Requirement for frzb and fzd7a in cranial neural crest convergence and extension mechanisms during zebrafish palate and jaw morphogenesis

Genetic-epigenetic interactions (meQTLs) in orofacial clefts etiology

Objectives

Nonsyndromic orofacial clefts (OFCs) etiology involves multiple genetic and environmental factors with over 60 identified risk loci; however, they account for only a minority of the estimated risk. Epigenetic factors such as differential DNA methylation (DNAm) are also associated with OFCs risk and can alter risk for different cleft types and modify OFCs penetrance. DNAm is a covalent addition of a methyl (CH3) group to the nucleotide cytosine that can lead to changes in expression of the targeted gene. DNAm can be affected by environmental influences and genetic variation via methylation quantitative loci (meQTLs). We hypothesize that aberrant DNAm and the resulting alterations in gene expression play a key role in the etiology of OFCs, and that certain common genetic variants that affect OFCs risk do so by influencing DNAm.

Methods

We used genotype from 10 cleft-associated SNPs and genome-wide DNA methylation data (Illumina 450K array) for 409 cases with OFCs and 456 controls and identified 23 cleft-associated meQTLs. We then used an independent cohort of 362 cleft-discordant sib pairs for replication. We used methylation-specific qPCR to measure methylation levels of each CpG site and combined genotypic and methylation data for an interaction analysis of each SNP-CpG pair using the R package MatrixeQTL in a linear model. We also performed a Paired T-test to analyze differences in DNA methylation between each member of the sibling pairs.

Results

We replicated 9 meQTLs, showing interactions between rs13041247 (MAFB) - cg18347630 (PLCG1) (P=0.04); rs227731 (NOG) - cg08592707 (PPM1E) (P=0.01); rs227731 (NOG) - cg10303698 (CUEDC1) (P=0.001); rs3758249 (FOXE1) - cg20308679 (FRZB) (P=0.04); rs8001641 (SPRY2) - cg19191560 (LGR4) (P=0.04); rs987525(8q24) - cg16561172(MYC) (P=0.00000963); rs7590268(THADA) - cg06873343 (TTYH3) (P=0.04); rs7078160 (VAX1) - cg09487139 (P=0.05); rs560426 (ABCA4/ARHGAP29) - cg25196715 (ABCA4/ARHGAP29) (P=0,03). Paired T-test showed significant differences for cg06873343 (TTYH3) (P=0.04); cg17103269 (LPIN3) (P=0.002), and cg19191560 (LGR4) (P=0.05).

Conclusions

Our results confirm previous evidence that some of the common non-coding variants detected through GWAS studies can influence the risk of OFCs via epigenetic mechanisms, such as DNAm, which can ultimately affect and regulate gene expression. Given the large prevalence of non-coding SNPs in most OFCs genome wide association studies, our findings can potentially address major knowledge gaps, like missing heritability, reduced penetrance, and variable expressivity associated with OFCs phenotypes.

Genetic requirement of dact1/2 to regulate noncanonical Wnt signaling and calpain 8 during embryonic convergent extension and craniofacial morphogenesis

Wnt signaling plays crucial roles in embryonic patterning including the regulation of convergent extension (CE) during gastrulation, the establishment of the dorsal axis, and later, craniofacial morphogenesis. Further, Wnt signaling is a crucial regulator of craniofacial morphogenesis. The adapter proteins Dact1 and Dact2 modulate the Wnt signaling pathway through binding to Disheveled. However, the distinct relative functions of Dact1 and Dact2 during embryogenesis remain unclear. We found that dact1 and dact2 genes have dynamic spatiotemporal expression domains that are reciprocal to one another suggesting distinct functions during zebrafish embryogenesis. Both dact1 and dact2 contribute to axis extension, with compound mutants exhibiting a similar CE defect and craniofacial phenotype to the wnt11f2 mutant. Utilizing single-cell RNAseq and an established noncanonical Wnt pathway mutant with a shortened axis (gpc4), we identified dact1/2-specific roles during early development. Comparative whole transcriptome analysis between wildtype and gpc4 and wildtype and dact1/2 compound mutants revealed a novel role for dact1/2 in regulating the mRNA expression of the classical calpain capn8. Overexpression of capn8 phenocopies dact1/2 craniofacial dysmorphology. These results identify a previously unappreciated role of capn8 and calcium-dependent proteolysis during embryogenesis. Taken together, our findings highlight the distinct and overlapping roles of dact1 and dact2 in embryonic craniofacial development, providing new insights into the multifaceted regulation of Wnt signaling.

Transforming growth factor beta signaling and craniofacial development: modeling human diseases in zebrafish

Humans and other jawed vertebrates rely heavily on their craniofacial skeleton for eating, breathing, and communicating. As such, it is vital that the elements of the craniofacial skeleton develop properly during embryogenesis to ensure a high quality of life and evolutionary fitness. Indeed, craniofacial abnormalities, including cleft palate and craniosynostosis, represent some of the most common congenital abnormalities in newborns. Like many other organ systems, the development of the craniofacial skeleton is complex, relying on specification and migration of the neural crest, patterning of the pharyngeal arches, and morphogenesis of each skeletal element into its final form. These processes must be carefully coordinated and integrated. One way this is achieved is through the spatial and temporal deployment of cell signaling pathways. Recent studies conducted using the zebrafish model underscore the importance of the Transforming Growth Factor Beta (TGF-β) and Bone Morphogenetic Protein (BMP) pathways in craniofacial development. Although both pathways contain similar components, each pathway results in unique outcomes on a cellular level. In this review, we will cover studies conducted using zebrafish that show the necessity of these pathways in each stage of craniofacial development, starting with the induction of the neural crest, and ending with the morphogenesis of craniofacial elements. We will also cover human skeletal and craniofacial diseases and malformations caused by mutations in the components of these pathways (e.g., cleft palate, craniosynostosis, etc.) and the potential utility of zebrafish in studying the etiology of these diseases. We will also briefly cover the utility of the zebrafish model in joint development and biology and discuss the role of TGF-β/BMP signaling in these processes and the diseases that result from aberrancies in these pathways, including osteoarthritis and multiple synostoses syndrome. Overall, this review will demonstrate the critical roles of TGF-β/BMP signaling in craniofacial development and show the utility of the zebrafish model in development and disease.

Transcriptomic analysis reveals the role of SIX1 in mouse cranial neural crest patterning and bone development

BACKGROUND

Genetic variants of the transcription factor SIX1 and its co-factor EYA1 underlie 50% of Branchio-oto-renal syndrome (BOR) cases. BOR is characterized by craniofacial defects, including malformed middle ear ossicles leading to conductive hearing loss. In this work, we expand our knowledge of the Six1 gene regulatory network by using a Six1-null mouse line to assess gene expression profiles of E10.5 mandibular arches, which give rise to the neural crest (NC)-derived middle ear ossicles and lower jaw, via bulk RNA sequencing.

RESULTS

Our transcriptomic analysis led to the identification of 808 differentially expressed genes that are related to translation, NC cell differentiation, osteogenesis, and chondrogenesis including components of the WNT signaling pathway. As WNT signaling is a known contributor to bone development, we demonstrated that SIX1 is required for expression of the WNT antagonist Frzb in the mandibular arch, and determined that SIX1 expression results in repression of WNT signaling.

CONCLUSION

Our results clarify the mechanisms by which SIX1 regulates the development of NC-derived craniofacial elements that are altered in SIX1-associated disorders. In addition, this work identifies novel genes that could be causative to this birth defect and establishes a link between SIX1 and WNT signaling during patterning of NC cells.

Loss of dlx5a/dlx6a Locus Alters Non-Canonical Wnt Signaling and Meckel's Cartilage Morphology

The dlx genes encode transcription factors that establish a proximal-distal polarity within neural crest cells to bestow a regional identity during craniofacial development. The expression regions of dlx paralogs are overlapping yet distinct within the zebrafish pharyngeal arches and may also be involved in progressive morphologic changes and organization of chondrocytes of the face. However, how each dlx paralog of dlx1a, dlx2a, dlx5a and dlx6a affects craniofacial development is still largely unknown. We report here that the average lengths of the Meckel's, palatoquadrate and ceratohyal cartilages in different dlx mutants were altered. Mutants for dlx5a-/- and dlx5i6-/-, where the entire dlx5a/dlx6a locus was deleted, have the shortest lengths for all three structures at 5 days post fertilization (dpf). This phenotype was also observed in 14 dpf larvae. Loss of dlx5i6 also resulted in increased proliferation of neural crest cells and expression of chondrogenic markers. Additionally, altered expression and function of non-canonical Wnt signaling were observed in these mutants suggesting a novel interaction between dlx5i6 locus and non-canonical Wnt pathway regulating ventral cartilage morphogenesis.

Predicting Modifiers of Genotype-Phenotype Correlations in Craniofacial Development

Most human birth defects are phenotypically variable even when they share a common genetic basis. Our understanding of the mechanisms of this variation is limited, but they are thought to be due to complex gene-environment interactions. Loss of the transcription factor Gata3 associates with the highly variable human birth defects HDR syndrome and microsomia, and can lead to disruption of the neural crest-derived facial skeleton. We have demonstrated that zebrafish gata3 mutants model the variability seen in humans, with genetic background and candidate pathways modifying the resulting phenotype. In this study, we sought to use an unbiased bioinformatic approach to identify environmental modifiers of gata3 mutant craniofacial phenotypes. The LINCs L1000 dataset identifies chemicals that generate differential gene expression that either positively or negatively correlates with an input gene list. These chemicals are predicted to worsen or lessen the mutant phenotype, respectively. We performed RNA-seq on neural crest cells isolated from zebrafish across control, Gata3 loss-of-function, and Gata3 rescue groups. Differential expression analyses revealed 551 potential targets of gata3. We queried the LINCs database with the 100 most upregulated and 100 most downregulated genes. We tested the top eight available chemicals predicted to worsen the mutant phenotype and the top eight predicted to lessen the phenotype. Of these, we found that vinblastine, a microtubule inhibitor, and clofibric acid, a PPAR-alpha agonist, did indeed worsen the gata3 phenotype. The Topoisomerase II and RNA-pol II inhibitors daunorubicin and triptolide, respectively, lessened the phenotype. GO analysis identified Wnt signaling and RNA polymerase function as being enriched in our RNA-seq data, consistent with the mechanism of action of some of the chemicals. Our study illustrates multiple potential pathways for Gata3 function, and demonstrates a systematic, unbiased process to identify modifiers of genotype-phenotype correlations.

Zebrafish endochondral growth zones as they relate to human bone size, shape and disease

Research on the genetic mechanisms underlying human skeletal development and disease have largely relied on studies in mice. However, recently the zebrafish has emerged as a popular model for skeletal research. Despite anatomical differences such as a lack of long bones in their limbs and no hematopoietic bone marrow, both the cell types in cartilage and bone as well as the genetic pathways that regulate their development are remarkably conserved between teleost fish and humans. Here we review recent studies that highlight this conservation, focusing specifically on the cartilaginous growth zones (GZs) of endochondral bones. GZs can be unidirectional such as the growth plates (GPs) of long bones in tetrapod limbs or bidirectional, such as in the synchondroses of the mammalian skull base. In addition to endochondral growth, GZs play key roles in cartilage maturation and replacement by bone. Recent studies in zebrafish suggest key roles for cartilage polarity in GZ function, surprisingly early establishment of signaling systems that regulate cartilage during embryonic development, and important roles for cartilage proliferation rather than hypertrophy in bone size. Despite anatomical differences, there are now many zebrafish models for human skeletal disorders including mutations in genes that cause defects in cartilage associated with endochondral GZs. These point to conserved developmental mechanisms, some of which operate both in cranial GZs and limb GPs, as well as others that act earlier or in parallel to known GP regulators. Experimental advantages of zebrafish for genetic screens, high resolution live imaging and drug screens, set the stage for many novel insights into causes and potential therapies for human endochondral bone diseases.

Corpuscles of Stannius development requires FGF signaling

The corpuscles of Stannius (CS) represent a unique endocrine organ of teleostean fish that secrets stanniocalcin-1 (Stc1) to maintain calcium homeostasis. Appearing at 20-25 somite stage in the distal zebrafish pronephros, stc1-expressing cells undergo apical constriction, and are subsequently extruded to form a distinct gland on top of the distal pronephric tubules at 50 ​h post fertilization (hpf). Several transcription factors (e.g. Hnf1b, Irx3b, Tbx2a/b) and signaling pathways (e.g. Notch) control CS development. We report now that Fgf signaling is required to commit tubular epithelial cells to differentiate into stc1-expressing CS cells. Inhibition of Fgf signaling by SU5402, dominant-negative Fgfr1, or depletion of fgf8a prevented CS formation and stc1 expression. Ablation experiments revealed that CS have the ability to partially regenerate via active cell migration involving extensive filopodia and lamellipodia formation. Activation of Wnt signaling curtailed stc1 expression, but had no effect on CS formation. Thus, our observations identify Fgf signaling as a crucial component of CS cell fate commitment.

The Mandibular and Hyoid Arches-From Molecular Patterning to Shaping Bone and Cartilage

The mandibular and hyoid arches collectively make up the facial skeleton, also known as the viscerocranium. Although all three germ layers come together to assemble the pharyngeal arches, the majority of tissue within viscerocranial skeletal components differentiates from the neural crest. Since nearly one third of all birth defects in humans affect the craniofacial region, it is important to understand how signalling pathways and transcription factors govern the embryogenesis and skeletogenesis of the viscerocranium. This review focuses on mouse and zebrafish models of craniofacial development. We highlight gene regulatory networks directing the patterning and osteochondrogenesis of the mandibular and hyoid arches that are actually conserved among all gnathostomes. The first part of this review describes the anatomy and development of mandibular and hyoid arches in both species. The second part analyses cell signalling and transcription factors that ensure the specificity of individual structures along the anatomical axes. The third part discusses the genes and molecules that control the formation of bone and cartilage within mandibular and hyoid arches and how dysregulation of molecular signalling influences the development of skeletal components of the viscerocranium. In conclusion, we notice that mandibular malformations in humans and mice often co-occur with hyoid malformations and pinpoint the similar molecular machinery controlling the development of mandibular and hyoid arches.

Variation in phenotypes from a Bmp-Gata3 genetic pathway is modulated by Shh signaling

We sought to understand how perturbation of signaling pathways and their targets generates variable phenotypes. In humans, GATA3 associates with highly variable defects, such as HDR syndrome, microsomia and choanal atresia. We previously characterized a zebrafish point mutation in gata3 with highly variable craniofacial defects to the posterior palate. This variability could be due to residual Gata3 function, however, we observe the same phenotypic variability in gata3 null mutants. Using hsp:GATA3-GFP transgenics, we demonstrate that Gata3 function is required between 24 and 30 hpf. At this time maxillary neural crest cells fated to generate the palate express gata3. Transplantation experiments show that neural crest cells require Gata3 function for palatal development. Via a candidate approach, we determined if Bmp signaling was upstream of gata3 and if this pathway explained the mutant's phenotypic variation. Using BRE:d2EGFP transgenics, we demonstrate that maxillary neural crest cells are Bmp responsive by 24 hpf. We find that gata3 expression in maxillary neural crest requires Bmp signaling and that blocking Bmp signaling, in hsp:DN-Bmpr1a-GFP embryos, can phenocopy gata3 mutants. Palatal defects are rescued in hsp:DN-Bmpr1a-GFP;hsp:GATA3-GFP double transgenic embryos, collectively demonstrating that gata3 is downstream of Bmp signaling. However, Bmp attenuation does not alter phenotypic variability in gata3 loss-of-function embryos, implicating a different pathway. Due to phenotypes observed in hypomorphic shha mutants, the Sonic Hedgehog (Shh) pathway was a promising candidate for this pathway. Small molecule activators and inhibitors of the Shh pathway lessen and exacerbate, respectively, the phenotypic severity of gata3 mutants. Importantly, inhibition of Shh can cause gata3 haploinsufficiency, as observed in humans. We find that gata3 mutants in a less expressive genetic background have a compensatory upregulation of Shh signaling. These results demonstrate that the level of Shh signaling can modulate the phenotypes observed in gata3 mutants.

A Multiplex Human Pluripotent Stem Cell Platform Defines Molecular and Functional Subclasses of Autism-Related Genes

Autism is a clinically heterogeneous neurodevelopmental disorder characterized by impaired social interactions, restricted interests, and repetitive behaviors. Despite significant advances in the genetics of autism, understanding how genetic changes perturb brain development and affect clinical symptoms remains elusive. Here, we present a multiplex human pluripotent stem cell (hPSC) platform, in which 30 isogenic disease lines are pooled in a single dish and differentiated into prefrontal cortex (PFC) lineages to efficiently test early-developmental hypotheses of autism. We define subgroups of autism mutations that perturb PFC neurogenesis and are correlated to abnormal WNT/βcatenin responses. Class 1 mutations (8 of 27) inhibit while class 2 mutations (5 of 27) enhance PFC neurogenesis. Remarkably, autism patient data reveal that individuals carrying subclass-specific mutations differ clinically in their corresponding language acquisition profiles. Our study provides a framework to disentangle genetic heterogeneity associated with autism and points toward converging molecular and developmental pathways of diverse autism-associated mutations.

The mevalonate pathway is a crucial regulator of tendon cell specification

Tendons and ligaments are crucial components of the musculoskeletal system, yet the pathways specifying these fates remain poorly defined. Through a screen of known bioactive chemicals in zebrafish, we identified a new pathway regulating tendon cell induction. We established that statin, through inhibition of the mevalonate pathway, causes an expansion of the tendon progenitor population. Co-expression and live imaging studies indicate that the expansion does not involve an increase in cell proliferation, but rather results from re-specification of cells from the neural crest-derived sox9a⁺/sox10⁺ skeletal lineage. The effect on tendon cell expansion is specific to the geranylgeranylation branch of the mevalonate pathway and is mediated by inhibition of Rac activity. This work establishes a novel role for the mevalonate pathway and Rac activity in regulating specification of the tendon lineage.

Chemical-induced craniofacial anomalies caused by disruption of neural crest cell development in a zebrafish model

Background

Craniofacial anomalies are among the most frequent birth defects worldwide, and are thought to be caused by gene‐environment interactions. Genetically manipulated zebrafish simulate human diseases and provide great advantages for investigating the etiology and pathology of craniofacial anomalies. Although substantial advances have been made in understanding genetic factors causing craniofacial disorders, limited information about the etiology by which environmental factors, such as teratogens, induce craniofacial anomalies is available in zebrafish.

Results

Zebrafish embryos displayed craniofacial malformations after teratogen treatments. Further observations revealed characteristic disruption of chondrocyte number, shape and stacking. These findings suggested aberrant development of cranial neural crest (CNC) cells, which was confirmed by gene expression analysis of the CNC. Notably, these observations suggested conserved etiological pathways between zebrafish and mammals including human. Furthermore, several of these chemicals caused malformations of the eyes, otic vesicle, and/or heart, representing a phenocopy of neurocristopathy, and these chemicals altered the expression levels of the responsible genes.

Conclusions

Our results demonstrate that chemical‐induced craniofacial malformation is caused by aberrant development of neural crest. This study indicates that zebrafish provide a platform for investigating contributions of environmental factors as causative agents of craniofacial anomalies and neurocristopathy.

Novel Ethanol-Sensitive Mutants Identified in an F3 Forward Genetic Screen

Background

Fetal alcohol spectrum disorders (FASD) collectively refer to all deleterious outcomes due to prenatal alcohol exposures. Alterations to the face are common phenotypes in FASD. While alcohol exposure is the underlying cause of FASD, many variables modify the outcomes of such exposures. Genetic risk is one such variable, yet we still have a limited understanding of the nature of the genetic loci mediating susceptibility to FASD.

Methods

We employed ENU‐based random mutagenesis in zebrafish to identify mutations that enhanced the teratogenicity of ethanol (EtOH). F3 embryos obtained from 126 inbred F2 families were exposed to 1% EtOH in the medium (approximately 41 mM tissue levels). Zebrafish stained with Alcian Blue and Alizarin Red were screened for qualitative alterations to the craniofacial skeleton between 4 and 7 days postfertilization (dpf).

Results

In all, we recovered 6 EtOH‐sensitive mutants, 5 from the genetic screen itself and one as a background mutation in one of our wild‐type lines. Each mutant has a unique EtOH‐induced phenotype relative to the other mutant lines. All but 1 mutation appears to be recessive in nature, and only 1 mutant, au29, has apparent craniofacial defects in the absence of EtOH. To validate the genetic screen, we genetically mapped au29 and found that it carries a mutation in a previously uncharacterized gene, si:dkey‐88l16.3.

Conclusions

The phenotypes of these EtOH‐sensitive mutants differ from those in previous characterizations of gene–EtOH interactions. Thus, each mutant is likely to provide novel insights into EtOH teratogenesis. Given that most of these mutants only have craniofacial defects in the presence of EtOH and our mapping of au29, it is also likely that many of the mutants will be previously uncharacterized. Collectively, our findings point to the importance of unbiased genetic screens in the identification, and eventual characterization, of risk alleles for FASD.

Wnt signaling in orofacial clefts: crosstalk, pathogenesis and models

Diverse signaling cues and attendant proteins work together during organogenesis, including craniofacial development. Lip and palate formation starts as early as the fourth week of gestation in humans or embryonic day 9.5 in mice. Disruptions in these early events may cause serious consequences, such as orofacial clefts, mainly cleft lip and/or cleft palate. Morphogenetic Wnt signaling, along with other signaling pathways and transcription regulation mechanisms, plays crucial roles during embryonic development, yet the signaling mechanisms and interactions in lip and palate formation and fusion remain poorly understood. Various Wnt signaling and related genes have been associated with orofacial clefts. This Review discusses the role of Wnt signaling and its crosstalk with cell adhesion molecules, transcription factors, epigenetic regulators and other morphogenetic signaling pathways, including the Bmp, Fgf, Tgfβ, Shh and retinoic acid pathways, in orofacial clefts in humans and animal models, which may provide a better understanding of these disorders and could be applied towards prevention and treatments.

Genetic Requirement of talin1 for Proliferation of Cranial Neural Crest Cells during Palate Development

Supplemental Digital Content is available in the text.

Background:

Craniofacial malformations are among the most common congenital anomalies. Cranial neural crest cells (CNCCs) form craniofacial structures involving multiple cellular processes, perturbations of which contribute to craniofacial malformations. Adhesion of cells to the extracellular matrix mediates bidirectional interactions of the cells with their extracellular environment that plays an important role in craniofacial morphogenesis. Talin (tln) is crucial in cell-matrix adhesion between cells, but its role in craniofacial morphogenesis is poorly understood.

Methods:

Talin gene expression was determined by whole mount in situ hybridization. Craniofacial cartilage and muscles were analyzed by Alcian blue in Tg(mylz2:mCherry) and by transmission electron microscopy. Pulse-chase photoconversion, 5-ethynyl-2’-deoxyuridine proliferation, migration, and apoptosis assays were performed for functional analysis.

Results:

Expression of tln1 was observed in the craniofacial cartilage structures, including the palate. The Meckel’s cartilage was hypoplastic, the palate was shortened, and the craniofacial muscles were malformed in tln1 mutants. Pulse-chase and EdU assays during palate morphogenesis revealed defects in CNCC proliferation in mutants. No defects were observed in CNCC migration and apoptosis.

Conclusions:

The work shows that tln1 is critical for craniofacial morphogenesis in zebrafish. Loss of tln1 leads to a shortened palate and Meckel’s cartilage along with disorganized skeletal muscles. Investigations into the cellular processes show that tln1 is required for CNCC proliferation during palate morphogenesis. The work will lead to a better understanding of the involvement of cytoskeletal proteins in craniofacial morphogenesis.

Wnt9a Is Required for the Aortic Amplification of Nascent Hematopoietic Stem Cells

All mature blood cell types in the adult animal arise from hematopoietic stem and progenitor cells (HSPCs). However, the developmental cues regulating HSPC ontogeny are incompletely understood. In particular, the details surrounding a requirement for Wnt/β-catenin signaling in the development of mature HSPCs are controversial and difficult to consolidate. Using zebrafish, we demonstrate that Wnt signaling is required to direct an amplification of HSPCs in the aorta. Wnt9a is specifically required for this process and cannot be replaced by Wnt9b or Wnt3a. This proliferative event occurs independently of initial HSPC fate specification, and the Wnt9a input is required prior to aorta formation. HSPC arterial amplification occurs prior to seeding of secondary hematopoietic tissues and proceeds, in part, through the cell cycle regulator myca (c-myc). Our results support a general paradigm, in which early signaling events, including Wnt, direct later HSPC developmental processes.

Hematopoietic stem and progenitor cells (HSPCs) give rise to all of the blood cells of the adult organism; however, how these cells are derived in vivo is still incompletely understood. Using zebrafish, Grainger et al. find that Wnt9a mediates amplification of HSPCs prior to their migration to secondary hematopoietic sites.

Restoration of polr1c in Early Embryogenesis Rescues the Type 3 Treacher Collins Syndrome Facial Malformation Phenotype in Zebrafish

Treacher Collins syndrome (TCS) is a rare congenital birth disorder (1 in 50,000 live births) characterized by severe craniofacial defects. Recently, the authors' group unfolded the pathogenesis of polr1c Type 3 TCS by using the zebrafish model. Facial development depends on the neural crest cells, in which polr1c plays a role in regulating their expression. In this study, the authors aimed to identify the functional time window of polr1c in TCS by the use of photo-morpholino to restore the polr1c expression at different time points. Results suggested that the restoration of polr1c at 8 hours after fertilization could rescue the TCS facial malformation phenotype by correcting the neural crest cell expression, reducing the cell death, and normalizing the p53 mRNA expression level in the rescued morphants. However, such recovery could not be reproduced if the polr1c is restored after 30 hours after fertilization.

Wnt signalling controls the response to mechanical loading during zebrafish joint development

Joint morphogenesis requires mechanical activity during development. Loss of mechanical strain causes abnormal joint development, which can impact long-term joint health. Although cell orientation and proliferation are known to shape the joint, dynamic imaging of developing joints in vivo has not been possible in other species. Using genetic labelling techniques in zebrafish we were able, for the first time, to dynamically track cell behaviours in intact moving joints. We identify that proliferation and migration, which contribute to joint morphogenesis, are mechanically controlled and are significantly reduced in immobilised larvae. By comparison with strain maps of the developing skeleton, we identify canonical Wnt signalling as a candidate for transducing mechanical forces into joint cell behaviours. We show that, in the jaw, Wnt signalling is reduced specifically in regions of high strain in response to loss of muscle activity. By pharmacological manipulation of canonical Wnt signalling, we demonstrate that Wnt acts downstream of mechanical activity and is required for joint patterning and chondrocyte maturation. Wnt16, which is also downstream of muscle activity, controls proliferation and migration, but plays no role in chondrocyte intercalation.

Early Craniofacial Defects in Zebrafish that Have Reduced Function of a Wnt-Interacting Extracellular Matrix Protein, Tinagl1

Objective

Tinagl1 has a weak genetic association with craniosynostosis, but its functions in cartilage and bone development are unknown. Knockdown of Tinagl1 in zebrafish embryos allowed an initial characterization of its potential effects on craniofacial cartilage development and a test of whether these effects could involve Wnt signaling.

Results

Tinagl1 knockdown resulted in dose-dependent reductions and defects in ventral pharyngeal arch cartilages as well as the ethmoid plate, a zebrafish correlate to the palate. These defects could be correlated to reduced numbers of cranial neural crest cells in the pharyngeal arches and could be reproduced with comanipulation of Tinagl1 and Wnt3a by morpholino-based knockdown.

Conclusions

These results suggest that Tinagl1 is required early in the proliferation or migration of cranial neural crest cells and that its effects are mediated via Wnt3a signaling. Because Wnt3a is among the Wnts that contribute to nonsyndromic cleft lip and cleft palate in mouse and man, further investigation of Tinagl1 may help to elucidate mechanisms underlying these disorders.

Novel adverse outcome pathways revealed by chemical genetics in a developing marine fish

Crude oil spills are a worldwide ocean conservation threat. Fish are particularly vulnerable to the oiling of spawning habitats, and crude oil causes severe abnormalities in embryos and larvae. However, the underlying mechanisms for these developmental defects are not well understood. Here, we explore the transcriptional basis for four discrete crude oil injury phenotypes in the early life stages of the commercially important Atlantic haddock (Melanogrammus aeglefinus). These include defects in (1) cardiac form and function, (2) craniofacial development, (3) ionoregulation and fluid balance, and (4) cholesterol synthesis and homeostasis. Our findings suggest a key role for intracellular calcium cycling and excitation-transcription coupling in the dysregulation of heart and jaw morphogenesis. Moreover, the disruption of ionoregulatory pathways sheds new light on buoyancy control in marine fish embryos. Overall, our chemical-genetic approach identifies initiating events for distinct adverse outcome pathways and novel roles for individual genes in fundamental developmental processes.

Bicoronal and metopic craniosynostosis in association with a de novo unbalanced t(2;7) chromosomal translocation

We report the case of a developmentally appropriate infant male with a de novo unbalanced chromosome translocation involving bands 2q32.1 and 7p21.3. The child was noted to have metopic and bicoronal craniosynostosis with closely spaced eyes, turricephaly, and flattening of the forehead. © 2016 Wiley Periodicals, Inc.

Signalling pathways in trophic skeletal development and morphogenesis: Insights from studies on teleost fish

During the development of the vertebrate feeding apparatus, a variety of complicated cellular and molecular processes participate in the formation and integration of individual skeletal elements. The molecular mechanisms regulating the formation of skeletal primordia and their development into specific morphological structures are tightly controlled by a set of interconnected signalling pathways. Some of these pathways, such as Bmp, Hedgehog, Notch and Wnt, are long known for their pivotal roles in craniofacial skeletogenesis. Studies addressing the functional details of their components and downstream targets, the mechanisms of their interactions with other signals as well as their potential roles in adaptive morphological divergence, are currently attracting considerable attention. An increasing number of signalling pathways that had previously been described in different biological contexts have been shown to be important in the regulation of jaw skeletal development and morphogenesis. In this review, I provide an overview of signalling pathways involved in trophic skeletogenesis emphasizing studies of the most species-rich group of vertebrates, the teleost fish, which through their evolutionary history have undergone repeated episodes of spectacular trophic diversification.

Crude oil exposures reveal roles for intracellular calcium cycling in haddock craniofacial and cardiac development

Recent studies have shown that crude oil exposure affects cardiac development in fish by disrupting excitation-contraction (EC) coupling. We previously found that eggs of Atlantic haddock (Melanogrammus aeglefinus) bind dispersed oil droplets, potentially leading to more profound toxic effects from uptake of polycyclic aromatic hydrocarbons (PAHs). Using lower concentrations of dispersed crude oil (0.7-7 μg/L ∑PAH), here we exposed a broader range of developmental stages over both short and prolonged durations. We quantified effects on cardiac function and morphogenesis, characterized novel craniofacial defects, and examined the expression of genes encoding potential targets underlying cardiac and craniofacial defects. Because of oil droplet binding, a 24-hr exposure was sufficient to create severe cardiac and craniofacial abnormalities. The specific nature of the craniofacial abnormalities suggests that crude oil may target common craniofacial and cardiac precursor cells either directly or indirectly by affecting ion channels and intracellular calcium in particular. Furthermore, down-regulation of genes encoding specific components of the EC coupling machinery suggests that crude oil disrupts excitation-transcription coupling or normal feedback regulation of ion channels blocked by PAHs. These data support a unifying hypothesis whereby depletion of intracellular calcium pools by crude oil-derived PAHs disrupts several pathways critical for organogenesis in fish.

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.

Actin capping protein CAPZB regulates cell morphology, differentiation, and neural crest migration in craniofacial morphogenesis†

CAPZB is an actin-capping protein that caps the growing end of F-actin and modulates the cytoskeleton and tethers actin filaments to the Z-line of the sarcomere in muscles. Whole-genome sequencing was performed on a subject with micrognathia, cleft palate and hypotonia that harbored a de novo, balanced chromosomal translocation that disrupts the CAPZB gene. The function of capzb was analyzed in the zebrafish model. capzb(-/-) mutants exhibit both craniofacial and muscle defects that recapitulate the phenotypes observed in the human subject. Loss of capzb affects cell morphology, differentiation and neural crest migration. Differentiation of both myogenic stem cells and neural crest cells requires capzb. During palate morphogenesis, defective cranial neural crest cell migration in capzb(-/-) mutants results in loss of the median cell population, creating a cleft phenotype. capzb is also required for trunk neural crest migration, as evident from melanophores disorganization in capzb(-/-) mutants. In addition, capzb over-expression results in embryonic lethality. Therefore, proper capzb dosage is important during embryogenesis, and regulates both cell behavior and tissue morphogenesis.

Multifaceted signaling regulators of chondrogenesis: Implications in cartilage regeneration and tissue engineering

Defects of articular cartilage present a unique clinical challenge due to its poor self-healing capacity and avascular nature. Current surgical treatment options do not ensure consistent regeneration of hyaline cartilage in favor of fibrous tissue. Here, we review the current understanding of the most important biological regulators of chondrogenesis and their interactions, to provide insight into potential applications for cartilage tissue engineering. These include various signaling pathways, including: fibroblast growth factors (FGFs), transforming growth factor β (TGF-β)/bone morphogenic proteins (BMPs), Wnt/β-catenin, Hedgehog, Notch, hypoxia, and angiogenic signaling pathways. Transcriptional and epigenetic regulation of chondrogenesis will also be discussed. Advances in our understanding of these signaling pathways have led to promising advances in cartilage regeneration and tissue engineering.

Systematic analysis of copy number variants of a large cohort of orofacial cleft patients identifies candidate genes for orofacial clefts

Orofacial clefts (OFCs) represent a large fraction of human birth defects and are one of the most common phenotypes affected by large copy number variants (CNVs). Due to the limited number of CNV patients in individual centers, CNV analyses of a large number of OFC patients are challenging. The present study analyzed 249 genomic deletions and 226 duplications from a cohort of 312 OFC patients reported in two publicly accessible databases of chromosome imbalance and phenotype in humans, DECIPHER and ECARUCA. Genomic regions deleted or duplicated in multiple patients were identified, and genes in these overlapping CNVs were prioritized based on the number of genes encompassed by the region and gene expression in embryonic mouse palate. Our analyses of these overlapping CNVs identified two genes known to be causative for human OFCs, SATB2 and MEIS2, and 12 genes (DGCR6, FGF2, FRZB, LETM1, MAPK3, SPRY1, THBS1, TSHZ1, TTC28, TULP4, WHSC1, WHSC2) that are associated with OFC or orofacial development. Additionally, we report 34 deleted and 24 duplicated genes that have not previously been associated with OFCs but are associated with the BMP, MAPK and RAC1 pathways. Statistical analyses show that the high number of overlapping CNVs is not due to random occurrence. The identified genes are not located in highly variable genomic regions in healthy populations and are significantly enriched for genes that are involved in orofacial development. In summary, we report a CNV analysis pipeline of a large cohort of OFC patients and identify novel candidate OFC genes.

Insulin treatment prevents the increase in D-serine in hippocampal CA1 area of diabetic rats

PURPOSE

Diabetes is a high risk factor for dementia. Employing a diabetic rat model, the present study was designed to determine whether the content of D-serine (D-Ser) in hippocampus is associated with the impairment of spatial learning and memory ability.

METHODS

Diabetes was induced by a single intravenous injection of streptozotocin (STZ). The insulin treatment began 3 days after STZ injection.

RESULTS

We found that both water maze learning and hippocampal CA1 long-term potentiation (LTP) were impaired in diabetic rats. The contents of glutamate, D-Ser, and serine racemase in the hippocampus of diabetic rats were significantly higher than those in the control group. Insulin treatment prevented the STZ-induced impairment in water maze learning and hippocampal CA1-LTP in diabetic rats and also maintained the contents of glutamate, D-Ser, and serine racemase at the normal range in hippocampus.

CONCLUSIONS

These results suggest that insulin treatment has a potent protection effect on CA1-LTP, spatial learning and memory ability of the diabetic rats in vivo. Furthermore, insulin may take effect by inhibiting the overactivation of N-methyl-d-aspartate receptors, which play a critical role in neurotoxicity.

Functional analysis of SPECC1L in craniofacial development and oblique facial cleft pathogenesis

BACKGROUND

Oblique facial clefts, also known as Tessier clefts, are severe orofacial clefts, the genetic basis of which is poorly understood. Human genetics studies revealed that disruption in SPECC1L resulted in oblique facial clefts, demonstrating that oblique facial cleft malformation has a genetic basis. An important step toward innovation in treatment of oblique facial clefts would be improved understanding of its genetic pathogenesis. The authors exploit the zebrafish model to elucidate the function of SPECC1L by studying its homolog, specc1lb.

METHODS

Gene and protein expression analysis was carried out by reverse-transcriptase polymerase chain reaction and immunohistochemistry staining. Morpholino knockdown, mRNA rescue, lineage tracing and terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling assays were performed for functional analysis.

RESULTS

Expression of specc1lb was detected in epithelia juxtaposed to chondrocytes. Knockdown of specc1lb resulted in bilateral clefts between median and lateral elements of the ethmoid plate, structures analogous to the frontonasal process and the paired maxillary processes. Lineage tracing analysis revealed that cranial neural crest cells contributing to the frontonasal prominence failed to integrate with the maxillary prominence populations. Cells contributing to lower jaw structures were able to migrate to their destined pharyngeal segment but failed to converge to form mandibular elements.

CONCLUSIONS

These results demonstrate that specc1lb is required for integration of frontonasal and maxillary elements and convergence of mandibular prominences. The authors confirm the role of SPECC1L in orofacial cleft pathogenesis in the first animal model of Tessier cleft, providing morphogenetic insight into the mechanisms of normal craniofacial development and oblique facial cleft pathogenesis.

The ECM-cell interaction of cartilage extracellular matrix on chondrocytes

Cartilage extracellular matrix (ECM) is composed primarily of the network type II collagen (COLII) and an interlocking mesh of fibrous proteins and proteoglycans (PGs), hyaluronic acid (HA), and chondroitin sulfate (CS). Articular cartilage ECM plays a crucial role in regulating chondrocyte metabolism and functions, such as organized cytoskeleton through integrin-mediated signaling via cell-matrix interaction. Cell signaling through integrins regulates several chondrocyte functions, including differentiation, metabolism, matrix remodeling, responses to mechanical stimulation, and cell survival. The major signaling pathways that regulate chondrogenesis have been identified as wnt signal, nitric oxide (NO) signal, protein kinase C (PKC), and retinoic acid (RA) signal. Integrins are a large family of molecules that are central regulators in multicellular biology. They orchestrate cell-cell and cell-matrix adhesive interactions from embryonic development to mature tissue function. In this review, we emphasize the signaling molecule effect and the biomechanics effect of cartilage ECM on chondrogenesis.

Neural crest development and craniofacial morphogenesis is coordinated by nitric oxide and histone acetylation

Cranial neural crest (CNC) cells are patterned and coalesce to facial prominences that undergo convergence and extension to generate the craniofacial form. We applied a chemical genetics approach to identify pathways that regulate craniofacial development during embryogenesis. Treatment with the nitric oxide synthase inhibitor 1-(2-[trifluoromethyl] phenyl) imidazole (TRIM) abrogated first pharyngeal arch structures and induced ectopic ceratobranchial formation. TRIM promoted a progenitor CNC fate and inhibited chondrogenic differentiation, which were mediated through impaired nitric oxide (NO) production without appreciable effect on global protein S-nitrosylation. Instead, TRIM perturbed hox gene patterning and caused histone hypoacetylation. Rescue of TRIM phenotype was achieved with overexpression of histone acetyltransferase kat6a, inhibition of histone deacetylase, and complementary NO. These studies demonstrate that NO signaling and histone acetylation are coordinated mechanisms that regulate CNC patterning, differentiation, and convergence during craniofacial morphogenesis.