Analysis of Zfhx1a mutant mice reveals palatal shelf contact-independent medial edge epithelial differentiation during palate fusion

Autophagy triggered by the ROS/ERK signaling pathway protects mouse embryonic palatal cells from apoptosis induced by nicotine

Maternal cigarette smoking during pregnancy is a known high-risk factor for having a child with a cleft lip and/or palate (CLP), a common congenital malformation. Nicotine is the major teratogen component of cigarettes and e-cigarettes, and nicotine plays an important role in the development of CLP. However, the mechanism underlying nicotine's effect on CLP remains unclear. Here, we aimed to determine the role and molecular mechanisms of nicotine-induced autophagy, an important process involved in regulating the cellular stress response in mouse embryonic palatal cells (MEPCs). First, we found that nicotine promoted MEPCs proliferation and inhibited their apoptosis from 0 to 12 h. After 12 h, the proliferation was inhibited, and apoptosis was promoted. The migration of MEPCs was also inhibited by nicotine. Simultaneously, long-term nicotine stimulation inhibited the osteogenic differentiation of MEPCs. We then found that nicotine significantly increased autophagy flux in MEPCs at 12 h by increasing the expression of microtubule-associated protein light chain 3 (LC3) and reducing P62 expression levels. After nicotine exposure, intracellular reactive oxygen species (ROS) and extracellular signal-regulated kinase-1/2 (ERK1/2) expression significantly increased, and the expression of ERK1/2 was reversed by the ROS scavenging agent N-acetylcysteine (NAC). Moreover, the autophagy induced by nicotine was reversed by SCH772984, a specific inhibitor of ERK1/2, and the autophagy inhibitor chloroquine (CQ). These results suggest that in the early stage of nicotine exposure, MEPCs may trigger autophagy through the ROS/ERK1/2 signaling pathway to avoid cell damage caused by nicotine.

In-frame deletion of SPECC1L microtubule association domain results in gain-of-function phenotypes affecting embryonic tissue movement and fusion events

Patients with autosomal dominant SPECC1L variants show syndromic malformations, including hypertelorism, cleft palate and omphalocele. These SPECC1L variants largely cluster in the second coiled-coil domain (CCD2), which facilitates association with microtubules. To study SPECC1L function in mice, we first generated a null allele (Specc1lΔEx4) lacking the entire SPECC1L protein. Homozygous mutants for these truncations died perinatally without cleft palate or omphalocele. Given the clustering of human variants in CCD2, we hypothesized that targeted perturbation of CCD2 may be required. Indeed, homozygotes for in-frame deletions involving CCD2 (Specc1lΔCCD2) resulted in exencephaly, cleft palate and ventral body wall closure defects (omphalocele). Interestingly, exencephaly and cleft palate were never observed in the same embryo. Further examination revealed a narrower oral cavity in exencephalic embryos, which allowed palatal shelves to elevate and fuse despite their defect. In the cell, wildtype SPECC1L was evenly distributed throughout the cytoplasm and colocalized with both microtubules and filamentous actin. In contrast, mutant SPECC1L-ΔCCD2 protein showed abnormal perinuclear accumulation with diminished overlap with microtubules, indicating that SPECC1L used microtubule association for trafficking in the cell. The perinuclear accumulation in the mutant also resulted in abnormally increased actin and non-muscle myosin II bundles dislocated to the cell periphery. Disrupted actomyosin cytoskeletal organization in SPECC1L CCD2 mutants would affect cell alignment and coordinated movement during neural tube, palate and ventral body wall closure. Thus, we show that perturbation of CCD2 in the context of full SPECC1L protein affects tissue fusion dynamics, indicating that human SPECC1L CCD2 variants are gain-of-function.

Loss of Wiz Function Affects Methylation Pattern in Palate Development and Leads to Cleft Palate

WIZ (Widely Interspaced Zinc Finger) is associated with the G9a-GLP protein complex, a key H3K9 methyltransferase suggesting a role in transcriptional repression. However, its role in embryonic development is poorly described. In order to assess the loss of function of WIZ, we generated CRISPR/Cas9 WIZ knockout mouse model with 32 nucleotide deletion. Observing the lethality status, we identified the WIZ knockouts to be subviable during embryonic development and non-viable after birth. Morphology of developing embryo was analyzed at E14.5 and E18.5 and our findings were supported by microCT scans. Wiz KO showed improper development in multiple aspects, specifically in the craniofacial area. In particular, shorter snout, cleft palate, and cleft eyelids were present in mutant embryos. Palatal shelves were hypomorphic and though elevated to a horizontal position on top of the tongue, they failed to make contact and fuse. By comparison of proliferation pattern and histone methylation in developing palatal shelves we brought new evidence of importance WIZ dependent G9a-GLP methylation complex in craniofacial development, especially in palate shelf fusion.

Isolation and Time-Lapse Imaging of Primary Mouse Embryonic Palatal Mesenchyme Cells to Analyze Collective Movement Attributes

Development of the palate is a dynamic process, which involves vertical growth of bilateral palatal shelves next to the tongue followed by elevation and fusion above the tongue. Defects in this process lead to cleft palate, a common birth defect. Recent studies have shown that palatal shelf elevation involves a remodeling process that transforms the orientation of the shelf from a vertical to a horizontal one. The role of the palatal shelf mesenchymal cells in this dynamic remodeling has been difficult to study. Time-lapse-imaging-based quantitative analysis has been recently used to show that primary mouse embryonic palatal mesenchymal (MEPM) cells can self-organize into a collective movement. Quantitative analyses could identify differences in mutant MEPM cells from a mouse model with palate elevation defects. This paper describes methods to isolate and culture MEPM cells from E13.5 embryos-specifically for time-lapse imaging-and to determine various cellular attributes of collective movement, including measures for stream formation, shape alignment, and persistence of direction. It posits that MEPM cells can serve as a proxy model for studying the role of palatal shelf mesenchyme during the dynamic process of elevation. These quantitative methods will allow investigators in the craniofacial field to assess and compare collective movement attributes in control and mutant cells, which will augment the understanding of mesenchymal remodeling during palatal shelf elevation. Furthermore, MEPM cells provide a rare mesenchymal cell model for investigation of collective cell movement in general.

SPECC1L-deficient primary mouse embryonic palatal mesenchyme cells show speed and directionality defects

Cleft lip and/or palate (CL/P) are common anomalies occurring in 1/800 live-births. Pathogenic SPECC1L variants have been identified in patients with CL/P, which signifies a primary role for SPECC1L in craniofacial development. Specc1l mutant mouse embryos exhibit delayed palatal shelf elevation accompanied by epithelial defects. We now posit that the process of palate elevation is itself abnormal in Specc1l mutants, due to defective remodeling of palatal mesenchyme. To characterize the underlying cellular defect, we studied the movement of primary mouse embryonic palatal mesenchyme (MEPM) cells using live-imaging of wound-repair assays. SPECC1L-deficient MEPM cells exhibited delayed wound-repair, however, reduced cell speed only partially accounted for this delay. Interestingly, mutant MEPM cells were also defective in coordinated cell movement. Therefore, we used open-field 2D cultures of wildtype MEPM cells to show that they indeed formed cell streams at high density, which is an important attribute of collective movement. Furthermore, activation of the PI3K-AKT pathway rescued both cell speed and guidance defects in Specc1l mutant MEPM cells. Thus, we show that live-imaging of primary MEPM cells can be used to assess mesenchymal remodeling defects during palatal shelf elevation, and identify a novel role for SPECC1L in collective movement through modulation of PI3K-AKT signaling.

Zeb1 Promotes Odontoblast Differentiation in a Stage-Dependent Manner

A comprehensive study of odontoblastic differentiation is essential to understand the process of tooth development and to achieve the ability of tooth regeneration in the future. Zinc finger E-box-binding homeobox 1 (Zeb1) is a transcription factor expressed in various neural crest-derived tissues, including the mesenchyme of the tooth germ. However, its role in odontoblastic differentiation remains unknown. In this study, we found the expression of Zeb1 gradually increased during odontoblast differentiation in vivo, as well as during induced differentiation of cultured primary murine dental papilla cells (mDPCs) in vitro. In addition, the differentiation of mDPCs was repressed in Zeb1-silenced cells. We used RNA sequencing (RNA-seq) to identify the transcriptome-wide targets of Zeb1 and used assay for transposase-accessible chromatin with high-throughput sequencing (ATAC-seq) to explore the direct targets of Zeb1 in both the early stage (embryonic day 16.5; E16.5) and the late stage (postnatal day 0; PN0) of tooth development. We identified the motifs of transcription factors enriched in Zeb1-dependent accessible chromatin regions and observed that only in the early stage of mDPCs could Zeb1 significantly change the accessibility of chromatin regions. In vivo and in vitro experiments confirmed that silencing of Zeb1 at E16.5 inhibited dentinogenesis. Analysis of RNA-seq and ATAC-seq resulted in the identification of Runx2, a gene directly regulated by Zeb1 during early odontoblast differentiation. Zeb1 enhances the expression of Runx2 by binding to its cis-elements, and ZEB1 interacts with RUNX2. In the late stage of tooth development, we found that ZEB1 could directly bind to and increase the enhancer activity of an element upstream of Dspp and promote dentinogenesis. In this study, for the first time, we revealed that ZEB1 promoted odontoblast differentiation in the early stage by altering chromatin accessibility of cis-elements near genes such as Runx2, while in the late stage, it directly enhanced Dspp transcription, thereby performing a dual role.

Extracellular Matrix in Secondary Palate Development

The secondary palate arises from outgrowths of epithelia-covered embryonic mesenchyme that grow from the maxillary prominence, remodel to meet over the tongue, and fuse at the midline. These events require the coordination of cell proliferation, migration, and gene expression, all of which take place in the context of the extracellular matrix (ECM). Palatal cells generate their ECM, and then stiffen, degrade, or otherwise modify its properties to achieve the required cell movement and organization during palatogenesis. The ECM, in turn, acts on the cells through their matrix receptors to change their gene expression and thus their phenotype. The number of ECM-related gene mutations that cause cleft palate in mice and humans is a testament to the crucial role the matrix plays in palate development and a reminder that understanding that role is vital to our progress in treating palate deformities. This article will review the known ECM constituents at each stage of palatogenesis, the mechanisms of tissue reorganization and cell migration through the palatal ECM, the reciprocal relationship between the ECM and gene expression, and human syndromes with cleft palate that arise from mutations of ECM proteins and their regulators. Anat Rec, 2019. © 2019 American Association for Anatomy.

Loss of Tbx3 in murine neural crest reduces enteric glia and causes cleft palate, but does not influence heart development or bowel transit

Transcription factors that coordinate migration, differentiation or proliferation of enteric nervous system (ENS) precursors are not well defined. To identify novel transcriptional regulators of ENS development, we performed microarray analysis at embryonic day (E) 17.5 and identified many genes that were enriched in the ENS compared to other bowel cells. We decided to investigate the T-box transcription factor Tbx3, which is prominently expressed in developing and mature ENS. Haploinsufficiency for TBX3 causes ulnar-mammary syndrome (UMS) in humans, a multi-organ system disorder. TBX3 also regulates several genes known to be important for ENS development. To test the hypothesis that Tbx3 is important for ENS development or function, we inactivated Tbx3 in all neural crest derivatives, including ENS progenitors using Wnt1-Cre and a floxed Tbx3 allele. Tbx3 fl/fl; Wnt1-Cre conditional mutant mice die shortly after birth with cleft palate and difficulty feeding. The ENS of mutants was well-organized with a normal density of enteric neurons and nerve fiber bundles, but small bowel glial cell density was reduced. Despite this, bowel motility appeared normal. Furthermore, although Tbx3 is expressed in cardiac neural crest, Tbx3 fl/fl; Wnt1-Cre mice had structurally normal hearts. Thus, loss of Tbx3 within neural crest has selective effects on Tbx3-expressing neural crest derivatives.

Inactivation of Fgfr2 gene in mouse secondary palate mesenchymal cells leads to cleft palate

Numerous studies have been conducted to understand the molecular mechanisms controlling mammalian secondary palate development such as growth, reorientation and fusion. However, little is known about the signaling factors regulating palate initiation. Mouse fibroblast growth factor (FGF) receptor 2 gene (Fgfr2) is expressed on E11.5 in the palate outgrowth within the maxillary process, in a region that is responsible for palate cell specification and shelf initiation. Fgfr2 continues to express in palate on E12.5 and E13.5 in both epithelial and mesenchymal cells, and inactivation of Fgfr2 expression in mesenchymal cells using floxed Fgfr2 allele and Osr2-Cre leads to cleft palate at various stages including reorientation, horizontal growth and fusion. Notably, some mutant embryos displayed no sign of palate shelf formation suggesting that FGF receptor 2 mediated FGF signaling may play an important role in palate initiation.

Computational Model of Secondary Palate Fusion and Disruption

Morphogenetic events are driven by cell-generated physical forces and complex cellular dynamics. To improve our capacity to predict developmental effects from chemical-induced cellular alterations, we built a multicellular agent-based model in CompuCell3D that recapitulates the cellular networks and collective cell behavior underlying growth and fusion of the mammalian secondary palate. The model incorporated multiple signaling pathways (TGFβ, BMP, FGF, EGF, and SHH) in a biological framework to recapitulate morphogenetic events from palatal outgrowth through midline fusion. It effectively simulated higher-level phenotypes (e.g., midline contact, medial edge seam (MES) breakdown, mesenchymal confluence, and fusion defects) in response to genetic or environmental perturbations. Perturbation analysis of various control features revealed model functionality with respect to cell signaling systems and feedback loops for growth and fusion, diverse individual cell behaviors and collective cellular behavior leading to physical contact and midline fusion, and quantitative analysis of the TGF/EGF switch that controls MES breakdown-a key event in morphogenetic fusion. The virtual palate model was then executed with theoretical chemical perturbation scenarios to simulate switch behavior leading to a disruption of fusion following chronic (e.g., dioxin) and acute (e.g., retinoic acid) chemical exposures. This computer model adds to similar systems models toward an integrative "virtual embryo" for simulation and quantitative prediction of adverse developmental outcomes following genetic perturbation and/or environmental disruption.

Ablation of the Sox11 Gene Results in Clefting of the Secondary Palate Resembling the Pierre Robin Sequence

Mouse gene inactivation has shown that the transcription factor Sox11 is required for mouse palatogenesis. However, whether Sox11 is primarily involved in the regulation of palatogenesis still remains elusive. In this study, we explored the role ofSox11in palatogenesis by analyzing the developmental mechanism in cleft palate formation in mutants deficient in Sox11. Sox11 is expressed both in the developing palatal shelf and in the surrounding structures, including the mandible. We found that cleft palate occurs only in the mutant in which Sox11is directly deleted. As in the wild type, the palatal shelves in the Sox11 mutant undergo outgrowth in a downward direction and exhibit potential for fusion and elevation. However, mutant palatal shelves encounter clefting, which is associated with a malpositioned tongue that results in physical obstruction of palatal shelf elevation at embryonic day 14.5 (E14.5). We found that loss of Sox11led to reduced cell proliferation in the developing mandibular mesenchyme via Cyclin D1, leading to mandibular hypoplasia, which blocks tongue descent. Extensive analyses of gene expression inSox11 deficiency identified FGF9 as a potential candidate target of Sox11 in the modulation of cell proliferation both in the mandible and the palatal shelf between E12.5 and E13.5. Finally we show, using in vitro assays, that Sox11 directly regulates the expression of Fgf9 and that application of FGF9 protein to Sox11-deficient palatal shelves restores the rate of BrdU incorporation. Taken together, the palate defects presented in the Sox11 loss mutant mimic the clefting in the Pierre Robin sequence in humans.

Strain-dependent effects of transforming growth factor-β1 and 2 during mouse secondary palate development

Cleft palate is a common birth defect affecting 1 in 700 births. Transforming growth factor-βs (TGF-βs) are important signaling molecules, and their functions in murine palate development have received great attention. TGF-β3 is expressed exclusively in palatal epithelial cells and mediates epithelial fusion, whereas the importance of TGF-β1 and 2 in palate have not yet been demonstrated in vivo, since inactivation of Tgf-β1 or Tgf-β2 genes in mice did not reveal significant palate defects. We hypothesized that TGF-β1 and TGF-β2 can compensate each other during palate formation. To test this, we generated Tgf-β1 and Tgf-β2 compound mutant mice and found that approximately 40% of [Tgf-β1(+/-); Tgf-β2(-/-)] compound mutant embryos display cleft palate on C57 background. In addition, 26% of Tgf-β2(-/-) embryos on 129 background, but not in C57 or Black Swiss, displayed cleft palate. TGF-β1 and 2 functions are required for murine palate development in strain-dependent manner.

Neural crest-specific deletion of Ldb1 leads to cleft secondary palate with impaired palatal shelf elevation

Background

LIM domain binding protein 1 (LDB1) is a transcriptional co-factor, which interacts with multiple transcription factors and other proteins containing LIM domains. Complete inactivation of Ldb1 in mice resulted in early embryonic lethality with severe patterning defects during gastrulation. Tissue-specific deletions using a conditional knockout allele revealed additional roles of Ldb1 in the development of the central nervous system, hematopoietic system, and limbs. The goal of the current study was to determine the importance of Ldb1 function during craniofacial development in mouse embryos.

Results

We generated tissue-specific Ldb1 mutants using Wnt1-Cre, which causes deletion of a floxed allele in the neural crest; neural crest-derived cells contribute to most of the mesenchyme of the developing face. All examined Wnt1-Cre;Ldb1^fl/- mutants suffered from cleft secondary palate. Therefore, we performed a series of experiments to investigate how Ldb1 regulated palate development. First, we examined the expression of Ldb1 during normal development, and found that Ldb1 was expressed broadly in the palatal mesenchyme during early stages of palate development. Second, we compared the morphology of the developing palate in control and Ldb1 mutant embryos using sections. We found that the mutant palatal shelves had abnormally blunt appearance, and failed to elevate above the tongue at the posterior domain. An in vitro head culture experiment indicated that the elevation defect was not due to interference by the tongue. Finally, in the Ldb1 mutant palatal shelves, cell proliferation was abnormal in the anterior, and the expression of Wnt5a, Pax9 and Osr2, which regulate palatal shelf elevation, was also altered.

Conclusions

The function of Ldb1 in the neural crest-derived palatal mesenchyme is essential for normal morphogenesis of the secondary palate.

Genome-wide profiling of in vivo LPS-responsive genes in splenic myeloid cells

Lipopolysaccharide (LPS), the major causative agent of bacterial sepsis, has been used by many laboratories in genome-wide expression profiling of the LPS response. However, these studies have predominantly used in vitro cultured macrophages (Macs), which may not accurately reflect the LPS response of these innate immune cells in vivo. To overcome this limitation and to identify inflammatory genes in vivo, we have profiled genome-wide expression patterns in non-lymphoid, splenic myeloid cells extracted directly from LPS-treated mice. Genes encoding factors known to be involved in mediating or regulating inflammatory processes, such as cytokines and chemokines, as well as many genes whose immunological functions are not well known, were strongly induced by LPS after 3 h or 8 h of treatment. Most of the highly LPS-responsive genes that we randomly selected from the microarray data were independently confirmed by quantitative RT-PCR, implying that our microarray data are quite reliable. When our in vivo data were compared to previously reported microarray data for in vitro LPS-treated Macs, a significant proportion (∼20%) of the in vivo LPS-responsive genes defined in this study were specific to cells exposed to LPS in vivo, but a larger proportion of them (∼60%) were influenced by LPS in both in vitro and in vivo settings. This result indicates that our in vivo LPS-responsive gene set includes not only previously identified in vitro LPS-responsive genes but also novel LPS-responsive genes. Both types of genes would be a valuable resource in the future for understanding inflammatory responses in vivo.

The etiology of cleft palate formation in BMP7-deficient mice

Palatogenesis is a complex process implying growth, elevation and fusion of the two lateral palatal shelves during embryogenesis. This process is tightly controlled by genetic and mechanistic cues that also coordinate the growth of other orofacial structures. Failure at any of these steps can result in cleft palate, which is a frequent craniofacial malformation in humans. To understand the etiology of cleft palate linked to the BMP signaling pathway, we studied palatogenesis in Bmp7-deficient mouse embryos. Bmp7 expression was found in several orofacial structures including the edges of the palatal shelves prior and during their fusion. Bmp7 deletion resulted in a general alteration of oral cavity morphology, unpaired palatal shelf elevation, delayed shelf approximation, and subsequent lack of fusion. Cell proliferation and expression of specific genes involved in palatogenesis were not altered in Bmp7-deficient embryos. Conditional ablation of Bmp7 with Keratin14-Cre or Wnt1-Cre revealed that neither epithelial nor neural crest-specific loss of Bmp7 alone could recapitulate the cleft palate phenotype. Palatal shelves from mutant embryos were able to fuse when cultured in vitro as isolated shelves in proximity, but not when cultured as whole upper jaw explants. Thus, deformations in the oral cavity of Bmp7-deficient embryos such as the shorter and wider mandible were not solely responsible for cleft palate formation. These findings indicate a requirement for Bmp7 for the coordination of both developmental and mechanistic aspects of palatogenesis.

BMP4 signaling mediates Zeb family in developing mouse tooth

Tooth morphogenesis is regulated by sequential and reciprocal interaction between oral epithelium and neural-crest-derived ectomesenchyme. The interaction is controlled by various signal molecules such as bone morphogenetic protein (BMP), Hedgehog, fibroblast growth factor (FGF), and Wnt. Zeb family is known as a transcription factor, which is essential for neural development and neural-crest-derived tissues, whereas the role of the Zeb family in tooth development remains unclear. Therefore, this study aimed to investigate the expression profiles of Zeb1 and Zeb2 during craniofacial development focusing on mesenchyme of palate, hair follicle, and tooth germ from E12.5 to E16.5. In addition, we examined the interaction between Zeb family and BMP4 during tooth development. Both Zeb1 and Zeb2 were expressed at mesenchyme of the palate, hair follicle, and tooth germ throughout the stages. In the case of tooth germ at the cap stage, the expression of Zeb1 and Zeb2 was lost in epithelium-separated dental mesenchyme. However, the expression of Zeb1 and Zeb2 in the dental mesenchyme was recovered by Bmp4 signaling via BMP4-soaked bead and tissue recombination. Our results suggest that Zeb1 and Zeb2, which were mediated by BMP4, play an important role in neural-crest-derived craniofacial organ morphogenesis, such as tooth development.

Palatogenesis: morphogenetic and molecular mechanisms of secondary palate development

Mammalian palatogenesis is a highly regulated morphogenetic process during which the embryonic primary and secondary palatal shelves develop as outgrowths from the medial nasal and maxillary prominences, respectively, remodel and fuse to form the intact roof of the oral cavity. The complexity of control of palatogenesis is reflected by the common occurrence of cleft palate in humans. Although the embryology of the palate has long been studied, the past decade has brought substantial new knowledge of the genetic control of secondary palate development. Here, we review major advances in the understanding of the morphogenetic and molecular mechanisms controlling palatal shelf growth, elevation, adhesion and fusion, and palatal bone formation.

miR-200b regulates cell migration via Zeb family during mouse palate development

Palate development requires coordinating proper cellular and molecular events in palatogenesis, including the epithelial-mesenchymal transition (EMT), apoptosis, cell proliferation, and cell migration. Zeb1 and Zeb2 regulate epithelial cadherin (E-cadherin) and EMT during organogenesis. While microRNA 200b (miR-200b) is known to be a negative regulator of Zeb1 and Zeb2 in cancer progression, its regulatory effects on Zeb1 and Zeb2 in palatogenesis have not yet been clarified. The aim of this study is to investigate the relationship between the regulators of palatal development, specifically, miR-200b and the Zeb family. Expression of both Zeb1 and Zeb2 was detected in the mesenchyme of the mouse palate, while miR-200b was expressed in the medial edge epithelium. After contact with the palatal shelves, miR-200b was expressed in the palatal epithelial lining and epithelial island around the fusion region but not in the palatal mesenchyme. The function of miR-200b was examined by overexpression via a lentiviral vector in the palatal shelves. Ectopic expression of miR-200b resulted in suppression of the Zeb family, upregulation of E-cadherin, and changes in cell migration and palatal fusion. These results suggest that miR-200b plays crucial roles in cell migration and palatal fusion by regulating Zeb1 and Zeb2 as a noncoding RNA during palate development.

Mesenchymal cell remodeling during mouse secondary palate reorientation

The formation of mammalian secondary palate requires a series of developmental events such as growth, elevation, and fusion. Despite recent advances in the field of palate development, the process of palate elevation remains poorly understood. The current consensus on palate elevation is that the distal end of the vertical palatal shelf corresponds to the medial edge of the elevated horizontal palatal shelf. We provide evidence suggesting that the prospective medial edge of the vertical palate is located toward the interior side (the side adjacent to the tongue), instead of the distal end, of the vertical palatal shelf and that the horizontal palatal axis is generated through palatal outgrowth from the side of the vertical palatal shelf rather than rotating the pre-existing vertical axis orthogonally. Because palate elevation represents a classic example of embryonic tissue re-orientation, our findings here may also shed light on the process of tissue re-orientation in general.

Human cleft lip and palate fibroblasts and normal nicotine-treated fibroblasts show altered in vitro expressions of genes related to molecular signaling pathways and extracellular matrix metabolism

Nonsyndromic cleft lip with or without cleft palate (CLP) is a frequent craniofacial malformation caused by both genetic and environmental factors. Maternal smoking during pregnancy is a known risk factor, due to the teratogenic role of nicotine. To assess and compare the impact of CLP and nicotine, we studied the quantitative expression of genes involved in signaling pathways and extracellular matrix (ECM) metabolism in human normal nicotine-treated (NicN) and CLP fibroblasts compared to normal control (CTRL) cells. Palatal fibroblast cultures from seven CLP children and seven age-matched CTRL subjects were established and subconfluent cells incubated for 24 h without (CTRL and CLP fibroblasts) or with (NicN fibroblasts) 0.6 mM nicotine. Gene expressions were analyzed by real-time quantitative PCR. For the first time, a regulated cholinergic signaling in our human fibroblasts in vitro was demonstrated. Members of TGF-beta, retinoic acid (RA), and GABA-ergic signaling systems were also differently regulated. Among the ECM genes, fibronectin, syndecan, integrin alpha2, and MMP13 genes were concordantly modulated, while integrin beta5, and decorin genes were discordantly modulated. Interestingly, nicotine treatment regulated gene expressions of CD44 and CLPTM1, two candidate genes for CLP. Our findings show a positive association between nicotine treatment and CLP phenotype. Results suggest that nicotine deranges normal palate development, which might contribute to the development of a CLP malformative phenotype, through the impairment of some important signaling systems and ECM composition.

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.

Regulation of Epithelial-Mesenchymal Transition in Palatal Fusion

During palatal fusion, the midline epithelial seam between the palatal shelves degrades to achieve mesenchymal confluence. Morphological and molecular evidence support the theory that the epithelial-mesenchymal transition is one mechanism that regulates palatal fusion. It appears that transforming growth factor (TGF)-β signaling plays a role in palatal EMT. TGFβ3 is the main inducer in palatal fusion and activates both Smad-dependent and -independent signaling pathways, including the key EMT transcription factors, Lef1, Twist, and Snail1, in the MEE prior to the palatal EMT program. The roles and interactions among these transcription factors will be discussed.

Genetic determinants of facial clefting: analysis of 357 candidate genes using two national cleft studies from Scandinavia

Background

Facial clefts are common birth defects with a strong genetic component. To identify fetal genetic risk factors for clefting, 1536 SNPs in 357 candidate genes were genotyped in two population-based samples from Scandinavia (Norway: 562 case-parent and 592 control-parent triads; Denmark: 235 case-parent triads).

Methodology/Principal Findings

We used two complementary statistical methods, TRIMM and HAPLIN, to look for associations across these two national samples. TRIMM tests for association in each gene by using multi-SNP genotypes from case-parent triads directly without the need to infer haplotypes. HAPLIN on the other hand estimates the full haplotype distribution over a set of SNPs and estimates relative risks associated with each haplotype. For isolated cleft lip with or without cleft palate (I-CL/P), TRIMM and HAPLIN both identified significant associations with IRF6 and ADH1C in both populations, but only HAPLIN found an association with FGF12. For isolated cleft palate (I-CP), TRIMM found associations with ALX3, MKX, and PDGFC in both populations, but only the association with PDGFC was identified by HAPLIN. In addition, HAPLIN identified an association with ETV5 that was not detected by TRIMM.

Conclusion/Significance

Strong associations with seven genes were replicated in the Scandinavian samples and our approach effectively replicated the strongest previously known association in clefting—with IRF6. Based on two national cleft cohorts of similar ancestry, two robust statistical methods and a large panel of SNPs in the most promising cleft candidate genes to date, this study identified a previously unknown association with clefting for ADH1C and provides additional candidates and analytic approaches to advance the field.

Micromanaging Palate Development

Development of the facial skeleton is one of the most intriguing and intricate events that occur during human development. Most of the bone, cartilage and connective tissue that compose the face and neck arise from a class of cells, referred to as neural crest cells, which are initially located at some distance from the facial primordium. A complex set of events regulated by specific gene products direct the formation, migration and differentiation of these cells, leading to what is viewed as "prototypical" adult facial features. These basic developmental processes are recapitulated during the formation of the palate, termed palatogenesis. In this review, we summarize the basic embryology leading to palate formation, discuss mechanisms that can lead to palatal dysmorphologies and highlight a new interaction that has recently been demonstrated to play a role in palate development. This interaction, involving small non-coding RNAs referred to as microRNAs, not only establishes a new level of regulation to cellular development, but may also serve as attractive targets for future efforts directed at clinical treatment of birth defect syndromes.