Maxillary Prominences Research Articles

Spatial and Temporal Analysis of Gene Expression during Growth and Fusion of the Mouse Facial Prominences

Orofacial malformations resulting from genetic and/or environmental causes are frequent human birth defects yet their etiology is often unclear because of insufficient information concerning the molecular, cellular and morphogenetic processes responsible for normal facial development. We have, therefore, derived a comprehensive expression dataset for mouse orofacial development, interrogating three distinct regions – the mandibular, maxillary and frontonasal prominences. To capture the dynamic changes in the transcriptome during face formation, we sampled five time points between E10.5–E12.5, spanning the developmental period from establishment of the prominences to their fusion to form the mature facial platform. Seven independent biological replicates were used for each sample ensuring robustness and quality of the dataset. Here, we provide a general overview of the dataset, characterizing aspects of gene expression changes at both the spatial and temporal level. Considerable coordinate regulation occurs across the three prominences during this period of facial growth and morphogenesis, with a switch from expression of genes involved in cell proliferation to those associated with differentiation. An accompanying shift in the expression of polycomb and trithorax genes presumably maintains appropriate patterns of gene expression in precursor or differentiated cells, respectively. Superimposed on the many coordinated changes are prominence-specific differences in the expression of genes encoding transcription factors, extracellular matrix components, and signaling molecules. Thus, the elaboration of each prominence will be driven by particular combinations of transcription factors coupled with specific cell:cell and cell:matrix interactions. The dataset also reveals several prominence-specific genes not previously associated with orofacial development, a subset of which we externally validate. Several of these latter genes are components of bidirectional transcription units that likely share cis-acting sequences with well-characterized genes. Overall, our studies provide a valuable resource for probing orofacial development and a robust dataset for bioinformatic analysis of spatial and temporal gene expression changes during embryogenesis.

RA-Noggin beads induce TBX22, a frontonasal mass-specific gene in the maxillary prominence, however over-expression causes clefting rather than a transformation in identity

RA-Noggin beads induce TBX22, a frontonasal mass-specific gene in the maxillary prominence, however over-expression causes clefting rather than a transformation in identity

Craniofacial and Pharyngeal Cephalometric Morphology in Seven-Year-Old Boys with Unoperated Submucous Cleft Palate and without a Cleft

To evaluate cephalometrically the craniofacial and pharyngeal morphology in 7-year-old boys with unoperated submucous cleft palate and to compare the findings with the morphology of 7-year-old boys without clefts. Thirty-two boys with unoperated submucous cleft palate and 49 boys without a cleft were compared retrospectively from lateral cephalograms taken at the mean age of 7 years (range, 5.5 to 8.6 years). A retrospective case-control study. Linear and angular measurements were obtained from lateral cephalograms. A Student's t test was used in the statistical analysis. The maxilla of the boys with submucous cleft palate was shorter and slightly more retrusive in relation to the cranial base than that of boys without clefts. Also, the mandible of the boys with submucous cleft palate was smaller, with a steeper mandibular plane. The relationship between the jaws was similar in both groups; although, those without clefts showed higher values for soft tissue maxillary prominence. In the pharyngeal area, the boys with submucous cleft palate had larger nasopharyngeal depths, smaller hypopharyngeal depths, and shorter soft palates than the boys without a cleft. This small study suggests that the boys with unoperated submucous cleft palate have minor distinctive morphological features in the maxillary, mandibular, and pharyngeal areas.

Midfacial Growth in a Consecutive Series of Preadolescent Children with Complete Unilateral Cleft Lip and Palate following a One-Stage Simultaneous Repair

To evaluate midfacial growth in prepubertal children with complete unilateral cleft lip and palate following one-stage simultaneous repair. A series of 28 consecutively treated subjects with complete unilateral cleft lip and palate were compared with age- and gender-matched controls with normal midfacial structure. On the lateral cephalograms taken at the age of approximately 10 years, size and position of the maxilla and upper dental arch were evaluated in vertical and horizontal planes. Statistical analysis included independent t tests and nonparametric Mann-Whitney tests. The maxilla was found to be retruded (sella-nasion-point A angle decreased by 4.5 degrees and nasion to point A distance increased by 4.2 mm) and rotated posteriorly (sella-nasion/palatal plane angle decreased by 4.5 degrees) in the cleft group. Maxillary length (pterygomaxillare-point A distance) was diminished by approximately 2 mm. Upper incisors were found retroclined in comparison to controls (both upper incisor axis/sella-nasion and upper incisor axis/palatal plane angles were decreased by 10.7 degrees and 6.1 degrees, respectively). Maxillary prominence, as measured with the sella-nasion-point A angle and the condylion-point A and articulare-point A distances, was decreased. Shortened length and posterior position of the maxillary body were responsible at a ratio of 60% to 40% for a decreased prominence of the maxillary complex. The palatal plane demonstrated a larger inclination to the sella-nasion plane by 4.5 degrees due to a decreased sella-posterior nasal spine distance.

A Cephalometric Intercenter Comparison of Patients with Unilateral Cleft Lip and Palate: Analysis at 5 and 10 Years of Age and Long Term

To compare the short- and long-term craniofacial growth of patients operated with the Milan protocol to those operated with the Oslo protocol. The Milan sample included 88 patients with unilateral cleft lip and palate (UCLP) at 5 years, 26 at 10 years, and 23 at the end of growth. The Oslo samples included 48 UCLP patients at 5 years, 29 at 10, and 23 at growth completion. Lateral cephalograms were used for comparison. An unpaired t test was run for the 5- and 10-year-old samples. The samples long term were matched for age and sex, and a paired t test was run. There was no significant cephalometric difference in the maxillary prominence at 5 years, a mild but significant difference at 10 years, and again no difference at the end of growth. Nevertheless, at an older age, the need for orthognathic surgery was larger in the Milan sample (26%) than in the Oslo sample (13%). Although no statistically significant differences in the cephalometric measurements were found long term, the need for orthognathic surgery was clinically judged to be larger in the Milan sample. On the other hand, although the Milan protocol seemed to require more final jaw surgery, only the cases that needed an additional orthognathic procedure in the Milan group will undertake a third surgical step, while the Oslo protocol included three surgical steps for all the patients.

FGF signals from the nasal pit are necessary for normal facial morphogenesis

Fibroblast growth factors (FGFs) are required for brain, pharyngeal arch, suture and neural crest cell development and mutations in the FGF receptors have been linked to human craniofacial malformations. To study the functions of FGF during facial morphogenesis we locally perturb FGF signalling in the avian facial prominences with FGFR antagonists, foil barriers and FGF2 protein. We tested 4 positions with antagonist-soaked beads but only one of these induced a facial defect. Embryos treated in the lateral frontonasal mass, adjacent to the nasal slit developed cleft beaks. The main mechanisms were a block in proliferation and an increase in apoptosis in those areas that were most dependent on FGF signaling. We inserted foil barriers with the goal of blocking diffusion of FGF ligands out of the lateral edge of the frontonasal mass. The barriers induced an upregulation of the FGF target gene, SPRY2 compared to the control side. Moreover, these changes in expression were associated with deletions of the lateral edge of the premaxillary bone. To determine whether we could replicate the effects of the foil by increasing FGF levels, beads soaked in FGF2 were placed into the lateral edge of the frontonasal mass. There was a significant increase in proliferation and an expansion of the frontonasal mass but the skeletal defects were minor and not the same as those produced by the foil. Instead it is more likely that the foil repressed FGF signaling perhaps mediated by the increase in SPRY2 expression. In summary, we have found that the nasal slit is a source of FGF signals and the function of FGF is to stimulate proliferation in the cranial frontonasal mass. The FGF independent regions correlate with those previously determined to be dependent on BMP signaling. We propose a new model whereby, FGF-dependent microenvironments exist in the cranial frontonasal mass and caudal maxillary prominence and these flank BMP-dependent regions. Coordination of the proliferation in these regions leads ultimately to normal facial morphogenesis.

Establishment of embryonic kidney and facial culture systems to evaluate the role of the transcription factor Six2 through RNAi

The Br mouse mutation results in frontonasal and renal hypodysplasia. Linkage analysis mapped the Br mutation close to the homeobox transcription factor Six2, which is normally expressed in the metanephric and facial mesenchyme during embryonic development. The purpose of this study is to evaluate Six2's role in nephrogenesis and craniofacial morphogenesis by silencing Six2 in embryonic kidney and facial prominence organ cultures. Kidney organ cultures were established from E11.5 mouse embryos, cultured for 48 hours, and immunostained to reveal ureteric bud branching patterns. Frontonasal (FNP), lateral nasal (LNP), and maxillary prominences (MXP) of E11.5 embryos were dissected and Six2 expression was measured with qRT‐PCR. Six2 expression was highest in the FNP, 3‐fold less in the MXP, and 6‐fold less in the LNP. This was confirmed by immunostaining in embryos at the same age. We evaluated five different shRNA constructs for silencing efficiency of Six2 using p19 embryonal carcinoma cells. As measured with qRT‐PCR, Six2 expression was unaffected using four of the constructs and decreased expression by 30–50% with the fifth. Using this shRNA construct, we will transfect our established culture systems, confirm Six2 expression is down‐regulated, and then evaluate differences in kidney tubule branching and FNP cell proliferation.

166. Modulation of Wnt Pathway Signaling Determines Ectopic Craniofacial Fusion and Orofacial Clefting

Introduction: The etiology of facial clefting is a complex synthesis of multiple environmental and genetic factors. Therefore few inroads have been made into the design or development of targeted preventions or treatments for these birth defects. The identification of a developmental signaling pathway that definitively regulates facial fusion would be a crucial first step. Previous gene expression studies in mice have demonstrated that Wnt genes are expressed in the right time and place to be critical for facial fusion. Studies of mouse strains prone to facial clefting have identified causative mutations in the Wnt9b locus. This study examines for the first time how the experimental manipulation of Wnt signaling at the pathway level influences the normal events of craniofacial morphogenesis. Here we use two animal models in which the early events of facial development are remarkably conserved, combining mouse transgenetics with in ovo viral-mediated gene transfer in developing chick embryos. Methods: Wild type (CD1) or Wnt reporter (BATGAL) mouse embryos and normal chicken embryos representing the normal course of craniofacial outgrowth and fusion were collected at E10.5-E13.5 (mouse) and St. 25-28 (E5-E7; chick). Gene expression was detected by non-radioactive in situ hybridization or X-gal detection of beta-galactosidase transgene activity in either whole-mount or sectioned embryos. To achieve viral-mediated gene transfer in chick embryos, adenovirus encoding the soluble Wnt inhibitor Dkk1 or retrovirus encoding Wnt3a ligand were delivered in ovo to the maxillary prominence (MXP) by microinjection. Results: in mouse and chick embryos, Wnt7b and Wnt9b ligand gene expression was found to localize to the surface ectoderm of fusing facial prominences. In BATGAL mice, Wnt-responsive cells were found in the surface ectoderm of the fusing lateral and frontonasal promences, as well as in the underlying mesenchyme of the developing facial prominences. To determine whether repression of Wnt pathway activity prevented normal facial fusion, Ad-Dkk1 or Ad-Fc (as a control) was injected into the developing maxillary prominence at St. 25 (E5.5). After 36 hours of incubation, facial clefts were visible in embryos treated with Ad-Dkk1, whereas the face had fused normally in controls. To assess whether exogenous Wnt pathway activation might induce ectopic fusion of craniofacial tissues, RCAS-Wnt3a or RCAS-AP (alkaline phosphatase) was injected into the developing maxillary facial prominence at St. 23 (E4). After 36 hours of incubation, the injected maxillary prominences of RCAS-Wnt3a treated embryos had grown out and fused to the frontonasal prominence, whereas the contralateral, uninjected maxillary facial prominence and the RCAS-AP injected MXP had not yet fused. Conclusions: Our gain- and loss-of-function data provide strong evidence that normal Wnt pathway activity is necessary for physiologic facial fusion, and that exogenous activation of the Wnt pathway by administration of the ligand is sufficient to induce ectopic fusion events within the craniofacial complex. Further studies using this model will determine how regulation of the Wnt pathway influence epithelial seam cell fate decisions during facial fusion, such as proliferation rates, apoptosis, migration, and epithelial-mesenchymal transformations. Finally, our model suggests that therapeutic modulation of a cell signaling pathway may be a viable strategy for in utero treatment of facial clefts.

Phenotypic variability and craniofacial dysmorphology: increased shape variance in a mouse model for cleft lip

Cleft lip and palate (CL/P), as is true of many craniofacial malformations in humans, is etiologically complex and highly variable in expression. A/WySn mice are an intriguing model for human CL/P because they develop this dysmorphology with a variable expression pattern, incomplete penetrance and frequent unilateral expression on a homogeneous genetic background. The developmental basis for this variation in expression is unknown, but of great significance for understanding such expression patterns in humans. As a step towards this goal, this study used three-dimensional geometric morphometric and novel high throughput morphometric techniques based on three-dimensional computed microtomography of mouse embryos to analyze craniofacial shape variation during primary palate formation. Our analysis confirmed previous findings based on two-dimensional analyses that the midface in A/WySn embryos, and the maxillary prominence in particular, is relatively reduced in size and appears to be developmentally delayed. In addition, we find that shape variance is increased in A/WySn embryos during primary palate formation compared to both C57BL/6J mice and the F1 crosses between these strains. If the reduction in midfacial growth caused by the Wnt9b hypomorphic mutation pushes A/WySn mice closer on average to the threshold for cleft lip formation, the elevated shape variance may explain why some, but not all, embryos develop the dysmorphology in a genetically homogeneous inbred line of mice.

Mouse genetic models of cleft lip with or without cleft palate

Nonsyndromic cleft lip and palate (CLP) is among the most common human birth defects. Transmission patterns suggest that the causes are "multifactorial" combinations of genetic and nongenetic factors, mostly distinct from those causing cleft secondary palate (CP). The major etiological factors are largely unknown, and the embryological mechanisms are not well understood. In contrast to CP or neural tube defects (NTD), CLP is uncommon in mouse mutants. Fourteen known mutants or strains express CLP, often as part of a severe syndrome, whereas nonsyndromic CLP is found in two conditional mutants and in two multifactorial models based on a hypomorphic variant with an epigenetic factor. This pattern suggests that human nonsyndromic CLP is likely caused by regulatory and hypomorphic gene variants, and may also involve epigenetics. The developmental pathogenic mechanism varies among mutants and includes deficiencies of growth of the medial, lateral or maxillary facial prominences, defects in the fusion process itself, and shifted midline position of the medial prominences. Several CLP mutants also have NTD, suggesting potential genetic overlap of the traits in humans. The mutants may reflect two interacting sets of genetic signaling pathways: Bmp4, Bmpr1a, Sp8, and Wnt9b may be in one set, and Tcfap2a and Sox11 may be in another. Combining the results of chromosomal linkage studies of unidentified human CLP genes with insights from the mouse models, the following previously unexamined genes are identified as strong candidate genes for causative roles in human nonsyndromic CLP: BMP4, BMPR1B, TFAP2A, SOX4, WNT9B, WNT3, and SP8.

Molecular mechanisms of cleft lip formation in CL/Fr mice

CL/Fr mice have a high incidence of cleft lip and the cleft lip is the result of incomplete fusion between the medial and lateral nasal prominences and the maxillary prominence at about day 11.5 of gestation. However, little is known about the molecular mechanisms that are responsible for the incomplete fusion. We made a molecular pathological investigation using 11.5-day CL/Fr embryos. Five embryos were each examined for real-time polymerase chain reaction (PCR) analysis. During the first palatal formation in normal development, an epithelial seam is formed when the medial and lateral nasal prominences first make contact. Some epithelial cells of the epithelial seam then undergo apoptosis, with remaining cells transforming into a mesenchymal phenotype (epithelial-mesenchymal transition, EMT). Mesenchymal cells of the medial and lateral nasal prominences then merge across the previous boundary of separation. In CL/Fr mice with cleft lip, neither apoptosis nor EMT occurs in the epithelial cells. Increased expression of claudin 6 mRNA is seen in epithelial cells of epithelial seam in cleft lip compared with that in normal embryos. Slug mRNA expression was also significantly reduced whereas noggin was increased in CL/Fr embryos with cleft lip. We suggest that EMT is prevented in CL/Fr mice with cleft lip by increased expression of claudin 6 and coexistent downregulation of slug in cells of the epithelial seam, and these altered concentrations of transcription factors/repressors prevent fusion of the medial and lateral nasal prominences, leading to clefts of the lip.

Repair of Transverse Facial Cleft in Hemifacial Microsomia: Long-Term Anthropometric Evaluation of Commissural Symmetry

Cleft of the oral commissure is an uncommon malformation that results from incomplete mesenchymal merging of the mandibular and maxillary prominences of the first pharyngeal arch. Many operative techniques have been proposed to repair this cutaneous and muscular defect. Most authors recommend cutaneous closure by Z-plasty or W-plasty, but these geometric techniques cause additional cutaneous scarring; furthermore, the risk of commissural migration after repair of a transverse facial cleft is poorly documented. Anthropometry was used to evaluate the operative outcome in 13 patients with hemifacial microsomia who underwent repair of a transverse facial cleft by the senior author between 1980 and 2001. The procedure included (1) apposition of the orbicularis oris muscle; (2) linear cutaneous closure; and (3) construction of the commissure using an inferiorly based, rectangular vermilion-mucosal flap. The average age at repair was 11 months, and the mean follow-up was 10.3 years. Comparing the cleft and noncleft sides, the position of the commissure was within 1 mm in all patients, whereas the melolabial fold was asymmetric in six patients. The average length of the scar was 17 mm, and the scar extended lateral to the melolabial fold in all but one patient. No patients were found to have had lateral commissural migration. The authors conclude that Z-plasty or W-plasty is unnecessary in repair of a transverse facial cleft. Closure of the orbicularis oris muscular ring is the critical step in the procedure to provide oral continence and a counterforce to the contraction of the cutaneous scar. There is no lateral creep of the commissure or hypertrophic scarring after straight-line cutaneous closure.

Wnt signaling mediates regional specification in the vertebrate face

At early stages of development, the faces of vertebrate embryos look remarkably similar, yet within a very short timeframe they adopt species-specific facial characteristics. What are the mechanisms underlying this regional specification of the vertebrate face? Using transgenic Wnt reporter embryos we found a highly conserved pattern of Wnt responsiveness in the developing mouse face that later corresponded to derivatives of the frontonasal and maxillary prominences. We explored the consequences of disrupting Wnt signaling, first using a genetic approach. Mice carrying compound null mutations in the nuclear mediators Lef1 and Tcf4 exhibited radically altered facial features that culminated in a hyperteloric appearance and a foreshortened midface. We also used a biochemical approach to perturb Wnt signaling and found that in utero delivery of a Wnt antagonist, Dkk1, produced similar midfacial malformations. We tested the hypothesis that Wnt signaling is an evolutionarily conserved mechanism controlling facial morphogenesis by determining the pattern of Wnt responsiveness in avian faces, and then by evaluating the consequences of Wnt inhibition in the chick face. Collectively, these data elucidate a new role for Wnt signaling in regional specification of the vertebrate face, and suggest possible mechanisms whereby species-specific facial features are generated.

Bilateral Cleft Lip and Palate: Improved Maxillary and Dental Development

Maxillary growth deficiency is still a problem in children with repaired cleft lip-cleft palate, and little progress has been made on research for its prevention. An increase in the early diagnosis of maxillary growth deficiency prompted this study to obtain an early indication of the efficacy of a new protocol for better dental and maxillary development. A new method for repair of the hard palate in infants with bilateral cleft lip-cleft palate that made innovative use of mucosa of the nasal septum and involved less extensive surgery was coupled with the repair of the lip at 18 months instead of at 8 months. Twelve consecutive cases were compared with 12 cases treated by the previous method. Records of dental occlusion and lateral head radiographs at 5 years were obtained prospectively for the new treatment group and retrospectively for the previous group. In the previous group, there was a high incidence of dental crossbite. Incisor crossbite was present in 10 of the 12 (83 percent), and all 12 had one or both cuspids in crossbite. In the new treatment group, the incisor crossbite was reduced to four of 12 cases (33 percent), with cuspid crossbite at 50 percent. The new treatment group also showed greater values for cephalometric measures in maxillary length, maxillary prominence, and the ANB angle. At the age of 5 years, a definite improvement in dental and maxillary development was evident in the new treatment group.

Craniofacial cephalometric morphology in 6-year-old children with isolated cleft lip, isolated submucous cleft palate, and combined cleft lip and submucous cleft palate

One hundred and twenty-one cleft children (67 with isolated cleft lip (CL), 32 with isolated submucous cleft palate (SMCP), and 22 with combined cleft lip and submucous cleft palate (CL + SMCP)) were compared retrospectively from lateral cephalograms taken at a mean age of 6.2 years (range 5.5-7.9). None of the children had had their palates repaired or been operated on to treat velopharyngeal insufficiency (VPI). The children with CL + SMCP and CL had similar morphology. They had greater maxillary length, greater maxillary and mandibular prominence, less vertical growth pattern, less deep nasopharyngeal airways, and thinner upper lips than those with isolated SMCP. After 6 years of age one patient with CL + SMCP, none with CL, and 16 with SMCP needed operations for VPI. This small series suggests that children with CL + SMCP and SMCP have different morphology. Although CL + SMCP is a combination of two types of clefts, it seems to be associated with similar morphology to CL.

Comparative morphometrics of embryonic facial morphogenesis: Implications for cleft‐lip etiology

Cleft lip (CL) with or without cleft palate (CL[P]) has a complex etiology but is thought to be due to either genetic or environmentally induced disruptions of developmental processes affecting the shape and size of the facial prominences (medial nasal, lateral nasal, and maxilla). Recent advances in landmark-based morphometrics enable a rigorous reanalysis of phenotypic shape variation associated with facial clefting. Here we use geometric morphometric (GM) tools to characterize embryonic shape variation in the midface and head of six strains of mice that are both cleft-liable (A, A/WySn, CL/Fr) and normal (BALB/cBy, C57BL, CD1). Data were comprised of two-dimensional landmarks taken from frontal and lateral photographs of embryos spanning the time period in which the facial prominences fuse (GD10-12). Results indicate that A/- strain mice, and particularly A/WySn, have overall smaller midfaces compared to other strains. The A/WySn strain also has significant differences in facial shape related to retarded development. Overall, CL/Fr strain mice are normal-sized, but tend to have undersized maxillary prominences that do not project anteriorly and have a small nasal contact area. These results suggest that the etiology of clefting differs in A/WySn and CL/Fr strains, with the former strain suffering disruptions to developmental processes affecting overall size (e.g., neural crest migration deficiencies and lower mitotic activity), while the latter strain has defects restricted to the shape and size of the maxilla. A combination of molecular experimentation and phenotypic analysis of shape is required to test these hypotheses further.

Patterns of Infantile Hemangiomas: New Clues to Hemangioma Pathogenesis and Embryonic Facial Development

Large facial infantile hemangiomas have higher rates of complications than small localized hemangiomas, more often require treatment, and can be associated with neurological, ophthalmologic, and cardiac anomalies (PHACE syndrome). The anatomic patterns of these hemangiomas are often referred to as "segmental" despite a lack of precise anatomic definitions. Our study aims to define "segmental" hemangiomas based on clinically observed patterns. Our secondary goal is to relate the observed patterns to currently accepted developmental patterns to gain insight into hemangioma pathogenesis and craniofacial development. Photographic data were extracted from a large cohort of patients with infantile hemangiomas. We mapped 294 hemangiomas and recorded common morphologic patterns. Anatomic descriptions of the most common patterns were described and compared with accepted concepts of craniofacial development. Four primary segments were identified (Seg1-Seg4). Seg2 and Seg3 correspond with the previously recognized maxillary and mandibular prominences. Seg1 and Seg4 differ from standard human embryology texts. The frontotemporal segment, Seg1, encompasses the lateral forehead, anterior temporal scalp, and lateral frontal scalp. The segment Seg4, encompassing the medial frontal scalp, nasal bridge, nasal tip, ala, and philtrum, is substantially narrower on the forehead than the previously described frontonasal prominence. The patterns provide new clues regarding facial development. The observed patterns resemble previously described facial developmental units on the lower face but are distinctly different on the upper face. The patterns suggest that neural crest derivatives may play a role in the development of facial hemangiomas. Finally, these patterns (Seg1-Seg4) help standardize the nomenclature of facial segmental hemangiomas to analyze more effectively hemangioma risks and behavior.

Development of the upper lip: Morphogenetic and molecular mechanisms

The vertebrate upper lip forms from initially freely projecting maxillary, medial nasal, and lateral nasal prominences at the rostral and lateral boundaries of the primitive oral cavity. These facial prominences arise during early embryogenesis from ventrally migrating neural crest cells in combination with the head ectoderm and mesoderm and undergo directed growth and expansion around the nasal pits to actively fuse with each other. Initial fusion is between lateral and medial nasal processes and is followed by fusion between maxillary and medial nasal processes. Fusion between these prominences involves active epithelial filopodial and adhering interactions as well as programmed cell death. Slight defects in growth and patterning of the facial mesenchyme or epithelial fusion result in cleft lip with or without cleft palate, the most common and disfiguring craniofacial birth defect. Recent studies of craniofacial development in animal models have identified components of several major signaling pathways, including Bmp, Fgf, Shh, and Wnt signaling, that are critical for proper midfacial morphogenesis and/or lip fusion. There is also accumulating evidence that these signaling pathways cross-regulate genetically as well as crosstalk intracellularly to control cell proliferation and tissue patterning. This review will summarize the current understanding of the basic morphogenetic processes and molecular mechanisms underlying upper lip development and discuss the complex interactions of the various signaling pathways and challenges for understanding cleft lip pathogenesis.

Focal preauricular dermal dysplasia: distinctive congenital lesions with a bilateral and symmetric distribution

We present three unrelated children with distinctive congenital facial skin lesions. All three children had two to three well-circumscribed, round or oval vesicular lesions, 1/2–1 cm in diameter on each cheek at birth. The lesions were located along an arc from the top of the ear to the corner of the mouth. Patient 1 was born with a unilateral cleft lip and palate, and a cutaneous hemangioma in the right palm. She is developing normally. Patient 2 has neurological sequelae after suffering an unexplained large left-sided intracerebral hemorrhage perinatally. Patient 3 has a small chin, somewhat cupped ears and a nevus on the left foot. He is developing normally. This condition has been described in the dermatological literature as focal facial dermal hypoplasia with preauricular localization. No cases with associated anomalies have been published previously. Most cases have been sporadic but familial occurrence compatible with autosomal dominant and autosomal recessive inheritance has been documented. If an embryonic fusion defect of the mandibular and maxillary prominences underlies the anomaly, the cleft lip and palate seen in one of our patients may be non-coincidental. No mutations in the TWIST2 gene were found in DNA extracted from peripheral leukocytes in the two children who were investigated.

Developmental origins and evolution of jaws: new interpretation of “maxillary” and “mandibular”

Cartilage of the vertebrate jaw is derived from cranial neural crest cells that migrate to the first pharyngeal arch and form a dorsal “maxillary” and a ventral “mandibular” condensation. It has been assumed that the former gives rise to palatoquadrate and the latter to Meckel's (mandibular) cartilage. In anamniotes, these condensations were thought to form the framework for the bones of the adult jaw and, in amniotes, appear to prefigure the maxillary and mandibular facial prominences. Here, we directly test the contributions of these neural crest condensations in axolotl and chick embryos, as representatives of anamniote and amniote vertebrate groups, using molecular and morphological markers in combination with vital dye labeling of late-migrating cranial neural crest cells. Surprisingly, we find that both palatoquadrate and Meckel's cartilage derive solely from the ventral “mandibular” condensation. In contrast, the dorsal “maxillary” condensation contributes to trabecular cartilage of the neurocranium and forms part of the frontonasal process but does not contribute to jaw joints as previously assumed. These studies reveal the morphogenetic processes by which cranial neural crest cells within the first arch build the primordia for jaw cartilages and anterior cranium.