cdon and boc affect trunk neural crest cell migration through a non-cell autonomous reduction of hedgehog signaling in zebrafish slow-twitch muscle

The immunoglobin superfamily members cdon and boc are transmembrane proteins implicated in regulating hedgehog signaling during vertebrate development. Recent work showing roles for these genes in axon guidance and neural crest cell migration further suggest that cdon/boc may play additional functions in regulating directed cell movements during development. Here we use novel and existing mutants to investigate a role for cdon and boc in zebrafish neural crest cell migration. We find that single cdon or boc mutant embryos exhibit normal neural crest phenotypes, but that neural crest migration is strikingly disrupted in double cdon/boc mutant embryos. We further show that this neural crest migration phenotype is associated with defects to the differentiation of slow-twitch muscle cells, and that this slow-twitch muscle phenotype is a consequence of reduced hedgehog signaling in mutant fish. While neural crest migratory ability is not affected in double mutant embryos, neural crest directionality is severely affected. These data suggest that neural crest migration defects are likely to be secondary to defects in slow-twitch muscle differentiation. Combined, our data add to a growing literature showing that cdon and boc act synergistically to promote hedgehog signaling during vertebrate development, and provide a foundation for using zebrafish to further study the function of these hedgehog receptor paralogs.

Pseudodiverticulum of the Cervical Esophagus With Remnant of Branchial Tissues in a Newborn: A Case Report

Congenital pseudodiverticula of the esophagus are very rare. This case report describes the presentation, management and histopathology of a peudodiverticulum of the cervical esophagus in a neonate. The infant presented with respiratory distress and a right neck mass that required surgical excision. Pathology revealed a pseudodiverticulum that contained ectopic thymic, thyroid, and parathyroid tissue within the wall of the lesion. The presence of ectopic tissues of branchial origin and an aberrant right subclavian artery suggest an error in branchial development and neural crest cell migration.

A simplified method for generating human inner ear organoids from pluripotent stem cells

The inner ear detects sound, head movements, and gravity using specialized epithelial cells and neurons. Decreased function in these cells can lead to hearing loss and dizziness. Inner ear disorders impact millions worldwide; however, current therapeutic options are limited. While animal models are a powerful system to assess auditory and vestibular dysfunction, in vitro inner ear models are gaining importance in translational research. Here, we provide a stepwise approach for generating inner ear organoids (IEOs), which contain supporting cells, hair cells, and neurons. Our differentiation regimen, using defined medium components and diluted extracellular matrix proteins, guides a 3D spheroid of pluripotent stem cells into otic progenitor cells by mimicking the environmental cues that occur during fetal development. Control of the TGF and BMP pathways early in the culture, promotes patterning of the spheroid, with an outer layer of surface ectoderm and an inner core of neuroectoderm. Later, FGF activation and BMP inhibition induce placode formation in the outer layer and neural crest cell migration from the core. These two cell lineages co-develop into otic vesicle-like structures surrounded by a layer of mesenchymal, neuronal, and glial cells that can be maintained in culture for over 100 days. The IEOs described in this protocol are a promising tool for otology research.

Dexamethasone Suppresses Palatal Cell Proliferation through miR-130a-3p

Cleft lip with or without cleft palate (CL/P) is one of the most common congenital birth defects. This study aims to identify novel pathogenic microRNAs associated with cleft palate (CP). Through data analyses of miRNA-sequencing for developing palatal shelves of C57BL/6J mice, we found that miR-449a-3p, miR-449a-5p, miR-449b, miR-449c-3p, and miR-449c-5p were significantly upregulated, and that miR-19a-3p, miR-130a-3p, miR-301a-3p, and miR-486b-5p were significantly downregulated, at embryonic day E14.5 compared to E13.5. Among them, overexpression of the miR-449 family (miR-449a-3p, miR-449a-5p, miR-449b, miR-449c-3p, and miR-449c-5p) and miR-486b-5p resulted in reduced cell proliferation in primary mouse embryonic palatal mesenchymal (MEPM) cells and mouse cranial neural crest cell line O9-1. On the other hand, inhibitors of miR-130a-3p and miR-301a-3p significantly reduced cell proliferation in MEPM and O9-1 cells. Notably, we found that treatment with dexamethasone, a glucocorticoid known to induce CP in mice, suppressed miR-130a-3p expression in both MEPM and O9-1 cells. Moreover, a miR-130a-3p mimic could ameliorate the cell proliferation defect induced by dexamethasone through normalization of Slc24a2 expression. Taken together, our results suggest that miR-130-3p plays a crucial role in dexamethasone-induced CP in mice.

Avian ceca are required for hindgut enteric nervous system development by inhibiting neuronal differentiation via non-canonical Wnt signaling and by promoting enteric neural crest cell proliferation

The enteric nervous system (ENS), which is derived from enteric neural crest cells (ENCCs), represents the neuronal innervation of the intestine. Compromised ENCC migration can lead to Hirschsprung Disease, which is characterized by an aganglionic distal bowel. During the craniocaudal migration of ENCCs along the gut, we find that their proliferation is greatest as the ENCC wavefront passes through the ceca, a paired structure at the midgut-hindgut junction in avian intestine. Removal of the ceca leads to hindgut aganglionosis, suggesting that they are required for ENS development. Comparative transcriptome profiling of the cecal buds compared to the interceca region shows that the non-canonical Wnt signaling pathway is preferentially expressed within the ceca. Specifically, Wnt11 is highly expressed, as confirmed by RNA in situ hybridization, leading us to hypothesize that cecal expression of Wnt11 is important for ENCC colonization of the hindgut. Organ cultures using E6 avian intestine show that Wnt11 inhibits enteric neuronal differentiation. These results reveal an essential role for the ceca during hindgut ENS formation and highlight an important function for non-canonical Wnt signaling in regulating ENCC differentiation.

Single-cell reconstruction with spatial context of migrating neural crest cells and their microenvironments during vertebrate head and neck formation

ABSTRACT The dynamics of multipotent neural crest cell differentiation and invasion as cells travel throughout the vertebrate embryo remain unclear. Here, we preserve spatial information to derive the transcriptional states of migrating neural crest cells and the cellular landscape of the first four chick cranial to cardiac branchial arches (BA1-4) using label-free, unsorted single-cell RNA sequencing. The faithful capture of branchial arch-specific genes led to identification of novel markers of migrating neural crest cells and 266 invasion genes common to all BA1-4 streams. Perturbation analysis of a small subset of invasion genes and time-lapse imaging identified their functional role to regulate neural crest cell behaviors. Comparison of the neural crest invasion signature to other cell invasion phenomena revealed a shared set of 45 genes, a subset of which showed direct relevance to human neuroblastoma cell lines analyzed after exposure to the in vivo chick embryonic neural crest microenvironment. Our data define an important spatio-temporal reference resource to address patterning of the vertebrate head and neck, and previously unidentified cell invasion genes with the potential for broad impact.

Cyclical fate restriction: a new view of neural crest cell fate specification

ABSTRACT Neural crest cells are crucial in development, not least because of their remarkable multipotency. Early findings stimulated two hypotheses for how fate specification and commitment from fully multipotent neural crest cells might occur, progressive fate restriction (PFR) and direct fate restriction, differing in whether partially restricted intermediates were involved. Initially hotly debated, they remain unreconciled, although PFR has become favoured. However, testing of a PFR hypothesis of zebrafish pigment cell development refutes this view. We propose a novel ‘cyclical fate restriction’ hypothesis, based upon a more dynamic view of transcriptional states, reconciling the experimental evidence underpinning the traditional hypotheses.