Abnormal lung development and cleft palate in mice lacking TGF-beta 3 indicates defects of epithelial-mesenchymal interaction

Trinucleotide repeat containing 6c (TNRC6c) is essential for microvascular maturation during distal airspace sacculation in the developing lung

GW182 (also known asTNRC6) family members are critically involved in the final effector phase of miRNA-mediated mRNA repression. The three mammalian paralogs, TNRC6a, b and c, are thought to be redundant based on Argonaute (Ago) binding, tethering assays, and RNAi silencing of individual members in cell lines. To test this idea, we generated TNRC6a, b and c knockout mice. TNRC6a mutants die at mid-gestation, while b- and c- deleted mice are born at a Mendelian ratio. However, the majority of TNRC6b and all TNRC6c mutants die within 24h after birth, the latter with respiratory failure. Necropsy of TNRC6c mutants revealed normal-appearing airways that give rise to abnormally thick-walled distal gas exchange sacs. Immunohistological analysis of mutant lungs demonstrated a normal distribution of bronchiolar and alveolar cells, indicating that loss of TNRC6c did not abrogate epithelial cell differentiation. The cellular kinetics and relative proportions of endothelial, epithelial, and mesenchymal cells were also not altered. However, the underlying capillary network was simplified and endothelial cells had failed to become tightly apposed to the surface epithelium in TNRC6c mutants, presumably causing the observed respiratory failure. TGFβ family mutant mice exhibit a similar lung phenotype of thick-walled air sacs and neonatal lethality, and qRT-PCR confirmed dynamic downregulation of TGFβ1 and TGFβR2 in TNRC6c mutant lungs during sacculation. VEGFR, but not VEGF-A ligand, was also lower, likely reflecting the overall reduced capillary density in TNRC6c mutants. Together, these results demonstrate that GW182 paralogs are not functionally redundant in vivo. Surprisingly, despite regulating a general cellular process, TNRC6c is selectively required only in the distal lung and not until late in gestation for proper expression of the TGFβ family genes that drive sacculation. These results imply a complex and indirect mode of regulation of sacculation by TNRC6c, mediated in part by dynamic transcriptional repression of an inhibitor of TGFβ family gene expression.

Periderm: Life-cycle and function during orofacial and epidermal development

Development of the secondary palate involves a complex series of embryonic events which, if disrupted, result in the common congenital anomaly cleft palate. The secondary palate forms from paired palatal shelves which grow initially vertically before elevating to a horizontal position above the tongue and fusing together in the midline via the medial edge epithelia. As the epithelia of the vertical palatal shelves are in contact with the mandibular and lingual epithelia, pathological fusions between the palate and the mandible and/or the tongue must be prevented. This function is mediated by the single cell layered periderm which forms in a distinct and reproducible pattern early in embryogenesis, exhibits highly polarised expression of adhesion complexes, and is shed from the outer surface as the epidermis acquires its barrier function. Disruption of periderm formation and/or function underlies a series of birth defects that exhibit multiple inter-epithelial adhesions including the autosomal dominant popliteal pterygium syndrome and the autosomal recessive cocoon syndrome and Bartsocas Papas syndrome. Genetic analyses of these conditions have shown that IRF6, IKKA, SFN, RIPK4 and GRHL3, all of which are under the transcriptional control of p63, play a key role in periderm formation. Despite these observations, the medial edge epithelia must rapidly acquire the capability to fuse if the palatal shelves are not to remain cleft. This process is driven by TGFβ3-mediated, down-regulation of p63 in the medial edge epithelia which allows periderm migration out of the midline epithelial seam and reduces the proliferative potential of the midline epithelial seam thereby preventing cleft palate. Together, these findings indicate that periderm plays a transient but fundamental role during embryogenesis in preventing pathological adhesion between intimately apposed, adhesion-competent epithelia.

TGF-β Family Signaling in Neural and Neuronal Differentiation, Development, and Function

Signaling by the transforming growth factor β (TGF-β) family is necessary for proper neural development and function throughout life. Sequential waves of activation, inhibition, and reactivation of TGF-β family members regulate numerous elements of the nervous system from the earliest stages of embryogenesis through adulthood. This review discusses the expression, regulation, and function of TGF-β family members in the central nervous system at various developmental stages, beginning with induction and patterning of the nervous system to their importance in the adult as modulators of inflammatory response and involvement in degenerative diseases.

Molecular and Cellular Mechanisms of Palate Development

Development of the mammalian secondary palate involves highly dynamic morphogenetic processes, including outgrowth of palatal shelves from the oral side of the embryonic maxillary prominences, elevation of the initially vertically oriented palatal shelves to the horizontal position above the embryonic tongue, and subsequently adhesion and fusion of the paired palatal shelves at the midline to separate the oral cavity from the nasal cavity. Perturbation of any of these processes could cause cleft palate, a common birth defect that significantly affects patients' quality of life even after surgical treatment. In addition to identifying a large number of genes required for palate development, recent studies have begun to unravel the extensive cross-regulation of multiple signaling pathways, including Sonic hedgehog, bone morphogenetic protein, fibroblast growth factor, transforming growth factor β, and Wnt signaling, and multiple transcription factors during palatal shelf growth and patterning. Multiple studies also provide new insights into the gene regulatory networks and/or dynamic cellular processes underlying palatal shelf elevation, adhesion, and fusion. Here we summarize major recent advances and integrate the genes and molecular pathways with the cellular and morphogenetic processes of palatal shelf growth, patterning, elevation, adhesion, and fusion.

Dichotomous roles of TGF-β in human cancer

Transforming growth factor-β (TGF-β) mediates numerous biological processes, including embryonic development and the maintenance of cellular homeostasis in a context-dependent manner. Consistent with its central role in maintaining cellular homeostasis, inhibition of TGF-β signaling results in disruption of normal homeostatic processes and subsequent carcinogenesis, defining the TGF-β signaling pathway as a tumor suppressor. However, once carcinogenesis is initiated, the TGF-β signaling pathway promotes cancer progression. This dichotomous function of the TGF-β signaling pathway is mediated through altering effects on both the cancer cells, by inducing apoptosis and inhibiting proliferation, and the tumor microenvironment, by promoting angiogenesis and inhibiting immunosurveillance. Current studies support inhibition of TGF-β signaling either alone, or in conjunction with anti-angiogenic therapy or immunotherapy as a promising strategy for the treatment of human cancers.

Radiation-Induced Fibrosis: Mechanisms and Opportunities to Mitigate. Report of an NCI Workshop, September 19, 2016

A workshop entitled "Radiation-Induced Fibrosis: Mechanisms and Opportunities to Mitigate" (held in Rockville, MD, September 19, 2016) was organized by the Radiation Research Program and Radiation Oncology Branch of the Center for Cancer Research (CCR) of the National Cancer Institute (NCI), to identify critical research areas and directions that will advance the understanding of radiation-induced fibrosis (RIF) and accelerate the development of strategies to mitigate or treat it. Experts in radiation biology, radiation oncology and related fields met to identify and prioritize the key areas for future research and clinical translation. The consensus was that several known and newly identified targets can prevent or mitigate RIF in pre-clinical models. Further, basic and translational research and focused clinical trials are needed to identify optimal agents and strategies for therapeutic use. It was felt that optimally designed preclinical models are needed to better study biomarkers that predict for development of RIF, as well as to understand when effective therapies need to be initiated in relationship to manifestation of injury. Integrating appropriate endpoints and defining efficacy in clinical trials testing treatment of RIF were felt to be critical to demonstrating efficacy. The objective of this meeting report is to (a) highlight the significance of RIF in a global context, (b) summarize recent advances in our understanding of mechanisms of RIF,

Transforming Growth Factor-β: Master Regulator of the Respiratory System in Health and Disease

In this article, we review the biology and physiological importance of transforming growth factor-β (TGF-β) to homeostasis in the respiratory system, its importance to innate and adaptive immune responses in the lung, and its pathophysiological role in various chronic pulmonary diseases including pulmonary arterial hypertension, chronic obstructive pulmonary disease, asthma, and pulmonary fibrosis. The TGF-β family is responsible for initiation of the intracellular signaling pathways that direct numerous cellular activities including proliferation, differentiation, extracellular matrix synthesis, and apoptosis. When TGF-β signaling is dysregulated or essential control mechanisms are unbalanced, the consequences of organ and tissue dysfunction can be profound. The complexities and myriad checkpoints built into the TGF-β signaling pathways provide attractive targets for the treatment of these disease states, many of which are currently being investigated. This review focuses on those aspects of TGF-β biology that are most relevant to pulmonary diseases and that hold promise as novel therapeutic targets.

p63 exerts spatio-temporal control of palatal epithelial cell fate to prevent cleft palate

Cleft palate is a common congenital disorder that affects up to 1 in 2500 live births and results in considerable morbidity to affected individuals and their families. The aetiology of cleft palate is complex with both genetic and environmental factors implicated. Mutations in the transcription factor p63 are one of the major individual causes of cleft palate; however, the gene regulatory networks in which p63 functions remain only partially characterized. Our findings demonstrate that p63 functions as an essential regulatory molecule in the spatio-temporal control of palatal epithelial cell fate to ensure appropriate fusion of the palatal shelves. Initially, p63 induces periderm formation and controls its subsequent maintenance to prevent premature adhesion between adhesion-competent, intra-oral epithelia. Subsequently, TGFβ3-induced down-regulation of p63 in the medial edge epithelia of the palatal shelves is a pre-requisite for palatal fusion by facilitating periderm migration from, and reducing the proliferative potential of, the midline epithelial seam thereby preventing cleft palate.

Cleft palate is a serious congenital condition which affects approximately 1 in every 2500 births. Cleft palate occurs when the palatal shelves fail to grow, adhere or fuse during development. Mutations in the gene encoding the transcription factor p63 result in cleft palate in humans and mice. However, the role of p63 and how it controls the network of genes to regulate palate development is not well understood.In this study, we demonstrate that p63 controls the spatio-temporal regulation of palatal epithelial cell fate to ensure appropriate palatal adhesion: p63 induces the formation of a flattened layer of epithelial (periderm) cells and controls its subsequent maintenance. We also demonstrate that TGFβ3-induced, down-regulation of p63 in the medial edge epithelial cells, through which the palatal shelves adhere and fuse, controls Jag2-induced periderm migration to the oral and nasal epithelial triangles. In addition, p63 plays a central role in maintaining the proliferative potential of the basal layer of the medial edge epithelia. Our study provides significant new insights into the mechanisms that regulate development of the palate by establishing the role of p63 in governing the fate of the midline epithelial cells.

Pdgfrb is a direct regulatory target of TGFβ signaling in atrioventricular cushion mesenchymal cells

Cushion formation is the initial step for the development of valvuloseptal structures in mammalian hearts. TGFβ signaling plays critical roles in multiple steps of cushion morphogenesis. We used a newly developed conditional immortal atrioventricular cushion mesenchymal cell line, tsA58-AVM, to identify the TGFβ regulatory target genes through microarray analysis. Expression of ~1350 genes was significantly altered by TGFβ1 treatment. Subsequent bioinformatic analysis of TGFβ activated genes revealed that PDGF-BB signaling is the top hit as the potential upstream regulator. Among the 37 target molecules, 10 genes known to be involved in valve development and hemostasis were selected for quantitative reverse transcription polymerase chain reaction (qRT-PCR) analysis. Our results confirmed that they are all upregulated by TGFβ1 stimulation in tsA58-AVM cells and in primary atrioventricular cushion cells. We focused on examining regulation of Pdgfrb by TGFβ1, which encodes a tyrosine kinase receptor for PDGF-BB. We found that the ~150bp Pdgfrb promoter can respond to TGFβ stimulation and that this response relies on the two SP1 binding sites within the promoter. Co-immunoprecipitation analysis confirmed SP1 interacts with SMAD2 in a TGFβ-dependent fashion. Furthermore, SMAD2 is associated with the Pdgfrb promoter and this association is diminished by knocking down expression of Sp1. Our data therefore collectively suggest that upon TGFβ stimulation, SP1 recruits SMAD2 to the promoter of Pdgfrb to up-regulate its expression and thus Pdgfrb is a direct downstream target of the TGFβ/SMAD2 signaling.

Biological Role and Therapeutic Targeting of TGF-β3 in Glioblastoma

Transforming growth factor (TGF)-β contributes to the malignant phenotype of glioblastoma by promoting invasiveness and angiogenesis and creating an immunosuppressive microenvironment. So far, TGF-β₁ and TGF-β₂ isoforms have been considered to act in a similar fashion without isoform-specific function in glioblastoma. A pathogenic role for TGF-β₃ in glioblastoma has not been defined yet. Here, we studied the expression and functional role of endogenous and exogenous TGF-β₃ in glioblastoma models. TGF-β₃ mRNA is expressed in human and murine long-term glioma cell lines as well as in human glioma-initiating cell cultures with expression levels lower than TGF-β₁ or TGF-β₂ in most cell lines. Inhibition of TGF-β₃ mRNA expression by ISTH2020 or ISTH2023, two different isoform-specific phosphorothioate locked nucleic acid (LNA)-modified antisense oligonucleotide gapmers, blocks downstream SMAD2 and SMAD1/5 phosphorylation in human LN-308 cells, without affecting TGF-β₁ or TGF-β₂ mRNA expression or protein levels. Moreover, inhibition of TGF-β₃ expression reduces invasiveness in vitro Interestingly, depletion of TGF-β₃ also attenuates signaling evoked by TGF-β₁ or TGF-β₂ In orthotopic syngeneic (SMA-560) and xenograft (LN-308) in vivo glioma models, expression of TGF-β₃ as well as of the downstream target, plasminogen-activator-inhibitor (PAI)-1, was reduced, while TGF-β₁ and TGF-β₂ levels were unaffected following systemic treatment with TGF-β₃ -specific antisense oligonucleotides. We conclude that TGF-β₃ might function as a gatekeeper controlling downstream signaling despite high expression of TGF-β₁ and TGF-β₂ isoforms. Targeting TGF-β₃in vivo may represent a promising strategy interfering with aberrant TGF-β signaling in glioblastoma. Mol Cancer Ther; 16(6); 1177-86. ©2017 AACR.

TGF-β regulation of encephalitogenic and regulatory T cells in multiple sclerosis

Transforming growth factor beta (TGF-β) is a pleiotropic cytokine that has been shown to influence the differentiation and function of T cells. The role that TGF-β plays in immune-mediated disease, such as multiple sclerosis (MS), has become a major area of investigation since CD4⁺ T cells appear to be a major mediator of autoimmunity. This review provides an analysis of the literature on the role that TGF-β plays in the generation and regulation of encephalitogenic and regulatory T cells (Treg) in experimental autoimmune encephalomyelitis (EAE), an animal model of MS, as well as in T cells of MS patients. Since TGF-β plays a major role in the development and function of both CD4⁺ effector and Treg, which are defective in MS patients, recent studies have found potential mechanisms to explain the basis for these T-cell defects to establish a foundation for potentially modulating TGF-β signaling to restore normal T-cell function in MS patients.

Mammary Gland Involution Provides a Unique Model to Study the TGF-β Cancer Paradox

Transforming Growth Factor-β (TGF-β) signaling in cancer has been termed the “TGF-β paradox”, acting as both a tumor suppresser and promoter. The complexity of TGF-β signaling within the tumor is context dependent, and greatly impacted by cellular crosstalk between TGF-β responsive cells in the microenvironment including adjacent epithelial, endothelial, mesenchymal, and hematopoietic cells. Here we utilize normal, weaning-induced mammary gland involution as a tissue microenvironment model to study the complexity of TGF-β function. This article reviews facets of mammary gland involution that are TGF-β regulated, namely mammary epithelial cell death, immune activation, and extracellular matrix remodeling. We outline how distinct cellular responses and crosstalk between cell types during physiologically normal mammary gland involution contribute to simultaneous tumor suppressive and promotional microenvironments. We also highlight alternatives to direct TGF-β blocking anti-cancer therapies with an emphasis on eliciting concerted microenvironmental-mediated tumor suppression.

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.

Linkage Disequilibrium between MSX1 and Non-syndromic Cleft Lip/Palate in the Chilean Population

Non-syndromic cleft lip/palate (NSCLP) is a complex genetic trait. Linkage and association studies have suggested that a clefting locus could be located on chromosome 4p. Sixty Chilean families were recruited for this study; from these, we used unrelated trios to evaluate the possible linkage disequilibrium between MSX1 and NSCLP. An intragenic marker, MSX1-CA, and an extragenic marker, D4S432 at a distance of 0.8 cM from MSX1, were analyzed by means of polymerase chain-reaction with fluorescent-labeled forward primers, followed by electrophoresis on a laser-fluorescent sequencer. We carried out a transmission/disequilibrium test (TDT) for multiple alleles to evaluate the presence of linkage disequilibrium. Results showed a preferential transmission of the 169-bp allele of MSX1 (p = 0.03). Although there was no preferential transmission for the D4S432 marker, the overall extended TDT (ETDT) showed a significant result (p = 0.01). The authors’ findings support the hypothesis of the contribution of MSX1 in the etiology of NSCLP in the Chilean population.

Determinants of orofacial clefting I: Effects of 5-Aza-2'-deoxycytidine on cellular processes and gene expression during development of the first branchial arch

In this study, we identify gene targets and cellular events mediating the teratogenic action(s) of 5-Aza-2'-deoxycytidine (AzaD), an inhibitor of DNA methylation, on secondary palate development. Exposure of pregnant mice (on gestation day (GD) 9.5) to AzaD for 12h resulted in the complete penetrance of cleft palate (CP) in fetuses. Analysis of cells of the embryonic first branchial arch (1-BA), in fetuses exposed to AzaD, revealed: 1) significant alteration in expression of genes encoding several morphogenetic factors, cell cycle inhibitors and regulators of apoptosis; 2) a decrease in cell proliferation; and, 3) an increase in apoptosis. Pyrosequencing of selected genes, displaying pronounced differential expression in AzaD-exposed 1-BAs, failed to reveal significant alterations in CpG methylation levels in their putative promoters or gene bodies. CpG methylation analysis suggested that the effects of AzaD on gene expression were likely indirect.

A synopsis of factors regulating beta cell development and beta cell mass

The insulin-secreting beta cells in the endocrine pancreas regulate blood glucose levels, and loss of functional beta cells leads to insulin deficiency, hyperglycemia (high blood glucose) and diabetes mellitus. Current treatment strategies for type-1 (autoimmune) diabetes are islet transplantation, which has significant risks and limitations, or normalization of blood glucose with insulin injections, which is clearly not ideal. The type-1 patients can lack insulin counter-regulatory mechanism; therefore, hypoglycemia is a potential risk. Hence, a cell-based therapy offers a better alternative for the treatment of diabetes. Past research was focused on attempting to generate replacement beta cells from stem cells; however, recently there has been an increasing interest in identifying mechanisms that will lead to the conversion of pre-existing differentiated endocrine cells into beta cells. The goal of this review is to provide an overview of several of the key factors that regulate new beta cell formation (neogenesis) and beta cell proliferation.

Mesenchymal Remodeling during Palatal Shelf Elevation Revealed by Extracellular Matrix and F-Actin Expression Patterns

During formation of the secondary palate in mammalian embryos, two vertically oriented palatal shelves rapidly elevate into a horizontal position above the tongue, meet at the midline, and fuse to form a single entity. Previous observations suggested that elevation occurs by a simple 90° rotation of the palatal shelves. More recent findings showed that the presumptive midline epithelial cells are not located at the tips of palatal shelves before elevation, but mostly toward their medial/lingual part. This implied extensive tissue remodeling during shelf elevation. Nevertheless, it is still not known how the shelf mesenchyme reorganizes during this process, and what mechanism drives it. To address this question, we mapped the distinct and restricted expression domains of certain extracellular matrix components within the developing palatal shelves. This procedure allowed to monitor movements of entire mesenchymal regions relative to each other during shelf elevation. Consistent with previous notions, our results confirm a flipping movement of the palatal shelves anteriorly, whereas extensive mesenchymal reorganization is observed more posteriorly. There, the entire lingual portion of the vertical shelves moves close to the midline after elevation, whereas the mesenchyme at the original tip of the shelves ends up ventrolaterally. Moreover, we observed that the mesenchymal cells of elevating palatal shelves substantially align their actin cytoskeleton, their extracellular matrix, and their nuclei in a ventral to medial direction. This indicates that, like in other morphogenetic processes, actin-dependent cell contractility is a major driving force for mesenchymal tissue remodeling during palatogenesis.

The role of integrins in TGFβ activation in the tumour stroma

TGFβ1 is the most pleiotropic of all known cytokines and thus, to avoid uncontrolled TGFβ-activated processes, its activity is tightly regulated. Studies in fibrosis have led to the discovery that αv integrins are the major regulators of the local activation of latent TGFβ in our tissues. Since all cells can express one or more types of αv integrins, this raises the possibility that, in the complex milieu of a developing cancer, multiple cell types including both cancer cells and stromal cells activate TGFβ. In normal tissues, TGFβ1 is a tumour suppressor through its ability to suppress epithelial cell division, whereas in cancer, in which tumour cells develop genetic escape mechanisms to become resistant to TGFβ growth suppression, TGFβ signalling creates a tumour-permissive environment by activating fibroblast-to-myofibroblast transition, by promoting angiogenesis, by suppressing immune cell populations and by promoting the secretion of both matrix proteins and proteases. In addition, TGFβ drives epithelial-to-mesenchymal transition (EMT) increasing the potential for metastasis. Since αv integrins activate TGFβ, they almost certainly drive TGFβ-dependent cancer progression. In this review, we discuss the data that are helping to develop this hypothesis and describe the evidence that αv integrins regulate the TGFβ promotion of cancer. Graphical Abstract Mechanisms of integrin-mediated transforming growth factor beta (TGFβ) activation and its effect on stromal processes. 1 Matrix-bound latent LAP-TGFβ1 binds αv integrins expressed by epithelial cells or fibroblasts (LAP latency-associated peptide). TGFβ1 becomes exposed. 2 Active TGFβ1 binds the TGFβ receptor in an autocrine or paracrine fashion. 3 TGFβ1 signalling increases integrin expression, LAP-TGFβ1 secretion and trans-differentiation of fibroblasts into contractile cells that secrete collagens and collagen cross-linking proteins. By contracting the matrix, latent TGFβ1 is stretched making the activation of latent TGFβ1 easier and creating a continuous cycle of TGFβ1 signalling. TGFβ1 promotes cancer progression by promoting angiogenesis, immune suppression and epithelial-to-mesenchymal transition (EMT).

Transforming Growth Factor β Drives Hemogenic Endothelium Programming and the Transition to Hematopoietic Stem Cells

Hematopoietic stem cells (HSCs) are self-renewing multipotent stem cells that generate mature blood lineages throughout life. They, together with hematopoietic progenitor cells (collectively known as HSPCs), emerge from hemogenic endothelium in the floor of the embryonic dorsal aorta by an endothelial-to-hematopoietic transition (EHT). Here we demonstrate that transforming growth factor β (TGFβ) is required for HSPC specification and that it regulates the expression of the Notch ligand Jagged1a in endothelial cells prior to EHT, in a striking parallel with the epithelial-to-mesenchymal transition (EMT). The requirement for TGFβ is two fold and sequential: autocrine via Tgfβ1a and Tgfβ1b produced in the endothelial cells themselves, followed by a paracrine input of Tgfβ3 from the notochord, suggesting that the former programs the hemogenic endothelium and the latter drives EHT. Our findings have important implications for the generation of HSPCs from pluripotent cells in vitro.

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TGFβ signaling is required for hematopoietic stem cell (HSC) emergence in embryos

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TGFβ regulates jag1a expression and programs endothelium to become hemogenic endothelium (HE)

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Tgfb1a/Tgfb1b and Tgfb3 act sequentially to program HE and give rise to HSCs

Temporal and Spatial Expression of Transforming Growth Factor-β after Airway Remodeling to Tobacco Smoke in Rats

Airway remodeling is strongly correlated with the progression of chronic obstructive pulmonary disease (COPD). In this study, our goal was to characterize progressive structural changes in site-specific airways, along with the temporal and spatial expression of transforming growth factor (TGF)-β in the lungs of male spontaneously hypertensive rats exposed to tobacco smoke (TS). Our studies demonstrated that TS-induced changes of the airways is dependent on airway generation and exposure duration for proximal, midlevel, and distal airways. Stratified squamous epithelial cell metaplasia was evident in the most proximal airways after 4 and 12 weeks but with minimal levels of TGF-β-positive epithelial cells after only 4 weeks of exposure. In contrast, epithelial cells in midlevel and distal airways were strongly TGF-β positive at both 4 and 12 weeks of TS exposure. Airway smooth muscle volume increased significantly at 4 and 12 weeks in midlevel airways. Immunohistochemistry of TGF-β was also found to be significantly increased at 4 and 12 weeks in lymphoid tissues and alveolar macrophages. ELISA of whole-lung homogenate demonstrated that TGF-β2 was increased after 4 and 12 weeks of TS exposure, whereas TGF-β1 was decreased at 12 weeks of TS exposure. Airway levels of messenger RNA for TGF-β2, as well as platelet-derived growth factor-A, granulocyte-macrophage colony-stimulating factor, and vascular endothelial growth factor-α, growth factors regulated by TGF-β, were significantly decreased in animals after 12 weeks of TS exposure. Our data indicate that TS increases TGF-β in epithelial and inflammatory cells in connection with airway remodeling, although the specific role of each TGF-β isoform remains to be defined in TS-induced airway injury and disease.

TGF-β and the TGF-β Family: Context-Dependent Roles in Cell and Tissue Physiology

The transforming growth factor-β (TGF-β) is the prototype of the TGF-β family of growth and differentiation factors, which is encoded by 33 genes in mammals and comprises homo- and heterodimers. This review introduces the reader to the TGF-β family with its complexity of names and biological activities. It also introduces TGF-β as the best-studied factor among the TGF-β family proteins, with its diversity of roles in the control of cell proliferation and differentiation, wound healing and immune system, and its key roles in pathology, for example, skeletal diseases, fibrosis, and cancer.

TGFβ-2 signaling is essential for osteoblast migration and differentiation during fracture healing in medaka fish

TGFβ is known as a canonical coupling factor based on its effects on bone formation and bone resorption. There are 3 different isoforms of it related to bone metabolism in mammals. TGFβ function in vivo is complicated, and each isoform shows a different function. Since TGFβs are secreted during inflammation accompanied by the release of latent TGFβ from inside of the bones where they are stored in the extracellular matrix, TGFβ function is potentially related to fracture healing. Although a few reports examined the TGFβ expression during fracture healing, the function of TGFβ in this process is poorly understood. To investigate TGFβ function during fracture healing in vivo, we used the fracture healing model of the medaka fish, which enabled us to observe the behavior and function of living cells in response to a bone-specific injury. RNA in-situ hybridization analysis showed that only tgfβ-2 of the 4 TGFβ isoforms in medaka was expressed in the bone-forming region. To examine the TGFβ-2 function for bone formation by osteoblasts, we used a medaka transgenic line, Tg (type X collagen: GFP); and the results revealed that type X collagen-positive immature osteoblasts migrated to the fracture site and differentiated to osterix-positive osteoblasts. However, only a few type X collagen-positive osteoblasts exhibited BrdU incorporation after the fracture. Then we inhibited TGFβ signaling by using a chemical TGFβ receptor kinase inhibitor (SB431542), and demonstrated that inhibition of TGFβ strongly impaired osteoblast migration and differentiation. In addition, this TGFβ inhibitor reduced the RANKL expression and caused a delay of osteoclast differentiation. Our findings thus demonstrated that TGFβ-2 functioned specifically during fracture healing to stimulate the migration of osteoblasts as well as the differentiation of osteoblasts and osteoclasts.

TGF-β and BMP signaling in osteoblast, skeletal development, and bone formation, homeostasis and disease

Transforming growth factor-beta (TGF-β) and bone morphogenic protein (BMP) signaling has fundamental roles in both embryonic skeletal development and postnatal bone homeostasis. TGF-βs and BMPs, acting on a tetrameric receptor complex, transduce signals to both the canonical Smad-dependent signaling pathway (that is, TGF-β/BMP ligands, receptors, and Smads) and the non-canonical-Smad-independent signaling pathway (that is, p38 mitogen-activated protein kinase/p38 MAPK) to regulate mesenchymal stem cell differentiation during skeletal development, bone formation and bone homeostasis. Both the Smad and p38 MAPK signaling pathways converge at transcription factors, for example, Runx2 to promote osteoblast differentiation and chondrocyte differentiation from mesenchymal precursor cells. TGF-β and BMP signaling is controlled by multiple factors, including the ubiquitin–proteasome system, epigenetic factors, and microRNA. Dysregulated TGF-β and BMP signaling result in a number of bone disorders in humans. Knockout or mutation of TGF-β and BMP signaling-related genes in mice leads to bone abnormalities of varying severity, which enable a better understanding of TGF-β/BMP signaling in bone and the signaling networks underlying osteoblast differentiation and bone formation. There is also crosstalk between TGF-β/BMP signaling and several critical cytokines’ signaling pathways (for example, Wnt, Hedgehog, Notch, PTHrP, and FGF) to coordinate osteogenesis, skeletal development, and bone homeostasis. This review summarizes the recent advances in our understanding of TGF-β/BMP signaling in osteoblast differentiation, chondrocyte differentiation, skeletal development, cartilage formation, bone formation, bone homeostasis, and related human bone diseases caused by the disruption of TGF-β/BMP signaling.

TGF-β1 and TGF-β2 abundance in liver diseases of mice and men

TGF-β1 is a major player in chronic liver diseases promoting fibrogenesis and tumorigenesis through various mechanisms. The expression and function of TGF-β2 have not been investigated thoroughly in liver disease to date. In this paper, we provide evidence that TGF-β2 expression correlates with fibrogenesis and liver cancer development.Using quantitative realtime PCR and ELISA, we show that TGF-β2 mRNA expression and secretion increased in murine HSCs and hepatocytes over time in culture and were found in the human-derived HSC cell line LX-2. TGF-β2 stimulation of the LX-2 cells led to upregulation of the TGF-β receptors 1, 2, and 3, whereas TGF-β1 treatment did not alter or decrease their expression. In liver regeneration and fibrosis upon CCl4 challenge, the transient increase of TGF-β2 expression was accompanied by TGF-β1 and collagen expression. In bile duct ligation-induced fibrosis, TGF-β2 upregulation correlated with fibrotic markers and was more prominent than TGF-β1 expression. Accordingly, MDR2-KO mice showed significant TGF-β2 upregulation within 3 to 15 months but minor TGF-β1 expression changes. In 5 of 8 hepatocellular carcinoma (HCC)/hepatoblastoma cell lines, relatively high TGF-β2 expression and secretion were observed, with some cell lines even secreting more TGF-β2 than TGF-β1. TGF-β2 was also upregulated in tumors of TGFα/cMyc and DEN-treated mice. The analysis of publically available microarray data of 13 human HCC collectives revealed considerable upregulation of TGF-β2 as compared to normal liver.Our study demonstrates upregulation of TGF-β2 in liver disease and suggests TGF-β2 as a promising therapeutic target for tackling fibrosis and HCC.

TCDD promoted EMT of hFPECs via AhR, which involved the activation of EGFR/ERK signaling

One critical step of second palatal fusion is the newly formed medial epithelia seam (MES) disintegration, which involves apoptosis, epithelial to mesenchymal transition (EMT), and cell migration. Although the environmental toxicant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) produces cleft palate at high rates, little is known about the effects of TCDD exposure on the fate of palatal epithelial cells. By using primary epithelial cells isolated from human fetal palatal shelves (hFPECs), we show that TCDD increased cell proliferation and EMT, as demonstrated by increased the epithelial markers (E-cadherin and cytokeratin14) and enhanced the mesenchymal markers (vimentin and fibronectin), but had no effect on cell migration and apoptosis. TCDD exposure led to a dose-dependent increase in Slug protein expression. Coimmunoprecipitation revealed that TCDD promoted AhR to form a protein complex with Slug. ChIP assay confirmed that TCDD exposure recruited AhR to the xenobiotic responsive element of Slug promoter. Knockdown of AhR by siRNA remarkably weakened TCDD-induced binding of AhR to the XRE promoter of slug, thereby suppressed TCDD-induced vimentin. Further experiment showed that TCDD stimulated EGFR phosphorylation did not influence the TGFβ3/Smad signaling; whereas TCDD increased phosphorylation of ERK1/2 and p38 with no effect on activation of JNK. By using varieties of inhibitors, we confirmed that TCDD promoted proliferation and EMT of hFPECs via activation of EGFR/ERK pathway. These data make a novel contribution to the molecular mechanism of cleft palate by TCDD.

Initial Suppression of Transforming Growth Factor-β Signaling and Loss of TGFBI Causes Early Alveolar Structural Defects Resulting in Bronchopulmonary Dysplasia

Septation of the gas-exchange saccules of the morphologically immature mouse lung requires regulated timing, spatial direction, and dosage of transforming growth factor (TGF)-β signaling. We found that neonatal hyperoxia acutely initially diminished saccular TGF-β signaling coincident with alveolar simplification. However, sustained hyperoxia resulted in a biphasic response and subsequent up-regulation of TGF-β signaling, ultimately resulting in bronchopulmonary dysplasia. Significantly, we found that the TGF-β-induced matricellular protein (TGFBI) was similarly biphasically altered in response to hyperoxia. Moreover, genetic ablation revealed that TGFBI was required for normal alveolar structure and function. Although the phenotype was not neonatal lethal, Tgfbi-deficient lungs were morphologically abnormal. Mutant septal tips were stunted, lacked elastin-positive tips, exhibited reduced proliferation, and contained abnormally persistent alveolar α-smooth muscle actin myofibroblasts. In addition, Tgfbi-deficient lungs misexpressed TGF-β-responsive follistatin and serpine 1, and transiently suppressed myofibroblast platelet-derived growth factor α differentiation marker. Finally, despite normal lung volume, Tgfbi-null lungs displayed diminished elastic recoil and gas exchange efficiency. Combined, these data demonstrate that initial suppression of the TGF-β signaling apparatus, as well as loss of key TGF-β effectors (like TGFBI), underlies early alveolar structural defects, as well as long-lasting functional deficits routinely observed in chronic lung disease of infancy patients. These studies underline the complex (and often contradictory) role of TGF-β and indicate a need to design studies to associate alterations with initial appearance of phenotypical changes suggestive of bronchopulmonary dysplasia.

HDAC3-Dependent Epigenetic Pathway Controls Lung Alveolar Epithelial Cell Remodeling and Spreading via miR-17-92 and TGF-β Signaling Regulation

The terminal stages of pulmonary development, called sacculation and alveologenesis, involve both differentiation of distal lung endoderm progenitors and extensive cellular remodeling of the resultant epithelial lineages. These processes are coupled with dramatic expansion of distal airspace and surface area. Despite the importance of these late developmental processes and their relation to neonatal respiratory diseases, little is understood about the molecular and cellular pathways critical for their successful completion. We show that a histone deacetylase 3 (Hdac3)-mediated epigenetic pathway is critical for the proper remodeling and expansion of the distal lung saccules into primitive alveoli. Loss of Hdac3 in the developing lung epithelium leads to a reduction of alveolar type 1 cell spreading and a disruption of lung sacculation. Hdac3 represses miR-17-92 expression, a microRNA cluster that regulates transforming growth factor β (TGF-β) signaling. De-repression of miR-17-92 in Hdac3-deficient lung epithelium results in decreased TGF-β signaling activity. Importantly, inhibition of TGF-β signaling and overexpression of miR-17-92 can phenocopy the defects observed in Hdac3 null lungs. Conversely, loss of miR-17-92 expression rescues many of the defects caused by loss of Hdac3 in the lung. These studies reveal an intricate epigenetic pathway where Hdac3 is required to repress miR-17-92 expression to allow for proper TGF-β signaling during lung sacculation.

Dopaminergic Neurons and Brain Reward Pathways: From Neurogenesis to Circuit Assembly

Midbrain dopaminergic (DA) neurons in the substantia nigra pars compacta and ventral tegmental area regulate extrapyramidal movement and important cognitive functions, including motivation, reward associations, and habit learning. Dysfunctions in DA neuron circuitry have been implicated in several neuropsychiatric disorders, including addiction and schizophrenia, whereas selective degeneration of DA neurons in substantia nigra pars compacta is a key neuropathological feature in Parkinson disease. Efforts to understand these disorders have focused on dissecting the underlying causes, as well as developing therapeutic strategies to replenish dopamine deficiency. In particular, the promise of cell replacement therapies for clinical intervention has led to extensive research in the identification of mechanisms involved in DA neuron development. It is hoped that a comprehensive understanding of these mechanisms will lead to therapeutic strategies that improve the efficiency of DA neuron production, engraftment, and function. This review provides a comprehensive discussion on how Wnt/β-catenin and sonic hedgehog-Smoothened signaling mechanisms control the specification and expansion of DA progenitors and the differentiation of DA neurons. We also discuss how mechanisms involving transforming growth factor-β and transcriptional cofactor homeodomain interacting protein kinase 2 regulate the survival and maturation of DA neurons in early postnatal life. These results not only reveal fundamental mechanisms regulating DA neuron development, but also provide important insights to their potential contributions to neuropsychiatric and neurodegenerative diseases.

Fibulin-4 deficiency increases TGF-β signalling in aortic smooth muscle cells due to elevated TGF-β2 levels

Fibulins are extracellular matrix proteins associated with elastic fibres. Homozygous Fibulin-4 mutations lead to life-threatening abnormalities such as aortic aneurysms. Aortic aneurysms in Fibulin-4 mutant mice were associated with upregulation of TGF-β signalling. How Fibulin-4 deficiency leads to deregulation of the TGF-β pathway is largely unknown. Isolated aortic smooth muscle cells (SMCs) from Fibulin-4 deficient mice showed reduced growth, which could be reversed by treatment with TGF-β neutralizing antibodies. In Fibulin-4 deficient SMCs increased TGF-β signalling was detected using a transcriptional reporter assay and by increased SMAD2 phosphorylation. Next, we investigated if the increased activity was due to increased levels of the three TGF-β isoforms. These data revealed slightly increased TGF-β1 and markedly increased TGF-β2 levels. Significantly increased TGF-β2 levels were also detectable in plasma from homozygous Fibulin-4(R/R) mice, not in wild type mice. TGF-β2 levels were reduced after losartan treatment, an angiotensin-II type-1 receptor blocker, known to prevent aortic aneurysm formation. In conclusion, we have shown increased TGF-β signalling in isolated SMCs from Fibulin-4 deficient mouse aortas, not only caused by increased levels of TGF-β1, but especially TGF-β2. These data provide new insights in the molecular interaction between Fibulin-4 and TGF-β pathway regulation in the pathogenesis of aortic aneurysms.

Structural insights into BMP receptors: Specificity, activation and inhibition

Bone morphogenetic proteins (BMPs) are members of the transforming growth factor-β family (TGFβ), which signal through hetero-tetrameric complexes of type I and type II receptors. In humans there are many more TGFβ ligands than receptors, leading to the question of how particular ligands can initiate specific signaling responses. Here we review structural features of the ligands and receptors that contribute to this specificity. Ligand activity is determined by receptor-ligand interactions, growth factor prodomains, extracellular modulator proteins, receptor assembly and phosphorylation of intracellular signaling proteins, including Smad transcription factors. Detailed knowledge about the receptors has enabled the development of BMP-specific type I receptor kinase inhibitors. In future these may help to treat human diseases such as fibrodysplasia ossificans progressiva.

A Decade of Discovery in the Genetic Understanding of Thoracic Aortic Disease

Aortic aneurysms are responsible for a significant number of all deaths in Western countries. In this review we provide a perspective on the important progress made over the past decade in the understanding of the genetics of this condition, with an emphasis on the more frequent forms of vascular smooth muscle and transforming growth factor β (TGF-β) signalling alterations. For several nonsyndromic and syndromic forms of thoracic aortic disease, a genetic basis has now been identified, with 3 main pathomechanisms that have emerged: perturbation of the TGF-β signalling pathway, disruption of the vascular smooth muscle cell (VSMC) contractile apparatus, and impairment of extracellular matrix synthesis. Because smooth muscle cells and proteins of the extracellular matrix directly regulate TGF-β signalling, this latter pathway emerges as a key component of thoracic aortic disease initiation and progression. These discoveries have revolutionized our understanding of thoracic aortic disease and provided inroads toward gene-specific stratification of treatment. Last, we outline how these genetic findings are translated into novel pharmaceutical approaches for thoracic aortic disease.

Tissue patterning and cellular mechanics

In development, cells organize into biological tissues through cell growth, migration, and differentiation. Globally, this process is dictated by a genetically encoded program in which secreted morphogens and cell-cell interactions prompt the adoption of unique cell fates. Yet, at its lowest level, development is achieved through the modification of cell-cell adhesion and actomyosin-based contractility, which set the level of tension within cells and dictate how they pack together into tissues. The regulation of tension within individual cells and across large groups of cells is a major driving force of tissue organization and the basis of all cell shape change and cell movement in development.

Muscleblind-like 1 is required for normal heart valve development in vivo

Background

Development of the valves and septa of the heart depends on the formation and remodeling of the endocardial cushions in the atrioventricular canal and outflow tract. These cushions are populated by mesenchyme produced from the endocardium by epithelial-mesenchymal transition (EMT). The endocardial cushions are remodeled into the valves at post-EMT stages via differentiation of the mesenchyme and changes in the extracellular matrix (ECM). Transforming growth factor β (TGFβ) signaling has been implicated in both the induction of EMT in the endocardial cushions and the remodeling of the valves at post-EMT stages. We previously identified the RNA binding protein muscleblind-like 1 (MBNL1) as a negative regulator of TGFβ signaling and EMT in chicken endocardial cushions ex vivo.  Here, we investigate the role of MBNL1 in endocardial cushion development and valvulogenesis in Mbnl1^∆E3/∆E3 mice, which are null for MBNL1 protein.

Methods

Collagen gel invasion assays, histology, immunohistochemistry, real-time RT-PCR, optical coherence tomography, and echocardiography were used to evaluate EMT and TGFβ signaling in the endocardial cushions, and morphogenesis, ECM composition, and function of the heart valves.

Results

As in chicken, the loss of MBNL1 promotes precocious TGFβ signaling and EMT in the endocardial cushions. Surprisingly, this does not lead to the production of excess mesenchyme, but later valve morphogenesis is aberrant. Adult Mbnl1^∆E3/∆E3 mice exhibit valve dysmorphia with elevated TGFβ signaling, changes in ECM composition, and increased pigmentation. This is accompanied by a high incidence of regurgitation across both inflow and outflow valves. Mbnl1^∆E3/∆E3 mice also have a high incidence of ostium secundum septal defects accompanied by atrial communication, but do not develop overt cardiomyopathy.

Conclusions

Together, these data indicate that MBNL1 plays a conserved role in negatively regulating TGFβ signaling, and is required for normal valve morphogenesis and homeostasis in vivo.

Electronic supplementary material

The online version of this article (doi:10.1186/s12861-015-0087-4) contains supplementary material, which is available to authorized users.

Environmental Influences on Endothelial to Mesenchymal Transition in Developing Implanted Cardiovascular Tissue-Engineered Grafts

Tissue-engineered grafts for cardiovascular structures experience biochemical stimuli and mechanical forces that influence tissue development after implantation such as the immunological response, oxidative stress, hemodynamic shear stress, and mechanical strain. Endothelial cells are a cell source of major interest in vascular tissue engineering because of their ability to form a luminal antithrombotic monolayer. In addition, through their ability to undergo endothelial to mesenchymal transition (EndMT), endothelial cells may yield a cell type capable of increased production and remodeling of the extracellular matrix (ECM). ECM is of major importance to the mechanical function of all cardiovascular structures. Tissue engineering approaches may employ EndMT to recapitulate, in part, the embryonic development of cardiovascular structures. Improved understanding of how the environment of an implanted graft could influence EndMT in endothelial cells may lead to novel tissue engineering strategies. This review presents an overview of biochemical and mechanical stimuli capable of influencing EndMT, discusses the influence of these stimuli as found in the direct environment of cardiovascular grafts, and discusses approaches to employ EndMT in tissue-engineered constructs.

From Bench to Bedside and Back: Improving Diagnosis and Treatment of Craniofacial Malformations Utilizing Animal Models

Craniofacial anomalies are among the most common birth defects and are associated with increased mortality and, in many cases, the need for lifelong treatment. Over the past few decades, dramatic advances in the surgical and medical care of these patients have led to marked improvements in patient outcomes. However, none of the treatments currently in clinical use address the underlying molecular causes of these disorders. Fortunately, the field of craniofacial developmental biology provides a strong foundation for improved diagnosis and for therapies that target the genetic causes of birth defects. In this chapter, we discuss recent advances in our understanding of the embryology of craniofacial conditions, and we focus on the use of animal models to guide rational therapies anchored in genetics and biochemistry.

Nicotine Exposure During Pregnancy Results in Persistent Midline Epithelial Seam With Improper Palatal Fusion

INTRODUCTION

Nonsyndromic cleft palate is a common birth defect (1:700) with a complex etiology involving both genetic and environmental risk factors. Nicotine, a major teratogen present in tobacco products, was shown to cause alterations and delays in the developing fetus.

METHODS

To demonstrate the postpartum effects of nicotine on palatal development, we delivered three different doses of nicotine (1.5, 3.0, and 4.5mg/kg/d) and sterile saline (control) into pregnant BALB/c mice throughout their entire pregnancy using subcutaneous micro-osmotic pump. Dams were allowed to deliver (~day 21 of pregnancy) and neonatal assessments (weight, length, nicotine levels) were conducted, and palatal tissues were harvested for morphological and molecular analyses, as well as transcriptional profiling using microarrays.

RESULTS

Consistent administration of nicotine caused developmental retardation, still birth, low birth weight, and significant palatal size and shape abnormality and persistent midline epithelial seam in the pups. Through microarray analysis, we detected that 6232 genes were up-regulated and 6310 genes were down-regulated in nicotine-treated groups compared to the control. Moreover, 46% of the cleft palate-causing genes were found to be affected by nicotine exposure. Alterations of a subset of differentially expressed genes were illustrated with hierarchal clustering and a series of formal pathway analyses were performed using the bioinformatics tools.

CONCLUSIONS

We concluded that nicotine exposure during pregnancy interferes with normal growth and development of the fetus, as well results in persistent midline epithelial seam with type B and C patterns of palatal fusion.

IMPLICATIONS

Although there are several studies analyzing the genetic and environmental causes of palatal deformities, this study primarily shows the morphological and large-scale genomic outcomes of gestational nicotine exposure in neonatal mice palate.The previous version was incorrect. New authors Ali Nawshad, Hasan Otu, Janki Sharma, and Elizabeth Sheldon have been included in this version; the funding and acknowledgement sections have been updated accordingly; the article title, some text, and one supplementary data file have been edited; and the corresponding author has been changed. The original corresponding author regrets these earlier errors.

Cellular and Molecular Mechanisms of Palatogenesis

Palatogenesis involves the initiation, growth, morphogenesis, and fusion of the primary and secondary palatal shelves from initially separate facial prominences during embryogenesis to form the intact palate separating the oral cavity from the nostrils. The palatal shelves consist mainly of cranial neural crest-derived mesenchymal cells covered by a simple embryonic epithelium. The growth and patterning of the palatal shelves are controlled by reciprocal epithelial-mesenchymal interactions regulated by multiple signaling pathways and transcription factors. During palatal shelf outgrowth, the embryonic epithelium develops a "teflon" coat consisting of a single, continuous layer of periderm cells that prevents the facial prominences and palatal shelves from forming aberrant interepithelial adhesions. Palatal fusion involves not only spatiotemporally regulated disruption of the periderm but also dynamic cellular and molecular processes that result in adhesion and intercalation of the palatal medial edge epithelia to form an intershelf epithelial seam, and subsequent dissolution of the epithelial seam to form the intact roof of the oral cavity. The complexity of regulation of these morphogenetic processes is reflected by the common occurrence of cleft palate in humans. This review will summarize major recent advances and discuss major remaining gaps in the understanding of cellular and molecular mechanisms controlling palatogenesis.

Cleft Palate, Moderate Lung Developmental Retardation and Early Postnatal Lethality in Mice Deficient in the Kir7.1 Inwardly Rectifying K+ Channel

Kir7.1 is an inwardly rectifying K⁺ channel of the Kir superfamily encoded by the kcnj13 gene. Kir7.1 is present in epithelial tissues where it colocalizes with the Na⁺/K⁺-pump probably serving to recycle K⁺ taken up by the pump. Human mutations affecting Kir7.1 are associated with retinal degeneration diseases. We generated a mouse lacking Kir7.1 by ablation of the Kcnj13 gene. Homozygous mutant null mice die hours after birth and show cleft palate and moderate retardation in lung development. Kir7.1 is expressed in the epithelium covering the palatal processes at the time at which palate sealing takes place and our results suggest it might play an essential role in late palatogenesis. Our work also reveals a second unexpected role in the development and the physiology of the respiratory system, where Kir7.1 is expressed in epithelial cells all along the respiratory tree.

A Tale from TGF-β Superfamily for Thymus Ontogeny and Function

Multiple signaling pathways control every aspect of cell behavior, organ formation, and tissue homeostasis throughout the lifespan of any individual. This review takes an ontogenetic view focused on the large superfamily of TGF-β/bone morphogenetic protein ligands to address thymus morphogenesis and function in T cell differentiation. Recent findings on a role of GDF11 for reversing aging-related phenotypes are also discussed.

Anti-Müllerian hormone is a gonadal cytokine with two circulating forms and cryptic actions

Anti-Müllerian hormone (AMH) is a multi-faceted gonadal cytokine. It is present in all vertebrates with its original function in phylogeny being as a regulator of germ cells in both sexes, and as a prime inducer of the male phenotype. Its ancient functions appear to be broadly conserved in mammals, but with this being obscured by its overt role in triggering the regression of the Müllerian ducts in male embryos. Sertoli and ovarian follicular cells primarily release AMH as a prohormone (proAMH), which forms a stable complex (AMHN,C) after cleavage by subtilisin/kexin-type proprotein convertases or serine proteinases. Circulating AMH is a mixture of proAMH and AMHN,C, suggesting that proAMH is activated within the gonads and putatively by its endocrine target-cells. The gonadal expression of the cleavage enzymes is subject to complex regulation, and the preliminary data suggest that this influences the relative proportions of proAMH and AMHN,C in the circulation. AMH shares an intracellular pathway with the bone morphogenetic protein (BMP) and growth differentiation factor (GDF) ligands. AMH is male specific during the initial stage of development, and theoretically should produce male biases throughout the body by adding a male-specific amplification of BMP/GDF signalling. Consistent with this, some of the male biases in neuron number and the non-sexual behaviours of mice are dependent on AMH. After puberty, circulating levels of AMH are similar in men and women. Putatively, the function of AMH in adulthood maybe to add a gonadal influence to BMP/GDF-regulated homeostasis.

Hippo and TGF-β interplay in the lung field

The Hippo pathway is comprised of a kinase cascade that involves mammalian Ste20-like serine/threonine kinases (MST1/2) and large tumor suppressor kinases (LATS1/2) and leads to inactivation of transcriptional coactivator with PDZ-binding motif (TAZ) and yes-associated protein (YAP). Protein stability and subcellular localization of TAZ/YAP determine its ability to regulate a diverse array of biological processes, including proliferation, apoptosis, differentiation, stem/progenitor cell properties, organ size control, and tumorigenesis. These actions are enabled by interactions with various transcription factors or through cross talk with other signaling pathways. Interestingly, mechanical stress has been shown to be an upstream regulator of TAZ/YAP activity, and this finding provides a novel clue for understanding how mechanical forces influence a broad spectrum of biological processes, which involve cytoskeletal structure, cell adhesion, and extracellular matrix (ECM) organization. Transforming growth factor-β (TGF-β) pathway is a critical component of lung development and the progression of lung diseases including emphysema, fibrosis, and cancer. In addition, TGF-β is a key regulator of ECM remodeling and cell differentiation processes such as epithelial-mesenchymal transition. In this review, we summarize the current knowledge of the Hippo pathway regarding lung development and diseases, with an emphasis on its interplay with TGF-β signaling.

Analysis of human soft palate morphogenesis supports regional regulation of palatal fusion

It is essential to complete palate closure at the correct time during fetal development, otherwise a serious malformation, cleft palate, will ensue. The steps in palate formation in humans take place between the 7th and 12th week and consist of outgrowth of palatal shelves from the paired maxillary prominences, reorientation of the shelves from vertical to horizontal, apposition of the medial surfaces, formation of a bilayered seam, degradation of the seam and bridging of mesenchyme. However, in the soft palate, the mechanism of closure is unclear. In previous studies it is possible to find support for both fusion and the alternative mechanism of merging. Here we densely sample the late embryonic-early fetal period between 54 and 74 days post-conception to determine the timing and mechanism of soft palate closure. We found the epithelial seam extends throughout the soft palates of 57-day specimens. Cytokeratin antibody staining detected the medial edge epithelium and distinguished clearly that cells in the midline retained their epithelial character. Compared with the hard palate, the epithelium is more rapidly degraded in the soft palate and only persists in the most posterior regions at 64 days. Our results are consistent with the soft palate following a developmentally more rapid program of fusion than the hard palate. Importantly, the two regions of the palate appear to be independently regulated and have their own internal clocks regulating the timing of seam removal. Considering data from human genetic and mouse studies, distinct anterior-posterior signaling mechanisms are likely to be at play in the human fetal palate.

IRF6 is the mediator of TGFβ3 during regulation of the epithelial mesenchymal transition and palatal fusion

Mutation in interferon regulatory factor 6 (IRF6) is known to cause syndromic and non-syndromic cleft lip/palate in human. In this study, we investigated the molecular mechanisms related to IRF6 during palatal fusion using palatal shelves organ culture. The results showed that ablation of Irf6 resulted in a delay in TGFβ3-regulated palatal fusion. Ectopic expression of IRF6 was able to promote palatal fusion and rescue shTgfβ3-induced fusion defect. These findings indicate that IRF6 is involved in TGFβ3-mediated palatal fusion. Molecular analysis revealed that ectopic expression of IRF6 increased the expression of SNAI2, an epithelial mesenchymal transition (EMT) regulator, and diminished the expression of various epithelial markers, such as E-cadherin, Plakophilin and ZO-1. In addition, knockdown of Irf6 expression decreased SNAI2 expression, and restored the expression of ZO-1 and Plakophilin that were diminished by TGFβ3. Blocking of Snai2 expression delayed palatal fusion and abolished the IRF6 rescuing effect associated with shTgfβ3-induced fusion defect. These findings indicate that TGFβ3 increases IRF6 expression and subsequently regulates SNAI2 expression, and IRF6 appears to regulate EMT during palatal fusion via SNAI2. Taken together, this study demonstrates that IRF6 is a mediator of TGFβ3, which regulates EMT and fusion process during the embryonic palate development.