Project description:The trigeminal ganglion is a critical structure in the peripheral nervous system, responsible for transmitting sensations of touch, pain, and temperature from craniofacial regions to the brain. Trigeminal ganglion development depends upon intrinsic cellular programming as well as extrinsic signals exchanged by diverse cell populations. With its complex anatomy and dual cellular origin from cranial placodes and neural crest cells, the trigeminal ganglion offers a rich context for examining diverse biological processes, including cell migration, fate determination, adhesion, and axon guidance. Avian models have, so far, enabled key insights into craniofacial and peripheral nervous system development. Yet, the molecular mechanisms driving trigeminal ganglion formation and subsequent nerve growth remain elusive. In this study, we performed RNA-sequencing at multiple stages of chick trigeminal ganglion development and generated a novel transcriptomic dataset that has been curated to illustrate temporally dynamic gene expression patterns. This publicly available resource identifies major pathways involved in trigeminal gangliogenesis, particularly with respect to the condensation and maturation of placode-derived neurons, thus inviting new lines of research into the essential processes governing trigeminal ganglion development.
Project description:Background: The trigeminal ganglion (TG) is a structure of the peripheral nervous system, composed of neuronal and non-neuronal cell types, that integrates sensory input from the face and jaw. The developing TG is derived from two embryonic cell populations: neural crest and cranial placode. Both populations play critical roles in TG development and must interact to coordinate changes in gene expression that regulate specification, differentiation, and organization. However, the molecular characteristics of the heterogeneous cell populations within the developing TG remain poorly defined. Results: We performed single-cell RNA-sequencing (scRNA-seq) on TG from developing chick embryos at HH17. Our high-resolution dataset (14 clusters, ~87000 cells) provides insight into cellular diversity within the developing TG. As expected, we identified placode-derived neurons as well as neural crest cells prior to neuronal differentiation. In addition to classic markers, we identified novel transcripts with unknown roles in TG development, including several long non-coding RNAs (lncRNAs). Conclusions: We generated a single-cell atlas of the developing chick trigeminal ganglion during early axonogenesis and defined the transcriptomic states of its diverse cell populations. Our results provide a useful resource for better understanding the cell populations contributing to TG development and gene expression that drives cell identity and differentiation.
Project description:The BAF chromatin remodeler regulates lineage commitment including cranial neural crest cell (CNCC) specification. BAF subunit mutations cause Coffin-Siris Syndrome (CSS), a congenital disorder characterized by distinct craniofacial features and intellectual disability. Approximately 50% of CSS patients carry mutations in one of the mutually exclusive BAF subunits, ARID1A/ARID1B. While Arid1a deletion in mouse neural crest causes severe craniofacial phenotypes, little is known about the role of ARID1A in CNCC specification. Using CSS patient-derived ARID1A+/- iPSCs to model CNCC specification, we discovered that ARID1A-haploinsufficency impairs epithelial to mesenchymal transition (EMT), a process necessary for CNCC delamination and migration from the neural tube. Furthermore, wild-type ARID1A-BAF regulates enhancers associated with EMT genes. ARID1A-BAF binding at these enhancers is impaired in heterozygotes, while binding at promoters is unaffected. At the sequence level, these EMT enhancers contain binding motifs for ZIC2, and ZIC2 binding at these sites is ARID1A-dependent. When excluded from EMT enhancers, ZIC2 relocates to neuronal enhancers, triggering aberrant neuronal gene activation. In mice, deletion of Zic2 impairs NCC delamination, while ZIC2 overexpression in chick embryos at pre-migratory neural crest stages elicits abnormal cell delamination from the neural tube. These findings reveal a novel ARID1A-ZIC2 axis essential for EMT and CNCC delamination.
Project description:General somatic sensation is conveyed to the central nervous system at cranial levels by the trigeminal ganglion (TG), and at spinal levels by the dorsal root ganglia (DRG). Although these ganglia have similar functions, they have distinct embryological origins, in that both contain neurons originating from the neural crest, while only the TG includes cells derived from the placodal ectoderm. Here we use microarray analysis of E13.5 embryos to demonstrate that the developing DRG and TG have very similar overall patterns of gene expression. In mice lacking the POU-domain transcription factor Brn3a the DRG and TG exhibit many common changes in downstream gene expression, but a subset of genes show increased expression only at cranial levels. Although silent in wild-type ganglia, the promoter regions of genes which are activated in the absence of Brn3a also exhibit increased histone H3-acetylation at levels similar to constitutively transcribed gene loci, and this H3-acetylation is tissue-specific for genes which are increased only in the TG. These results demonstrate that one developmental role of Brn3a is to repress potential differences in gene expression between sensory neurons generated at different axial levels, and to regulate a convergent program of developmental gene expression, in which functionally similar populations of neurons are generated from different embryological substrates. Experiment Overall Design: Microarrays used to compare the patterns of gene expression in the dorsal root ganglia and trigeminal ganglia of Brn3a knockout and wild-type mice. Embryonic day 13.5 (E13.5) was chosen because at this point in development mutant mice exhibit major defects in sensory axon growth, but have yet to undergo the period of extensive sensory neuron death associated with later stages.
Project description:Nogo-A is a major regulator of neural development and regeneration in the central nervous system, but its role in tooth innervation remains largely unknown. Neurons of the trigeminal ganglion innervate the teeth. We showed that Nogo-A is expressed in the trigeminal ganglion and tooth-related nerve fibres. Nogo-A deletion in mice leads to a less complex neuronal network when compared to wild-type animals. Bulk RNA sequencing on the trigeminal ganglia of Nogo-A KO and wild-type mice revealed gene expression changes associated with alterations in neurotrophin signalling and neuronal synaptic formation during the development and maturation of the trigeminal neurons.
Project description:Neural crest (NC) cells form a multipotent stem cell population specified during neurulation, which undergoes an epithelial-to-mesenchymal transition (EMT) and migrate extensively in the developing embryo, to generate numerous tissues and cell types including the craniofacial skeleton, the peripheral nervous system and pigment cells. The genetic and molecular details of neural crest specification are governed by a complex, yet still partially understood gene regulatory network (NC-GRN). In particular, the precise function of microRNAs in this network remains poorly known. MicroRNAs are short non-coding 20-22 nucleotides long RNAs which control gene expression through post-transcriptional repression. Since miRNA-196a is expressed in the developing neural and neural crest cells of Xenopus laevis embryos we here investigated miR-196a function in the NC-GRN, by knocking-down its expression using antisense morpholinos. Depletion of miR-196a revealed major neural crest and craniofacial phenotypes. These defects were preceded by the perturbed expression of key neural, neural border and neural crest markers such as sox2/3, zic1/3, pax3, sox10 and snail2. Using RNA sequencing of individual neural border and neural crest explants, we have identified a signature of genes up- and down-regulated by miR-196a and validate these with rescue experiments using a miR mimic. We show that Sox10, a predicted target of miR-196a, is lost following morpholino knockdown and rescued upon miR 196a mimic expression. Our study identifies miR-196a as a key actor of early patterning in the dorsal ectoderm, balancing the extent of immature neural plate progenitors with neural crest and placode specification, while also promoting neuron differentiation within the neural plate.
Project description:General somatic sensation is conveyed to the central nervous system at cranial levels by the trigeminal ganglion (TG), and at spinal levels by the dorsal root ganglia (DRG). Although these ganglia have similar functions, they have distinct embryological origins, in that both contain neurons originating from the neural crest, while only the TG includes cells derived from the placodal ectoderm. Here we use microarray analysis of E13.5 embryos to demonstrate that the developing DRG and TG have very similar overall patterns of gene expression. In mice lacking the POU-domain transcription factor Brn3a the DRG and TG exhibit many common changes in downstream gene expression, but a subset of genes show increased expression only at cranial levels. Although silent in wild-type ganglia, the promoter regions of genes which are activated in the absence of Brn3a also exhibit increased histone H3-acetylation at levels similar to constitutively transcribed gene loci, and this H3-acetylation is tissue-specific for genes which are increased only in the TG. These results demonstrate that one developmental role of Brn3a is to repress potential differences in gene expression between sensory neurons generated at different axial levels, and to regulate a convergent program of developmental gene expression, in which functionally similar populations of neurons are generated from different embryological substrates. Keywords: Gene expression in the developing nervous system
Project description:The sensitization of trigeminal ganglion neurons contributes to primary headache disorders such as migraine, but the specific neuronal and non-neuronal trigeminal subtypes involved remain unclear. We thus developed a cell atlas in which human and mouse trigeminal ganglia are transcriptionally and epigenomically profiled at single-cell resolution. These data describe evolutionarily conserved and human-specific gene expression patterns within each trigeminal ganglion cell type, as well as the transcription factors and gene regulatory elements that contribute to cell-type-specific gene expression. We then leverage these data to identify trigeminal ganglion cell types that are implicated both by human genetic variation associated with migraine and two mouse models of headache. This trigeminal ganglion cell atlas improves our understanding of the cell types, genes, and epigenomic features involved in headache pathophysiology and establishes a rich resource of cell-type-specific molecular features to guide the development of more selective treatments for headache and facial pain.
Project description:CHARGE syndrome is caused by heterozygous mutations in a chromatin remodeler CHD7 and characterized by a set of malformations historically postulated to arise from defects in the neural crest formation during embryogenesis. To better delineate neural crest defects in CHARGE syndrome, we generated induced pluripotent stem cells (iPSCs) from two patients with typical syndrome manifestations, and characterized neural crest cells differentiated in vitro from these iPSCs (iPSC-NCCs). We found that expression of genes associated with cell migration was altered in CHARGE iPSC-NCCs as compared to control iPSC-NCCs. Consistently, CHARGE iPSC-NCCs showed defective delamination, migration and motility in vitro, and their transplantation in ovo revealed overall defective migratory activity in the chick embryo. Altogether, our results support the historical inference that CHARGE syndrome patients have defects in neural crest migration and provide the first successful application of patient-derived iPSCs in modeling craniofacial disorders.