Bone is an evolutionary novelty of vertebrates, likely to have first emerged as part of ancestral dermal armor that consisted of osteogenic and odontogenic components. Whether these early vertebrate structures arose from mesoderm or neural crest cells has been a matter of considerable debate. To examine the developmental origin of the bony part of the dermal armor, we have performed in vivo lineage tracing in the sterlet sturgeon, a representative of nonteleost ray-finned fish that has retained an extensive postcranial dermal skeleton. The results definitively show that sterlet trunk neural crest cells give rise to osteoblasts of the scutes. Transcriptional profiling further reveals neural crest gene signature in sterlet scutes as well as bichir scales. Finally, histological and microCT analyses of ray-finned fish dermal armor show that their scales and scutes are formed by bone, dentin, and hypermineralized covering tissues, in various combinations, that resemble those of the first armored vertebrates. Taken together, our results support a primitive skeletogenic role for the neural crest along the entire body axis, that was later progressively restricted to the cranial region during vertebrate evolution. Thus, the neural crest was a crucial evolutionary innovation driving the origin and diversification of dermal armor along the entire body axis.

• Keywords
• neural crest, scales, skeleton, sterlet sturgeon, vertebrate evolution,
• MeSH
• Biological Evolution MeSH
• Neural Crest * MeSH
• Skull MeSH
• Vertebrates * genetics   MeSH
• Osteogenesis MeSH
• Fishes MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Research Support, N.I.H., Extramural MeSH
• Research Support, U.S. Gov't, Non-P.H.S. MeSH

Schwann cell precursors (SCPs) are nerve-associated progenitors that can generate myelinating and non-myelinating Schwann cells but also are multipotent like the neural crest cells from which they originate. SCPs are omnipresent along outgrowing peripheral nerves throughout the body of vertebrate embryos. By using single-cell transcriptomics to generate a gene expression atlas of the entire neural crest lineage, we show that early SCPs and late migratory crest cells have similar transcriptional profiles characterised by a multipotent "hub" state containing cells biased towards traditional neural crest fates. SCPs keep diverging from the neural crest after being primed towards terminal Schwann cells and other fates, with different subtypes residing in distinct anatomical locations. Functional experiments using CRISPR-Cas9 loss-of-function further show that knockout of the common "hub" gene Sox8 causes defects in neural crest-derived cells along peripheral nerves by facilitating differentiation of SCPs towards sympathoadrenal fates. Finally, specific tumour populations found in melanoma, neurofibroma and neuroblastoma map to different stages of SCP/Schwann cell development. Overall, SCPs resemble migrating neural crest cells that maintain multipotency and become transcriptionally primed towards distinct lineages.

• Keywords
• Schwann cell lineage, Schwann cell precursors, multipotency, neural crest, regulons,
• MeSH
• Cell Differentiation physiology   MeSH
• Neural Crest * MeSH
• Neurogenesis physiology   MeSH
• Peripheral Nerves MeSH
• Schwann Cells * metabolism   MeSH
• Publication type
• Journal Article MeSH

The cranial neural crest (CNC) arises within the developing central nervous system, but then migrates away from the neural tube in three consecutive streams termed mandibular, hyoid and branchial, respectively, according to the order along the anteroposterior axis. While the process of neural crest emigration generally follows a conserved anterior to posterior sequence across vertebrates, we find that ray-finned fishes (bichir, sterlet, gar, and pike) exhibit several heterochronies in the timing and order of CNC emergence that influences their subsequent migratory patterns. First, emigration of the cranial neural crest in these fishes occurs prematurely compared to other vertebrates, already initiating during early neurulation and well before neural tube closure. Second, delamination of the hyoid stream occurs prior to the more anterior mandibular stream; this is associated with early morphogenesis of key hyoid structures like external gills (bichir), a large opercular flap (gar) or first forming cartilage (pike). In sterlet, the hyoid and branchial CNC cells form a single hyobranchial sheet, which later segregates in concert with second pharyngeal pouch morphogenesis. Taken together, the results show that despite generally conserved migratory patterns, heterochronic alterations in the timing of emigration and pattern of migration of CNC cells accompanies morphological diversity of ray-finned fishes.

• Keywords
• Craniofacial, Evolution, Neural crest, Neurulation, Vertebrates,
• MeSH
• Biological Evolution * MeSH
• Neural Crest cytology   embryology   MeSH
• Embryo, Nonmammalian cytology   embryology   MeSH
• Cell Movement physiology   MeSH
• Fishes embryology   MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Research Support, N.I.H., Extramural MeSH

The neural crest is unique to vertebrates and has allowed the evolution of their complicated craniofacial structures. During vertebrate evolution, the acquisition of the neural crest must have been accompanied by the emergence of a new gene regulatory network (GRN). Here, to investigate the role of protein evolution in the emergence of the neural crest GRN, we examined the neural crest cell (NCC) differentiation-inducing activity of chordate FoxD genes. Amphioxus and vertebrate (Xenopus) FoxD proteins both exhibited transcriptional repressor activity in Gal4 transactivation assays and bound to similar DNA sequences in vitro. However, whereas vertebrate FoxD3 genes induced the differentiation of ectopic NCCs when overexpressed in chick neural tube, neither amphioxus FoxD nor any other vertebrate FoxD paralogs exhibited this activity. Experiments using chimeric proteins showed that the N-terminal portion of the vertebrate FoxD3 protein is critical to its NCC differentiation-inducing activity. Furthermore, replacement of the N-terminus of amphioxus FoxD with a 39-amino-acid segment from zebrafish FoxD3 conferred neural crest-inducing activity on amphioxus FoxD or zebrafish FoxD1. Therefore, fixation of this N-terminal amino acid sequence may have been crucial in the evolutionary recruitment of FoxD3 to the vertebrate neural crest GRN.

• Keywords
• Amphioxus, FoxD3, Neural crest,
• MeSH
• Neural Crest physiology   MeSH
• Forkhead Transcription Factors chemistry   genetics   physiology   MeSH
• Transcription, Genetic MeSH
• Cloning, Molecular MeSH
• Vertebrates embryology   MeSH
• Repressor Proteins physiology   MeSH
• Gene Expression Regulation, Developmental * MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Forkhead Transcription Factors MeSH
• Repressor Proteins MeSH

The neural crest (NC) is crucial for the evolutionary diversification of vertebrates. NC cells are induced at the neural plate border by the coordinated action of several signaling pathways, including Wnt/β-catenin. NC cells are normally generated in the posterior neural plate border, whereas the anterior neural fold is devoid of NC cells. Using the mouse model, we show here that active repression of Wnt/β-catenin signaling is required for maintenance of neuroepithelial identity in the anterior neural fold and for inhibition of NC induction. Conditional inactivation of Tcf7l1, a transcriptional repressor of Wnt target genes, leads to aberrant activation of Wnt/β-catenin signaling in the anterior neuroectoderm and its conversion into NC. This reduces the developing prosencephalon without affecting the anterior-posterior neural character. Thus, Tcf7l1 defines the border between the NC and the prospective forebrain via restriction of the Wnt/β-catenin signaling gradient.

• Keywords
• Forebrain, Mouse, Neural crest, Tcf/Lef, Wnt signaling, Zebrafish,
• MeSH
• beta Catenin metabolism   MeSH
• Biomarkers metabolism   MeSH
• Cell Lineage * MeSH
• Neural Crest cytology   metabolism   MeSH
• Zebrafish metabolism   MeSH
• Neural Tube Defects metabolism   pathology   MeSH
• Gene Deletion MeSH
• Phenotype MeSH
• Integrases metabolism   MeSH
• Humans MeSH
• Mice, Transgenic MeSH
• Prosencephalon embryology   metabolism   MeSH
• Transcription Factor 7-Like 1 Protein metabolism   MeSH
• Zebrafish Proteins metabolism   MeSH
• Repressor Proteins metabolism   MeSH
• Wnt Signaling Pathway MeSH
• Cell Transdifferentiation MeSH
• Transcription Factor AP-2 metabolism   MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• beta Catenin MeSH
• Biomarkers MeSH
• Cre recombinase MeSH Browser
• Integrases MeSH
• Transcription Factor 7-Like 1 Protein MeSH
• Zebrafish Proteins MeSH
• Repressor Proteins MeSH
• Tcf7l1 protein, mouse MeSH Browser
• tcf7l1a protein, zebrafish MeSH Browser
• Transcription Factor AP-2 MeSH

Cranial neural crest cells populate the future facial region and produce ectomesenchyme-derived tissues, such as cartilage, bone, dermis, smooth muscle, adipocytes, and many others. However, the contribution of individual neural crest cells to certain facial locations and the general spatial clonal organization of the ectomesenchyme have not been determined. We investigated how neural crest cells give rise to clonally organized ectomesenchyme and how this early ectomesenchyme behaves during the developmental processes that shape the face. Using a combination of mouse and zebrafish models, we analyzed individual migration, cell crowd movement, oriented cell division, clonal spatial overlapping, and multilineage differentiation. The early face appears to be built from multiple spatially defined overlapping ectomesenchymal clones. During early face development, these clones remain oligopotent and generate various tissues in a given location. By combining clonal analysis, computer simulations, mouse mutants, and live imaging, we show that facial shaping results from an array of local cellular activities in the ectomesenchyme. These activities mostly involve oriented divisions and crowd movements of cells during morphogenetic events. Cellular behavior that can be recognized as individual cell migration is very limited and short-ranged and likely results from cellular mixing due to the proliferation activity of the tissue. These cellular mechanisms resemble the strategy behind limb bud morphogenesis, suggesting the possibility of common principles and deep homology between facial and limb outgrowth.

• Keywords
• Early face development, clonal envelopes, embryonic development, migration, morphogenesis, neural crest cells,
• MeSH
• Models, Anatomic MeSH
• Cell Differentiation * MeSH
• Clone Cells cytology   MeSH
• Neural Crest cytology   MeSH
• Zebrafish MeSH
• Ectoderm cytology   embryology   MeSH
• Gene Expression MeSH
• Phenotype MeSH
• Mesoderm cytology   embryology   MeSH
• Morphogenesis * MeSH
• Mice MeSH
• Face embryology   MeSH
• Organogenesis * MeSH
• Cell Movement MeSH
• Genes, Reporter MeSH
• Imaging, Three-Dimensional MeSH
• Animals MeSH
• Check Tag
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Research Support, N.I.H., Extramural MeSH

The neural crest is an embryonic stem cell population unique to vertebrates1 whose expansion and diversification are thought to have promoted vertebrate evolution by enabling emergence of new cell types and structures such as jaws and peripheral ganglia2. Although jawless vertebrates have sensory ganglia, convention has it that trunk sympathetic chain ganglia arose only in jawed vertebrates3-8. Here, by contrast, we report the presence of trunk sympathetic neurons in the sea lamprey, Petromyzon marinus, an extant jawless vertebrate. These neurons arise from sympathoblasts near the dorsal aorta that undergo noradrenergic specification through a transcriptional program homologous to that described in gnathostomes. Lamprey sympathoblasts populate the extracardiac space and extend along the length of the trunk in bilateral streams, expressing the catecholamine biosynthetic pathway enzymes tyrosine hydroxylase and dopamine β-hydroxylase. CM-DiI lineage tracing analysis further confirmed that these cells derive from the trunk neural crest. RNA sequencing of isolated ammocoete trunk sympathoblasts revealed gene profiles characteristic of sympathetic neuron function. Our findings challenge the prevailing dogma that posits that sympathetic ganglia are a gnathostome innovation, instead suggesting that a late-developing rudimentary sympathetic nervous system may have been characteristic of the earliest vertebrates.

• MeSH
• Aorta anatomy & histology   embryology   MeSH
• Biological Evolution * MeSH
• Biosynthetic Pathways MeSH
• Cell Lineage * MeSH
• Neural Crest * cytology   metabolism   MeSH
• Dopamine beta-Hydroxylase metabolism   genetics   MeSH
• Embryonic Stem Cells cytology   metabolism   MeSH
• Catecholamines biosynthesis   metabolism   MeSH
• Neurons * cytology   metabolism   MeSH
• Vertebrates * anatomy & histology   embryology   genetics   MeSH
• Petromyzon anatomy & histology   embryology   genetics   MeSH
• Ganglia, Sympathetic cytology   metabolism   MeSH
• Sympathetic Nervous System * cytology   physiology   MeSH
• Tyrosine 3-Monooxygenase metabolism   genetics   MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Research Support, N.I.H., Extramural MeSH
• Names of Substances
• Dopamine beta-Hydroxylase MeSH
• Catecholamines MeSH
• Tyrosine 3-Monooxygenase MeSH

Adenosine deaminase acting on RNA 1 (ADAR1) is the principal enzyme for the adenosine-to-inosine RNA editing that prevents the aberrant activation of cytosolic nucleic acid sensors by endogenous double stranded RNAs and the activation of interferon-stimulated genes. In mice, the conditional neural crest deletion of Adar1 reduces the survival of melanocytes and alters the differentiation of Schwann cells that fail to myelinate nerve fibers in the peripheral nervous system. These myelination defects are partially rescued upon the concomitant removal of the Mda5 antiviral dsRNA sensor in vitro, suggesting implication of the Mda5/Mavs pathway and downstream effectors in the genesis of Adar1 mutant phenotypes. By analyzing RNA-Seq data from the sciatic nerves of mouse pups after conditional neural crest deletion of Adar1 (Adar1cKO), we here identified the transcription factors deregulated in Adar1cKO mutants compared to the controls. Through Adar1;Mavs and Adar1cKO;Egr1 double-mutant mouse rescue analyses, we then highlighted that the aberrant activation of the Mavs adapter protein and overexpression of the early growth response 1 (EGR1) transcription factor contribute to the Adar1 deletion associated defects in Schwann cell development in vivo. In silico and in vitro gene regulation studies additionally suggested that EGR1 might mediate this inhibitory effect through the aberrant regulation of EGR2-regulated myelin genes. We thus demonstrate the role of the Mda5/Mavs pathway, but also that of the Schwann cell transcription factors in Adar1-associated peripheral myelination defects.

• Keywords
• ADAR1, EGR1, MAVS, Schwann cells, differentiation, neural crest,
• MeSH
• Adenosine Deaminase * genetics   metabolism   MeSH
• Cell Differentiation * genetics   MeSH
• Neural Crest * metabolism   MeSH
• Interferon-Induced Helicase, IFIH1 genetics   metabolism   MeSH
• Myelin Sheath metabolism   MeSH
• Mice, Knockout * MeSH
• Mice MeSH
• Schwann Cells * metabolism   pathology   MeSH
• Animals MeSH
• Check Tag
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• ADAR1 protein, mouse MeSH Browser
• Adenosine Deaminase * MeSH
• Ifih1 protein, mouse MeSH Browser
• Interferon-Induced Helicase, IFIH1 MeSH

BACKGROUND: TALE-class homeodomain transcription factors Meis and Pbx play important roles in formation of the embryonic brain, eye, heart, cartilage or hematopoiesis. Loss-of-function studies of Pbx1, 2 and 3 and Meis1 documented specific functions in embryogenesis, however, functional studies of Meis2 in mouse are still missing. We have generated a conditional allele of Meis2 in mice and shown that systemic inactivation of the Meis2 gene results in lethality by the embryonic day 14 that is accompanied with hemorrhaging. RESULTS: We show that neural crest cells express Meis2 and Meis2-defficient embryos display defects in tissues that are derived from the neural crest, such as an abnormal heart outflow tract with the persistent truncus arteriosus and abnormal cranial nerves. The importance of Meis2 for neural crest cells is further confirmed by means of conditional inactivation of Meis2 using crest-specific AP2α-IRES-Cre mouse. Conditional mutants display perturbed development of the craniofacial skeleton with severe anomalies in cranial bones and cartilages, heart and cranial nerve abnormalities. CONCLUSIONS: Meis2-null mice are embryonic lethal. Our results reveal a critical role of Meis2 during cranial and cardiac neural crest cells development in mouse.

• MeSH
• Cartilage abnormalities   embryology   MeSH
• Neural Crest embryology   metabolism   MeSH
• Forkhead Transcription Factors biosynthesis   genetics   MeSH
• Cranial Nerves embryology   MeSH
• Homeodomain Proteins genetics   MeSH
• Hemorrhage genetics   MeSH
• Skull embryology   innervation   MeSH
• Mice, Inbred C57BL MeSH
• Mice, Knockout MeSH
• Mice MeSH
• Repressor Proteins biosynthesis   genetics   MeSH
• Heart embryology   MeSH
• SOX9 Transcription Factor biosynthesis   genetics   MeSH
• Heart Defects, Congenital embryology   genetics   MeSH
• Animals MeSH
• Check Tag
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Forkhead Transcription Factors MeSH
• Foxd3 protein, mouse MeSH Browser
• Homeodomain Proteins MeSH
• Mrg1 protein, mouse MeSH Browser
• Repressor Proteins MeSH
• Sox9 protein, mouse MeSH Browser
• SOX9 Transcription Factor MeSH

The colonization of limb buds by neural crest cells was studied in quail-chick chimeras and in chick embryos using HNK-1 and DiI staining and the LD-DOPA reaction. Two populations of neural crest cells were found to colonize the limb bud. They migrate successively and use different routes of migration. The first population migrates within the limb bud subectodermally at stages before the limb is innervated. In the wing bud the migration route is localized postaxially and in the leg bud preaxially. Two cell types were identified differentiating from this first population: melanoblasts and Merkel cells. The second population of crest cells invades the limb bud at a later stage. These cells follow the routes of ingrowing nerves and migrate along a dorsal and a ventral path which correspond to the position of nerves for extensor and flexor muscles. Crest cells were found here also in the absence of nerves. Schwann cells and terminal glial cells develop from this second population of neural crest cells.

• MeSH
• CD57 Antigens MeSH
• Antigens, CD metabolism   MeSH
• Chimera MeSH
• Coturnix MeSH
• Neural Crest cytology   embryology   MeSH
• Antigens, Differentiation, T-Lymphocyte metabolism   MeSH
• Dihydroxyphenylalanine metabolism   MeSH
• Fluorescent Dyes MeSH
• Immunohistochemistry MeSH
• Carbocyanines MeSH
• Extremities embryology   MeSH
• Chick Embryo MeSH
• Cell Movement MeSH
• Animals MeSH
• Check Tag
• Chick Embryo MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• 3,3'-dioctadecylindocarbocyanine MeSH Browser
• CD57 Antigens MeSH
• Antigens, CD MeSH
• Antigens, Differentiation, T-Lymphocyte MeSH
• Dihydroxyphenylalanine MeSH
• Fluorescent Dyes MeSH
• Carbocyanines MeSH