm, and cephalic neural crest cells (CNCCs). Before migration CNCCs are not committed to form any specific skull element, molecular signals exchanged in restricted regions of tissue interaction are crucial in providing positional identity to the CNCCs mesenchyme and activate the specific morphogenetic process of different skeletal components of the head. In particular, the endothelin-1 (Edn1)-dependent activation of Dlx5 and Dlx6 in CNCCs that colonize the first pharyngeal arch (PA1) is necessary and sufficient to specify maxillo-mandibular identity. Here, to better analyze the spatio-temporal dynamics of this process, we associate quantitative gene expression analysis with detailed examination of skeletal phenotypes resulting from combined allelic reduction of Edn1, Dlx5, and Dlx6. We show that Edn1-dependent and -independent regulatory pathways act at different developmental times in distinct regions of PA1. The Edn1-->Dlx5/6-->Hand2 pathway is already active at E9.5 during early stages of CNCCs colonization. At later stages (E10.5) the scenario is more complex: we propose a model in which PA1 is subdivided into four adjacent territories in which distinct regulations are taking place. This new developmental model may provide a conceptual framework to interpret the craniofacial malformations present in several mouse mutants and in human first arch syndromes. More in general, our findings emphasize the importance of quantitative gene expression in the fine control of morphogenetic events.

[To eat or to speak]. / Manger ou parler.

Human oro-pharyngeal feeding is old as mammals's (150 millions years). This fonction is performed and coordinated by the central and peripheric nervous system. Thus, eating and speaking use the same anatomic ducts and ways. To that purpose, the Broca praxic language area is close to the praxic area of the motor mastication and swallowing control in brain cortex. This area, a new innovation of human evolution, is connected directly with the old motor ways of preexisting oral feeding. The brain connectome and Foxp2 gene have contributed with efficiency to this linking when the language came.

TITLE: Manger ou parler. ABSTRACT: L'ingestion nutritionnelle oro-pharyngée humaine est ancienne, comme celle des mammifères, depuis 150 millions d'années. Cette fonction est assurée et coordonnée par le système nerveux central et périphérique. Or, Manger et parler utilisent les mêmes conduits et voies anatomiques. L'aire praxique1 du langage de Broca est contigüe à celle de la commande motrice de la mastication et de la déglutition dans le cortex moteur cérébral. Cette aire praxique de Broca, innovation récente de l'évolution humaine, s'est connectée aux voies motrices anciennes de l'oralité alimentaire qui préexistaient. Le connectome cérébral et le gène Foxp2 ont contribué de manière décisive à ce raccordement pour l'avènement du langage.

Neural crest derivatives in ocular and periocular structures.

In vertebrates, the eye is an ectodermal compound structure associating neurectodermal and placodal anlagen. In addition, it benefits early on from a mesenchymal ectoderm-derived component, the neural crest. In this respect, the construction of chimeras between quail and chick has been a turning point, instrumental in appraising the contribution of the cephalic neural crest to the development of ocular and periocular structures. Given the variety of crest derivatives underscored in the developing eye, this study illustrates the fascinating ability of this unique structure to finely adapt its differentiation to microenvironmental cues. This analysis of neural crest cell contribution to ocular development emphasizes their paramount role to design the anterior segment of the eye, supply refracting media and contribute to the homeostasy of the anterior optic chamber.

Prenatal diagnosis of cleft lip/palate: The surface rendered oro-palatal (SROP) view of the fetal lips and palate, a tool to improve information-sharing within the orofacial team and with the parents.

The ultrasonographic surface rendered oro-palatal (SROP) view is a 3D reconstructed view of the fetal perioral region, which combines ultrasound insonation in a trans oral, upward directed axial direction and the surface rendered mode. It allows the simultaneous visualization on a single scan of the superior lip, alveolar ridge and secondary palate. It corresponds prenatally to the submental intra oral photography of the palate of neonates. The aim of the study was to demonstrate the benefice of using the SROP view in the management of cleft lip with or without cleft palate, uni- or bi-lateral, diagnosed prenatally (22-28 gestational weeks). The SROP view allowed the representation on a single view of the characteristics of the defect useful to the different members of the orofacial team to exactly evaluate the difformity and to plan the ulterior therapeutic steps (e.g. side, extension of the cleft to the secondary palate, tooth organization). Also, being easier to read by lay people thanks to the use of a surface rendered representation rather than the usual multiplanar reconstructions in the three traditional orthogonal planes, the SROP view makes it easier to bring exact information to the parents about the malformation and its consequences.

Morphogenesis of the branchial vascular sector.

The branchial and dorsal cephalic vascular sectors correspond to the blood vessels contained within evolutionarily recent and ancestral parts of the head, respectively. Recent work demonstrates that neural crest cells (NCCs) provide the pericytes, and connective and smooth muscle cells to the entire branchial sector in an ordered fashion. Initial NCC position is transposed to the vascular distal-to-proximal axis, explaining why circumscribed cephalic vascular anomalies are often associated with reproducible malformations in head tissues derived from the neural crest. Unlike the rest of the central nervous system, the forebrain requires mesenchyme-containing vascular-competent NCCs to survive during embryogenesis and beyond.