Chromatin remodeller Chd7 is developmentally regulated in the neural crest by tissue-specific transcription factors.

Neurocristopathies such as CHARGE syndrome result from aberrant neural crest development. A large proportion of CHARGE cases are attributed to pathogenic variants in the gene encoding CHD7, chromodomain helicase DNA binding protein 7, which remodels chromatin. While the role for CHD7 in neural crest development is well documented, how this factor is specifically up-regulated in neural crest cells is not understood. Here, we use epigenomic profiling of chick and human neural crest to identify a cohort of enhancers regulating Chd7 expression in neural crest cells and other tissues. We functionally validate upstream transcription factor binding at candidate enhancers, revealing novel epistatic relationships between neural crest master regulators and Chd7, showing tissue-specific regulation of a globally acting chromatin remodeller. Furthermore, we find conserved enhancer features in human embryonic epigenomic data and validate the activity of the human equivalent CHD7 enhancers in the chick embryo. Our findings embed Chd7 in the neural crest gene regulatory network and offer potentially clinically relevant elements for interpreting CHARGE syndrome cases without causative allocation.

Roles of Wnt pathway genes wls, wnt9a, wnt5b, frzb and gpc4 in regulating convergent-extension during zebrafish palate morphogenesis.

The Wnt signaling pathway is crucial for tissue morphogenesis, participating in cellular behavior changes, notably during the process of convergent-extension. Interactions between Wnt-secreting and receiving cells during convergent-extension remain elusive. We investigated the role and genetic interactions of Wnt ligands and their trafficking factors Wls, Gpc4 and Frzb in the context of palate morphogenesis in zebrafish. We describe that the chaperon Wls and its ligands Wnt9a and Wnt5b are expressed in the ectoderm, whereas juxtaposed chondrocytes express Frzb and Gpc4. Using wls, gpc4, frzb, wnt9a and wnt5b mutants, we genetically dissected the Wnt signals operating between secreting ectoderm and receiving chondrocytes. Our analysis delineates that non-canonical Wnt signaling is required for cell intercalation, and that wnt5b and wnt9a are required for palate extension in the anteroposterior and transverse axes, respectively.

Occult Histopathology and Its Predictors in Contralateral and Bilateral Prophylactic Mastectomies.

BACKGROUND: The last decade has seen an increasing prevalence of prophylactic mastectomies with decreasing age of patients treated for breast cancer. Data are limited on the prevalence of histopathologic abnormalities in this population. This study aimed to measure the prevalence of histopathologic findings in contralateral prophylactic mastectomy (CPM) and bilateral prophylactic mastectomy (BPM) patients and identify predictors of findings. METHODS: Our institution's prophylactic mastectomies from 2004 to 2011 were reviewed. Breast specimens with prior malignancies were excluded. Patient factors and pathology reports were collected. Independent predictive factors were identified with univariate and multivariate logistic analysis. RESULTS: A total of 524 specimens in 454 patients were identified. Malignancy was found in 7.0% of CPM and 5.7% of BPM specimens. In CPM patients, ipsilateral lobular carcinoma-in situ [odds ratio (OR) 4.0] and mammogram risk group (OR 2.0) were predictive of malignancy. Age group (OR 1.5), ipsilateral lobular carcinoma-in situ (OR 2.3), and prior bilateral salpingo-oophorectomy (OR 0.3) were predictive of moderate- to high-risk histopathology. Only increasing age group was predictive of increased moderate- to high-risk histopathology in BPM patients (OR 2.3). There were no independent predictors of malignancy in BPM. BRCA status was not predictive in either CPM or BPM. CONCLUSIONS: Patients with lobular carcinoma-in situ in the index breast or high-risk mammograms have a higher prevalence of malignancies. Although BRCA patients may benefit from prophylactic mastectomy, the genetic diagnosis does not increase the prevalence of detecting occult pathology. BPM patients can be counseled about relative risk, where occult pathology increases with age.

Tissue-Specific In Vivo Biotin Chromatin Immunoprecipitation with Sequencing in Zebrafish and Chicken.

Chromatin immunoprecipitation with sequencing (ChIP-seq) has been instrumental in understanding transcription factor (TF) binding during gene regulation. ChIP-seq requires specific antibodies against desired TFs, which are not available for numerous species. Here, we describe a tissue-specific biotin ChIP-seq protocol for zebrafish and chicken embryos which utilizes AVI tagging of TFs, permitting their biotinylation by a co-expressed nuclear biotin ligase. Subsequently, biotinylated factors can be precipitated with streptavidin beads, enabling the user to construct TF genome-wide binding landscapes like conventional ChIP-seq methods. For complete details on the use and execution of this protocol, please see Lukoseviciute et al. (2018) and Ling and Sauka-Spengler (2019).

Early chromatin shaping predetermines multipotent vagal neural crest into neural, neuronal and mesenchymal lineages.

The enteric nervous system (ENS) predominantly originates from vagal neural crest (VNC) cells that emerge from the caudal hindbrain, invade the foregut and populate the gastrointestinal tract. However, the gene regulatory network (GRN) orchestrating the early specification of VNC remains unknown. Using an EdnrB enhancer, we generated a comprehensive temporal map of the chromatin and transcriptional landscape of VNC in the avian model, revealing three VNC cell clusters (neural, neurogenic and mesenchymal), each predetermined epigenetically prior to neural tube delamination. We identify and functionally validate regulatory cores (Sox10/Tfap2B/SoxB/Hbox) mediating each programme and elucidate their combinatorial activities with other spatiotemporally specific transcription factors (bHLH/NR). Our global deconstruction of the VNC-GRN in vivo sheds light on critical early regulatory mechanisms that may influence the divergent neural phenotypes in enteric neuropathies.

Reconstruction of the Global Neural Crest Gene Regulatory Network In Vivo.

Precise control of developmental processes is encoded in the genome in the form of gene regulatory networks (GRNs). Such multi-factorial systems are difficult to decode in vertebrates owing to their complex gene hierarchies and dynamic molecular interactions. Here we present a genome-wide in vivo reconstruction of the GRN underlying development of the multipotent neural crest (NC) embryonic cell population. By coupling NC-specific epigenomic and transcriptional profiling at population and single-cell levels with genome/epigenome engineering in vivo, we identify multiple regulatory layers governing NC ontogeny, including NC-specific enhancers and super-enhancers, novel trans-factors, and cis-signatures allowing reverse engineering of the NC-GRN at unprecedented resolution. Furthermore, identification and dissection of divergent upstream combinatorial regulatory codes has afforded new insights into opposing gene circuits that define canonical and neural NC fates early during NC ontogeny. Our integrated approach, allowing dissection of cell-type-specific regulatory circuits in vivo, has broad implications for GRN discovery and investigation.

A genome-wide assessment of the ancestral neural crest gene regulatory network.

The neural crest (NC) is an embryonic cell population that contributes to key vertebrate-specific features including the craniofacial skeleton and peripheral nervous system. Here we examine the transcriptional and epigenomic profiles of NC cells in the sea lamprey, in order to gain insight into the ancestral state of the NC gene regulatory network (GRN). Transcriptome analyses identify clusters of co-regulated genes during NC specification and migration that show high conservation across vertebrates but also identify transcription factors (TFs) and cell-adhesion molecules not previously implicated in NC migration. ATAC-seq analysis uncovers an ensemble of cis-regulatory elements, including enhancers of Tfap2B, SoxE1 and Hox-α2 validated in the embryo. Cross-species deployment of lamprey elements identifies the deep conservation of lamprey SoxE1 enhancer activity, mediating homologous expression in jawed vertebrates. Our data provide insight into the core GRN elements conserved to the base of the vertebrates and expose others that are unique to lampreys.

Visualization of Chondrocyte Intercalation and Directional Proliferation via Zebrabow Clonal Cell Analysis in the Embryonic Meckel's Cartilage.

Development of the vertebrate craniofacial structures requires precise coordination of cell migration, proliferation, adhesion and differentiation. Patterning of the Meckel's cartilage, a first pharyngeal arch derivative, involves the migration of cranial neural crest (CNC) cells and the progressive partitioning, proliferation and organization of differentiated chondrocytes. Several studies have described CNC migration during lower jaw morphogenesis, but the details of how the chondrocytes achieve organization in the growth and extension of Meckel's cartilage remains unclear. The sox10 restricted and chemically induced Cre recombinase-mediated recombination generates permutations of distinct fluorescent proteins (RFP, YFP and CFP), thereby creating a multi-spectral labeling of progenitor cells and their progeny, reflecting distinct clonal populations. Using confocal time-lapse photography, it is possible to observe the chondrocytes behavior during the development of the zebrafish Meckel's cartilage. Multispectral cell labeling enables scientists to demonstrate extension of the Meckel's chondrocytes. During extension phase of the Meckel's cartilage, which prefigures the mandible, chondrocytes intercalate to effect extension as they stack in an organized single-cell layered row. Failure of this organized intercalating process to mediate cell extension provides the cellular mechanistic explanation for hypoplastic mandible that we observe in mandibular malformations.