Early Craniofacial Development Research Articles

Key Roles of Gli1 and Ihh Signaling in Craniofacial Development.

The Hedgehog (Hh) signaling pathway orchestrates its influence through a dynamic interplay of Hh proteins, the cell surface receptor Ptch1, Smo, and Gli transcription factors, contributing to a myriad of developmental events. Indian Hedgehog (Ihh) and Gli zinc finger transcription factor 1 (Gli1) play crucial roles in developmental regulation within the Hh signaling pathway. Ihh regulates chondrocyte proliferation, differentiation, and bone formation, impacting the development of cranial bones, cartilage, and the temporomandibular joint (TMJ). Losing Ihh results in cranial bone malformation and decreased ossification and affects the formation of cranial base cartilage unions, TMJ condyles, and joint discs. Gli1 is predominantly expressed during early craniofacial development, and Gli1+ cells are identified as the primary mesenchymal stem cells (MSCs) for craniofacial bones, crucial for cell differentiation and morphogenesis. In addition, a complex mutual regulatory mechanism exists between Gli1 and Ihh, ensuring the normal function of the Hh signaling pathway by directly or indirectly regulating each other's expression levels. And the interaction between Ihh and Gli1 significantly impacts the normal development of craniofacial tissues. This review summarizes the pivotal roles of Gli1 and Ihh in the intricate landscape of mammalian craniofacial development and outlines the molecular regulatory mechanisms and intricate interactions governing the growth of bone and cartilage exhibited by Gli1 and Ihh, which provides new insights into potential therapeutic strategies for related diseases or researches of tissue regeneration.

Epigenetics and the evolution of form: Experimental manipulation of a chromatin modification causes species-specific changes to the craniofacial skeleton.

A central question in biology is the molecular origins of phenotypic diversity. While genetic changes are key to the genotype-phenotype relationship, alterations to chromatin structure and the physical packaging of histone proteins may also be important drivers of vertebrate divergence. We investigate the impact of such an epigenetic mechanism, histone acetylation, within a textbook example of an adaptive radiation. Cichlids of Lake Malawi have adapted diverse craniofacial structures, and here we investigate how histone acetylation influences morphological variation in these fishes. Specifically, we assessed the effect of inhibiting histone deacetylation using the drug trichostatin A (TSA) on developing facial structures. We examined this during three critical developmental windows in two cichlid species with alternate adult morphologies. Exposure to TSA during neural crest cell (NCC) migration and as postmigratory NCCs proliferate in the pharyngeal arches resulted in significant changes in lateral and ventral shape in Maylandia, but not in Tropheops. This included an overall shortening of the head, widening of the lower jaw, and steeper craniofacial profile, all of which are paedomorphic morphologies. In contrast, treatment with TSA during early chondrogenesis did not result in significant morphological changes in either species. Together, these data suggest a sensitivity to epigenetic alterations that are both time- and species-dependent. We find that morphologies are due to nonautonomous or potentially indirect effects on NCC development, including in part a global developmental delay. Our research bolsters the understanding that proper histone acetylation is essential for early craniofacial development and identifies a species-specific robustness to developmental change. Overall, this study demonstrates how epigenetic regulation may play an important role in both generating and buffering morphological variation.

Directionality of developing skeletal muscles is set by mechanical forces

Formation of oriented myofibrils is a key event in musculoskeletal development. However, the mechanisms that drive myocyte orientation and fusion to control muscle directionality in adults remain enigmatic. Here, we demonstrate that the developing skeleton instructs the directional outgrowth of skeletal muscle and other soft tissues during limb and facial morphogenesis in zebrafish and mouse. Time-lapse live imaging reveals that during early craniofacial development, myoblasts condense into round clusters corresponding to future muscle groups. These clusters undergo oriented stretch and alignment during embryonic growth. Genetic perturbation of cartilage patterning or size disrupts the directionality and number of myofibrils in vivo. Laser ablation of musculoskeletal attachment points reveals tension imposed by cartilage expansion on the forming myofibers. Application of continuous tension using artificial attachment points, or stretchable membrane substrates, is sufficient to drive polarization of myocyte populations in vitro. Overall, this work outlines a biomechanical guidance mechanism that is potentially useful for engineering functional skeletal muscle.

Hominin fossils from Kromdraai and Drimolen inform Paranthropus robustus craniofacial ontogeny

Ontogeny provides critical information about the evolutionary history of early hominin adult morphology. We describe fossils from the southern African sites of Kromdraai and Drimolen that provide insights into early craniofacial development in the Pleistocene robust australopith Paranthropus robustus. We show that while most distinctive robust craniofacial features appear relatively late in ontogeny, a few do not. We also find unexpected evidence of independence in the growth of the premaxillary and maxillary regions. Differential growth results in a proportionately larger and more postero-inferiorly rotated cerebral fossa in P. robustus infants than in the developmentally older Australopithecus africanus juvenile from Taung. The accumulated evidence from these fossils suggests that the iconic SK 54 juvenile calvaria is more likely early Homo than Paranthropus. It is also consistent with the hypothesis that P. robustus is more closely related to Homo than to A. africanus.

Morphometric analysis of the size-adjusted linear dimensions of the skull landmarks revealed craniofacial dysmorphology in Mid1-cKO mice

BackgroundThe early craniofacial development is a highly coordinated process involving neural crest cell migration, proliferation, epithelial apoptosis, and epithelial-mesenchymal transition (EMT). Both genetic defects and environmental factors can affect these processes and result in orofacial clefts. Mutations in MID1 gene cause X-linked Opitz Syndrome (OS), which is a congenital malformation characterized by craniofacial defects including cleft lip/palate (CLP). Previous studies demonstrated impaired neurological structure and function in Mid1 knockout mice, while no CLP was observed. However, given the highly variable severities of the facial manifestations observed in OS patients within the same family carrying identical genetic defects, subtle craniofacial malformations in Mid1 knockout mice could be overlooked in these studies. Therefore, we propose that a detailed morphometric analysis should be necessary to reveal mild craniofacial dysmorphologies that reflect the similar developmental defects seen in OS patients.ResultsIn this research, morphometric study of the P0 male Mid1-cKO mice were performed using Procrustes superimposition as well as EMDA analysis of the size-adjusted three-dimensional coordinates of 105 skull landmarks, which were collected on the bone surface reconstructed using microcomputed tomographic images. Our results revealed the craniofacial deformation such as the increased dimension of the frontal and nasal bone in Mid1-cKO mice, in line with the most prominent facial features such as hypertelorism, prominent forehead, broad and/or high nasal bridge seen in OS patients.Conclusion While been extensively used in evolutionary biology and anthropology in the last decades, geometric morphometric analysis was much less used in developmental biology. Given the high interspecies variances in facial anatomy, the work presented in this research suggested the advantages of morphometric analysis in characterizing animal models of craniofacial developmental defects to reveal phenotypic variations and the underlining pathogenesis.

A Systematic Review of the Role of Mitochondria in Cleft Pathology: A Forgotten General?

Orofacial clefts (OFC) are one of the most common birth defects that affects the lip, palate, or lip and palate of an infant. The deterioration of clefts is multifactorial involving multiple genes, various interactions from environmental factor and most forgotten, mitochondrial abnormality. The aim of this review is to highlight the importance of mitochondrial activity related to non-syndromic OFC deformity. Despite its important role in cells, the study on mitochondrial activity in cleft pathology was scarce and almost forgotten compared to other genetic investigations. This systematic review was completed based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) checklist. The literature search was done via the following databases: Google Scholar, Pubmed and Scopus with a total of nine studies of mitochondrial abnormalities were included. We hypothesise that mitochondria play an important role in early craniofacial development. A decreased in its function or activity may result in cleft lip formation. Hence, we would like to shed light on the remarkable role of mitochondria activity in the pathogenesis of non-syndromic OFC.

Neuroimaging appearance of hypothalamic hamartomas in monozygotic twins with Pallister-Hall syndrome: case report and review of the literature

BackgroundPallister-Hall syndrome (OMIM #146510) is a rare autosomal dominant condition caused by a mutation in the GLI3 gene. The cardinal feature of Pallister-Hall syndrome is the presence of hypothalamic hamartomas, which may manifest with seizures, panhypopituitarism and visual impairment. In Pallister-Hall syndrome, dysplastic histogenetic processes responsible for hypothalamic hamartomas are thought to disrupt early craniofacial development. The clinical presentation of Pallister-Hall syndrome may include: characteristic facies (low-set and posteriorly angulated ears, short nose with flat nasal bridge), cleft palate and uvula, bifid epiglottis and laryngotracheal cleft, limb anomalies (e.g., polysyndactyly, short limbs and nail dysplasia), anal atresia, genitourinary abnormalities and congenital heart defects.Case presentationWe report the case of two monochorionic diamniotic twins diagnosed with Pallister-Hall syndrome during the neonatal period, after the identification of a hypothalamic hamartoma on day 1 by cerebral ultrasound scan, later confirmed by brain magnetic resonance imaging. Cerebral ultrasound and magnetic resonance imaging presentations were identical in both twins.Discussion and conclusionsWe review previously published cases (four reports) of hypothalamic hamartomas identified via cerebral ultrasound and compare reported ultrasonographic features. Main differential diagnoses based on cerebral ultrasound findings are discussed. Full description of typical magnetic resonance imaging appearance is also provided. This is the first case reported in the literature of monochorionic diamniotic twins affected by genetically confirmed Pallister-Hall syndrome with identical hypothalamic hamartomas at cerebral ultrasound and magnetic resonance imaging. Moreover, this paper adds to the existing literature on the sonographic appearance of hypothalamic hamartomas. Considering the consistency in hypothalamic hamartomas’ sonographic appearance, we support the use of cerebral ultrasound as a first-line neuroimaging modality in case of clinical suspicion of Pallister-Hall syndrome.Graphical

BMP3 is a novel locus involved in the causality of ocular coloboma

Coloboma, a congenital disorder characterized by gaps in ocular tissues, is caused when the choroid fissure fails to close during embryonic development. Several loci have been associated with coloboma, but these represent less than 40% of those that are involved with this disease. Here, we describe a novel coloboma-causing locus, BMP3. Whole exome sequencing and Sanger sequencing of patients with coloboma identified three variants in BMP3, two of which are predicted to be disease causing. Consistent with this, bmp3 mutant zebrafish have aberrant fissure closure. bmp3 is expressed in the ventral head mesenchyme and regulates phosphorylated Smad3 in a population of cells adjacent to the choroid fissure. Furthermore, mutations in bmp3 sensitize embryos to Smad3 inhibitor treatment resulting in open choroid fissures. Micro CT scans and Alcian blue staining of zebrafish demonstrate that mutations in bmp3 cause midface hypoplasia, suggesting that bmp3 regulates cranial neural crest cells. Consistent with this, we see active Smad3 in a population of periocular neural crest cells, and bmp3 mutant zebrafish have reduced neural crest cells in the choroid fissure. Taken together, these data suggest that Bmp3 controls Smad3 phosphorylation in neural crest cells to regulate early craniofacial and ocular development.

Essential function and targets of BMP signaling during midbrain neural crest delamination

BMP signaling plays iterative roles during vertebrate neural crest development from induction through craniofacial morphogenesis. However, far less is known about the role of BMP activity in cranial neural crest epithelial-to-mesenchymal transition and delamination. By measuring canonical BMP signaling activity as a function of time from specification through early migration of avian midbrain neural crest cells, we found elevated BMP signaling during delamination stages. Moreover, inhibition of canonical BMP activity via a dominant negative mutant Type I BMP receptor showed that BMP signaling is required for neural crest migration from the midbrain, independent from an effect on EMT and delamination. Transcriptome profiling on control compared to BMP-inhibited cranial neural crest cells identified novel BMP targets during neural crest delamination and early migration including targets of the Notch pathway that are upregulated following BMP inhibition. These results suggest potential crosstalk between the BMP and Notch pathways in early migrating cranial neural crest and provide novel insight into mechanisms regulated by BMP signaling during early craniofacial development.

Shortened primary cilia in palatal mesenchyme of Specc1l ∆CCD2/∆CCD2 mouse model of cleft palate

Orofacial clefts are among the most common congenital malformations, affecting approximately 1 in 700 births. Mutations in SPECC1L have been identified in patients with syndromic and nonsyndromic cleft lip and/or palate. Syndromic SPECC1Lmutations cluster in the second coiled coil domain (CCD2), which facilitates interaction of this cytoskeletal protein with microtubules. Our recent studies indicate that mice with an in-frame deletion of SPECC1L-CCD2 exhibit cleft palate and exencephaly in a dominant-negative manner. Notably, orofacial clefts and exencephaly are common manifestations of ciliopathies – human disorders which arise from disruption of cilia – but an association between SPECC1L and cilia has not been reported. We investigated cilia in E13.5 Specc1l∆CCD2/∆CCD2 mutant palatal shelves. SPECC1L localizes to the cytoplasm and around the cilia base in wild-type palatal mesenchyme, but this localization is diminished in Specc1l∆CCD2/∆CCD2 palatal mesenchyme. In addition, primary cilia lengths are decreased in Specc1l∆CCD2/∆CCD2 palatal mesenchyme and epithelium relative to wild-type, on both the lingual and buccal sides of the palate. We hypothesize that an intracellular trafficking defect in the palatal mesenchyme results in shortened cilia and that the shortened cilia affects signaling in the palatal mesenchyme. Since the IFT-A mouse mutant, Thm1aln/aln, shares overlapping phenotypes with Specc1l mutant mice, including cleft palate, exencephaly, and shortened cilia, we crossed the two mutants to look for a genetic interaction. Indeed, ~30% of double heterozygous Specc1l∆CCD2/+;Thm1aln/+ mice show cleft palate. Interestingly, none of the double heterozygous mice showed exencephaly, indicating a palate specificity of the genetic interaction. Previous studies have shown that conditional loss of Thm1 in neural crest cells (NCCs), which give rise to the palatal mesenchyme, results in cleft palate, and that Specc1l deficiency leads to NCC delamination defect. Our recent analysis of Specc1l deficient embryos demonstrates that cilia are shorter in mutant NCC even compared with surrounding non-NCCs. While SPECC1L is broadly expressed during early craniofacial development, its expression is stronger in migrating NCCs. Thus, we propose that the genetic interaction between Specc1l and Thm1 initiates in the NCC. Overall, our studies indicate a novel role for SPECC1L in ciliogenesis and NCC function.

Mcrs1 interacts with Six1 to influence early craniofacial and otic development

The Six1 transcription factor plays a major role in craniofacial development. Mutations in SIX1 and its co-factor, EYA1, are causative for about 50% of Branchio-otic/Branchio-oto-renal syndrome (BOR) patients, who are characterized by variable craniofacial, otic and renal malformations. We previously screened for other proteins that might interact with Six1 to identify additional genes that may play a role in BOR, and herein characterize the developmental role of one of them, Microspherule protein 1 (Mcrs1). We found that in cultured cells, Mcrs1 bound to Six1 and in both cultured cells and embryonic ectoderm reduced Six1-Eya1 transcriptional activation. Knock-down of Mcrs1 in embryos caused an expansion of the domains of neural plate genes and two genes expressed in both the neural plate and neural crest (zic1, zic2). In contrast, two other genes expressed in pre-migratory neural crest (foxd3, sox9) were primarily reduced. Cranial placode genes showed a mixture of expanded and diminished expression domains. At larval stages, loss of Mcrs1 resulted in a significant reduction of otic vesicle gene expression concomitant with a smaller otic vesicle volume. Experimentally increasing Mcrs1 above endogenous levels favored the expansion of neural border and neural crest gene domains over cranial placode genes; it also reduced otic vesicle gene expression but not otic vesicle volume. Co-expression of Mcrs1 and Six1 as well as double knock-down and rescue experiments establish a functional interaction between Mcrs1 and Six1 in the embryo, and demonstrate that this interaction has an important role in the development of craniofacial tissues including the otic vesicle.

Cytotoxicity assay using a human pluripotent stem cell-derived cranial neural crest cell model.

Cleft lip and palate are the most common congenital abnormalities that occur early in pregnancy. The majority of cranial mesenchyme is derived from cranial neural crest cells that differentiate into odontoblasts, cartilage, craniofacial bone, and connective tissue. A subset of these cells differentiates into cranial ganglia. We have previously reported an induction protocol of cranial neural crest cell-like cells from human pluripotent stem cells. This study tested detection of the cytotoxic sensitivities of dental materials, including titanium ions, palladium ions, and hydroxyethyl methacrylate, on the cell viability of induced cranial neural crest cell-like cells (iNC-LCs) derived from Tic human induced pluripotent stem cell (hiPSC) line. Further, the sensitivity was compared with those of human fetal lung fibroblastic cell line MRC-5, which is origin of Tic hiPSC, and osteoblastic cell line MC3T3-E1 which was derived from mouse calvaria. The results suggested that this cell-based assay system using iNC-LCs is a potential method for in vitro screening as an alternative to animal testing to predict toxic effects of dental materials on early craniofacial development.

Regulation of cranial neural crest cell fate by Irf6 and Twist1 interaction

A wide variety of common craniofacial birth defects and pediatric cancers arise from errors in the development of cranial neural crest cells (CNCC) that give rise to craniofacial skeletal and peripheral nervous systems. Identification of the genetic and environmental factors that regulate cell fate of CNCCs is crucial for uncovering the causes behind craniofacial disorders. Our lab has identified a dual‐transcription factor pathway that regulates CNCCs during EMT and migration. Initially, we identified a causative mutation in a TWIST1 binding site within an Interferon Regulatory Factor 6 (IRF6) enhancer in a multi‐generational family affected with syndromic cleft lip and palate called Van der Woude syndrome. Our subsequent animal work has shown that Twist1 and Irf6 genetically interact during early craniofacial development, and that the compound heterozygotes exhibit craniofacial abnormalities. We recently demonstrated that Irf6 is required for neural tube and CNCC development and that it interacts with Twist1 during EMT and migration of CNCCs. We also showed that TWIST1 is highly phosphorylated in CNCCs and its phosphorylation is crucial for regulating Irf6 and potentially miR10 family members in CNCC‐derived craniofacial tissues. Our recent in‐vivo and neural tube explants using dual fluorescent cell tracing system showed that Twist1 conditional knockout (CKO) in CNCCs significantly reduced cell delamination and disrupted EMT. The detached Twist1 CKO in CNCCs retained their epithelial signatures and migrated as clusters of epithelial‐like cells over significantly shorter distances. Finally, Twist1 phospho‐incompetent mice for two serine residues were recently generated to determine their impact on TWIST1 activity. Our preliminary results showed that Twist1S68A/S68A phospho‐mutant mice have craniofacial bone defects and forebrain hemorrhage.Support or Funding InformationUTHealth start‐up funds and a small grant from theRolanette and Berdon Lawrence Bone Disease Program of Texas

Vitamin D Receptor Signaling Regulates Craniofacial Cartilage Development in Zebrafish.

Vitamin D plays essential roles in supporting the skeletal system. The active form of vitamin D functions through the vitamin D receptor (VDR). A hereditary vitamin-D-resistant rickets with facial dysmorphism has been reported, but the involvement of VDR signaling during early stages of craniofacial development remains to be elucidated. The present study investigated whether VDR signaling is implicated in zebrafish craniofacial cartilage development using a morpholino-based knockdown approach. Two paralogous VDR genes, vdra and vdrb, have been found in zebrafish embryos. Loss-of-vdra has no discernible effect on cartilage elements, whereas loss-of-vdrb causes reduction and malformation of craniofacial cartilages. Disrupting both vdra and vdrb leads to more severe defects or complete loss of cartilage. Notably, knockdown of vdrb results in elevated expression of follistatin a (fsta), a bone morphogenetic protein (BMP) antagonist, in the adjacent pharyngeal endoderm. Taken together, these findings strongly indicate that VDR signaling is required for early craniofacial cartilage development in zebrafish.

The Silent Treatment: miR199 Family Silences Shh during Craniofacial Development

Early craniofacial development requires precise timing and spatial regulation of key signaling pathways in order for proper facial structures to form. Perturbations, particularly in the sonic hedgehog (Shh) signaling pathway, can result in craniofacial birth defects that cause significant harm and financial costs. microRNAs (miRNA) play many roles in developing systems by repressing gene expression, but despite the enormous number of miRNAs that have been identified, few have been related to biological processes through direct targets. Here we identified the miR199 family as Shh‐regulated miRNAs during development of the upper jaw in a chick model.We performed a miRNA microarray analysis on chick embryonic ectoderm before (stage HH18) and after (stage HH22) formation of the Frontonasal Ectodermal Zone (FEZ) and after activating or blocking SHH signaling in the brain. We identified a family of miRNAs (miR199b, mir199* and miR199) that appeared to be regulated by SHH signaling in the brain. These are increased between stages HH18 and HH22, and increase upon activation of Shh signaling and decrease upon blockade of Shh signaling, and these data were confirmed by qPCR. To assess the function of this family of miRNAs during facial development, we performed miR199 knock‐down and overexpression experiments and examined the phenotypic and molecular changes. Up‐regulation of each miRNA led to decreased Shh expression in the FEZ and facial malformations that are consistent with decreased Shh signaling in the face. Using antagomirs to knockdown each miRNA, we observed that Shh expression was expanded and the faces were wider, reminiscent of SHH gain‐of‐function experiments. Hence, it appears that expression of these miRNAs in the FEZ are regulated by SHH signaling from the brain, and these miRNAs appear to regulate SHH signaling from the FEZ. We then identified Smurf2, Map3k4, Hif1alpha, and Dyrk1a as targets of the miR‐199 family of miRNAs via mir‐base. We confirmed that each of these genes behaved like targets in miR‐gain and loss‐of‐function experiments described above. Using pmirGLO luciferase, we identified MAP3K4 and HIF as direct targets of miR199. Finally, we generated a miRNA knockdown cassette to reduce expression of Hif1α and Map3k4. Blocking HIF1α resulted in a large reduction of Shh expression in the FEZ, and resulted in severe craniofacial malformations, while blocking Map3k4 altered facial morphology, resulting in altered mediolateral beak development at later stages. Overall, our results demonstrate that Shh signaling within the brain contributes to facial development by regulating a family of miRNAs that then regulate the expression of Shh in the FEZ via targeting the transcription factor Hif1α.Support or Funding InformationThis work was supported by the National Institutes of Health (R01 DE018234‐A1)This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Neural Crest Cell Models of Development and Toxicity: Cytotoxicity Assay Using Human Pluripotent Stem Cell-Derived Cranial Neural Crest Cell Model.

Cranial neural crest cells (NCCs) migrate to the branchial arches and give rise to the majority of cranial mesenchyme that eventually differentiates into odontoblasts, cartilage, craniofacial bone, and connective tissue; a subset of these cells differentiate into cranial ganglia. Here we present a protocol that describes directed differentiation method of human pluripotent stem cells into cranial NCC-like cells and a cytotoxicity assay using hPSC-derived cranial NCC-like cells. This cell-based assay system allows for high-sensitive cytotoxicity detection of test chemicals. These methods can be applied to predict drug/chemical toxicity effect on early craniofacial development.

Molecular Analysis of Gli3, Ihh, Rab23, and Jag1 in a Rabbit Model of Craniosynostosis: Likely Exclusion as the Loci of Origin.

Craniosynostosis (CS) involves the premature fusion of one or more cranial sutures. The etiology of CS is complex and mutations in more than 50 distinct genes have been causally linked to the disorder. Many of the genes that have been associated with CS in humans play an essential role in tissue patterning and early craniofacial development. Among these genes are members of the Hedgehog (HH) and Notch signal transduction pathways, including the GLI family member Gli3, Indian Hedgehog ( Ihh), the RAS oncogene family member Rab23, and the Notch ligand JAGGED1 ( Jag1). We have previously described a colony of rabbits with a heritable pattern of coronal suture synostosis, although the genetic basis for synostosis within this model remains unknown. The present study was performed to determine if coding errors in Gli3, Ihh, Rab23, or Jag1 could be causally linked to craniosynostosis in this unique animal model. Sequencing of cDNA templates was performed using samples obtained from wild-type and craniosynostotic rabbits. Several nucleotide polymorphisms were identified in Gli3, Ihh, and Rab23, although these variants failed to segregate by phenotype. No nucleotide polymorphisms were identified in Jag1. These data indicate that the causal locus for heritable craniosynostosis in this rabbit model is not located within the protein coding regions of Gli3, Ihh, Rab23, or Jag1.

Fluctuating dental asymmetry in rabbits with familial nonsyndromic coronal suture synostosis

Fluctuating dental asymmetry has been linked to conditions of unstable pre- and peri-natal development. Familial, nonsyndromic craniosynostosis disrupts early craniofacial development through localized excessive calvarial ossification leading to the premature fusion of the calvarial sutures. Such abnormal gene expression may also produce systemic stress resulting in developmental instability, thereby affecting normal trait symmetry. The present study was designed to test this hypothesis by examining fluctuating dental asymmetry in an inbred strain of rabbits with familial, nonsyndromic coronal craniosynostosis. The mesiodistal (MD) and buccolingual (BL) dimensions of the right and left maxillary first molars were measured in four groups of New Zealand white rabbits (N=176; n=40 with early-onset synostosis, n=65 with delayed-onset synostosis, n=46 in-colony, phenotypically normal rabbits, and n=25 wild-type normal controls). For each variable, raw signed asymmetry was calculated (left-right) and tested for assumptions of fluctuating asymmetry (i.e., normality and non-directionality). Any group that did not meet these assumptions was excluded from further analysis. Using a standard size-adjusted, fluctuating asymmetry index, mean fluctuating asymmetry was calculated and compared across groups with non-parametric statistics. For the MD dimension, no significant (p > 0.05) group differences in mean fluctuating asymmetry were observed among groups. In contrast, rabbits with early-onset synostosis had significantly (p < 0.05) more fluctuating asymmetry in the BL dimension compared to wild-type controls. Results demonstrate increased fluctuating dental asymmetry in rabbits with nonsyndromic, early-onset coronal suture synostosis and suggest that the molecular events producing suture synostosis locally may have also have systemic effects. Knowledge of these systemic interactions may contribute to a fuller understanding of the phenotypic spectrum observed in individuals with nonsyndromic craniosynostosis.

COLEC10 is mutated in 3MC patients and regulates early craniofacial development.

3MC syndrome is an autosomal recessive heterogeneous disorder with features linked to developmental abnormalities. The main features include facial dysmorphism, craniosynostosis and cleft lip/palate; skeletal structures derived from cranial neural crest cells (cNCC). We previously reported that lectin complement pathway genes COLEC11 and MASP1/3 are mutated in 3MC syndrome patients. Here we define a new gene, COLEC10, also mutated in 3MC families and present novel mutations in COLEC11 and MASP1/3 genes in a further five families. The protein products of COLEC11 and COLEC10, CL-K1 and CL-L1 respectively, form heteromeric complexes. We show COLEC10 is expressed in the base membrane of the palate during murine embryo development. We demonstrate how mutations in COLEC10 (c.25C>T; p.Arg9Ter, c.226delA; p.Gly77Glufs*66 and c.528C>G p.Cys176Trp) impair the expression and/or secretion of CL-L1 highlighting their pathogenicity. Together, these findings provide further evidence linking the lectin complement pathway and complement factors COLEC11 and COLEC10 to morphogenesis of craniofacial structures and 3MC etiology.

Constraint and diversification of developmental trajectories in cichlid facial morphologies.

BackgroundA major goal of evolutionary biology is to understand the origins of phenotypic diversity. Changes in development, for instance heterochrony, can be a potent source of phenotypic variation. On the other hand, development can also constrain the spectrum of phenotypes that can be produced. In order to understand these dual roles of development in evolution, we examined the developmental trajectory of a trait central to the extensive adaptive radiation of East African cichlid fishes: craniofacial adaptations that allow optimal exploitation of ecological niches. Specifically, we use geometric morphometric analysis to compare morphological ontogenies among six species of Lake Malawi cichlids (n > 500 individuals) that span a major ecomorphological axis. We further evaluate how modulation of Wnt signaling impacts the long-term developmental trajectory of facial development.ResultsWe find that, despite drastic differences in adult craniofacial morphologies, there are general similarities in the path of craniofacial ontogeny among species, suggesting that natural selection is working within a conserved developmental program. However, we also detect species-specific differences in the timing, direction, and/or duration of particular developmental trajectories, including evidence of heterochrony. Previous work in cichlids and other systems suggests that species-specific differences in adult morphology are due to changes in molecular signaling pathways that regulate early craniofacial development. In support of this, we demonstrate that modulation of Wnt signaling at early stages can shift a developmental trajectory into morphospace normally occupied by another species. However, without sustained modulation, craniofacial shape can recover by juvenile stages. This underscores the idea that craniofacial development is robust and that adult head shapes are the product of many molecular changes acting over extended periods of development.ConclusionsOur results are consistent with the hypothesis that development acts to both constrain and promote morphological diversity. They also illustrate the modular nature of the craniofacial skeleton and hence the ability of selection to act upon distinct anatomical features in an independent manner. We propose that trophic diversity among cichlids has been achieved via shifts in both specific (e.g., stage-specific changes in gene expression) and global (e.g., heterochrony) ontogenetic processes acting within a conserved developmental program.Electronic supplementary materialThe online version of this article (doi:10.1186/s13227-015-0020-8) contains supplementary material, which is available to authorized users.