Snail family members and cell survival in physiological and pathological cleft palates

Reciprocal Modulation of Tumour and Immune Cell Motility: Uncovering Dynamic Interplays and Therapeutic Approaches

Dysregulated cell movement is a hallmark of cancer progression and metastasis, the leading cause of cancer-related mortality. The metastatic cascade involves tumour cell migration, invasion, intravasation, dissemination, and colonisation of distant organs. These processes are influenced by reciprocal interactions between cancer cells and the tumour microenvironment (TME), including immune cells, stromal components, and extracellular matrix proteins. The epithelial-mesenchymal transition (EMT) plays a crucial role in providing cancer cells with invasive and stem-like properties, promoting dissemination and resistance to apoptosis. Conversely, the mesenchymal-epithelial transition (MET) facilitates metastatic colonisation and tumour re-initiation. Immune cells within the TME contribute to either anti-tumour response or immune evasion. These cells secrete cytokines, chemokines, and growth factors that shape the immune landscape and influence responses to immunotherapy. Notably, immune checkpoint blockade (ICB) has transformed cancer treatment, yet its efficacy is often dictated by the immune composition of the tumour site. Elucidating the molecular cross-talk between immune and cancer cells, identifying predictive biomarkers for ICB response, and developing strategies to convert cold tumours into immune-active environments is critical to overcoming resistance to immunotherapy and improving patient survival.

Exploiting transcription factors to target EMT and cancer stem cells for tumor modulation and therapy

Transcription factors (TFs) are essential in controlling gene regulatory networks that determine cellular fate during embryogenesis and tumor development. TFs are the major players in promoting cancer stemness by regulating the function of cancer stem cells (CSCs). Understanding how TFs interact with their downstream targets for determining cell fate during embryogenesis and tumor development is a critical area of research. CSCs are increasingly recognized for their significance in tumorigenesis and patient prognosis, as they play a significant role in cancer initiation, progression, metastasis, and treatment resistance. However, traditional therapies have limited effectiveness in eliminating this subset of cells, allowing CSCs to persist and potentially form secondary tumors. Recent studies have revealed that cancer cells and tumors with CSC-like features also exhibit genes related to the epithelial-to-mesenchymal transition (EMT). EMT-associated transcription factors (EMT-TFs) like TWIST and Snail/Slug can upregulate EMT-related genes and reprogram cancer cells into a stem-like phenotype. Importantly, the regulation of EMT-TFs, particularly through post-translational modifications (PTMs), plays a significant role in cancer metastasis and the acquisition of stem cell-like features. PTMs, including phosphorylation, ubiquitination, and SUMOylation, can alter the stability, localization, and activity of EMT-TFs, thereby modulating their ability to drive EMT and stemness properties in cancer cells. Although targeting EMT-TFs holds potential in tackling CSCs, current pharmacological approaches to do so directly are unavailable. Therefore, this review aims to explore the role of EMT- and CSC-TFs, their connection and impact in cellular development and cancer, emphasizing the potential of TF networks as targets for therapeutic intervention.

BMP4 Regulates EMT to be Involved in non-Syndromic Cleft lip With or Without Palate

OBJECTIVE

In the previous study, we identified bone morphogenetic protein 4 (BMP4) responsible for non-syndromic cleft lip with or without cleft palate (NSCL/P). We aimed to elucidate the effects and mechanisms of BMP4 on epithelial-mesenchymal transition (EMT) through Smad1 signaling pathway to be involved in NSCL/P.

METHODS

The human oral epidermoid carcinoma cells (KBs) were transfected with plasmids or small interfering RNA (siRNA) to build the models. The migration of the cells was evaluated by transwell assay. Western blotting and quantitative real-time reverse transcription-polymerase chain reaction (qRT-PCR) were used to detect the expressions of BMP4, E-cadherin, N-cadherin, EMT-related transcription factors snal1 and snal2, matrix metalloproteinase 2 (MMP2), MMP9, Smad1, and phosphorylated Smad1.

RESULTS

In the overexpression group, the migration number of cells was increased significantly. The protein expression of E-cadherin was decreased significantly, while the protein expression level of the N-cadherin was increased significantly. The protein and mRNA expressions of MMP2, MMP9, snal1, and snal2 were significantly higher. The expression level of Smad1 was not significantly changed, while the phosphorylation of Smad1 was significantly increased. In the BMP4-siRNA group, the migrating number cells was significantly decreased. The protein expression of E-cadherin was increased significantly, while the expression of N-cadherin was significantly decreased. The protein and mRNA expressions of MMP2, MMP9, snal1, and snal2 were significantly lower than that of the control group. The expressions of Smad1 and phosphorylation of Smad1 were not significantly changed.

CONCLUSIONS

BMP4 enhances cell migration and promotes cell EMT through Smad1 signaling pathway. Abnormal BMP4 mediates migration and EMT through other relevant signaling pathways resulting in NSCL/P. The study provides new insight into the mechanisms of NSCL/P associated with BMP4.n.

Proactive and reactive roles of TGF-β in cancer

Cancer cells adapt to varying stress conditions to survive through plasticity. Stem cells exhibit a high degree of plasticity, allowing them to generate more stem cells or differentiate them into specialized cell types to contribute to tissue development, growth, and repair. Cancer cells can also exhibit plasticity and acquire properties that enhance their survival. TGF-β is an unrivaled growth factor exploited by cancer cells to gain plasticity. TGF-β-mediated signaling enables carcinoma cells to alter their epithelial and mesenchymal properties through epithelial-mesenchymal plasticity (EMP). However, TGF-β is a multifunctional cytokine; thus, the signaling by TGF-β can be detrimental or beneficial to cancer cells depending on the cellular context. Those cells that overcome the anti-tumor effect of TGF-β can induce epithelial-mesenchymal transition (EMT) to gain EMP benefits. EMP allows cancer cells to alter their cell properties and the tumor immune microenvironment (TIME), facilitating their survival. Due to the significant roles of TGF-β and EMP in carcinoma progression, it is essential to understand how TGF-β enables EMP and how cancer cells exploit this plasticity. This understanding will guide the development of effective TGF-β-targeting therapies that eliminate cancer cell plasticity.

Gene Regulatory Networks and Signaling Pathways in Palatogenesis and Cleft Palate: A Comprehensive Review

Palatogenesis is a complex and intricate process involving the formation of the palate through various morphogenetic events highly dependent on the surrounding context. These events comprise outgrowth of palatal shelves from embryonic maxillary prominences, their elevation from a vertical to a horizontal position above the tongue, and their subsequent adhesion and fusion at the midline to separate oral and nasal cavities. Disruptions in any of these processes can result in cleft palate, a common congenital abnormality that significantly affects patient's quality of life, despite surgical intervention. Although many genes involved in palatogenesis have been identified through studies on genetically modified mice and human genetics, the precise roles of these genes and their products in signaling networks that regulate palatogenesis remain elusive. Recent investigations have revealed that palatal shelf growth, patterning, adhesion, and fusion are intricately regulated by numerous transcription factors and signaling pathways, including Sonic hedgehog (Shh), bone morphogenetic protein (Bmp), fibroblast growth factor (Fgf), transforming growth factor beta (Tgf-β), Wnt signaling, and others. These studies have also identified a significant number of genes that are essential for palate development. Integrated information from these studies offers novel insights into gene regulatory networks and dynamic cellular processes underlying palatal shelf elevation, contact, and fusion, deepening our understanding of palatogenesis, and facilitating the development of more efficacious treatments for cleft palate.

Increased miR-200c levels disrupt palatal fusion by affecting apoptosis, cell proliferation, and cell migration

The mammalian palate separates the oral and nasal cavities, facilitating proper feeding, respiration, and speech. Palatal shelves, composed of neural crest-derived mesenchyme and surrounding epithelium, are a pair of maxillary prominences contributing to this structure. Palatogenesis reaches completion upon the fusion of the midline epithelial seam (MES) following contact between medial edge epithelium (MEE) cells in the palatal shelves. This process entails numerous cellular and molecular occurrences, including apoptosis, cell proliferation, cell migration, and epithelial-mesenchymal transition (EMT). MicroRNAs (miRs) are small, endogenous, non-coding RNAs derived from double-stranded hairpin precursors that regulate gene expression by binding to target mRNA sequences. Although miR-200c is a positive regulator of E-cadherin, its role in palatogenesis remains unclear. This study aims to explore the role of miR-200c in palate development. Before contact with palatal shelves, mir-200c was expressed in the MEE along with E-cadherin. After palatal shelf contact, miR-200c was present in the palatal epithelial lining and epithelial islands surrounding the fusion region but absent in the mesenchyme. The function of miR-200c was investigated by utilizing a lentiviral vector to facilitate overexpression. Ectopic expression of miR-200c resulted in E-cadherin upregulation, impaired dissolution of the MES, and reduced cell migration for palatal fusion. The findings imply that miR-200c is essential in palatal fusion as it governs E-cadherin expression, cell death, and cell migration, acting as a non-coding RNA. This study may contribute to clarifying the underlying molecular mechanisms in palate formation and provides insights into potential gene therapies for cleft palate.

Exposure to b-LED Light While Exerting Antimicrobial Activity on Gram-Negative and -Positive Bacteria Promotes Transient EMT-like Changes and Growth Arrest in Keratinocytes

While blue LED (b-LED) light is increasingly being studied for its cytotoxic activity towards bacteria in therapy of skin-related infections, its effects on eukaryotic cells plasticity are less well characterized. Moreover, since different protocols are often used, comparing the effect of b-LED towards both microorganisms and epithelial surfaces may be difficult. The aim of this study was to analyze, in the same experimental setting, both the bactericidal activity and the effects on human keratinocytes. Exposure to b-LED induced an intense cytocidal activity against Gram-positive (i.e, Staphylococcus aureus) and Gram-negative (i.e., Pseudomonas aeruginosa) bacteria associated with catheter-related infections. Treatment with b-LED of a human keratinocyte cell line induced a transient cell cycle arrest. At the molecular level, exposure to b-LED induced a transient downregulation of Cyclin D1 and an upregulation of p21, but not signs of apoptosis. Interestingly, a transient induction of phosphor-histone γ-H2Ax, which is associated with genotoxic damages, was observed. At the same time, keratinocytes underwent a transient epithelial to mesenchymal transition (EMT)-like phenotype, characterized by E-cadherin downregulation and SNAIL/SLUG induction. As a functional readout of EMT induction, a scratch assay was performed. Surprisingly, b-LED treatment provoked a delay in the scratch closure. In conclusion, we demonstrated that b-LED microbicidal activity is associated with complex responses in keratinocytes that certainly deserve further analysis.

Endothelial-Mesenchymal Transition in Cardiovascular Disease

Endothelial-to-mesenchymal transition is a dynamic process in which endothelial cells suppress constituent endothelial properties and take on mesenchymal cell behaviors. To begin the process, endothelial cells loosen their cell-cell junctions, degrade the basement membrane, and migrate out into the perivascular surroundings. These initial endothelial behaviors reflect a transient modulation of cellular phenotype, that is, a phenotypic modulation, that is sometimes referred to as partial endothelial-to-mesenchymal transition. Loosening of endothelial junctions and migration are also seen in inflammatory and angiogenic settings such that endothelial cells initiating endothelial-to-mesenchymal transition have overlapping behaviors and gene expression with endothelial cells responding to inflammatory signals or sprouting to form new blood vessels. Reduced endothelial junctions increase permeability, which facilitates leukocyte trafficking, whereas endothelial migration precedes angiogenic sprouting and neovascularization; both endothelial barriers and quiescence are restored as inflammatory and angiogenic stimuli subside. Complete endothelial-to-mesenchymal transition proceeds beyond phenotypic modulation such that mesenchymal characteristics become prominent and endothelial functions diminish. In proadaptive, regenerative settings the new mesenchymal cells produce extracellular matrix and contribute to tissue integrity whereas in maladaptive, pathologic settings the new mesenchymal cells become fibrotic, overproducing matrix to cause tissue stiffness, which eventually impacts function. Here we will review what is known about how TGF (transforming growth factor) β influences this continuum from junctional loosening to cellular migration and its relevance to cardiovascular diseases.

Transcriptional analysis of cleft palate in TGFβ3 mutant mice

Cleft palate (CP) is one of the most common craniofacial birth defects, impacting about 1 in 800 births in the USA. Tgf-β3 plays a critical role in regulating murine palate development, and Tgf-β3 null mutants develop cleft palate with 100% penetrance. In this study, we compared global palatal transcriptomes of wild type (WT) and Tgf-β3 −/− homozygous (HM) mouse embryos at the crucial palatogenesis stages of E14.5, and E16.5, using RNA-seq data. We found 1,809 and 2,127 differentially expressed genes at E16.5 vs. E14.5 in the WT and HM groups, respectively (adjusted p < 0.05; |fold change|> 2.0). We focused on the genes that were uniquely up/downregulated in WT or HM at E16.5 vs. E14.5 to identify genes associated with CP. Systems biology analysis relating to cell behaviors and function of WT and HM specific genes identified functional non-Smad pathways and preference of apoptosis to epithelial-mesenchymal transition. We identified 24 HM specific and 11 WT specific genes that are CP-related and/or involved in Tgf-β3 signaling. We validated the expression of 29 of the 35 genes using qRT-PCR and the trend of mRNA expression is similar to that of RNA-seq data . Our results enrich our understanding of genes associated with CP that are directly or indirectly regulated via TGF-β.

EMT Factors and Metabolic Pathways in Cancer

The epithelial-mesenchymal transition (EMT) represents a biological program during which epithelial cells lose their cell identity and acquire a mesenchymal phenotype. EMT is normally observed during organismal development, wound healing and tissue fibrosis. However, this process can be hijacked by cancer cells and is often associated with resistance to apoptosis, acquisition of tissue invasiveness, cancer stem cell characteristics, and cancer treatment resistance. It is becoming evident that EMT is a complex, multifactorial spectrum, often involving episodic, transient or partial events. Multiple factors have been causally implicated in EMT including transcription factors (e.g., SNAIL, TWIST, ZEB), epigenetic modifications, microRNAs (e.g., miR-200 family) and more recently, long non-coding RNAs. However, the relevance of metabolic pathways in EMT is only recently being recognized. Importantly, alterations in key metabolic pathways affect cancer development and progression. In this review, we report the roles of key EMT factors and describe their interactions and interconnectedness. We introduce metabolic pathways that are involved in EMT, including glycolysis, the TCA cycle, lipid and amino acid metabolism, and characterize the relationship between EMT factors and cancer metabolism. Finally, we present therapeutic opportunities involving EMT, with particular focus on cancer metabolic pathways.

Histone Demethylase JMJD1A Promotes Tumor Progression via Activating Snail in Prostate Cancer

The histone demethylase JMJD1A plays a key functional role in spermatogenesis, sex determination, stem cell renewal, and cancer via removing mono- and di-methyl groups from H3K9 to epigenetically control gene expression. However, its role in prostate cancer progression remains unclear. Here, we found JMJD1A was significantly elevated in prostate cancer tissue compared with matched normal tissue. Ectopic JMJD1A expression in prostate cancer cells promoted proliferation, migration, and invasion in vitro, and tumorigenesis in vivo; JMJD1A knockdown exhibited the opposite effects. Mechanically, we revealed that JMJD1A directly interacted with the Snail gene promoter and regulated its transcriptional activity, promoting prostate cancer progression both in vitro and in vivo. Furthermore, we found that JMJD1A transcriptionally activated Snail expression via H3K9me1 and H3K9me2 demethylation at its special promoter region. In summary, our studies reveal JMJD1A plays an important role in regulating proliferation and progression of prostate cancer cells though Snail, and thus highlight JMJD1A as potential therapeutic target for advanced prostate cancer. IMPLICATIONS: Our studies identify that JMJD1A promotes the proliferation and progression of prostate cancer cells through enabling Snail transcriptional activation, and thus highlight JMJD1A as potential therapeutic target for advanced prostate cancer.

Epithelial-Mesenchymal Plasticity in Cancer Progression and Metastasis

Epithelial-to-mesenchymal transition (EMT) and its reversed process, mesenchymal-to-epithelial transition (MET), are fundamental processes in embryonic development and tissue repair but confer malignant properties to carcinoma cells, including invasive behavior, cancer stem cell activity, and greater resistance to chemotherapy and immunotherapy. Understanding the molecular and cellular basis of EMT provides fundamental insights into the etiology of cancer and may, in the long run, lead to new therapeutic strategies. Here, we discuss the regulatory mechanisms and pathological roles of epithelial-mesenchymal plasticity, with a focus on recent insights into the complexity and dynamics of this phenomenon in cancer.

New insights into the mechanisms of epithelial-mesenchymal transition and implications for cancer

Epithelial-mesenchymal transition (EMT) is a cellular programme that is known to be crucial for embryogenesis, wound healing and malignant progression. During EMT, cell-cell and cell-extracellular matrix interactions are remodelled, which leads to the detachment of epithelial cells from each other and the underlying basement membrane, and a new transcriptional programme is activated to promote the mesenchymal fate. In the context of neoplasias, EMT confers on cancer cells increased tumour-initiating and metastatic potential and a greater resistance to elimination by several therapeutic regimens. In this Review, we discuss recent findings on the mechanisms and roles of EMT in normal and neoplastic tissues, and the cell-intrinsic signals that sustain expression of this programme. We also highlight how EMT gives rise to a variety of intermediate cell states between the epithelial and the mesenchymal state, which could function as cancer stem cells. In addition, we describe the contributions of the tumour microenvironment in inducing EMT and the effects of EMT on the immunobiology of carcinomas.

Emulating the early phases of human tooth development in vitro

Functional in vitro models emulating the physiological processes of human organ formation are invaluable for future research and the development of regenerative therapies. Here, a developmentally inspired approach is pursued to reproduce fundamental steps of human tooth organogenesis in vitro using human dental pulp cells. Similar to the in vivo situation of tooth initiating mesenchymal condensation, a 3D self-organizing culture was pursued resulting in an organoid of the size of a human tooth germ with odontogenic marker expression. Furthermore, the model is capable of epithelial invagination into the condensed mesenchyme, mimicking the reciprocal tissue interactions of human tooth development. Comprehensive transcriptome analysis revealed activation of well-studied as well as rather less investigated signaling pathways implicated in human tooth organogenesis, such as the Notch signaling. Early condensation in vitro revealed a shift to the TGFß signal transduction pathway and a decreased RhoA small GTPase activity, connected to the remodeling of the cytoskeleton and actin-mediated mechanotransduction. Therefore, this in vitro model of tooth development provides a valuable model to study basic human developmental mechanisms.

Involvement of partial EMT in cancer progression

The epithelial-mesenchymal transition (EMT) provides an outstanding example of cellular plasticity during embryonic development and cancer progression. During EMT in embryonic development, epithelial cells lose all vestiges of their epithelial origin and acquire a fully mesenchymal phenotype, known as complete EMT, which is typically characterized by a so-called cadherin switch. Conversely, during EMT in cancer progression, cancer cells that originate from epithelial cells exhibit both mesenchymal and epithelial characteristics, that is the hybrid E/M phenotype in a process known as partial EMT. Partial EMT in cancer cells is thought to enhance their invasive properties, generate circulating tumour cells and cancer stem cells, and promote resistance to anti-cancer drugs. These phenotypic changes are regulated by extracellular matrix components, exosomes and soluble factors, which regulate several transcription factors known as EMT transcription factors. In this review, I summarize our current understanding of the EMT program during cancer progression.

Effect of modulation of epithelial-mesenchymal transition regulators Snail1 and Snail2 on cancer cell radiosensitivity by targeting of the cell cycle, cell apoptosis and cell migration/invasion

Cancer is one of the leading causes of cancer-associated mortality worldwide. Several strategies of treatment, including radiotherapy, have been developed and used to treat this disease. However, post-treatment metastasis and resistance to treatment are two major causes for the limited effectiveness of radiotherapy in cancer patients. Epithelial-mesenchymal transition (EMT) is regulated by SNAIL family transcription factors, including Snail1 and Snail2 (Slug), and serves important roles in progression and cancer resistance to treatment. Snail1 and Slug also have been shown to be implicated in cancer treatment resistance. For resolving the resistance to treatment problems, combining the modulation of gene expression with radiotherapy is a novel strategy to treat patients with cancer. The present review focuses on the effect of Snail1 and Slug on cancer radiosensitivity by targeting cell apoptosis, the cell cycle and cell migration/invasion.

Face morphogenesis is promoted by Pbx-dependent EMT via regulation of Snail1 during frontonasal prominence fusion

Human cleft lip with or without cleft palate (CL/P) is a common craniofacial abnormality caused by impaired fusion of the facial prominences. We have previously reported that, in the mouse embryo, epithelial apoptosis mediates fusion at the seam where the prominences coalesce. Here, we show that apoptosis alone is not sufficient to remove the epithelial layers. We observed morphological changes in the seam epithelia, intermingling of cells of epithelial descent into the mesenchyme and molecular signatures of epithelial-mesenchymal transition (EMT). Utilizing mouse lines with cephalic epithelium-specific Pbx loss exhibiting CL/P, we demonstrate that these cellular behaviors are Pbx dependent, as is the transcriptional regulation of the EMT driver Snail1. Furthermore, in the embryo, the majority of epithelial cells expressing high levels of Snail1 do not undergo apoptosis. Pbx1 loss- and gain-of-function in a tractable epithelial culture system revealed that Pbx1 is both necessary and sufficient for EMT induction. This study establishes that Pbx-dependent EMT programs mediate murine upper lip/primary palate morphogenesis and fusion via regulation of Snail1. Of note, the EMT signatures observed in the embryo are mirrored in the epithelial culture system.

miR-124 represses the mesenchymal features and suppresses metastasis in Ewing sarcoma

Metastasis is the most powerful predictor of poor outcome of Ewing sarcoma (ES). Thus, identification of new molecules involved in tumor metastasis is of crucial importance to reduce morbidity and mortality of this devastating disease. In this study, we found that miR-124, a highly conserved miRNA, was suppressed in ES tissues and might be associated with tumor metastasis through suppressing its mesenchymal features. Overexpression of miR-124 suppressed the invasion of ES cells in vitro and tumor metastasis in vivo, which might be achieved through suppressing its mesenchymal features, as overexpression of miR-124 could repress the mesenchymal genes expression, and inhibit cell differentiation to mesenchymal lineages in ES cells. However, when SLUG was experimentally restored in these cells, mesenchymal features including suppressed expression of mesenchymal genes and decreased invasive ability were observed. We also found that cyclin D2 (CCND2) was a novel target gene of miR-124, and was directly involved in miR-124-mediated suppressive effects on cell growth. Lastly, we found that treatment with 5-Aza-CdR restored the expression of miR-124, accompanied with suppressed cell proliferation, invasion and mesenchymal features of ES cells, which demonstrated that hypermethylation might be involved in the regulation of miR-124 expression. Collectively, our data suggest that hypermethylation-mediated suppression of miR-124 might be involved in the tumor initiation and metastasis through suppressing the mesenchymal features of ES cells.

Possible effect of SNAIL family transcriptional repressor 1 polymorphisms in non-syndromic cleft lip with or without cleft palate

OBJECTIVE

Orofacial development is a complex process subjected to failure impairing. Indeed, the cleft of the lip and/or of the palate is among the most frequent inborn malformations. The JARID2 gene has been suggested to be involved in non-syndromic cleft lip with or without cleft palate (nsCL/P) etiology. JARID2 interacts with the polycomb repressive complex 2 (PRC2) in regulating the expression patterns of developmental genes by modifying the chromatin state.

MATERIALS AND METHODS

Genes coding for the PRC2 components, as well as other genes active in cell differentiation and embryonic development, were selected for a family-based association study to verify their involvement in nsCL/P. A total of 632 families from Italy and Asia participated to the study.

RESULTS

Evidence of allelic association was found with polymorphisms of SNAI1; in particular, the rs16995010-G allele was undertransmitted to the nsCL/P cases [P = 0.004, odds ratio = 0.69 (95% C.I. 0.54-0.89)]. However, the adjusted significance value corrected for all the performed tests was P = 0.051.

CONCLUSIONS

The findings emerging by the present study suggest for the first time an involvement of SNAI1 in the nsCL/P onset.

CLINICAL RELEVANCE

Interestingly, SNAI1 is known to promote epithelial to mesenchymal transition by repressing E-cadherin expression, but it needs an intact PRC2 to act this function. Alterations of this process could contribute to the complex etiology of nsCL/P.

Potential Involvement of Snail Members in Neuronal Survival and Astrocytic Migration during the Gecko Spinal Cord Regeneration

Certain regenerative vertebrates such as fish, amphibians and reptiles are capable of regenerating spinal cord after injury. Most neurons of spinal cord will survive from the injury and regrow axons to repair circuits with an absence of glial scar formation. However, the underlying mechanisms of neuronal anti-apoptosis and glia-related responses have not been fully clarified during the regenerative process. Gecko has becoming an inspiring model to address spinal cord regeneration in amniotes. In the present study, we investigated the regulatory roles of Snail family members, the important transcriptional factors involved in both triggering of the cell migration and cell survival, during the spontaneous spinal cord regeneration. Both Snail1 and Snail3 have been shown to promote neuronal survival and astrocytic migration via anti-apoptotic and GTPases signaling following gecko tail amputation. Transforming growth factor-beta (TGFβ), together with other cytokines were involved in inducing expression of Snail protein. Our data indicate a conserved function of Snail proteins in embryonic development and tissue regeneration, which may provide clues for CNS repair in the mammals.

Gene Expression during Palate Fusion in vivo and in vitro

Failure of secondary palate fusion during embryogenesis is a cause of cleft palate. Disappearance of the medial epithelial seam (MES) is required to allow merging of the mesenchyme from both palatal shelves. This involves complex changes of the medial edge epithelial (MEE) cells and surrounding structures that are controlled by several genes whose spatio-temporal expression is tightly regulated. We have carried out morphological analyses and used a semi-quantitative RT-PCR technique to evaluate whether morphological changes and modulation in the expression of putative key genes, such as twist, snail, and E-cadherin, during the fusion process in palate organ culture parallel those observed in vivo, and show that this is indeed the case. We also show, using the organotypic model of palate fusion, that the down-regulation of the transcription factor snail that occurs with the progression of palate development is not dependent on fusion of the palatal shelves. Abbreviations: dsg1, desmoglein1; EMT, epithelial-mesenchymal transition; MEE, medial edge epithelium; MES, medial epithelial seam; RT-PCR, reverse-transcriptase polymerase chain-reaction.

The Role of Sonic Hedgehog in Craniofacial Patterning, Morphogenesis and Cranial Neural Crest Survival

Craniofacial defects (CFD) are a significant healthcare problem worldwide. Understanding both the morphogenetic movements which underpin normal facial development, as well as the molecular factors which regulate these processes, forms the cornerstone of future diagnostic, and ultimately, preventative therapies. The soluble morphogen Sonic hedgehog (Shh), a vertebrate orthologue of Drosophila hedgehog, is a key signalling factor in the regulation of craniofacial skeleton development in vertebrates, operating within numerous tissue types in the craniofacial primordia to spatiotemporally regulate the formation of the face and jaws. This review will provide an overview of normal craniofacial skeleton development, and focus specifically on the known roles of Shh in regulating the development and progression of the first pharyngeal arch, which in turn gives rise to both the upper jaw (maxilla) and lower jaw (mandible).

Involvement of ZEB1 and Snail1 in excessive production of extracellular matrix in Fuchs endothelial corneal dystrophy

Fuchs endothelial corneal dystrophy (FECD) due to corneal endothelial cell degeneration is a major cause of corneal transplantation. It is characterized by abnormal deposition of extracellular matrix (ECM), such as corneal guttae, accompanied by a loss of endothelial cells. Although recent studies have revealed several genomic factors, the molecular pathophysiology of FECD has not yet been revealed. In this study, we establish a cellular in vitro model by using immortalized corneal endothelial cells obtained from late-onset FECD and control patients and examined the involvement of epithelial mesenchymal transition (EMT) on excessive ECM production. We demonstrate that the EMT-inducing genes ZEB1 and SNAI1 were highly expressed in corneal endothelial cells in FECD and were involved in excessive production of ECM proteins, such as type I collagen and fibronectin through the transforming growth factor (TGF)-β signaling pathway. Furthermore, we found that SB431542, a specific inhibitor of TGF-β type I ALK receptors, suppressed the expression of ZEB1 and Snail1 followed by reduced production of ECM. These findings suggest that increased expression levels of ZEB1 and Snail1 in FECD cells were responsible for an increased responsiveness to TGF-β present in the aqueous humor and excessive production of ECM. In addition, these results suggest that the regulation of EMT-related genes by blocking the TGF-β signaling pathway may be a feasible therapeutic strategy for FECD.

SLUG: Critical regulator of epithelial cell identity in breast development and cancer

SLUG, a member of the SNAIL family of transcriptional repressors, is known to play a diverse number of roles in the cell, and its deregulation has been observed in a variety of cancers including breast. Here, we focus on SLUG's role as a master regulator of mammary epithelial cell (MEC) fate and lineage commitment in the normal mammary gland, and discuss how aberrant SLUG expression can influence breast tumor formation, phenotype, and progression. Specifically, we discuss SLUG's involvement in MEC differentiation, stemness, cellular plasticity, and the epithelial to mesenchymal transition (EMT), and highlight the complex connection between these programs during development and disease progression. Undoubtedly, delineating how molecular factors influence lineage identity and cell-state dynamics in the normal mammary gland will contribute to our understanding of breast tumor heterogeneity.

Epithelial Mesenchymal Transition: a double-edged sword

Epithelial mesenchymal transition (EMT) is a physiological process necessary to normal embryologic development. However in genesis of pathological situations, this transition can be perverted and signaling pathways have different regulations from those of normal physiology. In cancer invasion, such a mechanism leads to generation of circulating tumor cells. Epithelial cancer cells become motile mesenchymal cells able to shed from the primary tumor and enter in the blood circulation. This is the major part of the invasive way of cancer. EMT is also implicated in chronic diseases like fibrosis and particularly renal fibrosis. In adult organisms, healing is based on EMT which is beneficial to repair wounds even if it can sometimes exceed its goal and elicit fibrosis. In this review, we delineate the clinical significance of EMT in both physiological and pathological circumstances.

P-Akt/miR‑200 signaling regulates epithelial-mesenchymal transition, migration and invasion in circulating gastric tumor cells

Both circulating tumor cells (CTCs) and epithelial-mesenchymal transition (EMT) play an important role in invasion, migration and chemoresistant in tumor development. This study aimed to detect whether EMT occurred in human gastric CTCs and to explore the mechanism of EMT in human gastric CTCs. We analysed epithelial markers (pan-CK, E-cadherin), mesenchymal markers (N-cadherin, vimentin) EMT related miR‑200s, and Akt in gastric CTCs. The impact of miR‑200s on EMT, migration and invasion in CTCs was tested. We found that epithelial markers pan-CK, E-cadherin were decreased, and mesenchymal markers N-cadherin, vimentin were overexpressed in gastric CTCs. Expression of EMT related transcriptors, snail1, zeb1, twist1, were reversely correlated with miR‑200s, and were positively correlated with phospho-Akt. Upregulated of miR‑200s downregulated twist1 and zeb1 mRNA expression, and resulted in the supression of EMT, and impaired migration and invasion in gastric CTCs. Inhibition of p-Akt led to upregulation of miR‑200s. In conclusion, gastric CTCs exhibited remarkable EMT process, and p-Akt/miR‑200s signaling regulates EMT, migration and invasion in gastric CTCs.

Activation of phosphatidylinositol 3-kinase/Akt signaling mediates sorafenib-induced invasion and metastasis in hepatocellular carcinoma

Sorafenib, an antiangiogenic agent, can promote tumor invasion and metastasis. The phosphatidylinositol 3-kinase (PI3K)/Akt/Snail-dependent pathway plays an important role in tumor invasion and metastasis. Yet, little is known concerning the role of the PI3K/Akt/Snail-dependent pathway in sorafenib‑induced invasion and metastasis of hepatic carcinoma (HCC). A human HCC orthotopic xenograft model was established, and sorafenib (30 mg/kg/day) was administered orally. Tumor growth and intrahepatic metastasis were assessed, and immunohistochemistry was applied to analyze the activation of the PI3K/Akt/Snail-dependent pathway. HCC cell lines were treated with sorafenib (1, 5 and 10 µM), and proliferation, migration and invasion were assessed. Western blotting and real-time polymerase chain reaction (RT-PCR) were used to examine the related gene expression of epithelial-mesenchymal transition (EMT) markers and the PI3K/Akt/Snail-dependent pathway. Sorafenib inhibited tumor growth and promoted intrahepatic invasion and metastasis of the orthotopic tumors grown from SMMC7721-GFP cells in vivo. Additionally, sorafenib promoted EMT and invasion and metastasis of HCC cells in vitro. Importantly, sorafenib enhanced PI3K and Akt activation and upregulation of the expression of transcription factor Snail, a critical EMT mediator. The upregulation of transcription factor Snail expression by sorafenib may be related to activation of the PI3K/AKT signaling pathway. The PI3K/Akt/Snail-dependent pathway may mediate the pro-invasive and pro-metastatic effects of sorafenib on HCC by inducing EMT.

Classifying Common Oral Clefts: A New Approach after Descriptive Registration

Objective

Using the Dutch Oral Cleft Registration, which records the morphology and topography of common oral clefts, a new classification based on the (patho)embryology of the primary and secondary palates was tested.

Design

Prospective observational study.

Setting

The fifteen cleft palate teams in the Netherlands register patients to the national registry.

Patients

All unoperated patients with common oral clefts reported between 1997 and 2006 inclusive were included.

Main Outcome Measures

The classification is based on the pathoembryological events that ultimately result in various subphenotypes of common oral clefts. Patients within the three categories cleft lip/alveolus (CL/A), cleft lip/alveolus and palate (CL/AP), and cleft palate (CP) were divided into three subgroups: fusion defects, differentiation defects, and fusion and differentiation defects. A timetable was constructed to relate the type of clefting to the time of derailment during embryonic development.

Results

3512 patients were included. Patients with CL/A showed 22% fusion defects, 75% differentiation defects, and 3% fusion and differentiation defects. CL/AP patients and CP patients mostly showed fusion defects (70% and 89%, respectively). We were able to relate almost all (over 90%) cleft subphenotypes to specific weeks in embryonic development.

Conclusions

This classification provides new cleft subgroups that may be used for clinical and fundamental research. The subphenotypes of these subgroups originate from different time frames during embryonic development and different cell biological mechanisms, thereby enabling more accurate data for, e.g., gene identification and/or environmental factors.

The epithelial mesenchymal transition process may contribute to the pathogenesis of amniotic band syndrome

The etiology of the amniotic band syndrome is unknown, and has been subject of debate since the time of Hippocrates. The most accepted theories fail to cover all the abnomalities found in affected children. During organogenesis the epithelial-mesenchymal transition process (EMTP) participates in adequate formation of different organs from three embryo layers. Altered activation of EMTP occurs when the epithelial homeostasis is disturbed, the resulting myofibroblasts are able to secrete extracellular matrix proteins and deposit them on the tissues contributing to a fibrotic phenotype. If injury occurs during organogenesis, wound healing could be exaggerated and fibrotic response could be triggered. The molecule that regulates both of these processes (EMTP and fibrosis) is the transforming growth factor β (TGFβ); indeed null animals for TGFβ isoforms show similar defects than those seen in the amniotic band syndrome. Based on documented evidence this review intends to explain how the epithelial mesenchymal transition process may contribute to the pathogenesis of amniotic band syndrome.

Roles of retinoic acid signaling in normal and abnormal development of the palate and tongue

Palatogenesis involves various developmental events such as growth, elevation, elongation and fusion of opposing palatal shelves. Extrinsic factors such as mouth opening and subsequent tongue withdrawal are also needed for the horizontal elevation of palate shelves. Failure of any of these steps can lead to cleft palate, one of the most common birth defects in humans. It has been shown that retinoic acid (RA) plays important roles during palate development, but excess RA causes cleft palate in fetuses of both rodents and humans. Thus, the coordinated regulation of retinoid metabolism is essential for normal palatogenesis. The endogenous RA level is determined by the balance of RA-synthesizing (retinaldehyde dehydrogenases: RALDHs) and RA-degrading enzymes (CYP26s). Cyp26b1 is a key player in normal palatogenesis. In this review, we discuss recent progress in the study of the pathogenesis of RA-induced cleft palate, with special reference to the regulation of endogenous RA levels by RA-degrading enzymes.

Differential role of Snail1 and Snail2 zinc fingers in E-cadherin repression and epithelial to mesenchymal transition

Snail1 (Snail) and Snail2 (Slug) are transcription factors that share a similar DNA binding structure of four and five C2H2 zinc finger motifs (ZF), respectively. Both factors bind specifically to a subset of E-box motifs (E2-box: CAGGTG/CACCTG) in target promoters like the E-cadherin promoter and are key mediators of epithelial-to-mesenchymal transition (EMT). However, there are differences in the biological actions, in binding affinities to E-cadherin promoter, and in the target genes of Snail1 and Snail2, although the molecular bases are presently unknown. In particular, the role of each Snail1 and Snail2 ZF in the binding to E-boxes and in EMT induction has not been previously explored. We have approached this question by modeling Snail1 and Snail2 protein-DNA interactions and through mutational and functional assays of different ZFs. Results show that Snail1 efficient repression and binding to human and mouse E-cadherin promoter as well as EMT-inducing ability require intact ZF1 and ZF2, while for Snail2, either ZF3 or ZF4 is essential for those functions. Furthermore, the differential distribution of E2-boxes in mouse and human E-cadherin promoters also contributes to the differential Snail factor activity. These data indicate a non-equivalent role of Snail1 and Snail2 ZFs in gene repression, contributing to the elucidation of the molecular differences between these important EMT regulators.

Transcriptional and epigenetic regulation of neural crest induction during neurulation

Neurulation is one of the many important events in mammalian development. It is the stage of organogenesis in vertebrate embryos during which the neural tube is transformed into the primitive structures that will later develop into the central nervous system. Recent transcriptome analysis during neurulation and early organogenesis in humans and mice has identified the global dynamics of gene expression changes across developmental time. This has revealed a richer understanding of gene regulation and provides hints at the transcriptional regulatory networks that underlie these processes. Similarly, epigenome analysis, which collectively constitutes histone modifications, transcription factor binding, and other structural features associated with gene regulation, has given a renewed appreciation to the subtle mechanisms involving the process of neurulation. More specifically, the histone demethylases KDM4A and KDM6B have recently been shown to be key histone H3K4 and H3K27 modifiers that regulate neural crest specification and neural tube closure. Additionally, miRNAs have recently been shown to influence transcription of genes directly or by altering the levels of epigenetic modifiers and thus regulate gene expression. This mini review briefly summarizes the literature, highlighting the transcriptional and epigenetic regulation of key genes involved in neural crest induction and neural crest specification by transcription factors and miRNAs. Understanding how these mechanisms work individually and in clusters will shed light on pathways in the context of diseases associated with neural crest cell derivatives such as melanoma, cardiovascular defects and neuronal craniofacial defects.

Analysis of Snail1 function and regulation by Twist1 in palatal fusion

Palatal fusion is a tightly controlled process which comprises multiple cellular events, including cell movement and differentiation. Midline epithelial seam (MES) degradation is essential to palatal fusion. In this study, we analyzed the function of Snail1 during the degradation of the MES. We also analyzed the mechanism regulating the expression of the Snail1 gene in palatal shelves. Palatal explants treated with Snail1 siRNA did not degrade the MES and E-cadherin was not repressed leading to failure of palatal fusion. Transforming growth factor beta 3 (Tgfβ3) regulated Snail1 mRNA, as Snail1 expression decreased in response to Tgfβ3 neutralizing antibody and a PI-3 kinase (PI3K) inhibitor. Twist1, in collaboration with E2A factors, regulated the expression of Snail1. Twist1/E47 dimers bond to the Snail1 promoter to activate expression. Without E47, Twist1 repressed Snail1 expression. These results support the hypothesis that Tgfβ3 may signal through Twist1 and then Snail1 to downregulate E-cadherin expression during palatal fusion.

Cx31.1 acts as a tumour suppressor in non-small cell lung cancer (NSCLC) cell lines through inhibition of cell proliferation and metastasis

Reduced connexin expression and loss of gap junction function is a characteristic of many cancers, including lung cancer. However, there are little reports about the relation between Cx31.1 and lung cancer. This study was conducted to investigate the effect of Cx31.1 on non-small cell lung cancer (NSCLC). We found that the Cx31.1 was down-regulated in NSCLC cell lines, and the expression levels were reversely related with their metastatic potential. We ectopically expressed Cx31.1 in H1299 NSCLC cell line to examine the influence of Cx31.1 overexpression. The results showed that overexpression of Cx31.1 in H1299 cells reduced cell proliferation, induced a delay in the G₁ phase, inhibited anchorage-independent growth and suppressed cell migration and invasion. The cell cycle delay and cell migration and invasion suppressive effects of Cx31.1 were partially reversed by siRNA targeting mRNA of Cx31.1. Moreover, xenografts of Cx31.1 overexpressing H1299 cells showed reduced tumourigenicity. These results suggested that Cx31.1 has tumour-suppressive properties. Further investigation indicated that cyclin D3 may be responsible for Cx31.1-induced G₁ phase delay. Importantly, Cx31.1 increased the expression of epithelial markers, such as cytokeratin 18, and decreased expression of mesenchymal markers, such as vimentin, indicating a Cx31.1-mediated partial shift from a mesenchymal towards an epithelial phenotype. We concluded that Cx31.1 inhibit the malignant properties of NSCLC cell lines, the mechanisms under this may include regulation of EMT.

The role of Snail in prostate cancer

Prostate cancer is the second most frequently diagnosed cancer and the sixth leading cause of death from cancer in men. Epithelial-mesenchymal transition (EMT) is a process by which cancer cells invade and migrate, and is characterized by loss of cell-cell adhesion molecules such as E-cadherin and increased expression of mesenchymal proteins such as vimentin; EMT is also associated with resistance to therapy. Snail, a master regulator of EMT, has been extensively studied and reported in cancers such as breast and colon; however, its role in prostate cancer is not as widely reported. The purpose of this review is to put together recent facts that summarize Snail signaling in human prostate cancer. Snail is overexpressed in prostate cancer and its expression and activity is controlled via phosphorylation and growth factor signaling. Snail is involved in its canonical role of inducing EMT in prostate cancer cells; however, it plays a role in non-canonical pathways that do not involve EMT such regulation of bone turnover and neuroendocrine differentiation. Thus, studies indicate that Snail signaling contributes to prostate cancer progression and metastasis and therapeutic targeting of Snail in prostate cancer holds promise in future.

Induction of palate epithelial mesenchymal transition by transforming growth factor β3 signaling

Transforming growth factor (TGFβ)3 is essential for palate development, particularly during the late phase of palatogenesis when the disintegration of the palatal medial edge seam (MES) occurs resulting in mesenchymal confluence. The MES is composed of medial-edge epithelium (MEE) of opposite palatal shelves; its complete disintegration is essential for mediating correct craniofacial morphogenesis. This phenomenon is initiated by TGFβ3 upon adherence of opposing palatal shelves, and subsequently epithelial-mesenchymal transition (EMT) instigates the loss of E-Cadherin, causing the MES to break into small epithelial islands forming confluent palatal mesenchyme; however, apoptosis and cell migration or in combination of all are other established mechanisms of seam disintegration. To investigate the molecular mechanisms that cause this E-Cadherin loss, we isolated and cultured murine embryonic primary MES cells from adhered palates and employed several biological approaches to explore the mechanism by which TGFβ3 facilitates palatal seam disintegration. Here, we demonstrate that TGFβ3 signals by activating both Smad-dependent and Smad-independent pathways. However, activation of the two most common EMT related transcription factors, Snail and SIP, was facilitated by Smad-independent pathways, contrary to the commonly accepted Smad-dependent pathway. Finally, we provide the first evidence that TGFβ3-activated Snail and SIP1, combined with Smad4, bind to the E-Cadherin promoter to repress its transcription in response to TGFβ3 signaling. These results suggest that TGFβ3 uses multiple pathways to activate Snail and SIP1 and these transcription factors repress the cell-cell adhesion protein, E-Cadherin, to induce palatal epithelial seam EMT. Manipulation and intervention of the pathways stimulated by TGFβ3 during palate development may have a significant therapeutic potential.

Periderm cells covering palatal shelves have tight junctions and their desquamation reduces the polarity of palatal shelf epithelial cells in palatogenesis

In palatogenesis, bilateral palatal shelves grow and fuse with each other to establish mesenchyme continuity across the horizontal palate. The palatal shelves are covered with the medial edge epithelium (MEE) in which most apical cells are periderm cells. We investigated localization and roles of tight junction (TJ) and adherens junction (AJ) components and an apical membrane marker in the MEE in palatogenesis. Immunofluorescence and immunoelectron microscopy analyses revealed that TJs were located at the boundary between neighboring periderm cells, whereas AJ components were localized at the boundary between all epithelial cells in the MEE. Specifically, typical AJs were observed at the boundaries between neighboring periderm cells and between periderm cells and underlying epithelial cells where the signal for nectin-1 was observed. The TGF-β-induced desquamation of periderm cells reduced the polarity of remaining epithelial cells as estimated by changes of epithelial cell morphology and the staining of the polarity marker and the AJ components. These less polarized epithelial cells then intermingled and finally disappeared at least partly by apoptosis. These results indicate that periderm cells covering growing palatal shelves have bona fide TJs and their desquamation reduces the polarity of palatal shelf epithelial cells in palatogenesis.

Induction of the neural crest state: control of stem cell attributes by gene regulatory, post-transcriptional and epigenetic interactions

Neural crest cells are a population of multipotent stem cell-like progenitors that arise at the neural plate border in vertebrates, migrate extensively, and give rise to diverse derivatives such as melanocytes, craniofacial cartilage and bone, smooth muscle, peripheral and enteric neurons and glia. The neural crest gene regulatory network (NC-GRN) includes a number of key factors that are used reiteratively to control multiple steps in the development of neural crest cells, including the acquisition of stem cell attributes. It is therefore essential to understand the mechanisms that control the distinct functions of such reiteratively used factors in different cellular contexts. The context-dependent control of neural crest specification is achieved through combinatorial interaction with other factors, post-transcriptional and post-translational modifications, and the epigenetic status and chromatin state of target genes. Here we review the current understanding of the NC-GRN, including the role of the neural crest specifiers, their links to the control of "stemness," and their dynamic context-dependent regulation during the formation of neural crest progenitors.

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.

MiR-200b is involved in Tgf-β signaling to regulate mammalian palate development

Various cellular and molecular events are involved in palatogenesis, including apoptosis, epithelial-mesenchymal transition (EMT), cell proliferation, and cell migration. Smad2 and Snail, which are well-known key mediators of the transforming growth factor beta (Tgf-β) pathway, play a crucial role in the regulation of palate development. Regulatory effects of microRNA 200b (miR-200b) on Smad2 and Snail in palatogenesis have not yet been elucidated. The aim of this study is to determine the relationship between palate development regulators miR-200b and Tgf-β-mediated genes. Expression of miR-200b, E-cadherin, Smad2, and Snail was detected in the mesenchyme of the mouse palate, while miR-200b was expressed in the medial edge epithelium (MEE) and palatal mesenchyme. After the contact of palatal shelves, miR-200b was no longer expressed in the mesenchyme around the fusion region. The binding activity of miR-200b to both Smad2 and Snail was examined using a luciferase assay. MiR-200b directly targeted Smad2 and Snail at both cellular and molecular levels. The function of miR-200b was determined by overexpression via a lentiviral vector in the palatal shelves. Ectopic expression of miR-200b resulted in suppression of these Tgf-β-mediated regulators and changes of apoptosis and cell proliferation in the palatal fusion region. These results suggest that miR-200b plays a crucial role in regulating the Smad2, Snail, and in apoptosis during palatogenesis by acting as a direct non-coding, influencing factor. Furthermore, the molecular interactions between miR-200b and Tgf-β signaling are important for proper palatogenesis and especially for palate fusion. Elucidating the mechanism of palatogenesis may aid the design of effective gene-based therapies for the treatment of congenital cleft palate.

Mechanisms of transforming growth factor β induced cell cycle arrest in palate development

Immaculate and complete palatal seam disintegration, which takes place at the last phase of palate development, is essential for normal palate development. And in absence of palatal midline epithelial seam (MES) disintegration, cleft palate may arise. It has been established that transforming growth factor (TGF) β induces both epithelial mesenchymal transition (EMT) and/or apoptosis during MES disintegration. It is likely that MES might cease cell cycle to facilitate cellular changes prior to undergoing transformation or apoptosis, which has never been studied before. This study was designed to explore whether TGFβ, which is crucial for palatal MES disintegration, is capable of inducing cell cycle arrest. We studied the effects of TGFβ1 and TGFβ3, potent negative regulators of the cell cycle, on p15ink4b activity in MES cells. We surprisingly found that TGFβ1, but not TGFβ3, plays a major role in activation of the p15ink4b gene. In contrast, following successful cell cycle arrest by TGFβ1, it is TGFβ3 but not TGFβ1 that causes later cellular morphogenesis, such as EMT and apoptosis. Since TGFβ signaling activates Smads, we analyzed the roles of three Smad binding elements (SBEs) on the p15ink4b mouse promoter by site specific mutagenesis and found that these binding sites are functional. The ChIP assay demonstrated that TGFβ1, not TGFβ3, promotes Smad4 binding to two 5' terminal SBEs but not the 3' terminal site. Thus, TGFβ1 and TGFβ3 play separate yet complimentary roles in achieving cell cycle arrest and EMT/apoptosis and cell cycle arrest is a prerequisite for later cellular changes.

Epithelial Wnt/β-catenin signaling regulates palatal shelf fusion through regulation of Tgfβ3 expression

The canonical Wnt/β-catenin signaling plays essential role in development and diseases. Previous studies have implicated the canonical Wnt/β-catenin signaling in the regulation of normal palate development, but functional Wnt/β-catenin signaling and its tissue-specific activities remain to be accurately elucidated. In this study, we show that functional Wnt/β-catenin signaling operates primarily in the palate epithelium, particularly in the medial edge epithelium (MEE) of the developing mouse palatal shelves, consistent with the expression patterns of β-catenin and several Wnt ligands and receptors. Epithelial specific inactivation of β-catenin by the K14-Cre transgenic allele abolishes the canonical Wnt signaling activity in the palatal epithelium and leads to an abnormal persistence of the medial edge seam (MES), ultimately causing a cleft palate formation, a phenotype resembling that in Tgfβ3 mutant mice. Consistent with this phenotype is the down-regulation of Tgfβ3 and suppression of apoptosis in the MEE of the β-catenin mutant palatal shelves. Application of exogenous Tgfβ3 to the mutant palatal shelves in organ culture rescues the midline seam phenotype. On the other hand, expression of stabilized β-catenin in the palatal epithelium also disrupts normal palatogenesis by activating ectopic Tgfβ3 expression in the palatal epithelium and causing an aberrant fusion between the palate shelf and mandible in addition to severely deformed palatal shelves. Collectively, our results demonstrate an essential role for Wnt/β-catenin signaling in the epithelial component at the step of palate fusion during palate development by controlling the expression of Tgfβ3 in the MEE.

Occurrence of cleft-palate and alteration of Tgf-β(3) expression and the mechanisms leading to palatal fusion in mice following dietary folic-acid deficiency

Folic acid (FA) is essential for numerous bodily functions. Its decrease during pregnancy has been associated with an increased risk of congenital malformations in the progeny. The relationship between FA deficiency and the appearance of cleft palate (CP) is controversial, and little information exists on a possible effect of FA on palate development. We investigated the effect of a 2-8 weeks' induced FA deficiency in female mice on the development of CP in their progeny as well as the mechanisms leading to palatal fusion, i.e. cell proliferation, cell death, and palatal-shelf adhesion and fusion. We showed that an 8 weeks' maternal FA deficiency caused complete CP in the fetuses although a 2 weeks' maternal FA deficiency was enough to alter all the mechanisms analyzed. Since transforming growth factor-β(3) (TGF-β(3)) is crucial for palatal fusion and since most of the mechanisms impaired by FA deficiency were also observed in the palates of Tgf-β(3)null mutant mice, we investigated the presence of TGF-β(3) mRNA, its protein and phospho-SMAD2 in FA-deficient (FAD) mouse palates. Our results evidenced a large reduction in Tgf-β(3) expression in palates of embryos of dams fed an FAD diet for 8 weeks; Tgf-β(3) expression was less reduced in palates of embryos of dams fed an FAD diet for 2 weeks. Addition of TGF-β(3) to palatal-shelf cultures of embryos of dams fed an FAD diet for 2 weeks normalized all the altered mechanisms. Thus, an insufficient folate status may be a risk factor for the development of CP in mice, and exogenous TGF-β(3) compensates this deficit in vitro.