Odd-skipped related 2 (Osr2) encodes a key intrinsic regulator of secondary palate growth and morphogenesis

Differences in palatal shelf epithelial stiffness between the lingual/nasal and buccal/oral surfaces during palatal shelf elevation in developing mice

BACKGROUND

During secondary palate formation, bilateral palatal shelves grow vertically to a horizontal position. This morphological change of the palatal shelves, defined as the palatal shelf elevation, occurs from embryonic day (E)-13.5 to E14 in mice. Palatal shelves show regional differences in elevation patterns along the anterior-posterior (AP) axis; however, the underlying mechanisms remain unclear. Material properties of the lingual/nasal and buccal/oral surfaces, especially stiffness, possibly contribute to different elevation patterns.

RESULTS

Indentation test using atomic force microscopy was performed to measure the stiffness at the epithelial surface of the palatal shelf. Measurement of palatal shelf stiffness along the AP axis before and after elevation revealed that the lingual/nasal surface was softer than the buccal/oral surface in the posterior region before elevation and that the palatal shelf was stiffer after elevation than before elevation. Moreover, the thickness of epithelial cells on the lingual/nasal side was lower than that on the buccal/oral side before elevation.

CONCLUSION

Overall, our results suggest that epithelial cell thickness affects epithelial surface stiffness, causing regional differences in elevation patterns.

Loxl3 Affects Palatal Shelf Elevation by Regulating Cell Proliferation and Collagen Deposition

Cleft palate is one of the most common congenital abnormalities and one of the main symptoms of Stickler syndrome. Secondary palate development is a complex multi-step process that involves raising the palatal frame from a vertical to a horizontal position. Lysyl oxidase-like 3 (LOXL3), a member of the lysyl oxidase family responsible for the crosslinking in collagen, is also one of the mutated genes detected in Stickler syndrome. Loss of Loxl3 causes delayed palatal shelf elevation, which in turn resulted in cleft palate. However, the precise mechanisms of palatal shelf delayed elevation remain unclear. In this study, we deeply investigated the mechanism of Loxl3 induced delayed elevation in palatal shelves. We found that Loxl3 deficiency caused reduced cell proliferation in both medial and posterior palatal mesenchyme through BrdU labeling and Western blot analysis (p < 0.05, p < 0.01), decreased migration of palatal mesenchymal cells through cell scratch assay (p < 0.05), and decreased expression of genes associated with proliferation through Western blot analysis (p < 0.05, p < 0.01) at E14. We found that the specific deletion of Loxl3 in the palatal mesenchyme resulted in delayed elevation but normal fusion of palatal shelves, also reduced cell proliferation and collagen fibers deposition in medial palatal mesenchyme through BrdU labeling and histological analysis (p < 0.05, p < 0.01). Thus, our data suggest that Loxl3 regulates cell proliferation and collagen fibers deposition in the palatal mesenchyme, thus controlling palatal shelf elevation.

Discovery and validation of a novel dual-target blood test for the detection of hepatocellular carcinoma across stages from cirrhosis

BACKGROUND

Hepatocellular carcinoma (HCC) is one of the most common cancers. Early detection of HCC helps improve the patients' 5-year survival rate. Our goal was to identify superior methylation biomarkers to develop a methylation-specific quantitative PCR (MS‒qPCR) assay.

METHODS

A five-phase case-control study identified HCC methylation biomarkers via capture sequencing, TCGA/RNA-seq filtering, technical (MS-qPCR/Sanger) and biological (quadruplex MS-qPCR) validation. Methylated biomarkers were selected based on differential methylation expression using a tissue discovery cohort (43 HCC, 32 normal) and validated in plasma validation cohorts (Phase 1: 53 HCC, 52 cirrhosis, 20 benign, 50 healthy; Phase 2: 67 HCC, 81 cirrhosis). Then, the final assay's HCC detection performance was compared with existing blood-based surveillance methods.

RESULTS

Two methylated genes, OSR2 and TSPYL5, and a novel internal reference gene, SDF4, were identified and developed into an MS‒qPCR assay named Qliver. Qliver had an AUC of 0.955 (95% CI: 0.924-0.987) for distinguishing HCC patients from non-HCC patients in the Phase 1 plasma cohort, with a sensitivity of 88.68% (95% CI: 76.97%-95.73%) and a specificity of 89.34% (95% CI: 82.47%-94.20%), and 0.958 (95% CI: 0.927-0.989) for distinguishing HCC patients from cirrhosis patients in the Phase 2 plasma cohort, with a sensitivity of 88.06% (95% CI: 77.82%-94.70%) and a specificity of 92.59% (95% CI: 84.57%-97.23%). For the Phase 1 plus Plasma 2 cohort, Qliver had an AUC of at least 0.958 for detecting HCC in healthy individuals, cirrhosis patients and patients with benign liver diseases, which was superior to that of the GALAD score (AUC: 0.777 to 0.849). For BCLC stage 0 and A HCC patients, the sensitivity of Qliver ranged from 62.50% (95% CI: 24.49%-91.48%) to 72.73% (39.03%-93.98%), with a specificity of 90%. Overall, Qliver was superior to the AFP, AFP-L3, DCP and the GALAD score in terms of cirrhosis history, tumor stage, tumor size and tumor count.

CONCLUSIONS

Qliver demonstrated superior performance in detecting HCC compared with currently widely used blood biomarkers, suggesting its potential clinical benefit in HCC surveillance in high-risk populations.

MLL4 regulates postnatal palate growth and midpalatal suture development

MLL4, also known as KMT2D, is a histone methyltransferase that acts as an important epigenetic regulator in various organogenesis programs. Mutations in the MLL4 gene are the major cause of Kabuki syndrome, a human developmental disorder that involves craniofacial birth defects, including anomalies in the palate. This study aimed to investigate the role of MLL4 and the underlying mechanisms in the development and growth of the palate. We generated a novel conditional knockout (cKO) mouse model with tissue-specific deletion of Mll4 in the palatal mesenchyme. Using micro-computed tomography (CT), histological analysis, cell mechanism assays, and gene expression profiling, we examined palate development and growth in the Mll4-cKO mice. Gross craniofacial examination at adult stages revealed mild midfacial hypoplasia and midline defects of the palate in Mll4-cKO mice, including a widened midpalatal suture and disrupted midline rugae pattern. Micro-CT-based time-course skeletal analysis during postnatal palatogenesis through adulthood demonstrated a transverse growth deficit in overall palate width in Mll4-cKO mice. Whole-mount and histological staining at perinatal stages identified that the midline defects in the Mll4-cKO mice emerged as early as 1 day prior to birth, presenting as a widened midpalatal suture, accompanied by increased cell apoptosis in the suture mesenchyme. Genome-wide mRNA expression analysis of the midpalatal suture tissue revealed that MLL4 is essential for the timely expression of major cartilage development genes, such as Col2a1 and Acan, at birth. Immunofluorescence staining for osteochondral differentiation markers demonstrated a marked decrease in the chondrogenic marker COL2A1, while the expression of the osteogenic marker RUNX2 remained unchanged, in the Mll4-cKO midpalatal suture. Additionally, SOX9, a master regulator of chondrogenesis, exhibited a significant decrease in protein expression. Indeed, time-course histological analysis during postnatal palate growth revealed retardation in the development of the suture cartilage in Mll4-cKO mice. Taken together, our results demonstrate that MLL4 is essential for orchestrating key cellular and molecular events that ensure proper midpalatal suture development and palate growth.

MLL4 regulates postnatal palate growth and midpalatal suture development

MLL4, also known as KMT2D, is a histone methyltransferase that acts as an important epigenetic regulator in various organogenesis programs. Mutations in the MLL4 gene are the major cause of Kabuki syndrome, a human developmental disorder that involves craniofacial birth defects, including anomalies in the palate. This study aimed to investigate the role of MLL4 and the underlying mechanisms in the development and growth of the palate. We generated a novel conditional knockout (cKO) mouse model with tissue-specific deletion of Mll4 in the palatal mesenchyme. Using micro-computed tomography (CT), histological analysis, cell mechanism assays, and gene expression profiling, we examined palate development and growth in the Mll4-cKO mice. Gross craniofacial examination at adult stages revealed mild midfacial hypoplasia and midline defects of the palate in Mll4-cKO mice, including a widened midpalatal suture and disrupted midline rugae pattern. Micro-CT-based time-course skeletal analysis during postnatal palatogenesis through adulthood demonstrated a transverse growth deficit in overall palate width in Mll4-cKO mice. Whole-mount and histological staining at perinatal stages identified that the midline defects in the Mll4-cKO mice emerged as early as one day prior to birth, presenting as a widened midpalatal suture, accompanied by increased cell apoptosis in the suture mesenchyme. Genome-wide mRNA expression analysis of the midpalatal suture tissue revealed that MLL4 is essential for the timely expression of major cartilage development genes, such as Col2a1 and Acan, at birth.Immunofluorescence staining for osteochondral differentiation markers demonstrated a marked decrease in the chondrogenic marker COL2A1, while the expression of the osteogenic marker RUNX2 remained unchanged, in the Mll4-cKO midpalatal suture. Additionally, SOX9, a master regulator of chondrogenesis, exhibited a significant decrease in protein expression. Indeed, time-course histological analysis during postnatal palate growth revealed retardation in the development of the suture cartilage in Mll4-cKO mice. Taken together, our results demonstrate that MLL4 is essential for orchestrating key cellular and molecular events that ensure proper midpalatal suture development and palate growth.

Cell-cell interaction determines cell fate of mesoderm-derived cell in tongue development through Hh signaling

Dysfunction of primary cilia leads to genetic disorder, ciliopathies, which shows various malformations in many vital organs such as brain. Multiple tongue deformities including cleft, hamartoma, and ankyloglossia are also seen in ciliopathies, which yield difficulties in fundamental functions such as mastication and vocalization. Here, we found these tongue anomalies in mice with mutation of ciliary protein. Abnormal cranial neural crest-derived cells (CNCC) failed to evoke Hh signal for differentiation of mesoderm-derived cells into myoblasts, which resulted in abnormal differentiation of mesoderm-derived cells into adipocytes. The ectopic adipose subsequently arrested tongue swelling formation. Ankyloglossia was caused by aberrant cell migration due to lack of non-canonical Wnt signaling. In addition to ciliopathies, these tongue anomalies are often observed as non-familial condition in human. We found that these tongue deformities could be reproduced in wild-type mice by simple mechanical manipulations to disturb cellular processes which were disrupted in mutant mice. Our results provide hints for possible future treatment in ciliopathies.

Osr2 functions as a biomechanical checkpoint to aggravate CD8+ T cell exhaustion in tumor

Alterations in extracellular matrix (ECM) architecture and stiffness represent hallmarks of cancer. Whether the biomechanical property of ECM impacts the functionality of tumor-reactive CD8+ T cells remains largely unknown. Here, we reveal that the transcription factor (TF) Osr2 integrates biomechanical signaling and facilitates the terminal exhaustion of tumor-reactive CD8+ T cells. Osr2 expression is selectively induced in the terminally exhausted tumor-specific CD8+ T cell subset by coupled T cell receptor (TCR) signaling and biomechanical stress mediated by the Piezo1/calcium/CREB axis. Consistently, depletion of Osr2 alleviates the exhaustion of tumor-specific CD8+ T cells or CAR-T cells, whereas forced Osr2 expression aggravates their exhaustion in solid tumor models. Mechanistically, Osr2 recruits HDAC3 to rewire the epigenetic program for suppressing cytotoxic gene expression and promoting CD8+ T cell exhaustion. Thus, our results unravel Osr2 functions as a biomechanical checkpoint to exacerbate CD8+ T cell exhaustion and could be targeted to potentiate cancer immunotherapy.

From Bedside to Bench and Back: Advancing Our Understanding of the Pathophysiology of Cleft Palate and Implications for the Future

OBJECTIVE

To provide a comprehensive understanding of the pathophysiology of cleft palate (CP) and future perspectives.

DESIGN

Literature review.

SETTING

Setting varied across studies by level of care and geographical locations.

INTERVENTIONS

No interventions were performed.

MAIN OUTCOME MEASURE(S)

Primary outcome measures were to summarize our current understanding of palatogenesis in humans and animal models, the pathophysiology of CP, and potential future treatment modalities.

RESULTS

Animal research has provided considerable insight into the pathophysiology, molecular and cellular mechanisms of CP that have allowed for the development of novel treatment strategies. However, much work has yet to be done to connect our mouse model investigations and discoveries to CP in humans. The success of innovative strategies for tissue regeneration in mice provides promise for an exciting new avenue for improved and more targeted management of cleft care with precision medicine in patients. However, significant barriers to clinical translation remain. Among the most notable challenges include the differences in some aspects of palatogenesis and tissue repair between mice and humans, suggesting that potential therapies that have worked in animal models may not provide similar benefits to humans.

CONCLUSIONS

Increased translation of pathophysiological and tissue regeneration studies to clinical trials will bridge a wide gap in knowledge between animal models and human disease. By enhancing interaction between basic scientists and clinicians, and employing our animal model findings of disease mechanisms in concert with what we glean in the clinic, we can generate a more targeted and improved treatment algorithm for patients with CP.

odd skipped-related 2 as a novel mark for labeling the proximal convoluted tubule within the zebrafish kidney

The proximal convoluted tubule (PCT) of the kidney is a crucial functional segment responsible for reabsorption, secretion, and the maintenance of electrolyte and water balance within the renal tubule. However, there is a lack of a well-defined endogenous transgenic line for studying PCT morphogenesis. By analyzing single-cell transcriptome data from the adult zebrafish kidney, we have identified the expression of odd-skipped-related 2 (osr2, which encodes an odd-skipped zinc-finger transcription factor) in the PCT. To gain insight into the role of osr2 in PCT morphogenesis, we have generated a transgenic zebrafish line Tg(osr2:EGFP), expressing enhanced green fluorescent protein (EGFP). The EGFP expression pattern closely mirrors that of endogenous Osr2, faithfully recapitulating its native expression profile. During kidney development, we can use EGFP to track PCT development, which is also preserved in adult zebrafish. Additionally, osr2:EGFP-labeled zebrafish PCT fragments displayed short lengths with infrequent overlap, rendering them conducive for nephrons counting. The generation of Tg(osr2:EGFP) transgenic line is accompanied by simultaneous disruption of osr2 activity. Importantly, our findings demonstrate that osr2 inactivation had no discernible impact on the development and regeneration of Tg(osr2:EGFP) zebrafish nephrons. Overall, the establishment of this transgenic zebrafish line offers a valuable tool for both genetic and chemical analysis of PCT.

PDIA3 modulates genomic response to 1,25-dihydroxyvitamin D3 in squamous cell carcinoma of the skin

An active form of vitamin D3 (1,25-dihydroxyvitamin D3) acts through vitamin D receptor (VDR) initiating genomic response, but several studies described also non-genomic actions of 1,25-dihydroxyvitamin D3, implying the role of PDIA3 in the process. PDIA3 is a membrane-associated disulfide isomerase involved in disulfide bond formation, protein folding, and remodeling. Here, we used a transcriptome-based approach to identify changes in expression profiles in PDIA3-deficient squamous cell carcinoma line A431 after 1,25-dihydroxyvitamin D3 treatment. PDIA3 knockout led to changes in the expression of more than 2000 genes and modulated proliferation, cell cycle, and mobility of cells; suggesting an important regulatory role of PDIA3. PDIA3-deficient cells showed increased sensitivity to 1,25-dihydroxyvitamin D3, which led to decrease migration. 1,25-dihydroxyvitamin D3 treatment altered also genes expression profile of A431ΔPDIA3 in comparison to A431WT cells, indicating the existence of PDIA3-dependent genes. Interestingly, classic targets of VDR, including CAMP (Cathelicidin Antimicrobial Peptide), TRPV6 (Transient Receptor Potential Cation Channel Subfamily V Member 6), were regulated differently by 1,25-dihydroxyvitamin D3, in A431ΔPDIA3. Deletion of PDIA3 impaired 1,25-dihydroxyvitamin D3-response of genes, such as PTGS2, MMP12, and FOCAD, which were identified as PDIA3-dependent. Additionally, response to 1,25-dihydroxyvitamin D3 in cancerous A431 cells differed from immortalized HaCaT keratinocytes, used as non-cancerous control. Finally, silencing of PDIA3 and 1,25-dihydroxyvitamin D3, at least partially reverse the expression of cancer-related genes in A431 cells, thus targeting PDIA3 and use of 1,25-dihydroxyvitamin D3 could be considered in a prevention and therapy of the skin cancer. Taken together, PDIA3 has a strong impact on gene expression and physiology, including genomic response to 1,25-dihydroxyvitamin D3.

Mesenchymal β-catenin signaling affects palatogenesis by regulating α-actinin-4 and F-actin

OBJECTIVE

Our previous research have found that mesenchymal β-catenin may be involved in palatal shelf (PS) elevation by regulating F-actin. Here, we further investigated the exact mechanism of β-catenin/F-actin in the PS mesenchyme to regulate palatal reorientation.

MATERIALS AND METHODS

(1) Firstly, Ctnnb1ex3f (β-catenin) mice were conditionally overexpressed in the palatal mesenchyme by crossing with the Sox9-creERT2 mice (induced by Tamoxifen injections); (2) Subsequently, histology and immunohistochemistry were used to characterize the variations of PS morphology and expression of key molecules associated with developmental process; (3) Finally, experiments in vivo and ex vivo were employed to identify the critical mechanisms in β-catenin silenced and overexpressed models.

RESULTS

We found that the Sox9CreER; Ctnnb1ex3f mice exhibited failed palatal elevation and visible cleft palate, and overexpression of β-catenin disturbed the F-actin responsible for cytoskeletal remodeling in palatal mesenchymal cells. qRT-PCR results showed mRNA levels of α-actinin4, a gene involved in F-actin cross-linking, were associated with knockdown or overexpression of β-catenin in ex vivo, respectively. Experiments in vivo revealed that mesenchymal specific inactivation or overexpression of β-catenin exhibited decreased or increased α-actinin-4 expression.

CONCLUSIONS

Mesenchymal β-catenin/F-actin plays an essential role in PS reorientation, which mediate α-actinin-4 to regulate F-actin cytoskeleton reorganization.

Intestinal expression patterns of transcription factors and markers for interstitial cells in the larval zebrafish

For the digestion of food, it is important for the gut to be differentiated regionally and to have proper motor control. However, the number of transcription factors that regulate its development is still limited. Meanwhile, the interstitial cells of the gastrointestinal (GI) tract are necessary for intestinal motility in addition to the enteric nervous system. There are anoctamine1 (Ano1)-positive and platelet-derived growth factor receptor α (Pdgfra)-positive interstitial cells in mammal, but Pdgfra-positive cells have not been reported in the zebrafish. To identify new transcription factors involved in GI tract development, we used RNA sequencing comparing between larval and adult gut. We isolated 40 transcription factors that were more highly expressed in the larval gut. We demonstrated expression patterns of the 13 genes, 7 of which were newly found to be expressed in the zebrafish larval gut. Six of the 13 genes encode nuclear receptors. The osr2 is expressed in the anterior part, while foxP4 in its distal part. Also, we reported the expression pattern of pdgfra for the first time in the larval zebrafish gut. Our data provide fundamental knowledge for studying vertebrate gut regionalization and motility by live imaging using zebrafish.

Sonic hedgehog signaling in craniofacial development

Mutations in SHH and several other genes encoding components of the Hedgehog signaling pathway have been associated with holoprosencephaly syndromes, with craniofacial anomalies ranging in severity from cyclopia to facial cleft to midfacial and mandibular hypoplasia. Studies in animal models have revealed that SHH signaling plays crucial roles at multiple stages of craniofacial morphogenesis, from cranial neural crest cell survival to growth and patterning of the facial primordia to organogenesis of the palate, mandible, tongue, tooth, and taste bud formation and homeostasis. This article provides a summary of the major findings in studies of the roles of SHH signaling in craniofacial development, with emphasis on recent advances in the understanding of the molecular and cellular mechanisms regulating the SHH signaling pathway activity and those involving SHH signaling in the formation and patterning of craniofacial structures.

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.

Revisiting the embryogenesis of lip and palate development

Clefts of the lip and palate (CLP), the major causes of congenital facial malformation globally, result from failure of fusion of the facial processes during embryogenesis. With a prevalence of 1 in 500-2500 live births, CLP causes major morbidity throughout life as a result of problems with facial appearance, feeding, speaking, obstructive apnoea, hearing and social adjustment and requires complex, multi-disciplinary care at considerable cost to healthcare systems worldwide. Long-term outcomes for affected individuals include increased mortality compared with their unaffected siblings. The frequent occurrence and major healthcare burden imposed by CLP highlight the importance of dissecting the molecular mechanisms driving facial development. Identification of the genetic mutations underlying syndromic forms of CLP, where CLP occurs in association with non-cleft clinical features, allied to developmental studies using appropriate animal models is central to our understanding of the molecular events underlying development of the lip and palate and, ultimately, how these are disturbed in CLP.

Spatiotemporal Gene Expression Regions along the Anterior-Posterior Axis in Mouse Embryos before and after Palatal Elevation

The mammalian secondary palate is formed through complex developmental processes: growth, elevation, and fusion. Although it is known that the palatal elevation pattern changes along the anterior-posterior axis, it is unclear what molecules are expressed and whether their locations change before and after elevation. We examined the expression regions of molecules associated with palatal shelf elevation (Pax9, Osr2, and Tgfβ3) and tissue deformation (F-actin, E-cadherin, and Ki67) using immunohistochemistry and RT-PCR in mouse embryos at E13.5 (before elevation) and E14.5 (after elevation). Pax9 was expressed at significantly higher levels in the lingual/nasal region in the anterior and middle parts, as well as in the buccal/oral region in the posterior part at E13.5. At E14.5, Pax9 was expressed at significantly higher levels in both the lingual/nasal and buccal/oral regions in the anterior and middle parts and the buccal/oral regions in the posterior part. Osr2 was expressed at significantly higher levels in the buccal/oral region in all parts at E13.5 and was more strongly expressed at E13.5 than at E14.5 in all regions. No spatiotemporal changes were found in the other molecules. These results suggested that Pax9 and Osr2 are critical molecules leading to differences in the elevation pattern in palatogenesis.

Mouse models in palate development and orofacial cleft research: Understanding the crucial role and regulation of epithelial integrity in facial and palate morphogenesis

Cleft lip and cleft palate are common birth defects resulting from genetic and/or environmental perturbations of facial development in utero. Facial morphogenesis commences during early embryogenesis, with cranial neural crest cells interacting with the surface ectoderm to form initially partly separate facial primordia consisting of the medial and lateral nasal prominences, and paired maxillary and mandibular processes. As these facial primordia grow around the primitive oral cavity and merge toward the ventral midline, the surface ectoderm undergoes a critical differentiation step to form an outer layer of flattened and tightly connected periderm cells with a non-stick apical surface that prevents epithelial adhesion. Formation of the upper lip and palate requires spatiotemporally regulated inter-epithelial adhesions and subsequent dissolution of the intervening epithelial seam between the maxillary and medial/lateral nasal processes and between the palatal shelves. Proper regulation of epithelial integrity plays a paramount role during human facial development, as mutations in genes encoding epithelial adhesion molecules and their regulators have been associated with syndromic and non-syndromic orofacial clefts. In this chapter, we summarize mouse genetic studies that have been instrumental in unraveling the mechanisms regulating epithelial integrity and periderm differentiation during facial and palate development. Since proper epithelial integrity also plays crucial roles in wound healing and cancer, understanding the mechanisms regulating epithelial integrity during facial development have direct implications for improvement in clinical care of craniofacial patients.

Downregulation of Odd-Skipped Related 2, a Novel Regulator of Epithelial-Mesenchymal Transition, Enables Efficient Somatic Cell Reprogramming

Somatic cell reprogramming proceeds through a series of events to generate induced pluripotent stem cells (iPSCs). The early stage of reprogramming of mouse embryonic fibroblasts (MEFs) is characterized by rapid cell proliferation and morphological changes, which are accompanied by downregulation of mesenchyme-associated genes. However, the functional relevance of their downregulation to reprogramming remains poorly defined. In this study, we have screened transcriptional regulators that are downregulated immediately upon reprogramming, presumably through direct targeting by reprogramming factors. To test if these transcriptional regulators impact reprogramming when expressed continuously, we generated an expression vector that harbors human cytomegalovirus upstream open reading frame 2 (uORF2), which reduces translation to minimize the detrimental effect of an expressed protein. Screening of transcriptional regulators with this expression vector revealed that downregulation of odd-skipped related 2 (Osr2) is crucial for efficient reprogramming. Using a cell-based model for epithelial-mesenchymal transition (EMT), we show that Osr2 is a novel EMT regulator that acts through induction of TGF-β signaling. During reprogramming, Osr2 downregulation not only diminishes TGF-β signaling but also allows activation of Wnt signaling, thus promoting mesenchymal-epithelial transition (MET) toward acquisition of pluripotency. Our results illuminate the functional significance of Osr2 downregulation in erasing the mesenchymal phenotype at an early stage of somatic cell reprogramming.

Zfhx4 regulates endochondral ossification as the transcriptional platform of Osterix in mice

Endochondral ossification is regulated by transcription factors that include SRY-box transcription factor 9, runt-related protein 2 (Runx2), and Osterix. However, the sequential and harmonious regulation of the multiple steps of endochondral ossification is unclear. This study identified zinc finger homeodomain 4 (Zfhx4) as a crucial transcriptional partner of Osterix. We found that Zfhx4 was highly expressed in cartilage and that Zfhx4 deficient mice had reduced expression of matrix metallopeptidase 13 and inhibited calcification of cartilage matrices. These phenotypes were very similar to impaired chondrogenesis in Osterix deficient mice. Coimmunoprecipitation and immunofluorescence indicated a physical interaction between Zfhx4 and Osterix. Notably, Zfhx4 and Osterix double mutant mice showed more severe phenotype than Zfhx4 deficient mice. Additionally, Zfhx4 interacted with Runx2 that functions upstream of Osterix. Our findings suggest that Zfhx4 coordinates the transcriptional network of Osterix and, consequently, endochondral ossification.

Sox9CreER-mediated deletion of β-catenin in palatal mesenchyme results in delayed palatal elevation accompanied with repressed canonical Wnt signaling and reduced actin polymerization

Cleft palate is a good model to pushing us toward a deeper understanding of the molecular mechanisms of spatiotemporal patterns in tissues and organisms because of the multiple-step processes such as elevation and fusion. Previous studies have shown that the epithelial β-catenin is crucial for palatal fusion, however, the function of the mesenchymal β-catenin remains elusive. We investigate the role of mesenchymal β-catenin in palatal development by generating a β-catenin conditional knockout mouse (CKO) (Sox9CreER; Ctnnb1^F/F ). We found that the CKO mice exhibited delayed palatal elevation, leading to cleft palate in both in vivo and ex vivo. Abnormal cell proliferation and repressed mesenchymal canonical Wnt signaling were found in the CKO palate. Interestingly, Filamentous actin (F-actin) polymerization was significantly reduced in the palatal mesenchyme of mutant embryos. Furthermore, overexpression of adenovirus-mediated transfection with Acta1 in the mutant could help to elevate the palatal shelves but could not prevent cleft palate in ex vivo. Our results suggest that conditionally knock out β-catenin in the palatal mesenchyme by Sox9CreER leading to delayed palatal elevation, which results in repressed mesenchymal canonical Wnt signaling, decreased cell proliferation, and reduced actin polymerization, finally causes cleft palate.

RERE deficiency contributes to the development of orofacial clefts in humans and mice

Deletions of chromosome 1p36 are the most common telomeric deletions in humans and are associated with an increased risk of orofacial clefting. Deletion/phenotype mapping, combined with data from human and mouse studies, suggests the existence of multiple 1p36 genes associated with orofacial clefting including SKI, PRDM16, PAX7 and GRHL3. The arginine-glutamic acid dipeptide (RE) repeats gene (RERE) is located in the proximal critical region for 1p36 deletion syndrome and encodes a nuclear receptor co-regulator. Pathogenic RERE variants have been shown to cause neurodevelopmental disorder with or without anomalies of the brain, eye or heart (NEDBEH). Cleft lip has previously been described in one individual with NEDBEH. Here we report the first individual with NEDBEH to have a cleft palate. We confirm that RERE is broadly expressed in the palate during mouse embryonic development, and we demonstrate that the majority of RERE-deficient mouse embryos on C57BL/6 background have cleft palate. We go on to show that ablation of Rere in cranial neural crest (CNC) cells, mediated by a Wnt1-Cre, leads to delayed elevation of the palatal shelves and cleft palate and that proliferation of mesenchymal cells in the palatal shelves is significantly reduced in Rereflox/flox; Wnt1-Cre embryos. We conclude that loss of RERE function contributes to the development of orofacial clefts in individuals with proximal 1p36 deletions and NEDBEH and that RERE expression in CNC cells and their derivatives is required for normal palatal development.

Genome-Wide Association Study of Non-syndromic Orofacial Clefts in a Multiethnic Sample of Families and Controls Identifies Novel Regions

Orofacial clefts (OFCs) are among the most prevalent craniofacial birth defects worldwide and create a significant public health burden. The majority of OFCs are non-syndromic and vary in prevalence by ethnicity. Africans have the lowest prevalence of OFCs (~ 1/2,500), Asians have the highest prevalence (~1/500), Europeans and Latin Americans lie somewhere in the middle (~1/800 and 1/900, respectively). Thus, ethnicity appears to be a major determinant of the risk of developing OFC. The Pittsburgh Orofacial Clefts Multiethnic study was designed to explore this ethnic variance, comprising a large number of families and individuals (~12,000 individuals) from multiple populations worldwide: US and Europe, Asians, mixed Native American/Caucasians, and Africans. In this current study, we analyzed 2,915 OFC cases, 6,044 unaffected individuals related to the OFC cases, and 2,685 controls with no personal or family history of OFC. Participants were grouped by their ancestry into African, Asian, European, and Central and South American subsets, and genome-wide association run on the combined sample as well as the four ancestry-based groups. We observed 22 associations to cleft lip with or without cleft palate at 18 distinct loci with p-values < 1e-06, including 10 with genome-wide significance (<5e-08), in the combined sample and within ancestry groups. Three loci - 2p12 (rs62164740, p = 6.27e-07), 10q22.2 (rs150952246, p = 3.14e-07), and 10q24.32 (rs118107597, p = 8.21e-07) are novel. Nine were in or near known OFC loci - PAX7, IRF6, FAM49A, DCAF4L2, 8q24.21, NTN1, WNT3-WNT9B, TANC2, and RHPN2. The majority of the associations were observed only in the combined sample, European, and Central and South American groups. We investigated whether the observed differences in association strength were (a) purely due to sample sizes, (b) due to systematic allele frequency difference at the population level, or (c) due to the fact certain OFC-causing variants confer different amounts of risk depending on ancestral origin, by comparing effect sizes to observed allele frequencies of the effect allele in our ancestry-based groups. While some of the associations differ due to systematic differences in allele frequencies between groups, others show variation in effect size despite similar frequencies across ancestry groups.

Tissue-specific analysis of Fgf18 gene function in palate development

BACKGROUND

Previous studies showed that mice lacking Fgf18 function had cleft palate defects and that the FGF18 locus was associated with cleft lip and palate in humans, but what specific roles Fgf18 plays during palatogenesis are unclear.

RESULTS

We show that Fgf18 exhibits regionally restricted expression in developing palatal shelves, mandible, and tongue, during palatal outgrowth and fusion in mouse embryos. Tissue-specific inactivation of Fgf18 throughout neural crest-derived craniofacial mesenchyme caused shortened mandible and reduction in ossification of the frontal, nasal, and anterior cranial base skeletal elements in Fgf18c/c ;Wnt1-Cre mutant mice. About 64% of Fgf18c/c ;Wnt1-Cre mice exhibited cleft palate. Whereas palatal shelf elevation was impaired in many Fgf18c/c ;Wnt1-Cre embryos, no significant difference in palatal cell proliferation was detected between Fgf18c/c ;Wnt1-Cre embryos and their control littermates. Embryonic maxillary explants from Fgf18c/c ;Wnt1-Cre embryos showed successful palatal shelf elevation and fusion in organ culture similar to the maxillary explants from control embryos. Furthermore, tissue-specific inactivation of Fgf18 in the early palatal mesenchyme did not cause cleft palate.

CONCLUSION

These results demonstrate a critical role for Fgf18 expression in the neural crest-derived mesenchyme for the development of the mandible and multiple craniofacial bones but Fgf18 expression in the palatal mesenchyme is dispensable for palatogenesis.

FACEts of mechanical regulation in the morphogenesis of craniofacial structures

During embryonic development, organs undergo distinct and programmed morphological changes as they develop into their functional forms. While genetics and biochemical signals are well recognized regulators of morphogenesis, mechanical forces and the physical properties of tissues are now emerging as integral parts of this process as well. These physical factors drive coordinated cell movements and reorganizations, shape and size changes, proliferation and differentiation, as well as gene expression changes, and ultimately sculpt any developing structure by guiding correct cellular architectures and compositions. In this review we focus on several craniofacial structures, including the tooth, the mandible, the palate, and the cranium. We discuss the spatiotemporal regulation of different mechanical cues at both the cellular and tissue scales during craniofacial development and examine how tissue mechanics control various aspects of cell biology and signaling to shape a developing craniofacial organ.

Gene-Environment Interplay and MicroRNAs in Cleft Lip and Cleft Palate

Cleft lip (CL) with/without cleft palate (CP) (hereafter CL/P) is the second most common congenital birth defect, affecting 7.94 to 9.92 children per 10,000 live births worldwide, followed by Down syndrome. An increasing number of genes have been identified as affecting susceptibility and/or as causative genes for CL/P in mouse genetic and chemically-induced CL and CP studies, as well as in human genome-wide association studies and linkage analysis. While marked progress has been made in the identification of genetic and environmental risk factors for CL/P, the interplays between these factors are not yet fully understood. This review aims to summarize our current knowledge of CL and CP from genetically engineered mouse models and environmental factors that have been studied in mice. Understanding the regulatory mechanism(s) of craniofacial development may not only advance our understanding of craniofacial developmental biology, but could also provide approaches for the prevention of birth defects and for tissue engineering in craniofacial tissue regeneration.

Integrating GWAS and eQTL to predict genes and pathways for non-syndromic cleft lip with or without palate

OBJECTIVE

To explore susceptibility genes and pathways for non-syndromic cleft lip with or without cleft palate (NSCL/P).

MATERIALS AND METHODS

Two genome-wide association studies (GWAS) datasets, including 858 NSCL/P cases and 1,248 controls, were integrated with expression quantitative trait loci (eQTL) dataset identified by Genotype-Tissue Expression (GTEx) project in whole-blood samples. The expression of the candidate genes in mouse orofacial development was inquired from FaceBase. Protein-protein interaction (PPI) network was visualized to identify protein functions. Go and KEGG pathway analyses were performed to explore the underlying risk pathways.

RESULTS

A total of 233 eQTL single-nucleotide polymorphisms (SNPs) in 432 candidate genes were identified to be associated with the risk of NSCL/P. One hundred and eighty-three susceptible genes were expressed in mouse orofacial development according to FaceBase. PPI network analysis highlighted that these genes involved in ubiquitin-mediated proteolysis (KCTD7, ASB1, UBOX5, ANAPC4) and DNA synthesis (XRCC3, RFC3, KAT5, RHNO1) were associated with the risk of NSCL/P. GO and KEGG pathway analyses revealed that the fatty acid metabolism pathway (ACADL, HSD17B12, ACSL5, PPT1, MCAT) played an important role in the development of NSCL/P.

CONCLUSIONS

Our results identified novel susceptibility genes and pathways associated with the development of NSCL/P.

Innovative Molecular and Cellular Therapeutics in Cleft Palate Tissue Engineering

Clefts of the lip and/or palate are the most prevalent orofacial birth defects occurring in about 1:700 live human births worldwide. Early postnatal surgical interventions are extensive and staged to bring about optimal growth and fusion of palatal shelves. Severe cleft defects pose a challenge to correct with surgery alone, resulting in complications and sequelae requiring life-long, multidisciplinary care. Advances made in materials science innovation, including scaffold-based delivery systems for precision tissue engineering, now offer new avenues for stimulating bone formation at the site of surgical correction for palatal clefts. In this study, we review the present scientific literature on key developmental events that can go awry in palate development and the common surgical practices and challenges faced in correcting cleft defects. How key osteoinductive pathways implicated in palatogenesis inform the design and optimization of constructs for cleft palate correction is discussed within the context of translation to humans. Finally, we highlight new osteogenic agents and innovative delivery systems with the potential to be adopted in engineering-based therapeutic approaches for the correction of palatal defects. Impact statement Tissue-engineered scaffolds supplemented with osteogenic growth factors have attractive, largely unexplored possibilities to modulate molecular signaling networks relevant to driving palatogenesis in the context of congenital anomalies (e.g., cleft palate). Constructs that address this need may obviate current use of autologous bone grafts, thereby avoiding donor-site morbidity and other regenerative challenges in patients afflicted with palatal clefts. Combinations of biomaterials and drug delivery of diverse regenerative cues and biologics are currently transforming strategies exploited by engineers, scientists, and clinicians for palatal cleft repair.

Pax9's dual roles in modulating Wnt signaling during murine palatogenesis

BACKGROUND

Despite the strides made in understanding the complex network of key regulatory genes and cellular processes that drive palate morphogenesis, patients suffering from these conditions face treatment options that are limited to complex surgeries and multidisciplinary care throughout life. Hence, a better understanding of how molecular interactions drive palatal growth and fusion is critical for the development of treatment and preventive strategies for cleft palates in humans. Our previous work demonstrated that Pax9-dependent Wnt signaling is critical for the growth and fusion of palatal shelves. We showed that controlled intravenous delivery of small molecule Wnt agonists specifically blocks the action of Dkks (inhibitors of Wnt signaling) and corrects secondary palatal clefts in Pax9^-/- mice. While these data underscore the importance of the functional upstream relationship of Pax9 to the Wnt pathway, not much is known about how the genetic nature of Pax9's interactions in vivo and how it modulates the actions of these downstream effectors during palate formation.

RESULTS

Here, we show that the genetic reduction of Dkk1 during palatogenesis corrected secondary palatal clefts in Pax9^-/- mice with restoration of Wnt signaling activities. In contrast, genetically induced overexpression of Dkk1 mice phenocopied the defects in tooth and palate development visible in Pax9^-/- strains. Results of ChIP-qPCR assays showed that Pax9 can bind to regions near the transcription start sites of Dkk1 and Dkk2 as well as the intergenic region of Wnt9b and Wnt3 ligands that are downregulated in Pax9^-/- palates.

CONCLUSIONS

Taken together, these data suggest that the molecular mechanisms underlying Pax9's role in modulating Wnt signaling activity likely involve the inhibition of Dkk expression and the control of Wnt ligands during palatogenesis.

YAP/TAZ Regulate Elevation and Bone Formation of the Mouse Secondary Palate

Clefting of the secondary palate is one of the most common congenital anomalies, and the multiple corrective surgeries that individuals with isolated cleft palate undergo are associated with major costs and morbidities. Secondary palate development is a complex, multistep process that includes the elevation of the palatal shelves from a vertical to horizontal position, a process that is not well understood. The Hippo signaling cascade is a mechanosensory pathway that regulates morphogenesis, homeostasis, and regeneration by controlling cell proliferation, apoptosis, and differentiation, primarily via negative regulation of the downstream effectors, Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ). We deleted Yap/Taz throughout the palatal shelf mesenchyme as well as specifically in the posterior palatal shelf mesenchyme, using the Osr2^Cre and Col2^Cre drivers, respectively, which resulted in palatal shelf elevation delay and clefting of the secondary palate. In addition, the deletion resulted in undersized bones of the secondary palate. We next determined downstream targets of YAP/TAZ in the posterior palatal shelves, which included Ibsp and Phex, genes involved in mineralization, and Loxl4, which encodes a lysyl oxidase that catalyzes collagen crosslinking. Ibsp, Phex, and Loxl4 were expressed at decreased levels in the ossification region in the posterior palatal shelf mesenchyme upon deletion of Yap/Taz. Furthermore, collagen levels were decreased specifically in the same region prior to elevation. Thus, our data suggest that YAP/TAZ may regulate collagen crosslinking in the palatal shelf mesenchyme, thus controlling palatal shelf elevation, as well as mineralization of the bones of the secondary palate.

The Era of the Genome and Dental Medicine

Understanding the "code of life" and mapping the human genome have been monumental and era-defining scientific landmarks-analogous to setting foot on the moon. The last century has been characterized by exponential advances in our understanding of the biological and specifically molecular basis of health and disease. The early part of the 20th century was marked by fundamental theoretical and scientific advances in understanding heredity, the identification of the DNA molecule and genes, and the elucidation of the central dogma of biology. The second half was characterized by experimental and increasingly molecular investigations, including clinical and population applications. The completion of the Human Genome Project in 2003 and the continuous technological advances have democratized access to this information and the ability to generate health and disease association data; however, the realization of genomic and precision medicine, to practically improve people's health, has lagged. The oral health domain has made great strides and substantially benefited from the last century of advances in genetics and genomics. Observations regarding a hereditary component of dental caries were reported as early as the 1920s. Subsequent breakthroughs were made in the discovery of genetic causes of rare diseases, such as ectodermal dysplasias, orofacial clefts, and other craniofacial and dental anomalies. More recently, genome-wide investigations have been conducted and reported for several diseases and traits, including periodontal disease, dental caries, tooth agenesis, cancers of the head and neck, orofacial pain, temporomandibular disorders, and craniofacial morphometrics. Gene therapies and gene editing with CRISPR/Cas represent the latest frontier surpassed in the era of genomic medicine. Amid rapid genomics progress, several challenges and opportunities lie ahead. Importantly, systematic efforts supported by implementation science are needed to realize the full potential of genomics, including the improvement of public and practitioner genomics literacy, the promotion of individual and population oral health, and the reduction of disparities.

Wnt signaling in orofacial clefts: crosstalk, pathogenesis and models

Diverse signaling cues and attendant proteins work together during organogenesis, including craniofacial development. Lip and palate formation starts as early as the fourth week of gestation in humans or embryonic day 9.5 in mice. Disruptions in these early events may cause serious consequences, such as orofacial clefts, mainly cleft lip and/or cleft palate. Morphogenetic Wnt signaling, along with other signaling pathways and transcription regulation mechanisms, plays crucial roles during embryonic development, yet the signaling mechanisms and interactions in lip and palate formation and fusion remain poorly understood. Various Wnt signaling and related genes have been associated with orofacial clefts. This Review discusses the role of Wnt signaling and its crosstalk with cell adhesion molecules, transcription factors, epigenetic regulators and other morphogenetic signaling pathways, including the Bmp, Fgf, Tgfβ, Shh and retinoic acid pathways, in orofacial clefts in humans and animal models, which may provide a better understanding of these disorders and could be applied towards prevention and treatments.

The Function and Regulatory Network of Pax9 Gene in Palate Development

Cleft palate, a common congenital deformity, can arise from disruptions in any stage of palatogenesis, including palatal shelf growth, elevation, adhesion, and fusion. Paired box gene 9 (Pax9) is recognized as a vital regulator of palatogenesis with great relevance to cleft palate in humans and mice. Pax9-deficient murine palatal shelves displayed deficient elongation, postponed elevation, failed contact, and fusion. Pax9 is expressed in epithelium and mesenchyme, exhibiting a dynamic expression pattern that changes according to the proceeding of palatogenesis. Recent studies highlighted the Pax9-related genetic interactions and their critical roles during palatogenesis. During palate growth, PAX9 interacts with numerous molecules and members of pathways (e.g., OSR2, FGF10, SHOS2, MSX1, BARX1, TGFβ3, LDB1, BMP, WNT β-catenin dependent, and EDA) in the mesenchyme and functions as a key mediator in epithelial-mesenchymal communications with FGF8, TBX1, and the SHH pathway. During palate elevation, PAX9 is hypothesized to mediate the time point of the elevation event in the anterior and posterior parts of the palatal shelves. The delayed elevation of Pax9 mutant palatal shelves probably results from abnormal expressions of a series of genes ( Osr2 and Bmpr1a) leading to deficient palate growth, abnormal tongue morphology, and altered hyaluronic acid distribution. The interactions between PAX9 and genes encoding the OSR2, TGFβ3, and WNT β-catenin-dependent pathways provide evidence that PAX9 might participate in the regulation of palate fusion. This review summarizes the current understanding of PAX9’s functions and emphasizes the interactions between PAX9 and vital genes during palatogenesis. We hope to provide some clues for further exploration of the function and mechanism of PAX9, especially during palate elevation and fusion events.

Conditional deletion of Bmp2 in cranial neural crest cells recapitulates Pierre Robin sequence in mice

Bone morphogenetic protein (BMP) signaling plays a crucial role in the development of craniofacial organs. Mutations in numerous members of the BMP signaling pathway lead to several severe human syndromes, including Pierre Robin sequence (PRS) caused by heterozygous loss of BMP2. In this study, we generate mice carrying Bmp2-specific deletion in cranial neural crest cells using floxed Bmp2 and Wnt1-Cre alleles to mimic PRS in humans. Mutant mice exhibit severe PRS with a significantly reduced size of craniofacial bones, cleft palate, malformed tongue and micrognathia. Palate clefting is caused by the undescended tongue that prevents palatal shelf elevation. However, the tongue in Wnt1-Cre;Bmp2^f/f mice does not exhibit altered rates of cell proliferation and apoptosis, suggesting contribution of extrinsic defects to the failure of tongue descent. Further studies revealed obvious reduction in cell proliferation and differentiation of osteogenic progenitors in the mandible of the mutants, attributing to the micrognathia phenotype. Our study illustrates the pathogenesis of PRS caused by Bmp2 mutation, highlights the crucial role of BMP2 in the development of craniofacial bones and emphasizes precise coordination in the morphogenesis of palate, tongue and mandible during embryonic development.

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

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

Creating diversity in mammalian facial morphology: a review of potential developmental mechanisms

Mammals (class Mammalia) have evolved diverse craniofacial morphology to adapt to a wide range of ecological niches. However, the genetic and developmental mechanisms underlying the diversification of mammalian craniofacial morphology remain largely unknown. In this paper, we focus on the facial length and orofacial clefts of mammals and deduce potential mechanisms that produced diversity in mammalian facial morphology. Small-scale changes in facial morphology from the common ancestor, such as slight changes in facial length and the evolution of the midline cleft in some lineages of bats, could be attributed to heterochrony in facial bone ossification. In contrast, large-scale changes of facial morphology from the common ancestor, such as a truncated, widened face as well as the evolution of the bilateral cleft possessed by some bat species, could be brought about by changes in growth and patterning of the facial primordium (the facial processes) at the early stages of embryogenesis.

Gene expression profiling in the developing secondary palate in the absence of Tbx1 function

BACKGROUND

Microdeletion of chromosome 22q11 is associated with significant developmental anomalies, including disruption of the cardiac outflow tract, thymic/parathyroid aplasia and cleft palate. Amongst the genes within this region, TBX1 is a major candidate for many of these developmental defects. Targeted deletion of Tbx1 in the mouse has provided significant insight into the function of this transcription factor during early development of the cardiac and pharyngeal systems. However, less is known about its role during palatogenesis. To assess the influence of Tbx1 function on gene expression profile within the developing palate we performed a microarray screen using total RNA isolated from the secondary palate of E13.5 mouse embryos wild type, heterozygous and mutant for Tbx1.

RESULTS

Expression-level filtering and statistical analysis revealed a total of 577 genes differentially expressed across genotypes. Data were clustered into 3 groups based on comparison between genotypes. Group A was composed of differentially expressed genes in mutant compared to wild type (n = 89); Group B included differentially expressed genes in heterozygous compared to wild type (n = 400) and Group C included differentially expressed genes in mutant compared to heterozygous (n = 88). High-throughput quantitative real-time PCR (RT-PCR) confirmed a total of 27 genes significantly changed between wild type and mutant; and 27 genes between heterozygote and mutant. Amongst these, the majority were present in both groups A and C (26 genes). Associations existed with hypertrophic cardiomyopathy, cardiac muscle contraction, dilated cardiomyopathy, focal adhesion, tight junction and calcium signalling pathways. No significant differences in gene expression were found between wild type and heterozygous palatal shelves.

CONCLUSIONS

Significant differences in gene expression profile within the secondary palate of wild type and mutant embryos is consistent with a primary role for Tbx1 during palatogenesis.

Disruption of Hedgehog Signaling by Vismodegib Leads to Cleft Palate and Delayed Osteogenesis in Experimental Design

The function of hedgehog signaling has previously been shown to be crucial for craniofacial development. In this study, we treated C57/BL6J mice with the hedgehog pathway inhibitor vismodegib by oral gavage to establish a stable vismodegib-induced cleft palate model. At E10.5 and E12.5, mice in the experimental group were treated with 100 mg/kg of vismodegib, whereas mice in the control group were treated with solvent. The treated pregnant mice were sacrificed on E13.5, E14.5, E15.5, and E16.5. Palatal shelf growth was evaluated via histological and immunohistochemical analyses as well as palatal organ culture. Immunohistochemical staining was performed to examine the expression of osteogenic proteins in the palatal tissue. A high proportion of the mice administered 2 doses of 100 mg/kg of vismodegib displayed a cleft palate. Histologic examination revealed severely retarded palatal shelf growth and thickened epithelium in the experimental group. Vismodegib exposure induced complete cleft palate, which was attributed to a reduced cell proliferation rate in the palatal mesenchyme along the anterior-posterior axis. Moreover, this model also showed delayed ossification in the region of palatine bone with downregulation of Indian hedgehog (Ihh) protein. Our results suggest that vismodegib can be used to inhibit hedgehog signaling to affect palatal morphogenesis. Under treatment with this exogenous inhibitor, the cell proliferation rate of the palatal shelves and the osteogenic potential of the hard palate were decreased, which likely contributed to the complete cleft palate.

Six2 Plays an Intrinsic Role in Regulating Proliferation of Mesenchymal Cells in the Developing Palate

Cleft palate is a common congenital abnormality that results from defective secondary palate (SP) formation. The Sine oculis-related homeobox 2 (Six2) gene has been linked to abnormalities of craniofacial and kidney development. Our current study examined, for the first time, the specific role of Six2 in embryonic mouse SP development. Six2 mRNA and protein expression were identified in the palatal shelves from embryonic days (E)12.5 to E15.5, with peak levels during early stages of palatal shelf outgrowth. Immunohistochemical staining (IHC) showed that Six2 protein is abundant throughout the mesenchyme in the oral half of each palatal shelf, whereas there is a pronounced decline in Six2 expression by mesenchyme cells in the nasal half of the palatal shelf by stages E14.5-15.5. An opposite pattern was observed in the surface epithelium of the palatal shelf. Six2 expression was prominent at all stages in the epithelial cell layer located on the nasal side of each palatal shelf but absent from the epithelium located on the oral side of the palatal shelf. Six2 is a putative downstream target of transcription factor Hoxa2 and we previously demonstrated that Hoxa2 plays an intrinsic role in embryonic palate formation. We therefore investigated whether Six2 expression was altered in the developing SP of Hoxa2 null mice. Reverse transcriptase PCR and Western blot analyses revealed that Six2 mRNA and protein levels were upregulated in Hoxa2^-/- palatal shelves at stages E12.5-14.5. Moreover, the domain of Six2 protein expression in the palatal mesenchyme of Hoxa2^-/- embryos was expanded to include the entire nasal half of the palatal shelf in addition to the oral half. The palatal shelves of Hoxa2^-/- embryos displayed a higher density of proliferating, Ki-67 positive palatal mesenchyme cells, as well as a higher density of Six2/Ki-67 double-positive cells. Furthermore, Hoxa2^-/- palatal mesenchyme cells in culture displayed both increased proliferation and elevated Cyclin D1 expression relative to wild-type cultures. Conversely, siRNA-mediated Six2 knockdown restored proliferation and Cyclin D1 expression in Hoxa2^-/- palatal mesenchyme cultures to near wild-type levels. Our findings demonstrate that Six2 functions downstream of Hoxa2 as a positive regulator of mesenchymal cell proliferation during SP development.

Small-molecule Wnt agonists correct cleft palates in Pax9 mutant mice in utero

Clefts of the palate and/or lip are among the most common human craniofacial malformations and involve multiple genetic and environmental factors. Defects can only be corrected surgically and require complex life-long treatments. Our studies utilized the well-characterized Pax9^-/- mouse model with a consistent cleft palate phenotype to test small-molecule Wnt agonist therapies. We show that the absence of Pax9 alters the expression of Wnt pathway genes including Dkk1 and Dkk2, proven antagonists of Wnt signaling. The functional interactions between Pax9 and Dkk1 are shown by the genetic rescue of secondary palate clefts in Pax9^-/-Dkk1^f/+;Wnt1Cre embryos. The controlled intravenous delivery of small-molecule Wnt agonists (Dkk inhibitors) into pregnant Pax9^+/- mice restored Wnt signaling and led to the growth and fusion of palatal shelves, as marked by an increase in cell proliferation and osteogenesis in utero, while other organ defects were not corrected. This work underscores the importance of Pax9-dependent Wnt signaling in palatogenesis and suggests that this functional upstream molecular relationship can be exploited for the development of therapies for human cleft palates that arise from single-gene disorders.

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.

Identification of Osr2 Transcriptional Target Genes in Palate Development

Previous studies have identified the odd-skipped related 2 (Osr2) transcription factor as a key intrinsic regulator of palatal shelf growth and morphogenesis. However, little is known about the molecular program acting downstream of Osr2 in the regulation of palatogenesis. In this study, we isolated palatal mesenchyme cells from embryonic day 12.5 (E12.5) and E13.5 Osr2^RFP/+ and Osr2^RFP/- mutant mouse embryos and performed whole transcriptome RNA sequencing analyses. Differential expression analysis of the RNA sequencing datasets revealed that expression of 70 genes was upregulated and expression of 61 genes was downregulated by >1.5-fold at both E12.5 and E13.5 in the Osr2^RFP/- palatal mesenchyme cells, in comparison with Osr2^RFP/+ littermates. Gene ontology analysis revealed enrichment of signaling molecules and transcription factors crucial for skeletal development and osteoblast differentiation among those significantly upregulated in the Osr2 mutant palatal mesenchyme. Using quantitative real-time polymerase chain reaction (RT-PCR)and in situ hybridization assays, we validated that the Osr2^-/- embryos exhibit significantly increased and expanded expression of many osteogenic pathway genes, including Bmp3, Bmp5, Bmp7, Mef2c, Sox6, and Sp7 in the developing palatal mesenchyme. Furthermore, we demonstrate that expression of Sema3a, Sema3d, and Sema3e, is ectopically activated in the developing palatal mesenchyme in Osr2^-/- embryos. Through chromatin immunoprecipitation, followed by RT-PCR analysis, we demonstrate that endogenous Osr2 protein binds to the promoter regions of the Sema3a and Sema3d genes in the embryonic palatal mesenchyme. Moreover, Osr2 expression repressed the transcription from the Sema3a and Sema3d promoters in cotransfected cells. Since the Sema3 subfamily of signaling molecules plays diverse roles in the regulation of cell proliferation, migration, and differentiation, these data reveal a novel role for Osr2 in regulation of palatal morphogenesis through preventing aberrant activation of Sema3 signaling. Together, these data indicate that Osr2 controls multiple molecular pathways, including BMP and Sema3 signaling, in palate development.

Modulating Wnt Signaling Rescues Palate Morphogenesis in Pax9 Mutant Mice

Cleft palate is a common birth defect caused by disruption of palatogenesis during embryonic development. Although mutations disrupting components of the Wnt signaling pathway have been associated with cleft lip and palate in humans and mice, the mechanisms involving canonical Wnt signaling and its regulation in secondary palate development are not well understood. Here, we report that canonical Wnt signaling plays an important role in Pax9-mediated regulation of secondary palate development. We found that cleft palate pathogenesis in Pax9-deficient embryos is accompanied by significantly reduced expression of Axin2, an endogenous target of canonical Wnt signaling, in the developing palatal mesenchyme, particularly in the posterior regions of the palatal shelves. We found that expression of Dkk2, encoding a secreted Wnt antagonist, is significantly increased whereas the levels of active β-catenin protein, the essential transcriptional coactivator of canonical Wnt signaling, is significantly decreased in the posterior regions of the palatal shelves in embryonic day 13.5 Pax9-deficent embryos in comparison with control littermates. We show that small molecule-mediated inhibition of Dickkopf (DKK) activity in utero during palatal shelf morphogenesis partly rescued secondary palate development in Pax9-deficient embryos. Moreover, we found that genetic inactivation of Wise, which is expressed in the developing palatal shelves and encodes another secreted antagonist of canonical Wnt signaling, also rescued palate morphogenesis in Pax9-deficient mice. Furthermore, whereas Pax9^del/del embryos exhibit defects in palatal shelf elevation/reorientation and significant reduction in accumulation of hyaluronic acid-a high molecular extracellular matrix glycosaminoglycan implicated in playing an important role in palatal shelf elevation-80% of Pax9^del/del;Wise^-/- double-mutant mouse embryos exhibit rescued palatal shelf elevation/reorientation, accompanied by restored hyaluronic acid accumulation in the palatal mesenchyme. Together, these data identify a crucial role for canonical Wnt signaling in acting downstream of Pax9 to regulate palate morphogenesis.

Activin and Bmp4 Signaling Converge on Wnt Activation during Odontogenesis

Previous studies show that both activin and Bmp4 act as crucial mesenchymal odontogenic signals during early tooth development. Remarkably, mice lacking activin-βA ( Inhba^-/-) and mice with neural crest-specific inactivation of Bmp4 ( Bmp4^ncko/ncko) both exhibit bud-stage developmental arrest of the mandibular molar tooth germs while their maxillary molar tooth germs completed morphogenesis. In this study, we found that, whereas expression of Inhba and Bmp4 in the developing tooth mesenchyme is independent of each other, Bmp4^ncko/nckoInhba^-/- compound mutant mice exhibit early developmental arrest of all tooth germs. Moreover, genetic inactivation of Osr2, a negative regulator of the odontogenic function of the Bmp4-Msx1 signaling pathway, rescues mandibular molar morphogenesis in Inhba^-/- embryos. We recently reported that Osr2 and the Bmp4-Msx1 pathway control the bud-to-cap transition of tooth morphogenesis through antagonistic regulation of expression of secreted Wnt antagonists, including Dkk2 and Sfrp2, in the developing tooth mesenchyme. We show here that expression of Dkk2 messenger RNAs was significantly upregulated and expanded into the tooth bud mesenchyme in Inhba^-/- embryos in comparison with wild-type littermates. Furthermore, in utero treatment with either lithium chloride, an agonist of canonical Wnt signaling, or the DKK inhibitor IIIC3a rescued mandibular molar tooth morphogenesis in Inhba^-/- embryos. Together with our finding that the developing mandibular molar tooth bud mesenchyme expresses significantly higher levels of Dkk2 than the developing maxillary molar tooth mesenchyme, these data indicate that Bmp4 and activin signaling pathways converge on activation of the Wnt signaling pathway to promote tooth morphogenesis through the bud-to-cap transition and that the differential effects of loss of activin or Bmp4 signaling on maxillary and mandibular molar tooth morphogenesis are mainly due to the differential expression of Wnt antagonists, particularly Dkk2, in the maxillary and mandibular tooth mesenchyme.

Generation of an immortalized mouse embryonic palatal mesenchyme cell line

Palatogenesis is a complex morphogenetic process, disruptions in which result in highly prevalent birth defects in humans. In recent decades, the use of model systems such as genetically-modified mice, mouse palatal organ cultures and primary mouse embryonic palatal mesenchyme (MEPM) cultures has provided significant insight into the molecular and cellular defects underlying cleft palate. However, drawbacks in each of these systems have prevented high-throughput, large-scale studies of palatogenesis in vitro. Here, we report the generation of an immortalized MEPM cell line that maintains the morphology, migration ability, transcript expression and responsiveness to exogenous growth factors of primary MEPM cells, with increased proliferative potential over primary cultures. The immortalization method described in this study will facilitate the generation of palatal mesenchyme cells with an unlimited capacity for expansion from a single genetically-modified mouse embryo and enable mechanistic studies of palatogenesis that have not been possible using primary culture.

Analysis of transcription factors expressed at the anterior mouse limb bud

Limb bud patterning, outgrowth, and differentiation are precisely regulated in a spatio-temporal manner through integrated networks of transcription factors, signaling molecules, and downstream genes. However, the exact mechanisms that orchestrate morphogenesis of the limb remain to be elucidated. Previously, we have established EMBRYS, a whole-mount in situ hybridization database of transcription factors. Based on the findings from EMBRYS, we focused our expression pattern analysis on a selection of transcription factor genes that exhibit spatially localized and temporally dynamic expression patterns with respect to the anterior-posterior axis in the E9.5–E11.5 limb bud. Among these genes, Irx3 showed a posteriorly expanded expression domain in Shh^-/- limb buds and an anteriorly reduced expression domain in Gli3^-/- limb buds, suggesting their importance in anterior-posterior patterning. To assess the stepwise EMBRYS-based screening system for anterior regulators, we generated Irx3 transgenic mice in which Irx3 was expressed in the entire limb mesenchyme under the Prrx1 regulatory element. The Irx3 gain-of-function model displayed complex phenotypes in the autopods, including digit loss, radial flexion, and fusion of the metacarpal bones, suggesting that Irx3 may contribute to the regulation of limb patterning, especially in the autopods. Our results demonstrate that gene expression analysis based on EMBRYS could contribute to the identification of genes that play a role in patterning of the limb mesenchyme.

Epigenetic Alterations Affecting Transcription Factors and Signaling Pathways in Stromal Cells of Endometriosis

Endometriosis is characterized by growth of endometrial-like tissue outside the uterine cavity. Since its pathogenesis may involve epigenetic changes, we used Illumina 450K Methylation Beadchips to profile CpG methylation in endometriosis stromal cells compared to stromal cells from normal endometrium. We validated and extended the Beadchip data using bisulfite sequencing (bis-seq), and analyzed differential methylation (DM) at the CpG-level and by an element-level classification for groups of CpGs in chromatin domains. Genes found to have DM included examples encoding transporters (SLC22A23), signaling components (BDNF, DAPK1, ROR1, and WNT5A) and transcription factors (GATA family, HAND2, HOXA cluster, NR5A1, OSR2, TBX3). Intriguingly, among the TF genes with DM we also found JAZF1, a proto-oncogene affected by chromosomal translocations in endometrial stromal tumors. Using RNA-Seq we identified a subset of the DM genes showing differential expression (DE), with the likelihood of DE increasing with the extent of the DM and its location in enhancer elements. Supporting functional relevance, treatment of stromal cells with the hypomethylating drug 5aza-dC led to activation of DAPK1 and SLC22A23 and repression of HAND2, JAZF1, OSR2, and ROR1 mRNA expression. We found that global 5hmC is decreased in endometriotic versus normal epithelial but not stroma cells, and for JAZF1 and BDNF examined by oxidative bis-seq, found that when 5hmC is detected, patterns of 5hmC paralleled those of 5mC. Together with prior studies, these results define a consistent epigenetic signature in endometriosis stromal cells and nominate specific transcriptional and signaling pathways as therapeutic targets.

Bmp4-Msx1 signaling and Osr2 control tooth organogenesis through antagonistic regulation of secreted Wnt antagonists

Mutations in MSX1 cause craniofacial developmental defects, including tooth agenesis, in humans and mice. Previous studies suggest that Msx1 activates Bmp4 expression in the developing tooth mesenchyme to drive early tooth organogenesis. Whereas Msx1^-/- mice exhibit developmental arrest of all tooth germs at the bud stage, mice with neural crest-specific inactivation of Bmp4 (Bmp4^ncko/ncko), which lack Bmp4 expression in the developing tooth mesenchyme, showed developmental arrest of only mandibular molars. We recently demonstrated that deletion of Osr2, which encodes a zinc finger transcription factor expressed in a lingual-to-buccal gradient in the developing tooth bud mesenchyme, rescued molar tooth morphogenesis in both Msx1^-/- and Bmp4^ncko/ncko mice. In this study, through RNA-seq analyses of the developing tooth mesenchyme in mutant and wildtype embryos, we found that Msx1 and Osr2 have opposite effects on expression of several secreted Wnt antagonists in the tooth bud mesenchyme. Remarkably, both Dkk2 and Sfrp2 exhibit Osr2-dependent preferential expression on the lingual side of the tooth bud mesenchyme and expression of both genes was up-regulated and expanded into the tooth bud mesenchyme in Msx1^-/- and Bmp4^ncko/ncko mutant embryos. We show that pharmacological activation of canonical Wnt signaling by either lithium chloride (LiCl) treatment or by inhibition of DKKs in utero was sufficient to rescue mandibular molar tooth morphogenesis in Bmp4^ncko/ncko mice. Furthermore, whereas inhibition of DKKs or inactivation of Sfrp2 alone was insufficient to rescue tooth morphogenesis in Msx1^-/- mice, pharmacological inhibition of DKKs in combination with genetic inactivation of Sfrp2 and Sfrp3 rescued maxillary molar morphogenesis in Msx1^-/- mice. Together, these data reveal a novel mechanism that the Bmp4-Msx1 pathway and Osr2 control tooth organogenesis through antagonistic regulation of expression of secreted Wnt antagonists.

Genome-wide analysis reveals adaptation to high altitudes in Tibetan sheep

Tibetan sheep have lived on the Tibetan Plateau for thousands of years; however, the process and consequences of adaptation to this extreme environment have not been elucidated for important livestock such as sheep. Here, seven sheep breeds, representing both highland and lowland breeds from different areas of China, were genotyped for a genome-wide collection of single-nucleotide polymorphisms (SNPs). The FST and XP-EHH approaches were used to identify regions harbouring local positive selection between these highland and lowland breeds, and 236 genes were identified. We detected selection events spanning genes involved in angiogenesis, energy production and erythropoiesis. In particular, several candidate genes were associated with high-altitude hypoxia, including EPAS1, CRYAA, LONP1, NF1, DPP4, SOD1, PPARG and SOCS2. EPAS1 plays a crucial role in hypoxia adaption; therefore, we investigated the exon sequences of EPAS1 and identified 12 mutations. Analysis of the relationship between blood-related phenotypes and EPAS1 genotypes in additional highland sheep revealed that a homozygous mutation at a relatively conserved site in the EPAS1 3' untranslated region was associated with increased mean corpuscular haemoglobin concentration and mean corpuscular volume. Taken together, our results provide evidence of the genetic diversity of highland sheep and indicate potential high-altitude hypoxia adaptation mechanisms, including the role of EPAS1 in adaptation.

Golgb1 regulates protein glycosylation and is crucial for mammalian palate development

Cleft palate is a common major birth defect for which currently known causes account for less than 30% of pathology in humans. In this study, we carried out mutagenesis screening in mice to identify new regulators of palatogenesis. Through genetic linkage mapping and whole-exome sequencing, we identified a loss-of-function mutation in the Golgb1 gene that co-segregated with cleft palate in a new mutant mouse line. Golgb1 is a ubiquitously expressed large coiled-coil protein, also known as giantin, that is localized at the Golgi membrane. Using CRISPR/Cas9-mediated genome editing, we generated and analyzed developmental defects in mice carrying additional Golgb1 loss-of-function mutations, which supported a crucial requirement for Golgb1 in palate development. Through maxillary explant culture assays, we demonstrate that the Golgb1 mutant embryos have intrinsic defects in palatal shelf elevation. Just prior to the developmental stage of palatal shelf elevation in wild-type littermates, Golgb1 mutant embryos exhibit increased cell density, reduced hyaluronan accumulation and impaired protein glycosylation in the palatal mesenchyme. Together, these results demonstrate that, although it is a ubiquitously expressed Golgi-associated protein, Golgb1 has specific functions in protein glycosylation and tissue morphogenesis.

Using Xenopus to study genetic kidney diseases

Modern sequencing technology is revolutionizing our knowledge of inherited kidney disease. However, the molecular role of genes affected by the rapidly rising number of identified mutations is lagging behind. Xenopus is a highly useful, but underutilized model organism with unique properties excellently suited to decipher the molecular mechanisms of kidney development and disease. The embryonic kidney (pronephros) can be manipulated on only one side of the animal and its formation observed directly through the translucent skin. The moderate evolutionary distance between Xenopus and humans is a huge advantage for studying basic principles of kidney development, but still allows us to analyze the function of disease related genes. Optogenetic manipulations and genome editing by CRISPR/Cas are exciting additions to the toolbox for disease modelling and will facilitate the use of Xenopus in translational research. Therefore, the future of Xenopus in kidney research is bright.