The effect of hypoxia on facial shape variation and disease phenotypes in chicken embryos

Visualization of the Cartilage and Bone Elements in the Craniofacial Structures by Alcian Blue and Alizarin Red Staining

Craniofacial morphogenesis is underpinned by orchestrated growth and form-shaping activity of skeletal and soft tissues in the head and face. Disruptions during development can lead to dysmorphology of the skull, jaw, and the pharyngeal structures. Developmental disorders can be investigated in animal models to elucidate the molecular and cellular consequences of the morphogenetic defects. A first step in determining the disruption in the development of the head and face is to analyze the phenotypic features of the skeletal tissues. Examination of the anatomy of bones and cartilage over time and space will identify structural defects of head structures and guide follow-up analysis of the molecular and cellular attributes associated with the defects. Here we describe a protocol to simultaneously visualize the cartilage and bone elements by Alcian blue and Alizarin red staining, respectively, of wholemount specimens in mouse models.

miR-199 family contributes to regulation of sonic hedgehog expression during craniofacial development

BACKGROUND

The frontonasal ectodermal zone (FEZ) is a signaling center that regulates patterned development of the upper jaw, and Sonic hedgehog (SHH) mediates FEZ activity. Induction of SHH expression in the FEZ results from SHH-dependent signals from the brain and neural crest cells. Given the role of miRNAs in modulating gene expression, we investigated the extent to which miRNAs regulate SHH expression and FEZ signaling.

RESULTS

In the FEZ, the miR-199 family appears to be regulated by SHH-dependent signals from the brain; expression of this family increased from HH18 to HH22, and upon activation of SHH signaling in the brain. However, the miR-199 family is more broadly expressed in the mesenchyme of the frontonasal process and adjacent neuroepithelium. Downregulating the miR-199 genes expanded SHH expression in the FEZ, resulting in wider faces, while upregulating miR-199 genes resulted in decreased SHH expression and narrow faces. Hypoxia inducible factor 1 alpha (HIF1A) and mitogen-activated protein kinase kinase kinase 4 (MAP3K4) appear to be potential targets of miR-199b. Reduction of MAP3K4 altered beak development but increased apoptosis, while reducing HIF1A reduced expression of SHH in the FEZ and produced malformations independent of apoptosis.

CONCLUSIONS

Our results demonstrate that this miRNA family appears to participate in regulating SHH expression in the FEZ; however, specific molecular mechanisms remain unknown.

Msx1 deficiency interacts with hypoxia and induces a morphogenetic regulation during mouse lip development

Nonsyndromic clefts of the lip and palate are common birth defects resulting from gene-gene and gene-environment interactions. Mutations in human MSX1 have been linked to orofacial clefting and we show here that Msx1 deficiency causes a growth defect of the medial nasal process (Mnp) in mouse embryos. Although this defect alone does not disrupt lip formation, Msx1-deficient embryos develop a cleft lip when the mother is transiently exposed to reduced oxygen levels or to phenytoin, a drug known to cause embryonic hypoxia. In the absence of interacting environmental factors, the Mnp growth defect caused by Msx1 deficiency is modified by a Pax9-dependent 'morphogenetic regulation', which modulates Mnp shape, rescues lip formation and involves a localized abrogation of Bmp4-mediated repression of Pax9 Analyses of GWAS data revealed a genome-wide significant association of a Gene Ontology morphogenesis term (including assigned roles for MSX1, MSX2, PAX9, BMP4 and GREM1) specifically for nonsyndromic cleft lip with cleft palate. Our data indicate that MSX1 mutations could increase the risk for cleft lip formation by interacting with an impaired morphogenetic regulation that adjusts Mnp shape, or through interactions that inhibit Mnp growth.

The Morphology of Cross-Beaks and BMP4 Gene Expression in Huiyang Bearded Chickens

Simple Summary

Recently, the emergence of cross-beaks has been reported in several domestic chickens. Despite several candidate genes, bone morphogenetic protein 4 (BMP4) has been suggested as responsible for chicken cross-beaks. The subtypes of the morphology term, etiopathogenesis, and the relationship of the candidate BMP4 gene to cross-beaks are not yet known. The objective of this study was to describe the subtypes of cross-beaks by left or right and upper and lower jaw bones and to figure out the relationship between BMP4 and the development of craniofacial bones in Huiyang bearded chickens.

Abstract

Bird beaks are important for biological purposes such as food intake, removing parasites, and defining phenotypic attributes. Cross-beaks are a threat to poultry health and are harmful to productivity, wasting some units in the poultry industry. However, there is still limited research on subtypes of cross-beaks and the genetic basis of cross-beaks as well. Here, we described the subtypes of cross-beaks in terms of left or right and upper or lower jaw bones. We evaluated the impact of cross-beaks on craniofacial bones and figured out the relationship between bone morphogenetic protein 4 (BMP4) and the development of craniofacial bones in Huiyang bearded chickens. We identified five typical subtypes of cross-beaks by morphological assessment and X-ray scanning. We found that cross-beaks caused certain changes in the facial bone morphology, including changes to the length and width of the bone around the ocular area (p < 0.05). The relative expressions of BMP4 in lacrimal, mandible, premaxilla, frontal, and parietal bones were significantly higher in the severe cross-beak group, followed by that of the medium cross-beak group, weak cross-beak group, and control group (p < 0.05). Overall, we constructed a generally applicable method to classify cross-beaks in term of the angle. The skeleton around the ocular area was affected by the cross-beak. The expression levels of BMP4 in craniofacial bones may provide insight to potential role of BMP4 in the development of cross-beaks.

Differential proteomic analysis to identify proteins associated with beak deformity in chickens

The beak is the dominant avian facial feature, and beak deformity occurs in 0.5 to 2.5% of some indigenous chicken breeds, resulting in difficulties when eating, drinking, and performing natural behaviors. Previous studies on beak deformity focused largely on candidate molecules associated with skeletogenic development, providing insight into the molecular and genetic underpinnings of beak deformity. The present study was performed to identify candidate proteins related to this malformation in chickens. Three 12-day-old Beijing-You roosters with deformed beaks (D1, D2, and D3) and 3 with normal beaks (N1, N2, and N3) were used, and total beak proteins were isolated and subjected to standard iTRAQ labeling, strong cation-exchange chromatography, and liquid chromatography-tandem mass spectrometry. Mascot 2.3.02 was used to identify and quantitatively analyze proteins. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses were used to identify functions and metabolic pathways of differentially expressed proteins, and key proteins were further validated using western blot. A total of 2,370, 2,401, and 2,378 proteins were reliably quantified in 3 biological replicates, among which, 2,345 were common to all, and 92 were differentially expressed between the 2 groups. These included 37 upregulated and 55 downregulated proteins in deformed beaks. Pentraxin-related protein 3, hemopexin, lipoprotein lipase, retinoid-binding protein 7, and biliverdin reductase A were downregulated in all 3 sets, while parvalbumin, peptidyl-prolyl cis-trans isomerase, and ubiquitin-fold modifier 1 were upregulated. Pathway analysis returned no enriched pathways, and western blot validated the iTRAQ results. Parvalbumin and lipoprotein lipase could be firstly selected as key proteins in view of their known functions in regulating the buffering of intracellular free Ca2+ in both cartilage and bone cells and bone mass, respectively. Their potential roles in beak deformity, however, deserve further studies. In summary, the onset of beak deformity could be very complex, and this study will be helpful for future investigation of mechanistic explanation for beak deformity.

Prenatal retinoic acid exposure reveals candidate genes for craniofacial disorders

Syndromes that display craniofacial anomalies comprise a major class of birth defects. Both genetic and environmental factors, including prenatal retinoic acid (RA) exposure, have been associated with these syndromes. While next generation sequencing has allowed the discovery of new genes implicated in these syndromes, some are still poorly characterized such as Oculo-Auriculo-Vertebral Spectrum (OAVS). Due to the lack of clear diagnosis for patients, developing new strategies to identify novel genes involved in these syndromes is warranted. Thus, our study aimed to explore the link between genetic and environmental factors. Owing to a similar phenotype of OAVS reported after gestational RA exposures in humans and animals, we explored RA targets in a craniofacial developmental context to reveal new candidate genes for these related disorders. Using a proteomics approach, we detected 553 dysregulated proteins in the head region of mouse embryos following their exposure to prenatal RA treatment. This novel proteomic approach implicates changes in proteins that are critical for cell survival/apoptosis and cellular metabolism which could ultimately lead to the observed phenotype. We also identified potential molecular links between three major environmental factors known to contribute to craniofacial defects including maternal diabetes, prenatal hypoxia and RA exposure. Understanding these links could help reveal common key pathogenic mechanisms leading to craniofacial disorders. Using both in vitro and in vivo approaches, this work identified two new RA targets, Gnai3 and Eftud2, proteins known to be involved in craniofacial disorders, highlighting the power of this proteomic approach to uncover new genes whose dysregulation leads to craniofacial defects.

Crossed beaks in a local Swiss chicken breed

BACKGROUND

Crossed beaks have been reported to occur in Appenzeller Barthuhn, a local Swiss chicken breed. The assumed causes for this beak deformity which are also seen in other bird species including domestic chickens, range from environmental influences to genetic factors. The aim of this project was to characterize the prevalence, the phenotype, and the underlying genetics of crossed beaks in Appenzeller Barthuhn chickens.

RESULTS

The estimated prevalence of 7% crossed beaks in Appenzeller Barthuhn was significantly higher compared to two other local Swiss chicken breeds. A breeding trial showed significantly higher prevalence of offspring with deformed beaks from mating of affected parents compared to mating of non-affected parents. Examination of 77 Appenzeller Barthuhn chickens with crossed beaks showed a variable phenotype presentation. The deviation of the beak from the median plane through the head ranged from 1° to 61°. In more than 60% of the cases, the upper and lower beak were bent in the same direction, whereas the remaining cases showed different forms of crossed beaks. Computed tomographic scans and bone maceration of the head of two chickens with crossed beaks revealed that the maxilla and the mandibula were affected, while other parts of the skull appeared to be normal. The gene LOC426217, a member of the keratin family, was postulated as a candidate gene for beak deformity in domestic chickens. Sequencing of the coding region revealed two significantly associated synonymous variants for crossed beaks in Appenzeller Barthuhn chickens. A genome-wide association study and a comparative analysis of runs of homozygosity based on high-density SNP array genotyping data of 53 cases and 102 controls showed no evidence of association.

CONCLUSIONS

The findings suggest a hereditary cause of crossed beaks in Appenzeller Barthuhn chickens. However, the observed variation in the phenotype, together with the inconclusive molecular genetic results indicates the need for additional research to unravel the genetic architecture of this beak deformity.

Critical developmental windows for morphology and hematology revealed by intermittent and continuous hypoxic incubation in embryos of quail (Coturnix coturnix)

Hypoxia during embryonic growth in embryos is frequently a powerful determinant of development, but at least in avian embryos the effects appear to show considerable intra- and inter-specific variation. We hypothesized that some of this variation may arise from different protocols that may or may not result in exposure during the embryo’s critical window for hypoxic effects. To test this hypothesis, quail embryos (Coturnix coturnix) in the intact egg were exposed to hypoxia (~15% O₂) during “early” (Day 0 through Day 5, abbreviated as D0-D5), “middle” (D6-D10) or “late” (D11-D15) incubation or for their entire 16–18 day incubation (“continuous hypoxia”) to determine critical windows for viability and growth. Viability, body mass, beak and toe length, heart mass, and hematology (hematocrit and hemoglobin concentration) were measured on D5, D10, D15 and at hatching typically between D16 and D18 Viability rate was ~50–70% immediately following the exposure period in the early, middle and late hypoxic groups, but viability improved in the early and late groups once normoxia was restored. Middle hypoxia groups showed continuing low viability, suggesting a critical period from D6-D10 for embryo viability. The continuous hypoxia group experienced viability reaching <10% after D15. Hypoxia, especially during late and continuous hypoxia, also inhibited growth of body, beak and toe when measured at D15. Full recovery to normal body mass upon hatching occurred in all other groups except for continuous hypoxia. Contrary to previous avian studies, heart mass, hematocrit and hemoglobin concentration were not altered by any hypoxic incubation pattern. Although hypoxia can inhibit embryo viability and organ growth during most incubation periods, the greatest effects result from continuous or middle incubation hypoxic exposure. Hypoxic inhibition of growth can subsequently be “repaired” by catch-up growth if a final period of normoxic development is available. Collectively, these data indicate a critical developmental window for hypoxia susceptibility during the mid-embryonic period of development.

Placental labyrinth formation in mice requires endothelial FLRT2/UNC5B signaling

The placental labyrinth is the interface for gas and nutrient exchange between the embryo and the mother; hence its proper development is essential for embryogenesis. However, the molecular mechanism underlying development of the placental labyrinth, particularly in terms of its endothelial organization, is not well understood. Here, we determined that fibronectin leucine-rich transmembrane protein 2 (FLRT2), a repulsive ligand of the UNC5 receptor family for neurons, is unexpectedly expressed in endothelial cells specifically in the placental labyrinth. Mice lacking FLRT2 in endothelial cells exhibited embryonic lethality at mid-gestation, with systemic congestion and hypoxia. Although they lacked apparent deformities in the embryonic vasculature and heart, the placental labyrinths of these embryos exhibited aberrant alignment of endothelial cells, which disturbed the feto-maternal circulation. Interestingly, this vascular deformity was related to endothelial repulsion through binding to the UNC5B receptor. Our results suggest that the proper organization of the placental labyrinth depends on coordinated inter-endothelial repulsion, which prevents uncontrolled layering of the endothelium.

A neural crest origin for cohesinopathy heart defects

Mutations in subunits or regulators of cohesin cause a spectrum of disorders in humans known as the 'cohesinopathies'. Cohesinopathies, including the best known example Cornelia de Lange syndrome (CdLS), are characterized by broad spectrum, multifactorial developmental anomalies. Heart defects occur at high frequency and can reach up to 30% in CdLS. The mechanisms by which heart defects occur are enigmatic, but assumed to be developmental in origin. In this study, we depleted cohesin subunit Rad21 by 70-80% in a zebrafish cohesinopathy model. The hearts of Rad21-depleted animals were smaller, often failed to loop, and functioned less efficiently than size-matched controls. Functional deficiency was accompanied by valve defects and reduced ejection fraction. Interestingly, neural crest cells failed to populate the heart and instead exhibited a wandering behavior. Consequently, these cells also failed to condense correctly into pharyngeal arches. Transcriptome analysis revealed that Wnt pathway, chemokine and cadherin genes are dysregulated at the time of cardiac neural crest development. Our results give insight into the etiology of heart defects in the cohesinopathies, and raise the possibility that mild mutations in cohesin genes may be causative of a fraction of congenital heart disease in human populations.

Impact of retinoic acid exposure on midfacial shape variation and manifestation of holoprosencephaly in Twsg1 mutant mice

Holoprosencephaly (HPE) is a developmental anomaly characterized by inadequate or absent midline division of the embryonic forebrain and midline facial defects. It is believed that interactions between genes and the environment play a role in the widely variable penetrance and expressivity of HPE, although direct investigation of such effects has been limited. The goal of this study was to examine whether mice carrying a mutation in a gene encoding the bone morphogenetic protein (BMP) antagonist twisted gastrulation (Twsg1), which is associated with a low penetrance of HPE, are sensitized to retinoic acid (RA) teratogenesis. Pregnant Twsg1(+/-) dams were treated by gavage with a low dose of all-trans RA (3.75 mg/kg of body weight). Embryos were analyzed between embryonic day (E)9.5 and E11.5 by microscopy and geometric morphometric analysis by micro-computed tomography. P19 embryonal carcinoma cells were used to examine potential mechanisms mediating the combined effects of increased BMP and retinoid signaling. Although only 7% of wild-type embryos exposed to RA showed overt HPE or neural tube defects (NTDs), 100% of Twsg1(-/-) mutants exposed to RA manifested severe HPE compared to 17% without RA. Remarkably, up to 30% of Twsg1(+/-) mutants also showed HPE (23%) or NTDs (7%). The majority of shape variation among Twsg1(+/-) mutants was associated with narrowing of the midface. In P19 cells, RA induced the expression of Bmp2, acted in concert with BMP2 to increase p53 expression, caspase activation and oxidative stress. This study provides direct evidence for modifying effects of the environment in a genetic mouse model carrying a predisposing mutation for HPE in the Twsg1 gene. Further study of the mechanisms underlying these gene-environment interactions in vivo will contribute to better understanding of the pathogenesis of birth defects and present an opportunity to explore potential preventive interventions.

Co-ordinated brain and craniofacial development depend upon Patched1/XIAP regulation of cell survival

Congenital brain and craniofacial defects often occur together as a consequence of their developmental dependency on common progenitor tissue interactions and signaling pathways during embryogenesis. A classic example of this is perturbation of midline embryo development, and disruption of Hedgehog (Hh) signaling in the pathogenesis of holoprosencephaly. However, our understanding of how Hh signaling governs cell and tissue survival remains incomplete. Patched1 (Ptch1) is a well-known receptor for Hh ligands and Ptch1 overexpression is associated with cell and tissue-specific apoptosis. Here, we demonstrate that the X-linked inhibitory apoptosis protein (XIAP) associates with the C terminus of Ptch1 (Ptch1-C) in primary cilia to inhibit Ptch1-mediated cell death. Consistent with this observation, inhibition of XIAP suppresses cell proliferation, resulting in cell death and pathogenesis of an Hh loss-of-function phenotype. Thus, co-ordinated development of the brain and face is dependent in part upon XIAP mediation of Hh/Ptch1-regulated cell survival and apoptosis during embryogenesis.

Surface landmark quantification of embryonic mouse craniofacial morphogenesis

Background

Morphometric quantification of subtle craniofacial variation in studies of experimentally modified embryonic mice has proved valuable in determining the effects of developmental perturbations on craniofacial morphogenesis. The direct comparison of landmark coordinate data from embryos of many different mouse strains and mouse models can advance our understanding of the bases for craniofacial variation. We propose a standard set of craniofacial surface landmarks, for use with embryonic day (E) 10.5-12.5 mice, to serve as the foundation for this type of data compilation and analysis. We quantify the intra- and inter-observer landmark placement variation associated with each landmark and determine how the results of a simple ontogenetic analysis might be influenced by selection of landmark set.

Results

Intraobserver landmark placement error for experienced landmarkers generally remains below 0.1 mm, with some landmarks exhibiting higher values at E11.5 and E12.5. Interobserver error tends to increase with embryonic age and those landmarks defined on wide inflections of curves or facial processes exhibit the highest error. Landmarks with highest intra- or inter-observer are identified and we determine that their removal from the dataset does not significantly change the vectors of craniofacial shape change associated with an ontogenetic regression.

Conclusions

Our quantification of landmark placement error demonstrates that it is preferable for a single observer to identify all landmark coordinates within a single study and that significant training and experience are necessary before a landmarker can produce data for use in larger meta-analyses. However, we are confident that this standard landmark set, once landmarks with higher error are removed, can serve as a foundation for a comparative dataset of facial morphogenesis across various mouse populations to help identify the developmental bases for phenotypic variation in the craniofacial complex.

Quantitative analysis of orofacial development and median clefts in Xenopus laevis

Xenopus has become a useful tool to study the molecular mechanisms underlying orofacial development. However, few quantitative analyses exist to describe the anatomy of this region. In this study we combine traditional facial measurements with geometric morphometrics to describe anatomical changes in the orofacial region during normal and abnormal development. Facial measurements and principal component (PC) analysis indicate that during early tadpole development the face expands primarily in the midface region accounting for the development of the upper jaw and primary palate. The mouth opening correspondingly becomes flatter and wider as it incorporates the jaw elements. A canonical variate analysis of orofacial and mouth opening shape emphasized that changes in the orofacial shape occur gradually. Orofacial anatomy was quantified after altered levels of retinoic acid using all-trans retinoic acid or an inhibitor of retinoic acid receptors or by injecting antisense oligos targeting RALDH2. Such perturbations resulted in major decreases in the width of the midface and the mouth opening illustrated in facial measurements and a PC analysis. The mouth opening shape also had a gap in the primary palate resulting in a median cleft in the mouth opening that was only illustrated quantitatively in the morphometric analysis. Finally, canonical and discriminant function analysis statistically distinguished the orofacial and mouth opening shape changes among the different modes used to alter retinoic acid signaling levels. By combining quantitative analyses with molecular studies of orofacial development we will be better equipped to understand the complex morphogenetic processes involved in palate development and clefting.