Cross-regulatory interactions between Fgf8 and Shh in the avian frontonasal prominence

Mammalian face as an evolutionary novelty

The anterior end of the mammalian face is characteristically composed of a semimotile nose, not the upper jaw as in other tetrapods. Thus, the therian nose is covered ventrolaterally by the "premaxilla," and the osteocranium possesses only a single nasal aperture because of the absence of medial bony elements. This stands in contrast to those in other tetrapods in whom the premaxilla covers the rostral terminus of the snout, providing a key to understanding the evolution of the mammalian face. Here, we show that the premaxilla in therian mammals (placentals and marsupials) is not entirely homologous to those in other amniotes; the therian premaxilla is a composite of the septomaxilla and the palatine remnant of the premaxilla of nontherian amniotes (including monotremes). By comparing topographical relationships of craniofacial primordia and nerve supplies in various tetrapod embryos, we found that the therian premaxilla is predominantly of the maxillary prominence origin and associated with mandibular arch. The rostral-most part of the upper jaw in nonmammalian tetrapods corresponds to the motile nose in therian mammals. During development, experimental inhibition of primordial growth demonstrated that the entire mammalian upper jaw mostly originates from the maxillary prominence, unlike other amniotes. Consistently, cell lineage tracing in transgenic mice revealed a mammalian-specific rostral growth of the maxillary prominence. We conclude that the mammalian-specific face, the muzzle, is an evolutionary novelty obtained by overriding ancestral developmental constraints to establish a novel topographical framework in craniofacial mesenchyme.

Insights Into the Complexity of Craniofacial Development From a Cellular Perspective

The head represents the most complex part of the body and a distinctive feature of the vertebrate body plan. This intricate structure is assembled during embryonic development in the four-dimensional process of morphogenesis. The head integrates components of the central and peripheral nervous system, sensory organs, muscles, joints, glands, and other specialized tissues in the framework of a complexly shaped skull. The anterior part of the head is referred to as the face, and a broad spectrum of facial shapes across vertebrate species enables different feeding strategies, communication styles, and diverse specialized functions. The face formation starts early during embryonic development and is an enormously complex, multi-step process regulated on a genomic, molecular, and cellular level. In this review, we will discuss recent discoveries that revealed new aspects of facial morphogenesis from the time of the neural crest cell emergence till the formation of the chondrocranium, the primary design of the individual facial shape. We will focus on molecular mechanisms of cell fate specification, the role of individual and collective cell migration, the importance of dynamic and continuous cellular interactions, responses of cells and tissues to generated physical forces, and their morphogenetic outcomes. In the end, we will examine the spatiotemporal activity of signaling centers tightly regulating the release of signals inducing the formation of craniofacial skeletal elements. The existence of these centers and their regulation by enhancers represent one of the core morphogenetic mechanisms and might lay the foundations for intra- and inter-species facial variability.

Evolutionary and ontogenetic changes of the anatomical organization and modularity in the skull of archosaurs

Comparative anatomy studies of the skull of archosaurs provide insights on the mechanisms of evolution for the morphologically and functionally diverse species of crocodiles and birds. One of the key attributes of skull evolution is the anatomical changes associated with the physical arrangement of cranial bones. Here, we compare the changes in anatomical organization and modularity of the skull of extinct and extant archosaurs using an Anatomical Network Analysis approach. We show that the number of bones, their topological arrangement, and modular organization can discriminate birds from non-avian dinosaurs, and crurotarsans. We could also discriminate extant taxa from extinct species when adult birds were included. By comparing within the same framework, juveniles and adults for crown birds and alligator (Alligator mississippiensis), we find that adult and juvenile alligator skulls are topologically similar, whereas juvenile bird skulls have a morphological complexity and anisomerism more similar to those of non-avian dinosaurs and crurotarsans than of their own adult forms. Clade-specific ontogenetic differences in skull organization, such as extensive postnatal fusion of cranial bones in crown birds, can explain this pattern. The fact that juvenile and adult skulls in birds do share a similar anatomical integration suggests the presence of a specific constraint to their ontogenetic growth.

Is it possible to recognize children diagnosed with ADHD from their facial anthropometric measures? A case-control study

The recent main focus of the researches on Attention-deficit Hyperactivity Disorder is on identifying behavioral phenotypes. For this purpose, neuroanatomical factors have recently become a focus. This study aimed to investigate whether the individuals diagnosed with Attention-deficit Hyperactivity Disorder differ from healthy individuals in terms of facial anthropometric measurements. Forty children, diagnosed with Attention-deficit Hyperactivity Disorder, were included in the study as the case group, and forty healthy children were included in the study as the control group. Two photographs were taken from the facial region, and anthropometric measurements were performed using the computer program "Image J" in the computer environment. It was found that a strong relationship between Attention-deficit Hyperactivity Disorder and nasal width, ear length and upper face debt length. The results obtained from the research support the knowledge that there is a close relationship between the forebrain development process and the facial development process during the embryonic development process.

FGF8 and Shh promote the survival and maintenance of multipotent neural crest progenitors

The developmental mechanisms that control the building of the complex head of vertebrates and particularly, facial skeletogenesis, remain poorly known. Progenitor cells derived from the embryonic neural crest (NC) are the major constituents and players of facial tissue development. Deciphering the cellular and molecular machinery that controls NC cell (NCC) differentiation into bone, cartilage, fat and other mesenchymal tissues, is thus a main issue for understanding vertebrate facial variations. In this work, we investigated the effects of fibroblast growth factor 8 (FGF8) and Sonic Hedgehog (Shh), two signaling molecules essential for craniofacial development, on the in vitro differentiation and multipotentiality of mesencephalic NCCs (MNCCs) isolated from the quail embryo. Comparison of distinct temporal treatments with FGF8 and/or Shh showed that both promoted chondrogenesis of MNCCs by increasing the amount and size of cartilage nodules. Higher rates of chondrogenesis were observed when MNCCs were treated with FGF8 during the migration phase, thus mimicking the in vivo exposure of migrating NCCs to FGF8 secreted by the isthmic brain signaling center. An in vitro cell cloning assay revealed that, after concomitant treatment with FGF8 and Shh, about 80% of NC progenitors displayed chondrogenic potential, while in untreated cultures, only 18% exhibited this potential. In addition, colony analysis showed for the first time the existence of a highly multipotent progenitor able to clonally give rise to adipocytes in addition to other cephalic NC phenotypes (i.e. glial cells, neurons, melanocytes, smooth muscle cells and chondrocytes) (GNMFCA progenitor). This progenitor was observed only when clonal cultures were treated with both FGF8 and Shh. Several other types of multipotent cells, which generated four, five or six distinct phenotypes, accounted for 55% of the progenitors in FGF8 and Shh treated cultures, versus 13,5% in the untreated ones. Together, these data reveal an essential role for both FGF8 and Shh together in maintenance of MNCC multipotentiality by favoring the development of NC progenitors endowed with a broad array of mesectodermal potentials.

Fgf8 Expression and Degradation of Retinoic Acid Are Required for Patterning a High-Acuity Area in the Retina

Species that are highly reliant on their visual system have a specialized retinal area subserving high-acuity vision, e.g., the fovea in humans. Although of critical importance for our daily activities, little is known about the mechanisms driving the development of retinal high-acuity areas (HAAs). Using the chick as a model, we found a precise and dynamic expression pattern of fibroblast growth factor 8 (Fgf8) in the HAA anlage, which was regulated by enzymes that degrade retinoic acid (RA). Transient manipulation of RA signaling, or reduction of Fgf8 expression, disrupted several features of HAA patterning, including photoreceptor distribution, ganglion cell density, and organization of interneurons. Notably, patterned expression of RA signaling components was also found in humans, suggesting that RA also plays a role in setting up the human fovea.

Using frogs faces to dissect the mechanisms underlying human orofacial defects

In this review I discuss how Xenopus laevis is an effective model to dissect the mechanisms underlying orofacial defects. This species has been particularly useful in studying the understudied structures of the developing face including the embryonic mouth and primary palate. The embryonic mouth is the first opening between the foregut and the environment and is critical for adult mouth development. The final step in embryonic mouth formation is the perforation of a thin layer of tissue covering the digestive tube called the buccopharyngeal membrane. When this tissue does not perforate in humans it can pose serious health risks for the fetus and child. The primary palate forms just dorsal to the embryonic mouth and in non-amniotes it functions as the roof of the adult mouth. Defects in the primary palate result in a median oral cleft that appears similar across the vertebrates. In humans, these median clefts are often severe and surgically difficult to repair. Xenopus has several qualities that make it advantageous for craniofacial research. The free living embryo has an easily accessible face and we have also developed several new tools to analyze the development of the region. Further, Xenopus is readily amenable to chemical screens allowing us to uncover novel gene-environment interactions during orofacial development, as well as to define underlying mechanisms governing such interactions. In conclusion, we are utilizing Xenopus in new and innovative ways to contribute to craniofacial research.

A molecular mechanism for the origin of a key evolutionary innovation, the bird beak and palate, revealed by an integrative approach to major transitions in vertebrate history

The avian beak is a key evolutionary innovation whose flexibility has permitted birds to diversify into a range of disparate ecological niches. We approached the problem of the mechanism behind this innovation using an approach bridging paleontology, comparative anatomy, and experimental developmental biology. First, we used fossil and extant data to show the beak is distinctive in consisting of fused premaxillae that are geometrically distinct from those of ancestral archosaurs. To elucidate underlying developmental mechanisms, we examined candidate gene expression domains in the embryonic face: the earlier frontonasal ectodermal zone (FEZ) and the later midfacial WNT-responsive region, in birds and several reptiles. This permitted the identification of an autapomorphic median gene expression region in Aves. To test the mechanism, we used inhibitors of both pathways to replicate in chicken the ancestral amniote expression. Altering the FEZ altered later WNT responsiveness to the ancestral pattern. Skeletal phenotypes from both types of experiments had premaxillae that clustered geometrically with ancestral fossil forms instead of beaked birds. The palatal region was also altered to a more ancestral phenotype. This is consistent with the fossil record and with the tight functional association of avian premaxillae and palate in forming a kinetic beak.

A dynamic Shh expression pattern, regulated by SHH and BMP signaling, coordinates fusion of primordia in the amniote face

The mechanisms of morphogenesis are not well understood, yet shaping structures during development is essential for establishing correct organismal form and function. Here, we examine mechanisms that help to shape the developing face during the crucial period of facial primordia fusion. This period of development is a time when the faces of amniote embryos exhibit the greatest degree of similarity, and it probably results from the necessity for fusion to occur to establish the primary palate. Our results show that hierarchical induction mechanisms, consisting of iterative signaling by Sonic hedgehog (SHH) followed by Bone morphogenetic proteins (BMPs), regulate a dynamic expression pattern of Shh in the ectoderm covering the frontonasal (FNP) and maxillary (MxP) processes. Furthermore, this Shh expression domain contributes to the morphogenetic processes that drive the directional growth of the globular process of the FNP toward the lateral nasal process and MxP, in part by regulating cell proliferation in the facial mesenchyme. The nature of the induction mechanism that we discovered suggests that the process of fusion of the facial primordia is intrinsically buffered against producing maladaptive morphologies, such as clefts of the primary palate, because there appears to be little opportunity for variation to occur during expansion of the Shh expression domain in the ectoderm of the facial primordia. Ultimately, these results might explain why this period of development constitutes a phylotypic stage of facial development among amniotes.

Hand1 phosphoregulation within the distal arch neural crest is essential for craniofacial morphogenesis

In this study we examine the consequences of altering Hand1 phosphoregulation in the developing neural crest cells (NCCs) of mice. Whereas Hand1 deletion in NCCs reveals a nonessential role for Hand1 in craniofacial development and embryonic survival, altering Hand1 phosphoregulation, and consequently Hand1 dimerization affinities, in NCCs results in severe mid-facial clefting and neonatal death. Hand1 phosphorylation mutants exhibit a non-cell-autonomous increase in pharyngeal arch cell death accompanied by alterations in Fgf8 and Shh pathway expression. Together, our data indicate that the extreme distal pharyngeal arch expression domain of Hand1 defines a novel bHLH-dependent activity, and that disruption of established Hand1 dimer phosphoregulation within this domain disrupts normal craniofacial patterning.

Neural crest cells pattern the surface cephalic ectoderm during FEZ formation

BACKGROUND

Multiple fibroblast growth factor (Fgf) ligands are expressed in the forebrain and facial ectoderm, and vascular endothelial growth factor (VEGF) is expressed in the facial ectoderm. Both pathways activate the MAP kinase cascade and can be suppressed by SU5402. We placed a bead soaked in SU5402 into the brain after emigration of neural crest cells was complete.

RESULTS

Within 24 hr we observed reduced pMEK and pERK staining that persisted for at least 48 hr. This was accompanied by significant apoptosis in the face. By day 15, the upper beaks were truncated. Molecular changes in the FNP were also apparent. Normally, Shh is expressed in the frontonasal ectodermal zone and controls patterned growth of the upper jaw. In treated embryos, Shh expression was reduced. Both the structural and molecular deficits were mitigated after transplantation of FNP-derived mesenchymal cells.

CONCLUSIONS

Thus, mesenchymal cells actively participate in signaling interactions of the face, and the absence of neural crest cells in neurocristopathies may not be merely structural.

Wnt/β-catenin signaling and Msx1 promote outgrowth of the maxillary prominences

Facial morphogenesis requires a series of precisely orchestrated molecular events to promote the growth and fusion of the facial prominences. Cleft palate (CP) results from perturbations in this process. The transcriptional repressor Msx1 is a key participant in these molecular events, as demonstrated by the palatal clefting phenotype observed in Msx1^−/− embryos. Here, we exploited the high degree of conservation that exists in the gene regulatory networks that shape the faces of birds and mice, to gain a deeper understanding of Msx1 function in CP. Histomorphometric analyses indicated that facial development was disrupted as early as E12.5 in Msx1^−/− embryos, long before the palatal shelves have formed. By mapping the expression domain of Msx1 in E11.5 and E12.5 embryos, we found the structures most affected by loss of Msx1 function were the maxillary prominences. Maxillary growth retardation was accompanied by perturbations in angiogenesis that preceded the CP phenotype. Experimental chick manipulations and in vitro assays showed that the regulation of Msx1 expression by the Wnt/β-catenin pathway is highly specific. Our data in mice and chicks indicate a conserved role for Msx1 in regulating the outgrowth of the maxillary prominences, and underscore how imbalances in Msx1 function can lead of growth disruptions that manifest as CP.

Facial phenotypes in subgroups of prepubertal boys with autism spectrum disorders are correlated with clinical phenotypes

BACKGROUND

The brain develops in concert and in coordination with the developing facial tissues, with each influencing the development of the other and sharing genetic signaling pathways. Autism spectrum disorders (ASDs) result from alterations in the embryological brain, suggesting that the development of the faces of children with ASD may result in subtle facial differences compared to typically developing children. In this study, we tested two hypotheses. First, we asked whether children with ASD display a subtle but distinct facial phenotype compared to typically developing children. Second, we sought to determine whether there are subgroups of facial phenotypes within the population of children with ASD that denote biologically discrete subgroups.

METHODS

The 3dMD cranial System was used to acquire three-dimensional stereophotogrammetric images for our study sample of 8- to 12-year-old boys diagnosed with essential ASD (n = 65) and typically developing boys (n = 41) following approved Institutional Review Board protocols. Three-dimensional coordinates were recorded for 17 facial anthropometric landmarks using the 3dMD Patient software. Statistical comparisons of facial phenotypes were completed using Euclidean Distance Matrix Analysis and Principal Coordinates Analysis. Data representing clinical and behavioral traits were statistically compared among groups by using χ2 tests, Fisher's exact tests, Kolmogorov-Smirnov tests and Student's t-tests where appropriate.

RESULTS

First, we found that there are significant differences in facial morphology in boys with ASD compared to typically developing boys. Second, we also found two subgroups of boys with ASD with facial morphology that differed from the majority of the boys with ASD and the typically developing boys. Furthermore, membership in each of these distinct subgroups was correlated with particular clinical and behavioral traits.

CONCLUSIONS

Boys with ASD display a facial phenotype distinct from that of typically developing boys, which may reflect alterations in the prenatal development of the brain. Subgroups of boys with ASD defined by distinct facial morphologies correlated with clinical and behavioral traits, suggesting potentially different etiologies and genetic differences compared to the larger group of boys with ASD. Further investigations into genes involved in neurodevelopment and craniofacial development of these subgroups will help to elucidate the causes and significance of these subtle facial differences.

Shh and Gli3 regulate formation of the telencephalic-diencephalic junction and suppress an isthmus-like signaling source in the forebrain

In human holoprosencephaly (HPE), the forebrain does not separate fully into two hemispheres. Further, the border between the telencephalon and diencephalon, the telencephalic/diencephalic junction (TDJ), is often indistinct, and the ventricular system can be blocked at the third ventricle, creating a forebrain 'holosphere'. Mice deficient in Sonic Hedgehog (Shh) have previously been described to show HPE and associated cyclopia. Here we report that the third ventricle is blocked in Shh null mutants, similar to human HPE, and that characteristic telencephalic and diencephalic signaling centers, the cortical hem and zona limitans intrathalamica (ZLI), are merged, obliterating the TDJ. The resulting forebrain holosphere comprises Foxg1-positive telencephalic- and Foxg1-negative diencephalic territories. Loss of one functional copy of Gli3 in Shh nulls rescues ventricular collapse and substantially restores the TDJ. Characteristic regional gene expression patterns are rescued on the telencephalic side of the TDJ but not in the diencephalon. Further analysis of compound Shh;Gli3 mutants revealed an unexpected type of signaling center deregulation. In Shh;Gli3 mutants, adjacent rings of Fgf8 and Wnt3a expression are induced in the diencephalon at the ZLI, reminiscent of the Fgf8/Wnt1-expressing isthmic organizer. Neither Shh nor Gli3 single mutants show this forebrain double ring of Fgf/Wnt expression; thus both Shh and Gli3 are independently required to suppress it. Adjacent tissue is not respecified to a midbrain/hindbrain fate, but shows overgrowth, consistent with ectopic mitogen expression. Our observations indicate that the separation of the telencephalon and diencephalon depends on interactions between Shh and Gli3, and, moreover, demonstrate that both Shh and Gli3 suppress a potential Fgf/Wnt signaling source in the forebrain. That optional signaling centers are actively repressed in normal development is a striking new insight into the processes of vertebrate brain development.

Duplication of the EFNB1 gene in familial hypertelorism: imbalance in ephrin-B1 expression and abnormal phenotypes in humans and mice

Familial hypertelorism, characterized by widely spaced eyes, classically shows autosomal dominant inheritance (Teebi type), but some pedigrees are compatible with X-linkage. No mechanism has been described previously, but clinical similarity has been noted to craniofrontonasal syndrome (CFNS), which is caused by mutations in the X-linked EFNB1 gene. Here we report a family in which females in three generations presented with hypertelorism, but lacked either craniosynostosis or a grooved nasal tip, excluding CFNS. DNA sequencing of EFNB1 was normal, but further analysis revealed a duplication of 937 kb including EFNB1 and two flanking genes: PJA1 and STARD8. We found that the X chromosome bearing the duplication produces ∼1.6-fold more EFNB1 transcript than the normal X chromosome and propose that, in the context of X-inactivation, this difference in expression level of EFNB1 results in abnormal cell sorting leading to hypertelorism. To support this hypothesis, we provide evidence from a mouse model carrying a targeted human EFNB1 cDNA, that abnormal cell sorting occurs in the cranial region. Hence, we propose that X-linked cases resembling Teebi hypertelorism may have a similar mechanism to CFNS, and that cellular mosaicism for different levels of ephrin-B1 (as well as simple presence/absence) leads to craniofacial abnormalities. Hum Mutat 32:1–9, 2011. © 2011 Wiley-Liss, Inc.

Dlx5 and Dlx6 expression in the anterior neural fold is essential for patterning the dorsal nasal capsule

Morphogenesis of the vertebrate facial skeleton depends upon inductive interactions between cephalic neural crest cells (CNCCs) and cephalic epithelia. The nasal capsule is a CNCC-derived cartilaginous structure comprising a ventral midline bar (mesethmoid) overlaid by a dorsal capsule (ectethmoid). Although Shh signalling from the anterior-most region of the endoderm (EZ-I) patterns the mesethmoid, the cues involved in ectethmoid induction are still undefined. Here, we show that ectethmoid formation depends upon Dlx5 and Dlx6 expression in a restricted ectodermal territory of the anterior neural folds, which we name NF-ZA. In both chick and mouse neurulas, Dlx5 and Dlx6 expression is mostly restricted to NF-ZA. Simultaneous Dlx5 and Dlx6 inactivation in the mouse precludes ectethmoid formation, while the mesethmoid is still present. Consistently, siRNA-mediated downregulation of Dlx5 and Dlx6 in the cephalic region of the early avian neurula specifically prevents ectethmoid formation, whereas other CNCC-derived structures, including the mesethmoid, are not affected. Similarly, NF-ZA surgical removal in chick neurulas averts ectethmoid development, whereas grafting a supernumerary NF-ZA results in an ectopic ectethmoid. Simultaneous ablation or grafting of both NF-ZA and EZ-I result, respectively, in the absence or duplication of both dorsal and ventral nasal capsule components. The present work shows that early ectodermal and endodermal signals instruct different contingents of CNCCs to form the ectethmoid and the mesethmoid, which then assemble to form a complete nasal capsule.

Ectodermal Wnt/β-catenin signaling shapes the mouse face

The canonical Wnt/β-catenin pathway is an essential component of multiple developmental processes. To investigate the role of this pathway in the ectoderm during facial morphogenesis, we generated conditional β-catenin mouse mutants using a novel ectoderm-specific Cre recombinase transgenic line. Our results demonstrate that ablating or stabilizing β-catenin in the embryonic ectoderm causes dramatic changes in facial morphology. There are accompanying alterations in the expression of Fgf8 and Shh, key molecules that establish a signaling center critical for facial patterning, the frontonasal ectodermal zone (FEZ). These data indicate that Wnt/β-catenin signaling within the ectoderm is critical for facial development and further suggest that this pathway is an important mechanism for generating the diverse facial shapes of vertebrates during evolution.

Wdr5 is required for chick skeletal development

Wdr5, a bone morphogenetic protein 2 (BMP-2)-induced protein belonging to the family of the WD repeat proteins, is expressed in proliferating and hypertrophic chondrocytes of the growth plate and in osteoblasts. Although previous studies have provided insight into the mechanisms by which Wdr5 affects chondrocyte and osteoblast differentiation, whether Wdr5 is required in vivo for endochondral bone development has not been addressed. In this study, using an avian replication competent retrovirus (RCAS) system delivering Wdr5 short hairpin (sh) RNA to silence Wdr5 in the developing limb, we report that reduction of Wdr5 levels delays endochondral bone development and consequently results in shortening of the skeletal elements. Shortening of the skeletal elements was due to impaired chondrocyte maturation, evidenced by a significant reduction of Runx2, type X collagen, and osteopontin expression. A decrease in Runx2, type collagen I, and ostepontin expression in osteoblasts and a subsequent defect in mineralized bone was observed as well when Wdr5 levels were reduced. Most important, retroviral misexpression of Runx2 rescued the phenotype induced by Wdr5 shRNA. These findings suggest that during limb development, Wdr5 is required for endochondral bone formation and that Wdr5 influences this process, at least in part, by regulating Runx2 expression.

Molecular mechanisms of cranial neural crest cell migration and patterning in craniofacial development

During vertebrate craniofacial development, neural crest cells (NCCs) contribute much of the cartilage, bone and connective tissue that make up the developing head. Although the initial patterns of NCC segmentation and migration are conserved between species, the variety of vertebrate facial morphologies that exist indicates that a complex interplay occurs between intrinsic genetic NCC programs and extrinsic environmental signals during morphogenesis. Here, we review recent work that has begun to shed light on the molecular mechanisms that govern the spatiotemporal patterning of NCC-derived skeletal structures – advances that are central to understanding craniofacial development and its evolution.

Three-dimensional morphometric analysis of brain shape in nonsyndromic orofacial clefting

Previous studies report structural brain differences in individuals with nonsyndromic orofacial clefts (NSOFC) compared with healthy controls. These changes involve non-uniform shifts in tissue volume within the cerebral cortex and cerebellum, suggesting that the shape of the brain may be altered in cleft-affected individuals. To test this hypothesis, a landmark-based morphometric approach was utilized to quantify and compare brain shape in a sample of 31 adult males with cleft lip with or without cleft palate (CL/P), 14 adult males with cleft palate only (CPO) and 41 matched healthy controls. Fifteen midline and surface landmarks were collected from MRI brain scans and the resulting 3D coordinates were subjected to statistical shape analysis. First, a geometric morphometric analysis was performed in three steps: Procrustes superimposition of raw landmark coordinates, omnibus testing for group difference in shape, followed by canonical variates analysis (CVA) of shape coordinates. Secondly, Euclidean distance matrix analysis (EDMA) was carried out on scaled inter-landmark distances to identify localized shape differences throughout the brain. The geometric morphometric analysis revealed significant differences in brain shape among all three groups (P < 0.001). From CVA, the major brain shape changes associated with clefting included selective enlargement of the anterior cerebrum coupled with a relative reduction in posterior and/or inferior cerebral portions, changes in the medio-lateral position of the cerebral poles, posterior displacement of the corpus callosum, and reorientation of the cerebellum. EDMA revealed largely similar brain shape changes. Thus, compared with controls, major brain shape differences were present in adult males with CL/P and CPO. These results both confirm and expand previous findings from traditional volumetric studies of the brain in clefting and provide further evidence that the neuroanatomical phenotype in individuals with NSOFC is a primary manifestation of the defect and not a secondarily acquired characteristic.

Signaling integration in the rugae growth zone directs sequential SHH signaling center formation during the rostral outgrowth of the palate

Evolution of facial morphology arises from variation in the activity of developmental regulatory networks that guide the formation of specific craniofacial elements. Importantly, the acquisition of novel morphology must be integrated with a phylogenetically inherited developmental program. We have identified a unique region of the secondary palate associated with the periodic formation of rugae during the rostral outgrowth of the face. Rugae function as SHH signaling centers to pattern the elongating palatal shelves. We have found that a network of signaling genes and transcription factors is spatially organized relative to palatal rugae. Additionally, the first formed ruga is strategically positioned at the presumptive junction of the future hard and soft palate that defines anterior-posterior differences in regional growth, mesenchymal gene expression, and cell fate. We propose a molecular circuit integrating FGF and BMP signaling to control proliferation and differentiation during the sequential formation of rugae and inter-rugae domains in the palatal epithelium. The loss of p63 and Sostdc1 expression and failed rugae differentiation highlight that coordinated epithelial-mesenchymal signaling is lost in the Fgf10 mutant palate. Our results establish a genetic program that reiteratively organizes signaling domains to coordinate the growth of the secondary palate with the elongating midfacial complex.

Development and tissue origins of the mammalian cranial base

The vertebrate cranial base is a complex structure composed of bone, cartilage and other connective tissues underlying the brain; it is intimately connected with development of the face and cranial vault. Despite its central importance in craniofacial development, morphogenesis and tissue origins of the cranial base have not been studied in detail in the mouse, an important model organism. We describe here the location and time of appearance of the cartilages of the chondrocranium. We also examine the tissue origins of the mouse cranial base using a neural crest cell lineage cell marker, Wnt1-Cre/R26R, and a mesoderm lineage cell marker, Mesp1-Cre/R26R. The chondrocranium develops between E11 and E16 in the mouse, beginning with development of the caudal (occipital) chondrocranium, followed by chondrogenesis rostrally to form the nasal capsule, and finally fusion of these two parts via the midline central stem and the lateral struts of the vault cartilages. X-Gal staining of transgenic mice from E8.0 to 10 days post-natal showed that neural crest cells contribute to all of the cartilages that form the ethmoid, presphenoid, and basisphenoid bones with the exception of the hypochiasmatic cartilages. The basioccipital bone and non-squamous parts of the temporal bones are mesoderm derived. Therefore the prechordal head is mostly composed of neural crest-derived tissues, as predicted by the New Head Hypothesis. However, the anterior location of the mesoderm-derived hypochiasmatic cartilages, which are closely linked with the extra-ocular muscles, suggests that some tissues associated with the visual apparatus may have evolved independently of the rest of the "New Head".

Sonic hedgehog signalling from foregut endoderm patterns the avian nasal capsule

Morphogenesis of the facial skeleton depends on inductive interactions between cephalic neural crest cells and cephalic epithelia, including the foregut endoderm. We show that Shh expression in the most rostral zone of the endoderm, endoderm zone I (EZ-I), is necessary to induce the formation of the ventral component of the avian nasal capsule: the mesethmoid cartilage. Surgical removal of EZ-I specifically prevented mesethmoid formation, whereas grafting a supernumerary EZ-I resulted in an ectopic mesethmoid. EZ-I ablation was rescued by Shh-loaded beads, whereas inhibition of Shh signalling suppressed mesethmoid formation. This interaction between the endoderm and cephalic neural crest cells was reproduced in vitro,as evidenced by Gli1 induction. Our work bolsters the hypothesis that early endodermal regionalisation provides the blueprint for facial morphogenesis and that its disruption might cause foetal craniofacial defects,including those of the nasal region.

RCAS-RNAi: a loss-of-function method for the developing chick retina

BACKGROUND

The embryonic chick provides an excellent model system for studies of development. However, it has lacked an efficient loss-of-function method for studies of gene function.

RESULTS

We show that avian retroviruses can deliver hairpins mediating RNA interference to the developing chick eye. These viruses 'knock down' specific genes in infected areas of the retina. The knock down persists as the retina matures and can be detected using in situ hybridization. Furthermore, the amount of retinal tissue affected can be controlled by manipulating the degree of infection.

CONCLUSION

This technique provides a rapid and efficient loss-of-function option for studies in the developing chick retina.