barx1 is necessary for ectomesenchyme proliferation and osteochondroprogenitor condensation in the zebrafish pharyngeal arches

Insights into Craniofacial Development and Anomalies: Exploring Fgf Signaling in Zebrafish Models

PURPOSE OF REVIEW

To illustrate the value of using zebrafish to understand the role of the Fgf signaling pathway during craniofacial skeletal development under normal and pathological conditions.

RECENT FINDINGS

Recent data obtained from studies on zebrafish have demonstrated the genetic redundancy of Fgf signaling pathway and have identified new molecular partners of this signaling during the early stages of craniofacial skeletal development. Studies on zebrafish models demonstrate the involvement of the Fgf signaling pathway at every stage of craniofacial development. They particularly emphasize the central role of Fgf signaling pathway during the early stages of the development, which significantly impacts the formation of the various structures making up the craniofacial skeleton. This partly explains the craniofacial abnormalities observed in disorders associated with FGF signaling. Future research efforts should focus on investigating zebrafish Fgf signaling during more advanced stages, notably by establishing zebrafish models expressing mutations responsible for diseases such as craniosynostoses.

BARX1 repressed FOXF1 expression and activated Wnt/β-catenin signaling pathway to drive lung adenocarcinoma

BACKGROUND

Underlying molecular mechanisms of BARX homeobox 1 (BARX1) in lung adenocarcinoma (LUAD) remain elusive.

METHODS

Abnormally expressed genes in LUAD tissues were analyzed by RNA-sequencing. CCK-8, colony formation, transwell, and wound healing assays examined proliferation, colony formation, invasion, and migration of LUAD cells, respectively. Electrophoretic mobility shift assay and chromatin immunoprecipitation assay examined the interaction between BARX1 and Forkhead Box F1 (FOXF1). Xenograft mouse model of LUAD was constructed to monitor the growth and metastasis of tumor.

RESULTS

BARX1 was upregulated, FOXF1 was downregulated in LUAD tissues and cells. There was a negative correlation between BARX1 and FOXF1 expression. BARX1 deficiency limited malignant phenotypes of LUAD cells, including proliferation, invasion, migration and EMT. In vivo, BARX1 knockdown suppressed tumor growth and metastasis in A549-drove xenograft mouse model. BARX1 interacted with FOXF1 promoter and repressed FOXF1 expression. Upregulation of BARX1 promoted the expression of Wnt5a, β-catenin, and phosphorylated-glycogen synthase kinase-3 beta (p-GSK3β), whereas inhibited FOXF1, p-β-catenin, and GSK3β in LUAD cells. BARX1 knockdown caused an opposite result. Rescue assays uncovered that FOXF1 reversed the impact of BARX1 on malignant phenotypes and Wnt/β-catenin of LUAD cells.

CONCLUSION

BARX1 repressed FOXF1 expression and activated Wnt/β-catenin signaling pathway to drive lung adenocarcinoma.

Exploring Omega-3's Impact on the Expression of Bone-Related Genes in Meagre (Argyrosomus regius)

Dietary supplementation with Omega-3 fatty acids seems to promote skeletal health. Therefore, their consumption at imbalanced or excessive levels has offered less beneficial or even prejudicial effects. Fish produced in aquaculture regimes are prone to develop abnormal skeletons. Although larval cultures are usually fed with diets supplemented with Omega-3 Long Chain Polyunsaturated fatty acids (LC-PUFAs), the lack of knowledge about the optimal requirements for fatty acids or about their impact on mechanisms that regulate skeletal development has impeded the design of diets that could improve bone formation during larval stages when the majority of skeletal anomalies appear. In this study, Argyrosomus regius larvae were fed different levels of Omega-3s (2.6% and 3.6% DW on diet) compared to a commercial diet. At 28 days after hatching (DAH), their transcriptomes were analyzed to study the modulation exerted in gene expression dynamics during larval development and identify impacted genes that can contribute to skeletal formation. Mainly, both levels of supplementation modulated bone-cell proliferation, the synthesis of bone components such as the extracellular matrix, and molecules involved in the interaction and signaling between bone components or in important cellular processes. The 2.6% level impacted several genes related to cartilage development, denoting a special impact on endochondral ossification, delaying this process. However, the 3.6% level seemed to accelerate this process by enhancing skeletal development. These results offered important insights into the impact of dietary Omega-3 LC-PUFAs on genes involved in the main molecular mechanism and cellular processes involved in skeletal development.

nkx2.3 is responsible for posterior pharyngeal cartilage formation by inhibiting Fgf signaling

Nkx2.3, a transcription factor, plays important roles in various developmental processes. However, the mechanisms underlying nkx2.3's regulation of pouch and pharyngeal arch development in zebrafish remain unclear. In this study, we demonstrated that knockdown or knockout of nkx2.3 resulted in the absence of posterior ceratobranchial cartilages in zebrafish. The absence of posterior pharyngeal cartilages is a consequence of the compromised proliferation and differentiation and survival of cranial neural crest cells (CNCCs). Notably, we found that nkx2.3 was not involved in endoderm pouch formation. Additionally, our findings suggested that nkx2.3 negatively regulated Fibroblast growth factor (Fgf) signaling, as overexpression of fgf8 could mimic the phenotype observed in nkx2.3 morphants, suppressing CNCC differentiation. Moreover, inhibiting Fgf signaling restored the abnormalities in posterior cartilages induced by nkx2.3 knockdown. These findings establish the essential role of nkx2.3 in the development of posterior ceratobranchial cartilages through the inhibition of fgf8.

Molecular mechanism of synovial joint site specification and induction in developing vertebrate limbs

The vertebrate appendage comprises three primary segments, the stylopod, zeugopod and autopod, each separated by joints. The molecular mechanisms governing the specification of joint sites, which define segment lengths and thereby limb architecture, remain largely unknown. Existing literature suggests that reciprocal gradients of retinoic acid (RA) and fibroblast growth factor (FGF) signaling define the expression domains of the putative segment markers Meis1, Hoxa11 and Hoxa13. Barx1 is expressed in the presumptive joint sites. Our data demonstrate that RA-FGF signaling gradients define the expression domain of Barx1 in the first presumptive joint site. When misexpressed, Barx1 induces ectopic interzone-like structures, and its loss of function partially blocks interzone development. Simultaneous perturbations of RA-FGF signaling gradients result in predictable shifts of Barx1 expression domains along the proximo-distal axis and, consequently, in the formation of repositioned joints. Our data suggest that during early limb bud development in chick, Meis1 and Hoxa11 expression domains are overlapping, whereas the Barx1 expression domain resides within the Hoxa11 expression domain. However, once the interzone is formed, the expression domains are refined and the Barx1 expression domain becomes congruent with the border of these two putative segment markers.

Cartilage diversification and modularity drove the evolution of the ancestral vertebrate head skeleton

The vertebrate head skeleton has evolved a myriad of forms since their divergence from invertebrate chordates. The connection between novel gene expression and cell types is therefore of importance in this process. The transformation of the jawed vertebrate (gnathostome) head skeleton from oral cirri to jointed jaw elements required a diversity of cartilages as well as changes in the patterning of these tissues. Although lampreys are a sister clade to gnathostomes, they display skeletal diversity with distinct gene expression and histologies, a useful model for addressing joint evolution. Specifically, the lamprey tissue known as mucocartilage has noted similarities with the jointed elements of the mandibular arch in jawed vertebrates. We thus asked whether the cells in lamprey mucocartilage and gnathostome joint tissue could be considered homologous. To do this, we characterized new genes that are involved in gnathostome joint formation and characterized the histochemical properties of lamprey skeletal types. We find that most of these genes are minimally found in mucocartilage and are likely later innovations, but we do identify new activity for gdf5/6/7b in both hyaline and mucocartilage, supporting its role as a chondrogenic regulator. Contrary to previous works, our histological assays do not find any perichondrial fibroblasts surrounding mucocartilage, suggesting that mucocartilage is non-skeletogenic tissue that is partially chondrified. Interestingly, we also identify new histochemical features of the lamprey otic capsule that diverge from normal hyaline. Paired with our new insights into lamprey mucocartilage, we propose a broader framework for skeletal evolution in which an ancestral soxD/E and gdf5/6/7 network directs mesenchyme along a spectrum of cartilage-like features.

vwa1 Knockout in Zebrafish Causes Abnormal Craniofacial Chondrogenesis by Regulating FGF Pathway

Hemifacial microsomia (HFM), a rare disorder of first- and second-pharyngeal arch development, has been linked to a point mutation in VWA1 (von Willebrand factor A domain containing 1), encoding the protein WARP in a five-generation pedigree. However, how the VWA1 mutation relates to the pathogenesis of HFM is largely unknown. Here, we sought to elucidate the effects of the VWA1 mutation at the molecular level by generating a vwa1-knockout zebrafish line using CRISPR/Cas9. Mutants and crispants showed cartilage dysmorphologies, including hypoplastic Meckel’s cartilage and palatoquadrate cartilage, malformed ceratohyal with widened angle, and deformed or absent ceratobranchial cartilages. Chondrocytes exhibited a smaller size and aspect ratio and were aligned irregularly. In situ hybridization and RT-qPCR showed a decrease in barx1 and col2a1a expression, indicating abnormal cranial neural crest cell (CNCC) condensation and differentiation. CNCC proliferation and survival were also impaired in the mutants. Expression of FGF pathway components, including fgf8a, fgfr1, fgfr2, fgfr3, fgfr4, and runx2a, was decreased, implying a role for VWA1 in regulating FGF signaling. Our results demonstrate that VWA1 is essential for zebrafish chondrogenesis through effects on condensation, differentiation, proliferation, and apoptosis of CNCCs, and likely impacts chondrogenesis through regulation of the FGF pathway.

Genetically engineered zebrafish as models of skeletal development and regeneration

Zebrafish (Danio rerio) are aquatic vertebrates with significant homology to their terrestrial counterparts. While zebrafish have a centuries-long track record in developmental and regenerative biology, their utility has grown exponentially with the onset of modern genetics. This is exemplified in studies focused on skeletal development and repair. Herein, the numerous contributions of zebrafish to our understanding of the basic science of cartilage, bone, tendon/ligament, and other skeletal tissues are described, with a particular focus on applications to development and regeneration. We summarize the genetic strengths that have made the zebrafish a powerful model to understand skeletal biology. We also highlight the large body of existing tools and techniques available to understand skeletal development and repair in the zebrafish and introduce emerging methods that will aid in novel discoveries in skeletal biology. Finally, we review the unique contributions of zebrafish to our understanding of regeneration and highlight diverse routes of repair in different contexts of injury. We conclude that zebrafish will continue to fill a niche of increasing breadth and depth in the study of basic cellular mechanisms of skeletal biology.

Single cell atlas of developing mouse dental germs reveals populations of CD24+ and Plac8+ odontogenic cells

The spatiotemporal relationships in high-resolution during odontogenesis remain poorly understood. We report a cell lineage and atlas of developing mouse teeth. We performed a large-scale (92,688 cells) single cell RNA sequencing, tracing the cell trajectories during odontogenesis from embryonic days 10.5 to 16.5. Combined with an assay for transposase-accessible chromatin with high-throughput sequencing, our results suggest that mesenchymal cells show the specific transcriptome profiles to distinguish the tooth types. Subsequently, we identified key gene regulatory networks in teeth and bone formation and uncovered spatiotemporal patterns of odontogenic mesenchymal cells. CD24⁺ and Plac8⁺ cells from the mesenchyme at the bell stage were distributed in the upper half and preodontoblast layer of the dental papilla, respectively, which could individually induce nonodontogenic epithelia to form tooth-like structures. Specifically, the Plac8⁺ tissue we discovered is the smallest piece with the most homogenous cells that could induce tooth regeneration to date. Our work reveals previously unknown heterogeneity and spatiotemporal patterns of tooth germs that may lead to tooth regeneration for regenerative dentistry.

Ventx Family and Its Functional Similarities with Nanog: Involvement in Embryonic Development and Cancer Progression

The Ventx family is one of the subfamilies of the ANTP (antennapedia) superfamily and belongs to the NK-like (NKL) subclass. Ventx is a homeobox transcription factor and has a DNA-interacting domain that is evolutionarily conserved throughout vertebrates. It has been extensively studied in Xenopus, zebrafish, and humans. The Ventx family contains transcriptional repressors widely involved in embryonic development and tumorigenesis in vertebrates. Several studies have documented that the Ventx family inhibited dorsal mesodermal formation, neural induction, and head formation in Xenopus and zebrafish. Moreover, Ventx2.2 showed functional similarities to Nanog and Barx1, leading to pluripotency and neural-crest migration in vertebrates. Among them, Ventx protein is an orthologue of the Ventx family in humans. Studies have demonstrated that human Ventx was strongly associated with myeloid-cell differentiation and acute myeloid leukemia. The therapeutic potential of Ventx family inhibition in combating cancer progression in humans is discussed. Additionally, we briefly discuss genome evolution, gene duplication, pseudo-allotetraploidy, and the homeobox family in Xenopus.

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.

Fxr signaling and microbial metabolism of bile salts in the zebrafish intestine

Bile salt synthesis, secretion into the intestinal lumen, and resorption in the ileum occur in all vertebrate classes. In mammals, bile salt composition is determined by host and microbial enzymes, affecting signaling through the bile salt-binding transcription factor farnesoid X receptor (Fxr). However, these processes in other vertebrate classes remain poorly understood. We show that key components of hepatic bile salt synthesis and ileal transport pathways are conserved and under control of Fxr in zebrafish. Zebrafish bile salts consist primarily of a C27 bile alcohol and a C24 bile acid that undergo multiple microbial modifications including bile acid deconjugation that augments Fxr activity. Using single-cell RNA sequencing, we provide a cellular atlas of the zebrafish intestinal epithelium and uncover roles for Fxr in transcriptional and differentiation programs in ileal and other cell types. These results establish zebrafish as a nonmammalian vertebrate model for studying bile salt metabolism and Fxr signaling.

Differences in Cell Proliferation and Craniofacial Phenotype of Closely Related Species in the Pupfish Genus Cyprinodon

Understanding the genetic basis for phenotypic differences is fundamental to the study of macroevolutionary patterns of biological diversity. While technological advances in DNA sequencing have made researching genetic variation in wild taxa routine, fully understanding how these variants affect phenotype requires taking the next step to investigate how genetic changes alter cell and tissue interactions that ultimately produce phenotypes. In this article, we investigate a role for cell proliferation as a developmental source of craniofacial diversity in a radiation of 3 species of Cyprinodon from San Salvador Island, Bahamas. Patterns of cell proliferation in the heads of hatching-age fish differ among species of Cyprinodon, and correlate with differences in allometric growth rate among the jaws of 3 distinct species. Regional patterns of cell proliferation in the head are complex, resulting in an unintuitive result in which lower levels of cell proliferation in the posterior head region are associated with the development of relatively larger jaws in one species. We combine these data with previously published morphological and genomic data to show how studying the mechanisms generating phenotype at the cellular and tissue levels of biological organization can help mechanistically link genomic studies with classic morphological studies.

An atlas of neural crest lineages along the posterior developing zebrafish at single-cell resolution

Neural crest cells (NCCs) are vertebrate stem cells that give rise to various cell types throughout the developing body in early life. Here, we utilized single-cell transcriptomic analyses to delineate NCC-derivatives along the posterior developing vertebrate, zebrafish, during the late embryonic to early larval stage, a period when NCCs are actively differentiating into distinct cellular lineages. We identified several major NCC/NCC-derived cell-types including mesenchyme, neural crest, neural, neuronal, glial, and pigment, from which we resolved over three dozen cellular subtypes. We dissected gene expression signatures of pigment progenitors delineating into chromatophore lineages, mesenchyme cells, and enteric NCCs transforming into enteric neurons. Global analysis of NCC derivatives revealed they were demarcated by combinatorial hox gene codes, with distinct profiles within neuronal cells. From these analyses, we present a comprehensive cell-type atlas that can be utilized as a valuable resource for further mechanistic and evolutionary investigations of NCC differentiation.

Nucleoporin 62-Like Protein is Required for the Development of Pharyngeal Arches through Regulation of Wnt/β-Catenin Signaling and Apoptotic Homeostasis in Zebrafish

We have previously observed the predominant expression of nucleoporin 62-like (Nup62l) mRNA in the pharyngeal region of zebrafish, which raises the question whether Nup62l has important implications in governing the morphogenesis of pharyngeal arches (PA) in zebrafish. Herein, we explored the functions of Nup62l in PA development. The disruption of Nup62l with a CRISPR/Cas9-dependent gene knockout approach led to defective PA, which was characterized by a thinned and shortened pharyngeal region and a significant loss of pharyngeal cartilages. During pharyngeal cartilage formation, prechondrogenic condensation and chondrogenic differentiation were disrupted in homozygous nup62l-mutants, while the specification and migration of cranial neural crest cells (CNCCs) were unaffected. Mechanistically, the impaired PA region of nup62l-mutants underwent extensive apoptosis, which was mainly dependent on activation of p53-dependent apoptotic pathway. Moreover, aberrant activation of a series of apoptotic pathways in nup62l-mutants is closely associated with the inactivation of Wnt/β-catenin signaling. Thus, these findings suggest that the regulation of Wnt/β-catenin activity by Nup62l is crucial for PA formation in zebrafish.

The Role of the Wnt Signaling Pathway in Upper Jaw Development of Chick Embryo

Cleft lip with or without cleft palate (CLP) usually results from a failure of the medial nasal prominences to fuse with the lateral and maxillary prominences. This failure inhibits facial morphogenesis regulated by several major morphogenetic signaling pathways. We hypothesized that CLP results from the failure of the Wnt signaling pathway. To examine whether Wnt signaling can influences upper jaw development, we applied beads soaked with Dickkopf-1 (Dkk-1), Alsterpaullone (AL) or Wnt3a to the right side of the maxillary prominence of the chick embryo. The embryo showed a defect of the maxilla on the treated side, and skeletal staining revealed hypoplasia of the premaxilla and palatine bone as a result of Dkk-1-soaked bead implantation. 5-bromo-2'-deoxyuridine (BrdU)-positive cell numbers in the treated maxillary prominence were significantly lower at both 24 and 48 hr after implantation. Down-regulation of the expression of Bmp4, Tbx22, Sox9, and Barx1 was confirmed in the maxillary prominence treated with Dkk-1, which indicated that the deformity of the maxillary bone was controlled by gene targets of the Wnt signaling pathway. Expression of N-cadherin was seen immunohistochemically in the maxillary prominences of embryos at 6 hr and increased at 24 hr after AL treatment. Wnt signaling enhanced by AL or Wnt3a up-regulated the expression levels of Msx1, Bmp4, Tbx22, Sox9, and Barx1. Our data suggest that the Wnt signaling pathway regulates maxillary morphogenesis and growth through Bmp4, Tbx22, Sox9, and Barx1. Wnt signaling might regulate N-cadherin expression via Msx1, resulting in cell aggregation for osteochondrogenesis.

Metabolism as an early predictor of DPSCs aging

Tissue resident adult stem cells are known to participate in tissue regeneration and repair that follows cell turnover, or injury. It has been well established that aging impedes the regeneration capabilities at the cellular level, but it is not clear if the different onset of stem cell aging between individuals can be predicted or prevented at an earlier stage. Here we studied the dental pulp stem cells (DPSCs), a population of adult stem cells that is known to participate in the repair of an injured tooth, and its properties can be affected by aging. The dental pulp from third molars of a diverse patient group were surgically extracted, generating cells that had a high percentage of mesenchymal stem cell markers CD29, CD44, CD146 and Stro1 and had the ability to differentiate into osteo/odontogenic and adipogenic lineages. Through RNA seq and qPCR analysis we identified homeobox protein, Barx1, as a marker for DPSCs. Furthermore, using high throughput transcriptomic and proteomic analysis we identified markers for DPSC populations with accelerated replicative senescence. In particular, we show that the transforming growth factor-beta (TGF-β) pathway and the cytoskeletal proteins are upregulated in rapid aging DPSCs, indicating a loss of stem cell characteristics and spontaneous initiation of terminal differentiation. Importantly, using metabolic flux analysis, we identified a metabolic signature for the rapid aging DPSCs, prior to manifestation of senescence phenotypes. This metabolic signature therefore can be used to predict the onset of replicative senescence. Hence, the present study identifies Barx1 as a DPSCs marker and dissects the first predictive metabolic signature for DPSCs aging.

Molecular ontogeny of the stomach in the catshark Scyliorhinus canicula

The origin of extracellular digestion in metazoans was accompanied by structural and physiological alterations of the gut. These adaptations culminated in the differentiation of a novel digestive structure in jawed vertebrates, the stomach. Specific endoderm/mesenchyme signalling is required for stomach differentiation, involving the growth and transcription factors: 1) Shh and Bmp4, required for stomach outgrowth; 2) Barx1, Sfrps and Sox2, required for gastric epithelium development and 3) Cdx1 and Cdx2, involved in intestinal versus gastric identity. Thus, modulation of endoderm/mesenchyme signalling emerges as a plausible mechanism linked to the origin of the stomach. In order to gain insight into the ancient mechanisms capable of generating this structure in jawed vertebrates, we characterised the development of the gut in the catshark Scyliorhinus canicula. As chondrichthyans, these animals retained plesiomorphic features of jawed vertebrates, including a well-differentiated stomach. We identified a clear molecular regionalization of their embryonic gut, characterised by the expression of barx1 and sox2 in the prospective stomach region and expression of cdx1 and cdx2 in the prospective intestine. Furthermore, we show that gastric gland development occurs close to hatching, accompanied by the onset of gastric proton pump activity. Our findings favour a scenario in which the developmental mechanisms involved in the origin of the stomach were present in the common ancestor of chondrichthyans and osteichthyans.

Systematic review of hormonal and genetic factors involved in the nonsyndromic disorders of the lower jaw

Mandibular disorders are among the most common birth defects in humans, yet the etiological factors are largely unknown. Most of the neonates affected by mandibular abnormalities have a sequence of secondary anomalies, including airway obstruction and feeding problems, that reduce the quality of life. In the event of lacking corrective surgeries, patients with mandibular congenital disorders suffer from additional lifelong problems such as sleep apnea and temporomandibular disorders, among others. The goal of this systematic review is to gather evidence on hormonal and genetic factors that are involved in signaling pathways and interactions that are potentially associated with the nonsyndromic mandibular disorders. We found that members of FGF and BMP pathways, including FGF8/10, FGFR2/3, BMP2/4/7, BMPR1A, ACVR1, and ACVR2A/B, have a prominent number of gene-gene interactions among all identified genes in this review. Gene ontology of the 154 genes showed that the functional gene sets are involved in all aspects of cellular processes and organogenesis. Some of the genes identified by the genome-wide association studies of common mandibular disorders are involved in skeletal formation and growth retardation based on animal models, suggesting a potential direct role as genetic risk factors in the common complex jaw disorders. Developmental Dynamics 248:162-172, 2019. © 2018 Wiley Periodicals, Inc.

Evolution and development of the fish jaw skeleton

The evolution of the jaw represents a key innovation in driving the diversification of vertebrate body plans and behavior. The pharyngeal apparatus originated as gill bars separated by slits in chordate ancestors to vertebrates. Later, with the acquisition of neural crest, pharyngeal arches gave rise to branchial basket cartilages in jawless vertebrates (agnathans), and later bone and cartilage of the jaw, jaw support, and gills of jawed vertebrates (gnathostomes). Major events in the evolution of jaw structure from agnathans to gnathostomes include axial regionalization of pharyngeal elements and formation of a jaw joint. Hox genes specify the anterior-posterior identity of arches, and edn1, dlx, hand2, Jag1b-Notch2 signaling, and Nr2f factors specify dorsal-ventral identity. The formation of a jaw joint, an important step in the transition from an un-jointed pharynx in agnathans to a hinged jaw in gnathostomes involves interaction between nkx3.2, hand2, and barx1 factors. Major events in jaw patterning between fishes and reptiles include changes to elements of the second pharyngeal arch, including a loss of opercular and branchiostegal ray bones and transformation of the hyomandibula into the stapes. Further changes occurred between reptiles and mammals, including the transformation of the articular and quadrate elements of the jaw joint into the malleus and incus of the middle ear. Fossils of transitional jaw phenotypes can be analyzed from a developmental perspective, and there exists potential to use genetic manipulation techniques in extant taxa to test hypotheses about the evolution of jaw patterning in ancient vertebrates. This article is categorized under: Comparative Development and Evolution > Evolutionary Novelties Early Embryonic Development > Development to the Basic Body Plan Comparative Development and Evolution > Body Plan Evolution.

Comparing atmospheric and hypoxic cultured mesenchymal stem cell transcriptome: implication for stem cell therapies targeting intervertebral discs

Background

Mesenchymal stem cells (MSCs) represent an attractive avenue for cellular therapies targeting degenerative diseases. MSC in vitro expansion is required in order to obtain therapeutic numbers during the manufacturing process. It is known that culture conditions impact cellular properties and behavior after in vivo transplantation. In this study, we aimed at evaluating the benefit of hypoxic culturing of human bone marrow derived mesenchymal stem cells on cell fitness and whole genome expression and discussed its implication on cellular therapies targeting orthopedic diseases such as chronic lower back pain.

Methods

Human bone marrow mesenchymal stem cells (hBMMSCs) were isolated from fresh human anticoagulated whole bone marrow and were cultured side by side in atmospheric (20% O₂) and hypoxic (5% O₂) oxygen partial pressure for up to 3 passages. Stem cell fitness was assessed by clonogenic assay, cell surface marker expression and differentiation potential. Whole genome expression was performed by mRNA sequencing. Data from clonogenic assays, cell surface marker by flow cytometry and gene expression by quantitative PCR were analyzed by two-tailed paired Student’s t-test. Data from mRNA sequencing were aligned to hg19 using Tophat-2.0.13 and analyzed using Cufflinks-2.1.1.

Results

Hypoxic culturing of hBMMSCs had positive effects on cell fitness, as evidenced by an increased clonogenicity and improved differentiation potential towards adipocyte and chondrocyte lineages. No difference in osteoblast differentiation or in cell surface markers were observed. Only a small subset of genes (34) were identified by mRNA sequencing to be significantly dysregulated by hypoxia. When clustered by biological function, these genes were associated with chondrogenesis and cartilage metabolism, inflammation and immunomodulation, cellular survival, migration and proliferation, vasculogenesis and angiogenesis.

Conclusions

Hypoxic culturing positively impacted hBMMSCs fitness and transcriptome, potentially improving inherent properties of these cells that are critical for the development of successful cellular therapies. Hypoxic culturing should be considered for the in vitro expansion of hBMMSCs during manufacturing of cellular therapies targeting orthopedic disorders such as lower back pain.

GATA4 as a novel regulator involved in the development of the neural crest and craniofacial skeleton via Barx1

The role of GATA-binding protein 4 (GATA4) in neural crest cells (NCCs) is poorly defined. Here we showed that mouse NCCs lacking GATA4 exhibited developmental defects in craniofacial bone, teeth, and heart. The defects likely occurred due to decreased cell proliferation at the developmental stage. The in vitro results were consistent with the mouse model. The isobaric tags for relative and absolute quantitation assay revealed that BARX1 is one of the differentially expressed proteins after GATA4 knockdown in NCCs. On the basis of the results of dual-luciferase, electro-mobility shift, and chromatin immunoprecipitation assays, Barx1 expression is directly regulated by GATA4 in NCCs. In zebrafish, gata4 knockdown affects the development of NCCs derivatives. However, the phenotype in zebrafish could be partly rescued by co-injection of gata4 morpholino oligomers and barx1 mRNA. This study identified new downstream targets of GATA4 in NCCs and uncovered additional evidence of the complex regulatory functions of GATA4 in NCC development.

AP-2α and AP-2β cooperatively orchestrate homeobox gene expression during branchial arch patterning

The evolution of a hinged moveable jaw with variable morphology is considered a major factor behind the successful expansion of the vertebrates. DLX homeobox transcription factors are crucial for establishing the positional code that patterns the mandible, maxilla and intervening hinge domain, but how the genes encoding these proteins are regulated remains unclear. Herein, we demonstrate that the concerted action of the AP-2α and AP-2β transcription factors within the mouse neural crest is essential for jaw patterning. In the absence of these two proteins, the hinge domain is lost and there are alterations in the size and patterning of the jaws correlating with dysregulation of homeobox gene expression, with reduced levels of Emx, Msx and Dlx paralogs accompanied by an expansion of Six1 expression. Moreover, detailed analysis of morphological features and gene expression changes indicate significant overlap with various compound Dlx gene mutants. Together, these findings reveal that the AP-2 genes have a major function in mammalian neural crest development, influencing patterning of the craniofacial skeleton via the DLX code, an effect that has implications for vertebrate facial evolution, as well as for human craniofacial disorders.

Low-set ears and associated anomalies in human foetuses

OBJECTIVES

To determine the prevalence of low-set ears (LSE) in a group of human foetuses, to analyse the associated anomalies, and to review the development mechanisms possibly involved.

METHODS

A total of 1759 human foetuses from spontaneous abortion were evaluated. Foetuses were obtained from the Foetuses and Embryos Collection of the Embryology Department of the Faculty of Medicine of the Autonomous University of Nuevo León. The Ethics Committee gave its approval for this study (EH-230-16). The position of the auricles was determined according to the standards recommended by the Elements of Morphology. Two study groups were created: foetuses with LSE and foetuses with normal ears. In both groups, a detailed examination of the external morphology was performed, followed by thoraco-abdominal micro dissection. Statistical analysis was performed.

RESULTS

Two hundred two of the foetuses presented LSE (1148 per 10,000). In this group, 68.8% did not present associated anomalies, while 31.2% had an associated anomaly. The most frequently affected organ was the heart (53.6%), followed by the digestive tract (23.9%), urinary system (16.9%), head and neck (4.2%), and limbs (1.4%). In the group of foetuses with normal ears, only 7.4% of the specimens had associated anomalies, which was a significant difference compared with the LSE group.

CONCLUSIONS

Based on the obtained results, we consider that LSE can be used as a sensitive indicator of major anomalies. It is recommended to include a systematic assessment of the position of the auricles in the initial clinical evaluation of any newborn.

Temporal Changes in Transcription Factor Expression Associated with the Differentiation State of Cerebellar Neural Stem/Progenitor Cells During Development

During central nervous development, multi-potent neural stem/progenitor cells located in the ventricular/subventricular zones are temporally regulated to mostly produce neurons during early developmental stages and to produce glia during later developmental stages. After birth, the rodent cerebellum undergoes further dramatic development. It is also known that neural stem/progenitor cells are present in the white matter (WM) of the postnatal cerebellum until around P10, although the fate of these cells has yet to be determined. In the present study, it was revealed that primary neurospheres generated from cerebellar neural stem/progenitor cells at postnatal day 3 (P3) mainly differentiated into astrocytes and oligodendrocytes. In contrast, primary neurospheres generated from cerebellar neural stem/progenitor cells at P8 almost exclusively differentiated into astrocytes, but not oligodendrocytes. These results suggest that the differentiation potential of primary neurospheres changes depending on the timing of neural stem/progenitor cell isolation from the cerebellum. To identify the candidate transcription factors involved in regulating this temporal change, we utilized DNA microarray analysis to compare global gene-expression profiles of primary neurospheres generated from neural stem/progenitor cells isolated from either P3 or P8 cerebellum. The expression of zfp711, zfp618, barx1 and hoxb3 was higher in neurospheres generated from P3 cerebellum than from P8 by real-time quantitative PCR. Several precursor cells were found to express zfp618, barx1 or hoxb3 in the WM of the cerebellum at P3, but these transcription factors were absent from the WM of the P8 cerebellum.

Loss of Barx1 promotes hepatocellular carcinoma metastasis through up-regulating MGAT5 and MMP9 expression and indicates poor prognosis

Metastasis is the major dominant reason for poor prognosis of hepatocellular carcinoma (HCC) after surgical treatment. However, the molecular mechanism of metastasis has not been well characterzied. Here, we report a novel function of Barx homeobox1 (Barx1) in inhibiting HCC invasion and metastasis. Barx1 expression is significantly decreased in human HCC tissues than in adjacent non-tumorous tissues and normal liver tissues. Low Barx1 expression is correlated with higher tumor-nodule-metastasis stage and indicates poor prognosis. Down-regulation of Barx1 promotes HCC migration, invasion and metastasis, whereas up-regulation of Barx1 inhibits HCC migration, invasion and metastasis. Mannosyl (alpha-1,6-)-glycoprotein beta-1,6-N-acetyl-glucosaminyltransferase 5 (MGAT5) and matrix metallopeptidase 9 (MMP9) are direct target genes of Barx1. Knockdown of Barx1 up-regulates MGAT5 and MMP9 expression in HCC cells with low metastatic capability, whereas over-expression of Barx1 suppresses their expression in HCC cells with high metastatic capability. Knockdown of both MGAT5 and MMP9 significantly decreases the invasion and metastasis abilities induced by Barx1 knockdown. Barx1 expression is negatively correlated with MGAT5 and MMP9 expression in human HCC tissues. Patients with low expression of Barx1 and high expression of MGAT5 or MMP9 are associated with poorer prognosis. Thus, loss of Barx1 represents a prognostic biomarker in human HCC patients.

Separate development of the maxilla and mandible is controlled by regional signaling of the maxillomandibular junction during avian development

BACKGROUND

Syngnathia is a congenital craniofacial disorder characterized by bony or soft tissue fusion of upper and lower jaws. Previous studies suggested some causative signals, such as Foxc1 or Bmp4, cause the disruption of maxillomandibular identity, but their location and the interactive signals involved remain unexplored. We wanted to examine the embryonic origin of syngnathia based on the assumption that it may be located at the separation between the maxillary and mandibular processes. This region, known as the maxillomandibular junction (MMJ), is involved in segregation of cranial neural crest-derived mesenchyme into the presumptive upper and lower jaws.

RESULTS

Here we investigated the role of Fgf, Bmp, and retinoid signaling during development of MMJ in chicken embryos. By changing the levels of these signals with bead implants, we induced syngnathia with microstomia on the treated side, which showed increased Barx1 and neural cell adhesion molecule (NCAM) expression. Redistribution of proliferating cells was also observed at the proximal region to maxillary and mandibular arch around MMJ.

CONCLUSIONS

We propose that interactive molecular signaling by Fgfs, Bmps, and retinoids around MMJ is required for normal separation of the maxilla and mandible, as well as the proper positioning of beak commissure during early facial morphogenesis. Developmental Dynamics 246:28-40, 2017. © 2016 Wiley Periodicals, Inc.

Competition between Jagged-Notch and Endothelin1 Signaling Selectively Restricts Cartilage Formation in the Zebrafish Upper Face

The intricate shaping of the facial skeleton is essential for function of the vertebrate jaw and middle ear. While much has been learned about the signaling pathways and transcription factors that control facial patterning, the downstream cellular mechanisms dictating skeletal shapes have remained unclear. Here we present genetic evidence in zebrafish that three major signaling pathways − Jagged-Notch, Endothelin1 (Edn1), and Bmp − regulate the pattern of facial cartilage and bone formation by controlling the timing of cartilage differentiation along the dorsoventral axis of the pharyngeal arches. A genomic analysis of purified facial skeletal precursors in mutant and overexpression embryos revealed a core set of differentiation genes that were commonly repressed by Jagged-Notch and induced by Edn1. Further analysis of the pre-cartilage condensation gene barx1, as well as in vivo imaging of cartilage differentiation, revealed that cartilage forms first in regions of high Edn1 and low Jagged-Notch activity. Consistent with a role of Jagged-Notch signaling in restricting cartilage differentiation, loss of Notch pathway components resulted in expanded barx1 expression in the dorsal arches, with mutation of barx1 rescuing some aspects of dorsal skeletal patterning in jag1b mutants. We also identified prrx1a and prrx1b as negative Edn1 and positive Bmp targets that function in parallel to Jagged-Notch signaling to restrict the formation of dorsal barx1+ pre-cartilage condensations. Simultaneous loss of jag1b and prrx1a/b better rescued lower facial defects of edn1 mutants than loss of either pathway alone, showing that combined overactivation of Jagged-Notch and Bmp/Prrx1 pathways contribute to the absence of cartilage differentiation in the edn1 mutant lower face. These findings support a model in which Notch-mediated restriction of cartilage differentiation, particularly in the second pharyngeal arch, helps to establish a distinct skeletal pattern in the upper face.

The exquisite functions of the vertebrate face require the precise formation of its underlying bones. Remarkably, many of the genes required to shape the facial skeleton are the same from fish to man. In this study, we use the powerful zebrafish system to understand how the skeletal components of the face acquire different shapes during development. To do so, we analyze a series of mutants that disrupt patterning of the facial skeleton, and then assess how the genes affected in these mutants control cell fate in skeletal progenitor cells. From these genetic studies, we found that several pathways converge to control when and where progenitor cells commit to a cartilage fate, thus controlling the size and shape of cartilage templates for the later-arising bones. Our work thus reveals how regulating the timing of when progenitor cells make skeleton helps to shape the bones of the zebrafish face. As mutations in many of the genes studied are implicated in human craniofacial defects, differences in the timing of progenitor cell differentiation may also explain the wonderful diversity of human faces.

[Retinoic acid signal pathway regulation of zebra fish tooth development through manipulation of the differentiation of neural crest]

OBJECTIVE

To investigate the mechanism of retinoic acid (RA) signal in dental evolution, RA is used to explore the influence of the mechanism on neural crest's migration during the early stage of zebra fish embryos.

METHODS

We divided embryos of wild type and transgenic line zebra fish into three groups. 1 x 10(-7) to 6 x 10(-7) mol x L(-1) RA and 1 x 10(-7) mo x L(-1) 4-diethylaminobenzaldehyde (DEAB) were added into egg water at 24 hpf for 9 h. Dimethyl sulfoxid (DMSO) with the concentration was used as control group. Then, antisense probes of dlx2a, dlx2b, and barxl were formulated to perform whole-mount in situ hybridization to check the expressions of the genes in 48 hpf to 72 hpf embryos. We observed fluorescence of transgenic line in 4 dpf embryos.

RESULTS

We obtained three mRNA probes successfully. Compared with DMSO control group, a low concentration (1 x 10(-7) mol x L(-1)) of RA could up-regulate the expression of mRNA (barx1, dlx2a) in neural crest. Obvious migration trend was observed toward the pharyngeal arch in which teeth adhered. Transgenic fish had spreading fluorescence tendency in pharyngeal arch. However, a high concentration (4 x 10(-7) mol x L(-1)) of RA malformed the embryos and killed them after treatment. One third of the embryos of middle concentration (3 x 10(-7) mo x L(-1)) exhibited delayed development. DEAB resulted in neural crest dysplasia. The expression of barxl and dlx2a were suppressed, and the appearance of dlx2b in tooth was delayed.

CONCLUSION

RA signal pathway can regulate the progenitors of tooth by controlling the growth of the neural crest and manipulating tooth development

Genetic Defects in TAPT1 Disrupt Ciliogenesis and Cause a Complex Lethal Osteochondrodysplasia

The evolutionarily conserved transmembrane anterior posterior transformation 1 protein, encoded by TAPT1, is involved in murine axial skeletal patterning, but its cellular function remains unknown. Our study demonstrates that TAPT1 mutations underlie a complex congenital syndrome, showing clinical overlap between lethal skeletal dysplasias and ciliopathies. This syndrome is characterized by fetal lethality, severe hypomineralization of the entire skeleton and intra-uterine fractures, and multiple congenital developmental anomalies affecting the brain, lungs, and kidneys. We establish that wild-type TAPT1 localizes to the centrosome and/or ciliary basal body, whereas defective TAPT1 mislocalizes to the cytoplasm and disrupts Golgi morphology and trafficking and normal primary cilium formation. Knockdown of tapt1b in zebrafish induces severe craniofacial cartilage malformations and delayed ossification, which is shown to be associated with aberrant differentiation of cranial neural crest cells.

prdm1a functions upstream of itga5 in zebrafish craniofacial development

Cranial neural crest cells are specified and migrate into the pharyngeal arches where they subsequently interact with the surrounding environment. Signaling and transcription factors, such as prdm1a regulate this interaction, but it remains unclear which specific factors are required for posterior pharyngeal arch development. Previous analysis suggests that prdm1a is required for posterior ceratobranchial cartilages in zebrafish and microarray analysis between wildtype and prdm1a mutants at 25 h post fertilization demonstrated that integrin α5 (itga5) is differentially expressed in prdm1a mutants. Here, we further investigate the interaction between prdm1a and itga5 in zebrafish craniofacial development. In situ hybridization for itga5 demonstrates that expression of itga5 is decreased in prdm1a mutants between 18 and 31 h post fertilization and itga5 expression overlaps with prdm1a in the posterior arches, suggesting a temporal window for interaction. Double mutants for prdm1a;itga5 have an additive viscerocranium phenotype more similar to prdm1a mutants, suggesting that prdm1a acts upstream of itga5. Consistent with this, loss of posterior pharyngeal arch expression of dlx2a, ceratobranchial cartilages 2-5, and cell proliferation in prdm1a mutants can be rescued with itga5 mRNA injection. Taken together, these data suggest that prdm1a acts upstream of itga5 and are both necessary for posterior pharyngeal arch development in zebrafish.

Sonic hedgehog from pharyngeal arch 1 epithelium is necessary for early mandibular arch cell survival and later cartilage condensation differentiation

BACKGROUND

Morphogenesis of vertebrate craniofacial skeletal elements is dependent on a key cell population, the cranial neural crest cells (NCC). Cranial NCC are formed dorsally in the cranial neural tube and migrate ventrally to form craniofacial skeletal elements as well as other tissues. Multiple extracellular signaling pathways regulate the migration, survival, proliferation, and differentiation of NCC.

RESULTS

In this study, we demonstrate that Shh expression in the oral ectoderm and pharyngeal endoderm is essential for mandibular development. We show that a loss of Shh in these domains results in increased mesenchymal cell death in pharyngeal arch 1 (PA1) after NCC migration. This increased cell death can be rescued in utero by pharmacological inhibition of p53. Furthermore, we show that epithelial SHH is necessary for the early differentiation of mandibular cartilage condensations and, therefore, the subsequent development of Meckel's cartilage, around which the dentary bone forms. Nonetheless, a rescue of the cell death phenotype does not rescue the defect in cartilage condensation formation.

CONCLUSIONS

Our results show that SHH produced by the PA1 epithelium is necessary for the survival of post-migratory NCC, and suggests a key role in the subsequent differentiation of chondrocytes to form Meckel's cartilage.

Holmgren's principle of delamination during fin skeletogenesis

During fin morphogenesis, several mesenchyme condensations occur to give rise to the dermal skeleton. Although each of them seems to create distinctive and unique structures, they all follow the premises of the same morphogenetic principle. Holmgren's principle of delamination was first proposed to describe the morphogenesis of skeletal elements of the cranium, but Jarvik extended it to the development of the fin exoskeleton. Since then, some cellular or molecular explanations, such as the "flypaper" model (Thorogood et al.), or the evolutionary description by Moss, have tried to clarify this topic. In this article, we review new data from zebrafish studies to meet these criteria described by Holmgren and other authors. The variety of cell lineages involved in these skeletogenic condensations sheds light on an open discussion of the contributions of mesoderm- versus neural crest-derived cell lineages to the development of the head and trunk skeleton. Moreover, we discuss emerging molecular studies that are disclosing conserved regulatory mechanisms for dermal skeletogenesis and similarities during fin development and regeneration, which may have important implications in the potential use of the zebrafish fin as a model for regenerative medicine.

A gene expression map of the larval Xenopus laevis head reveals developmental changes underlying the evolution of new skeletal elements

The morphology of the vertebrate head skeleton is highly plastic, with the number, size, shape, and position of its components varying dramatically between groups. While this evolutionary flexibility has been key to vertebrate success, its developmental and genetic bases are poorly understood. The larval head skeleton of the frog Xenopus laevis possesses a unique combination of ancestral tetrapod features and anuran-specific novelties. We built a detailed gene expression map of the head mesenchyme in X. laevis during early larval development, focusing on transcription factor families with known functions in vertebrate head skeleton development. This map was then compared to homologous gene expression in zebrafish, mouse, and shark embryos to identify conserved and evolutionarily flexible aspects of vertebrate head skeleton development. While we observed broad conservation of gene expression between X. laevis and other gnathostomes, we also identified several divergent features that correlate to lineage-specific novelties. We noted a conspicuous change in dlx1/2 and emx2 expression in the second pharyngeal arch, presaging the differentiation of the reduced dorsal hyoid arch skeletal element typical of modern anamniote tetrapods. In the first pharyngeal arch we observed a shift in the expression of the joint inhibitor barx1, and new expression of the joint marker gdf5, shortly before skeletal differentiation. This suggests that the anuran-specific infrarostral cartilage evolved by partitioning of Meckel's cartilage with a new paired joint. Taken together, these comparisons support a model in which early patterning mechanisms divide the vertebrate head mesenchyme into a highly conserved set of skeletal precursor populations. While subtle changes in this early patterning system can affect skeletal element size, they do not appear to underlie the evolution of new joints or cartilages. In contrast, later expression of the genes that regulate skeletal element differentiation can be clearly linked to the evolution of novel skeletal elements. We posit that changes in the expression of downstream regulators of skeletal differentiation, like barx1 and gdf5, is one mechanism by which head skeletal element number and articulation are altered during evolution.

The serine-threonine protein kinase PAK4 is dispensable in zebrafish: identification of a morpholino-generated pseudophenotype

TALEN-based inactivation of the zebrafish pak4 gene resulted in embryos and adult fish that appear normal and fertile. This is in contrast to our previously published studies which were based on the use of antisense morpholino oligonucleotides (MOs). We have excluded potential explanations such as gene duplication, alternate splicing, cryptic initiation of translation, and translation-independent RNA function. Our conclusion is that pak4 is dispensable in zebrafish, and that even when corroborated by robust controls, such as RNA rescue, MOs may elicit misleading pseudophenotypes that do not correspond to results obtained by genetic mutations, and should thus be used with caution.

Comparison of long noncoding RNA and mRNA expression profiles in mesenchymal stem cells derived from human periodontal ligament and bone marrow

Mesenchymal stem cells (MSCs) in different anatomic locations possess diverse biological activities. Maintaining the pluripotent state and differentiation depend on the expression and regulation of thousands of genes, but it remains unclear which molecular mechanisms underlie MSC diversity. Thus, potential MSC applications are restricted. Long noncoding RNAs (lncRNAs) are implicated in the complex molecular circuitry of cellular processes. We investigated differences in lncRNA and mRNA expression profiles between bone marrow stem cells (BMSCs) and periodontal ligament stem cells (PDLSCs) with lncRNA microarray assays and bioinformatics analysis. In PDLSCs, numerous lncRNAs were significantly upregulated (n = 457) or downregulated (n = 513) compared to BMSCs. Furthermore, 1,578 mRNAs were differentially expressed. These genes implicated cellular pathways that may be associated with MSC characteristics, including apoptosis, MAPK, cell cycle, and Wnt signaling pathway. Signal-net analysis indicated that phospholipase C beta 4, filamin B beta, calcium/calmodulin-dependent protein kinase II gamma, and the ionotropic glutamate receptor, AMPA 1, had the highest betweenness centrality among significant genes in the differential gene profile network. A comparison between the coding-noncoding gene coexpression networks of PDLSCs and BMSCs identified chemokine (C-X-C motif) ligand 12 as a core regulatory factor in MSC biology. These results provided insight into the mechanisms underlying MSC biology.

Roles for FGF in lamprey pharyngeal pouch formation and skeletogenesis highlight ancestral functions in the vertebrate head

A defining feature of vertebrates (craniates) is a pronounced head supported and protected by a cellularized endoskeleton. In jawed vertebrates (gnathostomes), the head skeleton is made of rigid three-dimensional elements connected by joints. By contrast, the head skeleton of modern jawless vertebrates (agnathans) consists of thin rods of flexible cellular cartilage, a condition thought to reflect the ancestral vertebrate state. To better understand the origin and evolution of the gnathostome head skeleton, we have been analyzing head skeleton development in the agnathan, lamprey. The fibroblast growth factors FGF3 and FGF8 have various roles during head development in jawed vertebrates, including pharyngeal pouch morphogenesis, patterning of the oral skeleton and chondrogenesis. We isolated lamprey homologs of FGF3, FGF8 and FGF receptors and asked whether these functions are ancestral features of vertebrate development or gnathostome novelties. Using gene expression and pharmacological agents, we found that proper formation of the lamprey head skeleton requires two phases of FGF signaling: an early phase during which FGFs drive pharyngeal pouch formation, and a later phase when they directly regulate skeletal differentiation and patterning. In the context of gene expression and functional studies in gnathostomes, our results suggest that these roles for FGFs arose in the first vertebrates and that the evolution of the jaw and gnathostome cellular cartilage was driven by changes developmentally downstream from pharyngeal FGF signaling.

barx1 represses joints and promotes cartilage in the craniofacial skeleton

The evolution of joints, which afford skeletal mobility, was instrumental in vertebrate success. Here, we explore the molecular genetics and cell biology that govern jaw joint development. Genetic manipulation experiments in zebrafish demonstrate that functional loss, or gain, of the homeobox-containing gene barx1 produces gain, or loss, of joints, respectively. Ectopic joints in barx1 mutant animals are present in every pharyngeal segment, and are associated with disrupted attachment of bone, muscles and teeth. We find that ectopic joints develop at the expense of cartilage. Time-lapse experiments suggest that barx1 controls the skeletal precursor cell choice between differentiating into cartilage versus joint cells. We discovered that barx1 functions in this choice, in part, by regulating the transcription factor hand2. We further show that hand2 feeds back to negatively regulate barx1 expression. We consider the possibility that changes in barx1 function in early vertebrates were among the key innovations fostering the evolution of skeletal joints.

Molars and incisors: show your microarray IDs

Background

One of the key questions in developmental biology is how, from a relatively small number of conserved signaling pathways, is it possible to generate organs displaying a wide range of shapes, tissue organization, and function. The dentition and its distinct specific tooth types represent a valuable system to address the issues of differential molecular signatures. To identify such signatures, we performed a comparative transcriptomic analysis of developing murine lower incisors, mandibular molars and maxillary molars at the developmental cap stage (E14.5).

Results

231 genes were identified as being differentially expressed between mandibular incisors and molars, with a fold change higher than 2 and a false discovery rate lower than 0.1, whereas only 96 genes were discovered as being differentially expressed between mandibular and maxillary molars. Numerous genes belonging to specific signaling pathways (the Hedgehog, Notch, Wnt, FGF, TGFβ/BMP, and retinoic acid pathways), and/or to the homeobox gene superfamily, were also uncovered when a less stringent fold change threshold was used. Differential expressions for 10 out of 12 (mandibular incisors versus molars) and 9 out of 10 selected genes were confirmed by quantitative reverse transcription-PCR (qRT-PCR). A bioinformatics tool (Ingenuity Pathway Analysis) used to analyze biological functions and pathways on the group of incisor versus molar differentially expressed genes revealed that 143 genes belonged to 9 networks with intermolecular connections. Networks with the highest significance scores were centered on the TNF/NFκB complex and the ERK1/2 kinases. Two networks ERK1/2 kinases and tretinoin were involved in differential molar morphogenesis.

Conclusion

These data allowed us to build several regulatory networks that may distinguish incisor versus molar identity, and may be useful for further investigations of these tooth-specific ontogenetic programs. These programs may be dysregulated in transgenic animal models and related human diseases leading to dental anomalies.

Redundant roles of PRDM family members in zebrafish craniofacial development

BACKGROUND

PRDM proteins are evolutionary conserved Zn-Finger transcription factors that share a characteristic protein domain organization. Previous studies have shown that prdm1a is required for the specification and differentiation of neural crest cells in the zebrafish.

RESULTS

Here we examine other members of this family, specifically prdm3, 5, and 16, in the differentiation of the zebrafish craniofacial skeleton. prdm3 and prdm16 are strongly expressed in the pharyngeal arches, while prdm5 is expressed specifically in the area of the forming neurocranium. Knockdown of prdm3 and prdm16 results in a reduction in the neural crest markers dlx2a and barx1 and defects in both the viscerocranium and the neurocranium. The knockdown of prdm3 and prdm16 in combination is additive in the neurocranium, but not in the viscerocranium. Injection of sub-optimal doses of prdm1a with prdm3 or prdm16 Morpholinos together leads to more severe phenotypes in the viscerocranium and neurocranium. prdm5 mutants have defects in the neurocranium and prdm1a and prdm5 double mutants also show more severe phenotypes.

CONCLUSIONS

Overall, our data reveal that prdm3, 5, and 16 are involved in the zebrafish craniofacial development and that prdm1a may interact with prdm3, 5, and 16 in the formation of the craniofacial skeleton in zebrafish.

Rbms3 functions in craniofacial development by posttranscriptionally modulating TGF-β signaling

Rbms3 regulates TGF-βr signaling, a critical pathway for chondrogenesis, by binding and stabilizing Smad2 transcripts.

Cranial neural crest cells form much of the facial skeleton, and abnormalities in their development lead to severe birth defects. In a novel zebrafish protein trap screen, we identified an RNA-binding protein, Rbms3, that is transiently expressed in the cytoplasm of condensing neural crest cells within the pharyngeal arches. Morphants for rbms3 displayed reduced proliferation of prechondrogenic crest and significantly altered expression for chondrogenic/osteogenic lineage markers. This phenotype strongly resembles cartilage/crest defects observed in Tgf-βr2:Wnt1-Cre mutants, which suggests a possible link with TGF-β signaling. Consistent with this are the findings that: (a) Rbms3 stabilized a reporter transcript with smad2 3′ untranslated region, (b) RNA immunoprecipitation with full-length Rbms3 showed enrichment for smad2/3, and (c) pSmad2 levels were reduced in rbms3 morphants. Overall, these results suggest that Rbms3 posttranscriptionally regulates one of the major pathways that promotes chondrogenesis, the transforming growth factor β receptor (TGF-βr) pathway.

New perspectives on pharyngeal dorsoventral patterning in development and evolution of the vertebrate jaw

Patterning of the vertebrate facial skeleton involves the progressive partitioning of neural-crest-derived skeletal precursors into distinct subpopulations along the anteroposterior (AP) and dorsoventral (DV) axes. Recent evidence suggests that complex interactions between multiple signaling pathways, in particular Endothelin-1 (Edn1), Bone Morphogenetic Protein (BMP), and Jagged-Notch, are needed to pattern skeletal precursors along the DV axis. Rather than directly determining the morphology of individual skeletal elements, these signals appear to act through several families of transcription factors, including Dlx, Msx, and Hand, to establish dynamic zones of skeletal differentiation. Provocatively, this patterning mechanism is largely conserved from mouse and zebrafish to the jawless vertebrate, lamprey. This implies that the diversification of the vertebrate facial skeleton, including the evolution of the jaw, was driven largely by modifications downstream of a conversed pharyngeal DV patterning program.