A regulatory sub-circuit downstream of Wnt signaling controls developmental transitions in neural crest formation

Changes in chromatin accessibility and transcriptional landscape induced by HDAC inhibitors in TP53 mutated patient-derived colon cancer organoids

Here we present the generation and characterization of patient-derived organoids (PDOs) from colorectal cancer patients. PDOs derived from two patients with TP53 mutations were tested with two different HDAC inhibitors (SAHA and NKL54). Cell death induction, transcriptome, and chromatin accessibility changes were analyzed. HDACIs promote the upregulation of low expressed genes and the downregulation of highly expressed genes. A similar differential effect is observed at the level of chromatin accessibility. Only SAHA is a potent inducer of cell death, which is characterized by the upregulation of BH3-only genes BIK and BMF. Up-regulation of BIK is associated with increased accessibility in an intronic region that has enhancer properties. SAHA, but not NKL54, also causes downregulation of BCL2L1 and decreases chromatin accessibility in three distinct regions of the BCL2L1 locus. Both inhibitors upregulate the expression of innate immunity genes and members of the MHC family. In summary, our exploratory study indicates a mechanism of action for SAHA and demonstrate the low efficacy of NKL54 as a single agent for apoptosis induction, using two PDOs. These observations need to be validated in a larger cohort of PDOs.

Evolutionarily conserved Wnt/Sp5 signaling is critical for anterior-posterior axis patterning in sea urchin embryos

Studies across a diverse group of metazoan embryos indicate that Wnt signaling often activates the transcription factor Sp5, forming a signaling 'cassette' that plays critical roles in many developmental processes. This study explores the role of Wnt/Sp5 signaling during the specification and patterning of the primary germ layers during early anterior-posterior axis formation in the deuterostome sea urchin embryo. Our functional analyses show that Sp5 is critical for endomesoderm specification downstream of Wnt/β-catenin in posterior cells as well as anterior neuroectoderm patterning downstream of non-canonical Wnt/JNK signaling in anterior cells. Interestingly, expression and functional data comparisons show that Wnt/Sp5 signaling often plays similar roles in posterior endomesoderm as well as neuroectoderm patterning along the AP axis of several deuterostome embryos, including vertebrates. Thus, our findings provide strong support for the idea that Wnt-Sp5 signaling cassettes were critical for the establishment of early germ layers in the common deuterostome ancestor.

Neural crest cells development and neuroblastoma progression: Role of Wnt signaling

Neuroblastoma (NB) is one of the most common heterogeneous extracranial cancers in infancy that arises from neural crest (NC) cells of the sympathetic nervous system. The Wnt signaling pathway, both canonical and noncanonical pathway, is a highly conserved signaling pathway that regulates the development and differentiation of the NC cells during embryogenesis. Reports suggest that aberrant activation of Wnt ligands/receptors in Wnt signaling pathways promote progression and relapse of NB. Wnt signaling pathways regulate NC induction and migration in a similar manner; it regulates proliferation and metastasis of NB. Inhibiting the Wnt signaling pathway or its ligands/receptors induces apoptosis and abrogates proliferation and tumorigenicity in all major types of NB cells. Here, we comprehensively discuss the Wnt signaling pathway and its mechanisms in regulating the development of NC and NB pathogenesis. This review highlights the implications of aberrant Wnt signaling in the context of etiology, progression, and relapse of NB. We have also described emerging strategies for Wnt-based therapies against the progression of NB that will provide new insights into the development of Wnt-based therapeutic strategies for NB.

Pax2a, Sp5a and Sp5l act downstream of Fgf and Wnt to coordinate sensory-neural patterning in the inner ear

In zebrafish, sensory epithelia and neuroblasts of the inner ear form simultaneously in abutting medial and lateral domains, respectively, in the floor of the otic vesicle. Previous studies support regulatory roles for Fgf and Wnt, but how signaling is coordinated is poorly understood. We investigated this problem using pharmacological and transgenic methods to alter Fgf or Wnt signaling from early placodal stages to evaluate later changes in growth and patterning. Blocking Fgf at any stage reduces proliferation of otic tissue and terminates both sensory and neural specification. Wnt promotes proliferation in the otic vesicle but is not required for sensory or neural development. However, sustained overactivation of Wnt laterally expands sensory epithelia and blocks neurogenesis. pax2a, sp5a and sp5l are coregulated by Fgf and Wnt and show overlapping expression in the otic placode and vesicle. Gain- and loss-of-function studies show that these genes are together required for Wnt's suppression of neurogenesis, as well as some aspects of sensory development. Thus, pax2a, sp5a and sp5l are critical for mediating Fgf and Wnt signaling to promote spatially localized sensory and neural development.

Cellular plasticity in the neural crest and cancer

In vertebrates, neural crest cells (NCCs) are a multipotent embryonic population generating both neural/neuronal and mesenchymal derivatives, and thus the neural crest (NC) is often referred to as the fourth germ layer. NC development is a dynamic process, where NCCs possess substantial plasticity in transcriptional and epigenomic profiles. Recent technical advances in single-cell and low-input sequencing have empowered fine-resolution characterisation of NC development. In this review, we summarise the latest models underlying NC-plasticity acquirement and cell-fate restriction, outline the connections between NC plasticity and NC-derived cancer and envision the new opportunities in studying NC plasticity and its link to cancer.

Single-cell atlas of early chick development reveals gradual segregation of neural crest lineage from the neural plate border during neurulation

The epiblast of vertebrate embryos is comprised of neural and non-neural ectoderm, with the border territory at their intersection harboring neural crest and cranial placode progenitors. Here, we a generate single-cell atlas of the developing chick epiblast from late gastrulation through early neurulation stages to define transcriptional changes in the emerging ‘neural plate border’ as well as other regions of the epiblast. Focusing on the border territory, the results reveal gradual establishment of heterogeneous neural plate border signatures, including novel genes that we validate by fluorescent in situ hybridization. Developmental trajectory analysis infers that segregation of neural plate border lineages only commences at early neurulation, rather than at gastrulation as previously predicted. We find that cells expressing the prospective neural crest marker Pax7 contribute to multiple lineages, and a subset of premigratory neural crest cells shares a transcriptional signature with their border precursors. Together, our results suggest that cells at the neural plate border remain heterogeneous until early neurulation, at which time progenitors become progressively allocated toward defined neural crest and placode lineages. The data also can be mined to reveal changes throughout the developing epiblast.

Cell Fate Decisions in the Neural Crest, from Pigment Cell to Neural Development

The neural crest shows an astonishing multipotency, generating multiple neural derivatives, but also pigment cells, skeletogenic and other cell types. The question of how this process is controlled has been the subject of an ongoing debate for more than 35 years. Based upon new observations of zebrafish pigment cell development, we have recently proposed a novel, dynamic model that we believe goes some way to resolving the controversy. Here, we will firstly summarize the traditional models and the conflicts between them, before outlining our novel model. We will also examine our recent dynamic modelling studies, looking at how these reveal behaviors compatible with the biology proposed. We will then outline some of the implications of our model, looking at how it might modify our views of the processes of fate specification, differentiation, and commitment.

Review: The Role of Wnt/β-Catenin Signalling in Neural Crest Development in Zebrafish

The neural crest (NC) is a multipotent cell population in vertebrate embryos with extraordinary migratory capacity. The NC is crucial for vertebrate development and forms a myriad of cell derivatives throughout the body, including pigment cells, neuronal cells of the peripheral nervous system, cardiomyocytes and skeletogenic cells in craniofacial tissue. NC induction occurs at the end of gastrulation when the multipotent population of NC progenitors emerges in the ectodermal germ layer in the neural plate border region. In the process of NC fate specification, fate-specific markers are expressed in multipotent progenitors, which subsequently adopt a specific fate. Thus, NC cells delaminate from the neural plate border and migrate extensively throughout the embryo until they differentiate into various cell derivatives. Multiple signalling pathways regulate the processes of NC induction and specification. This review explores the ongoing role of the Wnt/β-catenin signalling pathway during NC development, focusing on research undertaken in the Teleost model organism, zebrafish (Danio rerio). We discuss the function of the Wnt/β-catenin signalling pathway in inducing the NC within the neural plate border and the specification of melanocytes from the NC. The current understanding of NC development suggests a continual role of Wnt/β-catenin signalling in activating and maintaining the gene regulatory network during NC induction and pigment cell specification. We relate this to emerging models and hypotheses on NC fate restriction. Finally, we highlight the ongoing challenges facing NC research, current gaps in knowledge, and this field's potential future directions.

The connectome of neural crest enhancers reveals regulatory features of signaling systems

Cell fate commitment is controlled by cis-regulatory elements often located in remote regions of the genome. To examine the role of long-range DNA interactions in early development, we generated a high-resolution contact map of active enhancers in avian neural crest cells. This analysis uncovered a diverse repertoire of enhancers that are part of the gene regulatory network underlying specification. We found that neural crest identity is largely regulated by cis-regulatory elements that propagate signaling inputs to network components. These genomic sensors display a combination of optimal and suboptimal TCF/LEF-binding sites, which allow cells to respond to Wnt signaling in a position-dependent manner. We propose that, rather than acting as upstream activators, signaling systems feed into regulatory circuits in a hub-and-spoke architecture. These results shed light on the tridimensional organization of the neural crest genome and define how signaling systems provide progenitors with spatial cues that transform their molecular identity.