The forkhead/winged helix gene Mf1 is disrupted in the pleiotropic mouse mutation congenital hydrocephalus

Meningeal-derived retinoic acid regulates neurogenesis via suppression of Notch and Sox2

The meninges act as a regulator of brain development by secreting ligands that act on neural cells to regulate neurogenesis and neuronal migration. Meningeal-derived retinoic acid (RA) promotes neocortical neural progenitor cell cycle exit; however, the underlying molecular mechanism is unknown. Here, we used spatial transcriptomics and profiling of retinoic acid receptor α (RARα) DNA binding in Foxc1-mutant embryos that lack meninges-derived signals to identify potential neurogenic transcriptional mechanisms of RA signaling in telencephalic neural progenitors. This identified upregulation of Sox2 and Notch pathway genes, and RARα binds to the Sox2ot promoter, a long noncoding RNA that regulates Sox2 expression. Our experiments using maternal RA treatment and in utero electroporation in Foxc1 mutants support that meningeal-derived RA promotes neurogenesis by suppressing Notch signaling, a progenitor self-renewal pathway. Our findings elucidate a previously unknown mechanism of how meningeal RA coordinates neocortical development and provide insight into how defects in meningeal development may cause neurodevelopmental disorders.

Genetic and molecular mechanisms of hydrocephalus

Hydrocephalus is a neurological condition caused by aberrant circulation and/or obstructed cerebrospinal fluid (CSF) flow after cerebral ventricle abnormal dilatation. In the past 50 years, the diagnosis and treatment of hydrocephalus have remained understudied and underreported, and little progress has been made with respect to prevention or treatment. Further research on the pathogenesis of hydrocephalus is essential for developing new diagnostic, preventive, and therapeutic strategies. Various genetic and molecular abnormalities contribute to the mechanisms of hydrocephalus, including gene deletions or mutations, the activation of cellular inflammatory signaling pathways, alterations in water channel proteins, and disruptions in iron metabolism. Several studies have demonstrated that modulating the expression of key proteins, including TGF-β, VEGF, Wnt, AQP, NF-κB, and NKCC, can significantly influence the onset and progression of hydrocephalus. This review summarizes and discusses key mechanisms that may be involved in the pathogenesis of hydrocephalus at both the genetic and molecular levels. While obstructive hydrocephalus can often be addressed by removing the obstruction, most cases require treatment strategies that involve merely slowing disease progression by correcting CSF circulation patterns. There have been few new research breakthroughs in the prevention and treatment of hydrocephalus.

Forkhead box C1 promotes the pathology of osteoarthritis in subchondral bone osteoblasts via the Piezo1/YAP axis

Subchondral bone sclerosis is a key characteristic of osteoarthritis (OA). Prior research has shown that Forkhead box C1 (FoxC1) plays a role in the synovial inflammation of OA, but its specific role in the subchondral bone of OA has not been explored. Our research revealed elevated expression levels of FoxC1 and Piezo1 in OA subchondral bone tissues. Further experiments on OA subchondral bone osteoblasts with FoxC1 or Piezo1 overexpression showed increased cell proliferation activity, expression of Yes-associated Protein 1 (YAP) and osteogenic markers, and secretion of proinflammatory factors. Mechanistically, the overexpression of FoxC1 through Piezo1 activation, in combination with downstream YAP signaling, led to increased levels of alkaline phosphatase (ALP), collagen type 1 (COL1) A1, RUNX2, Osteocalcin, matrix metalloproteinase (MMP) 3, and MMP9 expression. Notably, inhibition of Piezo1 reversed the regulatory function of FoxC1. The binding of FoxC1 to the targeted area (ATATTTATTTA, residues +612 to +622) and the activation of Piezo1 transcription were verified by the dual luciferase assays. Additionally, Reduced subchondral osteosclerosis and microangiogenesis were observed in knee joints from FoxC1-conditional knockout (CKO) and Piezo1-CKO mice, indicating reduced lesions. Collectively, our study reveals the significant involvement of FoxC1 in the pathologic process of OA subchondral bone via the Piezo1/YAP signaling pathway, potentially establishing a novel therapeutic target.

Pleiotropy in FOXC1-attributable phenotypes involves altered ciliation and cilia-dependent signaling

Alterations to cilia are responsible for a wide range of severe disease; however, understanding of the transcriptional control of ciliogenesis remains incomplete. In this study we investigated whether altered cilia-mediated signaling contributes to the pleiotropic phenotypes caused by the Forkhead transcription factor FOXC1. Here, we show that patients with FOXC1-attributable Axenfeld-Rieger Syndrome (ARS) have a prevalence of ciliopathy-associated phenotypes comparable to syndromic ciliopathies. We demonstrate that altering the level of Foxc1 protein, via shRNA mediated inhibition, CRISPR/Cas9 mutagenesis and overexpression, modifies cilia length in vitro. These structural changes were associated with substantially perturbed cilia-dependent signaling [Hedgehog (Hh) and PDGFRα], and altered ciliary compartmentalization of the Hh pathway transcription factor, Gli2. Consistent with these data, in primary cultures of murine embryonic meninges, cilia length was significantly reduced in heterozygous and homozygous Foxc1 mutants compared to controls. Meningeal expression of the core Hh signaling components Gli1, Gli3 and Sufu was dysregulated, with comparable dysregulation of Pdgfrα signaling evident from significantly altered Pdgfrα and phosphorylated Pdgfrα expression. On the basis of these clinical and experimental findings, we propose a model that altered cilia-mediated signaling contributes to some FOXC1-induced phenotypes.

FOXC1 and FOXC2 regulate growth plate chondrocyte maturation towards hypertrophy in the embryonic mouse limb skeleton

The Forkhead box transcription factors FOXC1 and FOXC2 are expressed in condensing mesenchyme cells at the onset of endochondral ossification. We used the Prx1-cre mouse to ablate Foxc1 and Foxc2 in limb skeletal progenitor cells. Prx1-cre;Foxc1Δ/Δ;Foxc2Δ/Δ limbs were shorter than controls, with worsening phenotypes in distal structures. Cartilage formation and mineralization was severely disrupted in the paws. The radius and tibia were malformed, whereas the fibula and ulna remained unmineralized. Chondrocyte maturation was delayed, with fewer Indian hedgehog-expressing, prehypertrophic chondrocytes forming and a smaller hypertrophic chondrocyte zone. Later, progression out of chondrocyte hypertrophy was slowed, leading to an accumulation of COLX-expressing hypertrophic chondrocytes and formation of a smaller primary ossification center with fewer osteoblast progenitor cells populating this region. Targeting Foxc1 and Foxc2 in hypertrophic chondrocytes with Col10a1-cre also resulted in an expanded hypertrophic chondrocyte zone and smaller primary ossification center. Our findings suggest that FOXC1 and FOXC2 direct chondrocyte maturation towards hypertrophic chondrocyte formation. At later stages, FOXC1 and FOXC2 regulate function in hypertrophic chondrocyte remodeling to allow primary ossification center formation and osteoblast recruitment.

FOXC1 transcriptionally suppresses ABHD5 to inhibit the progression of renal cell carcinoma through AMPK/mTOR pathway

BACKGROUND

Increased activity of the transcription factor FOXC1 leads to elevated transcription of target genes, ultimately facilitating the progression of various cancer types. However, there are currently no literature reports on the role of FOXC1 in renal cell carcinoma.

METHODS

By using RT-qPCR, immunohistochemistry and Western blotting, FOXC1 mRNA and protein expression was evaluated. Gain of function experiments were utilized to assess the proliferation and metastasis ability of cells. A nude mouse model was created for transplanting tumors and establishing a lung metastasis model to observe cell proliferation and spread in a living organism. Various techniques including biological analysis, CHIP assay, luciferase assay, RT-qRCR and Western blotting experiments were utilized to investigate how FOXC1 contributes to the transcription of ABHD5 on a molecular level. FOXC1 was assessed by Western blot for its impact on AMPK/mTOR signaling pathway.

RESULTS

FOXC1 is down-regulated in RCC, causing unfavorable prognosis of patients with RCC. Further experiments showed that forced FOXC1 expression significantly restrains RCC cell growth and cell metastasis. Mechanically, FOXC1 promotes the transcription of ABHD5 to activate AMPK signal pathway to inhibit mTOR signal pathway. Finally, knockdown of ABHD5 recovered the inhibitory role of FOXC1 overexpression induced cell growth and metastasis suppression.

CONCLUSION

In general, our study demonstrates that FOXC1 exerts its tumor suppressor role by promoting ABHD5 transcription to regulating AMPK/mTOR signal pathway. FOXC1 could serve as both a diagnostic indicator and potential treatment focus for RCC.

In-silico identification of deleterious non-synonymous SNPs of TBX1 gene: Functional and structural impact towards 22q11.2DS

The TBX1 gene plays a critical role in the development of 22q11.2 deletion syndrome (22q11.2DS), a complex genetic disorder associated with various phenotypic manifestations. In this study, we performed in-silico analysis to identify potentially deleterious non-synonymous single nucleotide polymorphisms (nsSNPs) within the TBX1 gene and evaluate their functional and structural impact on 22q11.2DS. A comprehensive analysis pipeline involving multiple computational tools was employed to predict the pathogenicity of nsSNPs. This study assessed protein stability and explored potential alterations in protein-protein interactions. The results revealed the rs751339103(C>A), rs780800634(G>A), rs1936727304(T>C), rs1223320618(G>A), rs1248532217(T>C), rs1294927055 (C>T), rs1331240435 (A>G, rs1601289406 (A>C), rs1936726164 (G>A), and rs911796187(G>A) with a high-risk potential for affecting protein function and stability. These nsSNPs were further analyzed for their impact on post-translational modifications and structural characteristics, indicating their potential disruption of molecular pathways associated with TBX1 and its interacting partners. These findings provide a foundation for further experimental studies and elucidation of potential therapeutic targets and personalized treatment approaches for individuals affected by 22q11.2DS.

Increasing the diagnostic yield of childhood glaucoma cases recruited into the 100,000 Genomes Project

Childhood glaucoma (CG) encompasses a heterogeneous group of genetic eye disorders that is responsible for approximately 5% of childhood blindness worldwide. Understanding the molecular aetiology is key to improving diagnosis, prognosis and unlocking the potential for optimising clinical management. In this study, we investigated 86 CG cases from 78 unrelated families of diverse ethnic backgrounds, recruited into the Genomics England 100,000 Genomes Project (GE100KGP) rare disease cohort, to improve the genetic diagnostic yield. Using the Genomics England/Genomic Medicine Centres (GE/GMC) diagnostic pipeline, 13 unrelated families were solved (13/78, 17%). Further interrogation using an expanded gene panel yielded a molecular diagnosis in 7 more unrelated families (7/78, 9%). This analysis effectively raises the total number of solved CG families in the GE100KGP to 26% (20/78 families). Twenty-five percent (5/20) of the solved families had primary congenital glaucoma (PCG), while 75% (15/20) had secondary CG; 53% of this group had non-acquired ocular anomalies (including iris hypoplasia, megalocornea, ectopia pupillae, retinal dystrophy, and refractive errors) and 47% had non-acquired systemic diseases such as cardiac abnormalities, hearing impairment, and developmental delay. CYP1B1 was the most frequently implicated gene, accounting for 55% (11/20) of the solved families. We identified two novel likely pathogenic variants in the TEK gene, in addition to one novel pathogenic copy number variant (CNV) in FOXC1. Variants that passed undetected in the GE100KGP diagnostic pipeline were likely due to limitations of the tiering process, the use of smaller gene panels during analysis, and the prioritisation of coding SNVs and indels over larger structural variants, CNVs, and non-coding variants.

FOXC1 regulates endothelial CD98 (LAT1/4F2hc) expression in retinal angiogenesis and blood-retina barrier formation

Angiogenesis, the growth of new blood vessels from pre-existing vasculature, is essential for the development of new organ systems, but transcriptional control of angiogenesis remains incompletely understood. Here we show that FOXC1 is essential for retinal angiogenesis. Endothelial cell (EC)-specific loss of Foxc1 impairs retinal vascular growth and expression of Slc3a2 and Slc7a5, which encode the heterodimeric CD98 (LAT1/4F2hc) amino acid transporter and regulate the intracellular transport of essential amino acids and activation of the mammalian target of rapamycin (mTOR). EC-Foxc1 deficiency diminishes mTOR activity, while administration of the mTOR agonist MHY-1485 rescues perturbed retinal angiogenesis. EC-Foxc1 expression is required for retinal revascularization and resolution of neovascular tufts in a model of oxygen-induced retinopathy. Foxc1 is also indispensable for pericytes, a critical component of the blood-retina barrier during retinal angiogenesis. Our findings establish FOXC1 as a crucial regulator of retinal vessels and identify therapeutic targets for treating retinal vascular disease.

A De Novo Noncoding RARB Variant Associated with Complex Microphthalmia Alters a Putative Regulatory Element

Retinoic acid receptor beta (RARB) is a transcriptional regulator crucial for coordinating retinoic acid- (RA-) mediated morphogenic movements, cell growth, and differentiation during eye development. Loss- or gain-of-function RARB coding variants have been associated with microphthalmia, coloboma, and anterior segment defects. We identified a de novo variant c.157+1895G>A located within a conserved region (CR1) in the first intron of RARB in an individual with complex microphthalmia and significant global developmental delay. Based on the phenotypic overlap, we further investigated the possible effects of the variant on mRNA splicing and/or transcriptional regulation through in silico and functional studies. In silico analysis identified the possibility of alternative splicing, suggested by one out of three (HSF, SpliceAI, and MaxEntScan) splicing prediction programs, and a strong indication of regulatory function based on publicly available DNase hypersensitivity, histone modification, chromatin folding, and ChIP-seq data sets. Consistent with the predictions of SpliceAI and MaxEntScan, in vitro minigene assays showed no effect on RARB mRNA splicing. Evaluation of CR1 for a regulatory role using luciferase reporter assays in human lens epithelial cells demonstrated a significant increase in the activity of the RARB promoter in the presence of wild-type CR1. This activity was further significantly increased in the presence of CR1 carrying the c.157+1895G>A variant, suggesting that the variant may promote RARB overexpression in human cells. Induction of RARB overexpression in human lens epithelial cells resulted in increased cell proliferation and elevated expression of FOXC1, a known downstream target of RA signaling and a transcription factor whose down- and upregulation is associated with ocular phenotypes overlapping the RARB spectrum. These results support a regulatory role for the CR1 element and suggest that the de novo c.157+1895G>A variant affecting this region may alter the proper regulation of RARB and, as a result, its downstream genes, possibly leading to abnormal development.

Endothelial FOXC1 and FOXC2 promote intestinal regeneration after ischemia-reperfusion injury

Intestinal ischemia underlies several clinical conditions and can result in the loss of the intestinal mucosal barrier. Ischemia-induced damage to the intestinal epithelium is repaired by stimulation of intestinal stem cells (ISCs), and paracrine signaling from the vascular niche regulates intestinal regeneration. Here, we identify FOXC1 and FOXC2 as essential regulators of paracrine signaling in intestinal regeneration after ischemia-reperfusion (I/R) injury. Vascular endothelial cell (EC)- and lymphatic EC (LEC)-specific deletions of Foxc1, Foxc2, or both in mice worsen I/R-induced intestinal damage by causing defects in vascular regrowth, expression of chemokine CXCL12 and Wnt activator R-spondin 3 (RSPO3) in blood ECs (BECs) and LECs, respectively, and activation of Wnt signaling in ISCs. Both FOXC1 and FOXC2 directly bind to regulatory elements of the CXCL12 and RSPO3 loci in BECs and LECs, respectively. Treatment with CXCL12 and RSPO3 rescues the I/R-induced intestinal damage in EC- and LEC-Foxc mutant mice, respectively. This study provides evidence that FOXC1 and FOXC2 are required for intestinal regeneration by stimulating paracrine CXCL12 and Wnt signaling.

Case report: Extending the spectrum of clinical and molecular findings in FOXC1 haploinsufficiency syndrome

FOXC1 is a ubiquitously expressed forkhead transcription factor that plays a critical role during early development. Germline pathogenic variants in FOXC1 are associated with anterior segment dysgenesis and Axenfeld-Rieger syndrome (ARS, #602482), an autosomal dominant condition with ophthalmologic anterior segment abnormalities, high risk for glaucoma and extraocular findings including distinctive facial features, as well as dental, skeletal, audiologic, and cardiac anomalies. De Hauwere syndrome is an ultrarare condition previously associated with 6p microdeletions and characterized by anterior segment dysgenesis, joint instability, short stature, hydrocephalus, and skeletal abnormalities. Here, we report clinical findings of two unrelated adult females with FOXC1 haploinsufficiency who have ARS and skeletal abnormalities. Final molecular diagnoses of both patients were achieved using genome sequencing. Patient 1 had a complex rearrangement involving a 4.9 kB deletion including FOXC1 coding region (Hg19; chr6:1,609,721-1,614,709), as well as a 7 MB inversion (Hg19; chr6:1,614,710-8,676,899) and a second deletion of 7.1 kb (Hg19; chr6:8,676,900-8,684,071). Patient 2 had a heterozygous single nucleotide deletion, resulting in a frameshift and a premature stop codon in FOXC1 (NM_001453.3): c.467del, p.(Pro156Argfs*25). Both individuals had moderate short stature, skeletal abnormalities, anterior segment dysgenesis, glaucoma, joint laxity, pes planovalgus, dental anomalies, hydrocephalus, distinctive facial features, and normal intelligence. Skeletal surveys revealed dolichospondyly, epiphyseal hypoplasia of femoral and humeral heads, dolichocephaly with frontal bossin gand gracile long bones. We conclude that haploinsufficiency of FOXC1 causes ARS and a broad spectrum of symptoms with variable expressivity that at its most severe end also includes a phenotype overlapping with De Hauwere syndrome.

Foxc1 and Foxc2 function in osteochondral progenitors for the progression through chondrocyte hypertrophy and mineralization of the primary ossification center

The forkhead box transcription factor genes Foxc1 and Foxc2 are expressed in the condensing mesenchyme of the developing skeleton prior to the onset of chondrocyte differentiation. To determine the roles of these transcription factors in limb development we deleted both Foxc1 and Foxc2 in lateral plate mesoderm using the Prx1-cre mouse line. Resulting compound homozygous mice died shortly after birth with exencephaly, and malformations to this sternum and limb skeleton. Notably distal limb structures were preferentially affected, with the autopods displaying reduced or absent mineralization. The radius and tibia bowed and the ulna and fibula were reduced to an unmineralized rudimentary structure. Molecular analysis revealed reduced expression of Ihh leading to reduced proliferation and delayed chondrocyte hypertrophy at E14.5. At later ages, Prx1-cre;Foxc1Δ/ Δ;Foxc2 Δ / Δ embryos exhibited restored Ihh expression and an expanded COLX-positive hypertrophic chondrocyte region, indicating a delayed exit and impaired remodeling of the hypertrophic chondrocytes. Osteoblast differentiation and mineralization were disrupted at the osteochondral junction and in the primary ossification center (POC). Levels of OSTEOPONTIN were elevated in the POC of compound homozygous mutants, while expression of Phex was reduced, indicating that impaired OPN processing by PHEX may underlie the mineralization defect we observe. Together our findings suggest that Foxc1 and Foxc2 act at different stages of endochondral ossification. Initially these genes act during the onset of chondrogenesis leading to the formation of hypertrophic chondrocytes. At later stages Foxc1 and Foxc2 are required for remodeling of HC and for Phex expression required for mineralization of the POC.

Axenfeld-Rieger syndrome: more than meets the eye

BACKGROUND

Axenfeld-Rieger syndrome (ARS) is characterised by typical anterior segment anomalies, with or without systemic features. The discovery of causative genes identified ARS subtypes with distinct phenotypes, but our understanding is incomplete, complicated by the rarity of the condition.

METHODS

Genetic and phenotypic characterisation of the largest reported ARS cohort through comprehensive genetic and clinical data analyses.

RESULTS

128 individuals with causative variants in PITX2 or FOXC1, including 81 new cases, were investigated. Ocular anomalies showed significant overlap but with broader variability and earlier onset of glaucoma for FOXC1-related ARS. Systemic anomalies were seen in all individuals with PITX2-related ARS and the majority of those with FOXC1-related ARS. PITX2-related ARS demonstrated typical umbilical anomalies and dental microdontia/hypodontia/oligodontia, along with a novel high rate of Meckel diverticulum. FOXC1-related ARS exhibited characteristic hearing loss and congenital heart defects as well as previously unrecognised phenotypes of dental enamel hypoplasia and/or crowding, a range of skeletal and joint anomalies, hypotonia/early delay and feeding disorders with structural oesophageal anomalies in some. Brain imaging revealed highly penetrant white matter hyperintensities, colpocephaly/ventriculomegaly and frequent arachnoid cysts. The expanded phenotype of FOXC1-related ARS identified here was found to fully overlap features of De Hauwere syndrome. The results were used to generate gene-specific management plans for the two types of ARS.

CONCLUSION

Since clinical features of ARS vary significantly based on the affected gene, it is critical that families are provided with a gene-specific diagnosis, PITX2-related ARS or FOXC1-related ARS. De Hauwere syndrome is proposed to be a FOXC1opathy.

The phenotypic spectrum of terminal and subterminal 6p deletions based on a social media-derived cohort and literature review

BACKGROUND

Terminal 6p deletions are rare, and information on their clinical consequences is scarce, which impedes optimal management and follow-up by clinicians. The parent-driven Chromosome 6 Project collaborates with families of affected children worldwide to better understand the clinical effects of chromosome 6 aberrations and to support clinical guidance. A microarray report is required for participation, and detailed phenotype information is collected directly from parents through a multilingual web-based questionnaire. Information collected from parents is then combined with case data from literature reports. Here, we present our findings on 13 newly identified patients and 46 literature cases with genotypically well-characterised terminal and subterminal 6p deletions. We provide phenotype descriptions for both the whole group and for subgroups based on deletion size and HI gene content.

RESULTS

The total group shared a common phenotype characterised by ocular anterior segment dysgenesis, vision problems, brain malformations, congenital defects of the cardiac septa and valves, mild to moderate hearing impairment, eye movement abnormalities, hypotonia, mild developmental delay and dysmorphic features. These characteristics were observed in all subgroups where FOXC1 was included in the deletion, confirming a dominant role for this gene. Additional characteristics were seen in individuals with terminal deletions exceeding 4.02 Mb, namely complex heart defects, corpus callosum abnormalities, kidney abnormalities and orofacial clefting. Some of these additional features may be related to the loss of other genes in the terminal 6p region, such as RREB1 for the cardiac phenotypes and TUBB2A and TUBB2B for the cerebral phenotypes. In the newly identified patients, we observed previously unreported features including gastrointestinal problems, neurological abnormalities, balance problems and sleep disturbances.

CONCLUSIONS

We present an overview of the phenotypic characteristics observed in terminal and subterminal 6p deletions. This reveals a common phenotype that can be highly attributable to haploinsufficiency of FOXC1, with a possible additional effect of other genes in the 6p25 region. We also delineate the developmental abilities of affected individuals and report on previously unrecognised features, showing the added benefit of collecting information directly from parents. Based on our overview, we provide recommendations for clinical surveillance to support clinicians, patients and families.

Podocyte-specific Transcription Factors: Could MafB Become a Therapeutic Target for Kidney Disease?

The increasing number of patients with chronic kidney disease (CKD) is being recognized as an emerging global health problem. Recently, it has become clear that injury and loss of glomerular visceral epithelial cells, known as podocytes, is a common early event in many forms of CKD. Podocytes are highly specialized epithelial cells that cover the outer layer of the glomerular basement membrane. They serve as the final barrier to urinary protein loss through the formation and maintenance of specialized foot-processes and an interposed slit-diaphragm. We previously reported that the transcription factor MafB regulates the podocyte slit diaphragm protein production and transcription factor Tcf21. We showed that the forced expression of MafB was able to prevent CKD. In this review, we discuss recent advances and offer an updated overview of the functions of podocyte-specific transcription factors in kidney biology, aiming to present new perspectives on the progression of CKD and respective therapeutic strategies.

Posterior segment findings in Axenfeld-Rieger syndrome

Axenfeld-Rieger syndrome (ARS) is characterized by posterior embryotoxon, Axenfeld anomaly (adherent iris strands to Schwalbe's line), and Rieger anomaly (iris hypoplasia with corectopia or pseudopolycoria). There are a few case reports of optic nerve abnormalities associated with 6p25 deletion syndrome, which is a multigenic region that contains the FOXC1 gene. We present 4 patients with ARS, including 1 with a FOXC1 nonsense mutation, who also have prominent congenital optic nerve abnormalities.

Neuroimmune signaling at the brain borders

The central nervous system (CNS) has been viewed as an immunologically privileged site, but emerging works are uncovering a large array of neuroimmune interactions primarily occurring at its borders. CNS barriers sites host diverse population of both innate and adaptive immune cells capable of, directly and indirectly, influence the function of the residing cells of the brain parenchyma. These structures are only starting to reveal their role in controlling brain function under normal and pathological conditions and represent an underexplored therapeutic target for the treatment of brain disorders. This review will highlight the development of the CNS barriers to host neuro-immune interactions and emphasize their newly described roles in neurodevelopmental, neurological, and neurodegenerative disorders, particularly for the meninges.

Foxc1a regulates zebrafish vascular integrity and brain vascular development through targeting amotl2a and ctnnb1

Accumulating evidences have pointed that foxc1a is essential for vascular development and integrity maintenance through regulating the expression of downstream genes and interacting with signaling pathways. However, the underling cellular and molecular mechanisms of foxc1a in regulating vascular development remain undetermined. Based on two different foxc1a mutant zebrafish lines (foxc1a^nju18 and foxc1a^nju19 which generated predicted truncated foxc1a proteins with 50aa and 315aa respectively), we found that around 30 % of foxc1a^nju18 zebrafish exhibited severe vascular developmental defects with obvious hemorrhage in hindbrain and trunk at embryonic stages. Confocal imaging analysis revealed that the formation of middle cerebral vein (MCeV), intra-cerebral central arteries (CtAs) and dorsal longitudinal vein (DLV) of brain vessels was significantly blocked in foxc1a^nju18enbryos. Injection of exogenous full length and foxc1a^nju19 truncated foxc1a mRNA both rescued the deficiency of foxc1a^nju18 embryos. Transcriptome analysis revealed 186 DEGs in foxc1a^nju18 zebrafish among which amotl2a and ctnnb1 expression were reduced and functionally associated with adherens junctions. Dual-Luciferase assays validated amotl2a and ctnnb1 were both directly transactivated by foxc1a. Rescue experiments demonstrated that amotl2a was mainly responsible for the vascular integrity caused by foxc1a mutation and also coordinated with ctnnb1 to regulate brain vascular development. Our data point to a novel clue that foxc1a regulates vascular integrity and brain vascular development through targeting amotl2a and ctnnb1.

Quantifying concordant genetic effects of de novo mutations on multiple disorders

Exome sequencing on tens of thousands of parent-proband trios has identified numerous deleterious de novo mutations (DNMs) and implicated risk genes for many disorders. Recent studies have suggested shared genes and pathways are enriched for DNMs across multiple disorders. However, existing analytic strategies only focus on genes that reach statistical significance for multiple disorders and require large trio samples in each study. As a result, these methods are not able to characterize the full landscape of genetic sharing due to polygenicity and incomplete penetrance. In this work, we introduce EncoreDNM, a novel statistical framework to quantify shared genetic effects between two disorders characterized by concordant enrichment of DNMs in the exome. EncoreDNM makes use of exome-wide, summary-level DNM data, including genes that do not reach statistical significance in single-disorder analysis, to evaluate the overall and annotation-partitioned genetic sharing between two disorders. Applying EncoreDNM to DNM data of nine disorders, we identified abundant pairwise enrichment correlations, especially in genes intolerant to pathogenic mutations and genes highly expressed in fetal tissues. These results suggest that EncoreDNM improves current analytic approaches and may have broad applications in DNM studies.

Endogenous ROS production in early differentiation state suppresses endoderm differentiation via transient FOXC1 expression

Oxidative stress plays a pivotal role in the differentiation and proliferation of cells and programmed cell death. However, studies on the role of oxidative stress in differentiation have mainly employed the detection of reactive oxygen species (ROS) during differentiation or generated by ROS inducers. Therefore, it is difficult to clarify the significance of endogenous ROS production in the differentiation of human cells. We developed a system to control the intracellular level of ROS in the initial stage of differentiation in human iPS cells. By introducing a specific substitution (I69E) into the SDHC protein, a component of the mitochondrial respiratory chain complex, the endogenous ROS level increased. This caused impaired endoderm differentiation of iPS cells, and this impairment was reversed by overproduction of mitochondrial-targeted catalase, an anti-oxidant enzyme. Expression of tumor-related FOXC1 transcription factor increased transiently as early as 4 h after ROS-overproduction in the initial stage of differentiation. Knockdown of FOXC1 markedly improved impaired endoderm differentiation, suggesting that endogenous ROS production in the early differentiation state suppresses endoderm differentiation via transient FOXC1 expression.

De novo PBX1 variant in a patient with glaucoma, kidney anomalies, and developmental delay: An expansion of the CAKUTHED phenotype

An infant was referred for evaluation of congenital glaucoma and corneal clouding. In addition, he had a pelvic kidney, hypotonia, patent ductus arteriosus, abnormal pinnae, and developmental delay. Exome sequencing identified a previously unpublished de novo single nucleotide insertion in PBX1 c.400dupG (NM_002585.3), predicted to cause a frameshift resulting in a truncated protein with loss of function (p.Ala134Glyfs*65). Identification of this loss of function variant supports the diagnosis of congenital anomalies of the kidney and urinary tract syndrome with or without hearing loss, abnormal ears, or developmental delay (CAKUTHED). Here, we propose glaucoma as an extra-renal manifestation associated with PBX1-related disease due to the relationship of PBX1 with MEIS1, MEIS2, and FOXC1 transcription factors associated with eye development.

Molecular Mechanisms and Risk Factors for the Pathogenesis of Hydrocephalus

Hydrocephalus is a neurological condition due to the aberrant circulation and/or obstruction of cerebrospinal fluid (CSF) flow with consequent enlargement of cerebral ventricular cavities. However, it is noticed that a lot of patients may still go through symptomatic progression despite standard shunting procedures, suggesting that hydrocephalus is far more complicated than a simple CSF circulative/obstructive disorder. Growing evidence indicates that genetic factors play a fundamental role in the pathogenesis of some hydrocephalus. Although the genetic research of hydrocephalus in humans is limited, many genetic loci of hydrocephalus have been defined in animal models. In general, the molecular abnormalities involved in the pathogenesis of hydrocephalus include brain development and ependymal cell dysfunction, apoptosis, inflammation, free radical generation, blood flow, and cerebral metabolism. Moreover, recent studies have indicated that the molecular abnormalities relevant to aberrant cerebral glymphatic drainage turn into an attractive subject in the CSF circulation disorder. Furthermore, the prevalent risk factors could facilitate the development of hydrocephalus. In this review, we elicited some possible fundamental molecular mechanisms and facilitating risk factors involved in the pathogenesis of hydrocephalus, and aimed to widen the diagnosis and therapeutic strategies for hydrocephalus management. Such knowledge could be used to improve patient care in different ways, such as early precise diagnosis and effective therapeutic regimens.

Cellular Niches for Hematopoietic Stem Cells and Lympho-Hematopoiesis in Bone Marrow During Homeostasis and Blood Cancers

Most types of blood cells, including immune cells are generated from hematopoietic stem cells (HSCs) within bone marrow in the adult. Most HSCs are in contact with and require the special microenvironment known as a niche for their maintenance. It has been thought that HSC niches comprise various types of support cells that provide critical signals, including cytokines and extracellular matrix for HSC regulation. However, among these cells, several lines of evidence have demonstrated that the population of bone marrow-specific mesenchymal stem cells, termed CXC chemokine ligand 12 (CXCL12)-abundant reticular (CAR) cells, which overlap strongly with leptin receptor-expressing (LepR⁺) cells, is the major cellular component of HSC niches. CAR/LepR⁺ cells give rise to most adipocytes and osteoblasts in adult bone marrow and express much higher levels of HSC niche factors, including cytokines CXCL12 and stem cell factor (SCF), which are essential for HSC maintenance, and transcription factors Foxc1 and Ebf3, which are essential for the formation and maintenance of HSC niches than other types of cells. CAR/LepR⁺ cells are present in human bone marrow, undergo fibrotic expansion, and have reduced expression of HSC niche factors in hematopoietic malignancies.

Genome-scale actions of master regulators directing skeletal development

The mammalian skeleton develops through two distinct modes of ossification: intramembranous ossification and endochondral ossification. During the process of skeletal development, SRY-box containing gene 9 (Sox9), runt-related transcription factor 2 (Runx2), and Sp7 work as master transcription factors (TFs) or transcriptional regulators, underlying cell fate specification of the two distinct populations: bone-forming osteoblasts and cartilage-forming chondrocytes. In the past two decades, core transcriptional circuits underlying skeletal development have been identified mainly through mouse genetics and biochemical approaches. Recently emerging next-generation sequencer (NGS)-based studies have provided genome-scale views on the gene regulatory landscape programmed by the master TFs/transcriptional regulators. With particular focus on Sox9, Runx2, and Sp7, this review aims to discuss the gene regulatory landscape in skeletal development, which has been identified by genome-scale data, and provide future perspectives in this field.

Back and forth: History of and new insights on the vertebrate lymphatic valve

Lymphatic valves develop from pre‐existing endothelial cells through a step‐wise process involving complex changes in cell shape and orientation, along with extracellular matrix interactions, to form two intraluminal leaflets. Once formed, valves prevent back‐flow within the lymphatic system to ensure drainage of interstitial fluid back into the circulatory system, thereby serving a critical role in maintaining fluid homeostasis. Despite the extensive anatomical characterization of lymphatic systems across numerous genus and species dating back several hundred years, valves were largely thought to be phylogenetically restricted to mammals. Accordingly, most insights into molecular and genetic mechanisms involved in lymphatic valve development have derived from mouse knockouts, as well as rare diseases in humans. However, we have recently used a combination of imaging and genetic analysis in the zebrafish to demonstrate that valves are a conserved feature of the teleost lymphatic system. Here, we provide a historical overview of comparative lymphatic valve anatomy together with recent efforts to define molecular pathways that contribute to lymphatic valve morphogenesis. Finally, we integrate our findings in zebrafish with previous work and highlight the benefits that this model provides for investigating lymphatic valve development.

Therapeutically Targeting Cancers That Overexpress FOXC1: A Transcriptional Driver of Cell Plasticity, Partial EMT, and Cancer Metastasis

Metastasis accounts for more than 90% of cancer related mortality, thus the most pressing need in the field of oncology today is the ability to accurately predict future onset of metastatic disease, ideally at the time of initial diagnosis. As opposed to current practice, what would be desirable is that prognostic, biomarker-based detection of metastatic propensity and heightened risk of cancer recurrence be performed long before overt metastasis has set in. Without such timely information it will be impossible to formulate a rational therapeutic treatment plan to favorably alter the trajectory of disease progression. In order to help inform rational selection of targeted therapeutics, any recurrence/metastasis risk prediction strategy must occur with the paired identification of novel prognostic biomarkers and their underlying molecular regulatory mechanisms that help drive cancer recurrence/metastasis (i.e. recurrence biomarkers). Traditional clinical factors alone (such as TNM staging criteria) are no longer adequately prognostic for this purpose in the current molecular era. FOXC1 is a pivotal transcription factor that has been functionally implicated to drive cancer metastasis and has been demonstrated to be an independent predictor of heightened metastatic risk, at the time of initial diagnosis. In this review, we present our viewpoints on the master regulatory role that FOXC1 plays in mediating cancer stem cell traits that include cellular plasticity, partial EMT, treatment resistance, cancer invasion and cancer migration during cancer progression and metastasis. We also highlight potential therapeutic strategies to target cancers that are, or have evolved to become, “transcriptionally addicted” to FOXC1. The potential role of FOXC1 expression status in predicting the efficacy of these identified therapeutic approaches merits evaluation in clinical trials.

An In Vitro and In Vivo Comparison of Osteogenic Differentiation of Human Mesenchymal Stromal/Stem Cells

The use of stem cells in regenerative medicine, including tissue engineering and transplantation, has generated a great deal of enthusiasm. Mesenchymal stromal/stem cells (MSCs) can be isolated from various tissues, most commonly, bone marrow but more recently adipose tissue, dental pulp, and Wharton's jelly, to name a few. MSCs display varying phenotypic profiles and osteogenic differentiating capacity depending and their site of origin. MSCs have been successfully differentiated into osteoblasts both in vitro an in vivo but discrepancies exist when the two are compared: what happens in vitro does not necessarily happen in vivo, and it is therefore important to understand why these differences occur. The osteogenic process is a complex network of transcription factors, stimulators, inhibitors, proteins, etc., and in vivo experiments are helpful in evaluating the various aspects of this osteogenic process without distractions and confounding variables. With that in mind, the results of in vitro experiments need to be carefully considered and interpreted with caution as they do not perfectly replicate the conditions found within living organisms. This is where in vivo experiments help us better understand interactions that might occur in the osteogenic process that cannot be replicated in vitro. Potentially, these differences could also be exploited to develop an optimal MSC cell therapeutic product that can be used for bone disorders. There are many bone disorders, most of which cause a great deal of discomfort. Clinically acceptable protocols could be developed in which MSCs are used to aid in bone regeneration providing relief for patients with chronic pain. The aim of this review is to examine the differences between studies conducted in vitro and in vivo with regard to the osteogenic process to better define the gaps in current osteogenic research. By better understanding osteogenic differentiation, we can better define treatment strategies for various bone disorders.

Loss of Foxc1 and Foxc2 function in chondroprogenitor cells disrupts endochondral ossification

Endochondral ossification initiates the growth of the majority of the mammalian skeleton and is tightly controlled through gene regulatory networks. The forkhead box transcription factors Foxc1 and Foxc2 regulate aspects of osteoblast function in the formation of the skeleton, but their roles in chondrocytes to control endochondral ossification are less clear. Here, we demonstrate that Foxc1 expression is directly regulated by the activity of SRY (sex-determining region Y)-box 9, one of the earliest transcription factors to specify the chondrocyte lineage. Moreover, we demonstrate that elevated expression of Foxc1 promotes chondrocyte differentiation in mouse embryonic stem cells and loss of Foxc1 function inhibits chondrogenesis in vitro. Using chondrocyte-targeted deletion of Foxc1 and Foxc2 in mice, we reveal a role for these factors in chondrocyte differentiation in vivo. Loss of both Foxc1 and Foxc2 caused a general skeletal dysplasia predominantly affecting the vertebral column. The long bones of the limbs were smaller, mineralization was reduced, and organization of the growth plate was disrupted; in particular, the stacked columnar organization of the proliferative chondrocyte layer was reduced in size and cell proliferation was decreased. Differential gene expression analysis indicated disrupted expression patterns of chondrogenesis and ossification genes throughout the entire process of endochondral ossification in chondrocyte-specific Foxc1/Foxc2 KO embryos. Our results suggest that Foxc1 and Foxc2 are required for normal chondrocyte differentiation and function, as loss of both genes results in disorganization of the growth plate, reduced chondrocyte proliferation, and delays in chondrocyte hypertrophy that prevents ossification of the skeleton.

Cell lineage- and expression-based inference of the roles of forkhead box transcription factor Foxc2 in craniofacial development

BACKGROUND

Foxc2 is a member of the winged helix/forkhead (Fox) box family of transcription factors. Loss of function of Foxc2 causes craniofacial abnormalities such as cleft palate and deformed cranial base, but its role during craniofacial development remains to be elucidated.

RESULTS

The contributions of Foxc2-positive and its descendant cells to the craniofacial structure at E18.5 were examined using a tamoxifen-inducible Cre driver mouse (Foxc2-CreERT2) crossed with the R26R-LacZ reporter mouse. Foxc2 expression at E8.5 is restricted to the cranial mesenchyme, contributing to specific components including the cranial base, sensory capsule, tongue, upper incisor, and middle ear. Expression at E10.5 was still positively regulated in most of those regions. In situ hybridization analysis of Foxc2 and its closely related gene, Foxc1, revealed that expression domains of these genes largely overlap in the cephalic mesenchyme. Meanwhile, the tongue expressed Foxc2 but not Foxc1, and its development was affected by the neural crest-specific deletion of Foxc2 in mice (Wnt1-Cre; Foxc2^fl/fl ).

CONCLUSIONS

Foxc2 is expressed in cranial mesenchyme that contributes to specific craniofacial tissue components from an early stage, and it seems to be involved in their development in cooperation with Foxc1. Foxc2 also has its own role in tongue development.

Tumor-specific overexpression of histone gene, H3C14 in gastric cancer is mediated through EGFR-FOXC1 axis

Incorporation of different H3 histone isoforms/variants have been reported to differentially regulate gene expression via alteration in chromatin organization during diverse cellular processes. However, the differential expression of highly conserved histone H3.2 genes, H3C14 and H3C13 in human cancer has not been delineated. In this study, we investigated the expression of H3.2 genes in primary human gastric, brain, breast, colon, liver, and head and neck cancer tissues and tumor cell lines. The data showed overexpression of H3.2 transcripts in tumor samples and cell lines with respect to normal counterparts. Furthermore, TCGA data of individual and TCGA PANCAN cohort also showed significant up-regulation of H3.2 genes. Further, overexpressed H3C14 gene coding for H3.2 protein was regulated by FOXC1 transcription factor and G4-cassette in gastric cancer cell lines. Elevated expression of FOXC1 protein and transcripts were also observed in human gastric cancer samples and cell lines. Further, FOXC1 protein was predominantly localized in the nuclei of neoplastic gastric cells compared to normal counterpart. In continuation, studies with EGF induction, FOXC1 knockdown, and ChIP-qPCR for the first time identified a novel axis, EGFR-FOXC1-H3C14 for regulation of H3C14 gene overexpression in gastric cancer. Therefore, the changes the epigenomic landscape due to incorporation of differential expression H3 variant contributes to change in gene expression pattern and thereby contributing to pathogenesis of cancer.

FOXC1 Downregulates Nanog Expression by Recruiting HDAC2 to Its Promoter in F9 Cells Treated by Retinoic Acid

FOXC1, a transcription factor involved in cell differentiation and embryogenesis, is demonstrated to be a negative regulator of Nanog in this study. FOXC1 is up-regulated in retinoic acid-induced differentiation of F9 Embryonal Carcinoma (EC) cells; furthermore, FOXC1 specifically inhibits the core pluripotency factor Nanog by binding to the proximal promoter. Overexpression of FOXC1 in F9 or knockdown in 3T3 results in the down-regulation or up-regulation of Nanog mRNA and proteins, respectively. In order to explain the mechanism by which FOXC1 inhibits Nanog expression, we identified the co-repressor HDAC2 from the FOXC1 interactome. FOXC1 recruits HDAC2 to Nanog promoter to decrease H3K27ac enrichment, resulting in transcription inhibition of Nanog. To the best of our knowledge, this is the first report that FOXC1 is involved in the epigenetic regulation of gene expression.

The spatial phenotype of genotypically distinct meningiomas demonstrate potential implications of the embryology of the meninges

Meningiomas are the most common primary brain tumor and their incidence and prevalence is increasing. This review summarizes current evidence regarding the embryogenesis of the human meninges in the context of meningioma pathogenesis and anatomical distribution. Though not mutually exclusive, chromosomal instability and pathogenic variants affecting the long arm of chromosome 22 (22q) result in meningiomas in neural-crest cell-derived meninges, while variants affecting Hedgehog signaling, PI3K signaling, TRAF7, KLF4, and POLR2A result in meningiomas in the mesodermal-derived meninges of the midline and paramedian anterior, central, and ventral posterior skull base. Current evidence regarding the common pathways for genetic pathogenesis and the anatomical distribution of meningiomas is presented alongside existing understanding of the embryological origins for the meninges prior to proposing next steps for this work.

Foxc1 establishes enhancer accessibility for craniofacial cartilage differentiation

The specification of cartilage requires Sox9, a transcription factor with broad roles for organogenesis outside the skeletal system. How Sox9 and other factors gain access to cartilage-specific cis-regulatory regions during skeletal development was unknown. By analyzing chromatin accessibility during the differentiation of neural crest cells into chondrocytes of the zebrafish head, we find that cartilage-associated chromatin accessibility is dynamically established. Cartilage-associated regions that become accessible after neural crest migration are co-enriched for Sox9 and Fox transcription factor binding motifs. In zebrafish lacking Foxc1 paralogs, we find a global decrease in chromatin accessibility in chondrocytes, consistent with a later loss of dorsal facial cartilages. Zebrafish transgenesis assays confirm that many of these Foxc1-dependent elements function as enhancers with region- and stage-specific activity in facial cartilages. These results show that Foxc1 promotes chondrogenesis in the face by establishing chromatin accessibility at a number of cartilage-associated gene enhancers.

Dlx5-augmentation in neural crest cells reveals early development and differentiation potential of mouse apical head mesenchyme

Neural crest cells (NCCs) give rise to various tissues including neurons, pigment cells, bone and cartilage in the head. Distal-less homeobox 5 (Dlx5) is involved in both jaw patterning and differentiation of NCC-derivatives. In this study, we investigated the differentiation potential of head mesenchyme by forcing Dlx5 to be expressed in mouse NCC (NCC^Dlx5). In NCC^Dlx5 mice, differentiation of dermis and pigment cells were enhanced with ectopic cartilage (ec) and heterotopic bone (hb) in different layers at the cranial vertex. The ec and hb were derived from the early migrating mesenchyme (EMM), the non-skeletogenic cell population located above skeletogenic supraorbital mesenchyme (SOM). The ec developed within Foxc1⁺-dura mater with increased PDGFRα signalling, and the hb formed with upregulation of BMP and WNT/β-catenin signallings in Dermo1⁺-dermal layer from E11.5. Since dermal cells express Runx2 and Msx2 in the control, osteogenic potential in dermal cells seemed to be inhibited by an anti-osteogenic function of Msx2 in normal context. We propose that, after the non-skeletogenic commitment, the EMM is divided into dermis and meninges by E11.5 in normal development. Two distinct responses of the EMM, chondrogenesis and osteogenesis, to Dlx5-augmentation in the NCC^Dlx5 strongly support this idea.

The miR-204-5p/FOXC1/GDF7 axis regulates the osteogenic differentiation of human adipose-derived stem cells via the AKT and p38 signalling pathways

BACKGROUND

Human adipose-derived stem cells (hADSCs) are stem cells with the potential to differentiate in multiple directions. miR-204-5p is expressed at low levels during the osteogenic differentiation of hADSCs, and its specific regulatory mechanism remains unclear. Here, we aimed to explore the function and possible molecular mechanism of miR-204-5p in the osteogenic differentiation of hADSCs.

METHODS

The expression patterns of miR-204-5p, Runx2, alkaline phosphatase (ALP), osteocalcin (OCN), forkhead box C1 (FOXC1) and growth differentiation factor 7 (GDF7) in hADSCs during osteogenesis were detected by qRT-PCR. Then, ALP and alizarin red staining (ARS) were used to detect osteoblast activities and mineral deposition. Western blotting was conducted to confirm the protein levels. The regulatory relationship among miR-204-5p, FOXC1 and GDF7 was verified by dual-luciferase activity and chromatin immunoprecipitation (ChIP) assays.

RESULTS

miR-204-5p expression was downregulated in hADSC osteogenesis, and overexpression of miR-204-5p suppressed osteogenic differentiation. Furthermore, the levels of FOXC1 and GDF7 were decreased in the miR-204-5p mimics group, which indicates that miR-204-5p overexpression suppresses the expression of FOXC1 and GDF7 by binding to their 3'-untranslated regions (UTRs). Overexpression of FOXC1 or GDF7 improved the inhibition of osteogenic differentiation of hADSCs induced by the miR-204-5p mimics. Moreover, FOXC1 was found to bind to the promoter of miR-204-5p and GDF7, promote the deacetylation of miR-204-5p and reduce the expression of miR-204-5p, thus promoting the expression of GDF7 during osteogenic differentiation. GDF7 induced hADSC osteogenesis differentiation by activating the AKT and P38 signalling pathways.

CONCLUSIONS

Our results demonstrated that the miR-204-5p/FOXC1/GDF7 axis regulates the osteogenic differentiation of hADSCs via the AKT and p38 signalling pathways. This study further revealed the regulatory mechanism of hADSC differentiation from the perspective of miRNA regulation.

Meningiomas from a developmental perspective: exploring the crossroads between meningeal embryology and tumorigenesis

Meningiomas are tumors arising from the meninges and represent the most frequent central nervous system tumors in adults. Recent large-scale genetic studies and preclinical meningioma mouse modelling led to a better comprehension of meningioma development and suggested evidences of close relationships between meningeal embryology and tumorigenesis. In this non-systematic review, we summarize the current knowledge on meningeal embryology and developmental biology, and illustrate how meningioma tumorigenesis is deeply related to meningeal embryology, concerning the potential cell of origin, the role of reactivation of embryonic stem cells, the influence of the embryonic tissue of origin, and the parallelism between topography-dependant molecular pathways involved in normal meninges and in meningioma development. Our study emphasizes why future studies on meningeal embryology are mandatory to affine our comprehension of mechanisms underlying meningioma initiation and development.

Periocular neural crest cell differentiation into corneal endothelium is influenced by signals in the nascent corneal environment

During ocular development, periocular neural crest cells (pNC) migrate into the region between the lens and presumptive corneal epithelium to form the corneal endothelium and stromal keratocytes. Although defects in neural crest cell development are associated with ocular dysgenesis, very little is known about the molecular mechanisms involved in this process. This study focuses on the corneal endothelium, a monolayer of specialized cells that are essential for maintaining normal hydration and transparency of the cornea. In avians, corneal endothelial cells are first to be specified from the pNC during their migration into the presumptive corneal region. To investigate the signals required for formation of the corneal endothelium, we utilized orthotopic and heterotopic injections of dissociated quail pNC into chick ocular regions. We find that pNC are multipotent and that the nascent cornea is competent to induce differentiation of ectopically injected pNC into corneal endothelium. Injected pNC downregulate expression of multipotency transcription factors and upregulate genes that are consistent with ontogenesis of the chick corneal endothelium. Importantly, we showed that TGFβ2 is expressed by the nascent lens and the corneal endothelium, and that TGFβ signaling plays a critical role in changing the molecular signature of pNC in vitro. Collectively, our results demonstrate the significance of the ocular environmental cues towards pNC differentiation, and have potential implications for clinical application of stem cells in the anterior segment.

FOXCUT Promotes the Proliferation and Invasion by Activating FOXC1/PI3K/AKT Pathway in Colorectal Cancer

Introduction

Colorectal cancer (CRC) is the third most commonly diagnosed world cancer. Long noncoding RNAs (lncRNAs) serve important regulatory roles in tumorigenesis. However, the contributions of lncRNAs to human CRC remain largely unknown.

Material and Methods

FOXC1 and FOXCUT lncRNA expression levels were detected in a panel of paired specimens obtained from 48 patients’ tissues and cell lines with CRC using RT-qPCR. RNA interference was used to investigate potential correlations between FOXC1 and FOXCUT expression in HT29. Cell proliferation was assessed by MTT assay and EdU incorporation assay. The migration and invasion of CRC cells were detected by transwell assay. Western blot was applied to assess the protein expression and PI3K/AKT signaling pathway.

Results

In this study, a novel long noncoding RNA (FOXCUT) was frequently overexpressed in CRC tissues and cell lines. In addition, the expressions of FOXCUT and FOXC1 were positively correlated. When the expression of FOXCUT was downregulated by small interfering RNA (siRNA), the expression of FOXC1 was also decreased. Moreover, knockdown of FOXCUT significantly inhibited proliferation and invasion of CRC cell lines and resulted in downregulated expression of the matrix metalloproteinase 1 (MMP-1). Mechanistically, FOXCUT promotes the expression of FOXC1 to activate PI3K/AKT signaling pathway for its regulation of cell growth and proliferation.

Conclusion

In summary, our findings indicate that FOXCUT plays an important oncogenic role and may serve as a novel biomarker and therapeutic target in CRC progression.

Axenfeld-Rieger syndrome-associated mutants of the transcription factor FOXC1 abnormally regulate NKX2-5 in model zebrafish embryos

FOXC1 is a member of the forkhead family of transcription factors, and whose function is poorly understood. A variety of FOXC1 mutants have been identified in patients diagnosed with the autosomal dominant disease Axenfeld-Rieger syndrome, which is mainly characterized by abnormal development of the eyes, particularly those who also have accompanying congenital heart defects (CHD). However, the role of FOXC1 in CHD, and how these mutations might impact FOXC1 function, remains elusive. Our previous work provided one clue to possible function, demonstrating that zebrafish foxc1a, an orthologue of human FOXC1 essential for heart development, directly regulates the expression of nkx2.5, encoding a transcriptional regulator of cardiac progenitor cells. Abnormal expression of Nkx2-5 leads to CHD in mice and is also associated with CHD patients. Whether this link extends to the human system, however, requires investigation. In this study, we demonstrate that FOXC1 does regulate human NKX2-5 expression in a dose-dependent manner via direct binding to its proximal promoter. A comparison of FOXC1 mutant function in the rat cardiac cell line H9c2 and zebrafish embryos suggested that the zebrafish embryos might serve as a more representative model system than the H9c2 cells. Finally, we noted that three of the Axenfeld-Rieger syndrome FOXC1 mutations tested increased, whereas a fourth repressed the expression of NKX2-5 These results imply that mutant FOXC1s might play etiological roles in CHD by abnormally regulating NKX2-5 in the patients. And zebrafish embryos can serve as a useful in vivo platform for rapidly evaluating disease-causing roles of mutated genes.

Shear stimulation of FOXC1 and FOXC2 differentially regulates cytoskeletal activity during lymphatic valve maturation

Mutations in the transcription factor FOXC2 are predominately associated with lymphedema. Herein, we demonstrate a key role for related factor FOXC1, in addition to FOXC2, in regulating cytoskeletal activity in lymphatic valves. FOXC1 is induced by laminar, but not oscillatory, shear and inducible, endothelial-specific deletion impaired postnatal lymphatic valve maturation in mice. However, deletion of Foxc2 induced valve degeneration, which is exacerbated in Foxc1; Foxc2 mutants. FOXC1 knockdown (KD) in human lymphatic endothelial cells increased focal adhesions and actin stress fibers whereas FOXC2-KD increased focal adherens and disrupted cell junctions, mediated by increased ROCK activation. ROCK inhibition rescued cytoskeletal or junctional integrity changes induced by inactivation of FOXC1 and FOXC2 invitro and vivo respectively, but only ameliorated valve degeneration in Foxc2 mutants. These results identify both FOXC1 and FOXC2 as mediators of mechanotransduction in the postnatal lymphatic vasculature and posit cytoskeletal signaling as a therapeutic target in lymphatic pathologies.

Phenotype expansion of heterozygous FOXC1 pathogenic variants toward involvement of congenital anomalies of the kidneys and urinary tract (CAKUT)

PURPOSE

Congenital anomalies of the kidney and urinary tract (CAKUT) are the most common cause of chronic kidney disease in childhood and adolescence. We aim to identify novel monogenic causes of CAKUT.

METHODS

Exome sequencing was performed in 550 CAKUT-affected families.

RESULTS

We discovered seven FOXC1 heterozygous likely pathogenic variants within eight CAKUT families. These variants are either never reported, or present in <5 alleles in the gnomAD database with ~141,456 controls. FOXC1 is a causal gene for Axenfeld-Rieger syndrome type 3 and anterior segment dysgenesis 3. Pathogenic variants in FOXC1 have not been detected in patients with CAKUT yet. Interestingly, mouse models for Foxc1 show severe CAKUT phenotypes with incomplete penetrance and variable expressivity. The FOXC1 variants are enriched in the CAKUT cohort compared with the control. Genotype-phenotype correlations showed that Axenfeld-Rieger syndrome or anterior segment dysgenesis can be caused by both truncating and missense pathogenic variants, and the missense variants are located at the forkhead domain. In contrast, for CAKUT, there is no truncating pathogenic variant, and all variants except one are located outside the forkhead domain.

CONCLUSION

We thereby expanded the phenotype of FOXC1 pathogenic variants toward involvement of CAKUT, which can potentially be explained by allelism.

Identification of a novel microRNA-141-3p/Forkhead box C1/β-catenin axis associated with rheumatoid arthritis synovial fibroblast function in vivo and in vitro

Rationale: Rheumatoid arthritis (RA) is a prototype of inflammatory arthritis in which synovial fibroblasts (SFs) play key roles in cartilage and bone destruction through tumor-like proliferation, migration, invasion and inflammation. This study aimed to research forkhead box protein C1 (FoxC1) and microRNA (miR)-141-3p, which modulate pathological changes in the synovial membrane, to find possible strategies for treating RA.

Methods: FoxC1, β-catenin and miR-141-3p gene expression in synovial tissues and SFs was quantified by real-time PCR; FoxC1 and β-catenin protein levels were evaluated by immunohistochemistry, immunofluorescence, and Western blotting. We transiently transfected human SFs with FoxC1 and β-catenin overexpression and silencing vectors and assessed proliferation, migration, invasion and inflammation by cell function and enzyme-linked immunosorbent assays. We also assessed downstream signaling activation using immunofluorescence, real-time PCR and Western blotting. Double luciferase, coimmunoprecipitation and chromatin immunoprecipitation assays were used to verify miR-141-3p, FoxC1 and β-catenin gene and protein combinations. Finally, the therapeutic effects of FoxC1 silencing and miR-141-3p overexpression were evaluated in type II collagen-induced arthritis (CIA) rats.

Results: We found that FoxC1 expression was significantly upregulated in synovium and SFs in both RA patients and rats with collagen-induced arthritis (CIA). FoxC1 overexpression increased β-catenin messenger RNA (mRNA) and protein levels and upregulated cyclin D1, c-Myc, fibronectin and matrix metalloproteinase 3 (MMP3) mRNA and protein expression in RA SFs (RASFs). In contrast, FoxC1 knockdown reduced β-catenin mRNA and protein levels as well as cyclin D1, c-Myc, and fibronectin mRNA and protein levels in RASFs. Furthermore, altering FoxC1 expression did not significantly change GSK3β and pGSK3β levels. FoxC1 overexpression promoted proliferation, migration, invasion and proinflammatory cytokine (interleukin (IL)-1β, IL-6, and tumor necrosis factor-α (TNF-α)) production and reduced anti-inflammatory cytokine (IL-10) levels in RASFs. FoxC1 bound to the β-catenin promoter, and β-catenin mediated the FoxC1-induced pathological changes. We also observed downregulated microRNA (miR)-141-3p expression in SFs from both RA patients and CIA rats and further found that miR-141-3p bound to the FoxC1 3′UTR and suppressed FoxC1 expression. Intra-ankle miR-141-3p agomir or FoxC1-specific siRNA injection hindered CIA development in rats.

Conclusions: FoxC1 and miR-141-3p participate in RA pathogenesis by mediating inflammation and SF proliferation, migration, and invasion and thus could be novel targets for RA therapy as a nonimmunosuppressive approach.

Primary cilia deficiency in neural crest cells models anterior segment dysgenesis in mouse

Defects affecting tissues of the anterior segment (AS) of the eye lead to a group of highly debilitating disorders called Anterior Segment Dysgenesis (ASD). Despite the identification of some causative genes, the pathogenesis of ASD remains unclear. Interestingly, several ciliopathies display conditions of the AS. Using conditional targeting of Ift88 with Wnt1-Cre, we show that primary cilia of neural crest cells (NCC), precursors of most AS structures, are indispensable for normal AS development and their ablation leads to ASD conditions including abnormal corneal dimensions, defective iridocorneal angle, reduced anterior chamber volume and corneal neovascularization. Mechanistically, NCC cilia ablation abolishes hedgehog (Hh) signaling in the periocular mesenchyme (POM) canonically activated by choroid-secreted Indian Hh, reduces proliferation of POM cells surrounding the retinal pigment epithelium and decreases the expression of Foxc1 and Pitx2, two transcription factors identified as major ASD causative genes. Thus, we uncovered a signaling axis linking cilia and ASD.

Childhood glaucoma genes and phenotypes: Focus on FOXC1 mutations causing anterior segment dysgenesis and hearing loss

Childhood glaucoma is an important cause of blindness world-wide. Eleven genes are currently known to cause inherited forms of glaucoma with onset before age 20. While all the early-onset glaucoma genes cause severe disease, considerable phenotypic variability is observed among mutations carriers. In particular, FOXC1 genetic variants are associated with a broad range of phenotypes including multiple forms of glaucoma and also systemic abnormalities, especially hearing loss. FOXC1 is a member of the forkhead family of transcription factors and is involved in neural crest development necessary for formation of anterior eye structures and also pharyngeal arches that form the middle ear bones. In this study we review the clinical phenotypes reported for known FOXC1 mutations and show that mutations in patients with reported ocular anterior segment abnormalities and hearing loss primarily disrupt the critically important forkhead domain. These results suggest that optimal care for patients affected with anterior segment dysgenesis should include screening for FOXC1 mutations and also testing for hearing loss.

p38-regulated FOXC1 stability is required for colorectal cancer metastasis

Aberrant expression of forkhead box C1 (FOXC1) promotes tumor metastasis in multiple human malignant tumors. However, the upstream modulating mode and downstream molecular mechanism of FOXC1 in metastasis of colorectal cancer (CRC) remain unclear. Herein we describe a systematic analysis of FOXC1 expression and prognosis in CRC performed on our clinical data and public databases, which indicated that FOXC1 upregulation in CRC samples was significantly associated with poor prognosis. FOXC1 knockdown inhibited migration and invasion, whereas FOXC1 overexpression caused the opposite phenotype in vitro and in vivo. Furthermore, MMP10, SOX4 and SOX13 were verified as the target genes of FOXC1 for promoting CRC metastasis. MMP10 was demonstrated as the direct target and mediator of FOXC1. Interestingly, Ser241 and Ser272 of FOXC1 were identified as the key sites to interact with p38 and phosphorylation, which were critically required for maintaining the stability of FOXC1 protein. Moreover, FOXC1 was dephosphorylated by protein phosphatase 2A and phosphorylated by p38, which maintained FOXC1 protein stability through inhibiting ubiquitination. Expression of p38 was correlated with FOXC1 and MMP10 expression, indirectly indicating that FOXC1 was regulated by p38 MAPK. Therefore, FOXC1 is strongly suggested as a pro-metastatic gene in CRC by transcriptionally activating MMP10, SOX4 and SOX13; p38 interacts with and phosphorylates the Ser241 and ser272 sites of FOXC1 to maintain its stability by inhibiting ubiquitination and degradation. In conclusion, the protein stability of FOXC1 mediated by p38 contributes to the metastatic effect in CRC. © 2019 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Aniridia and Axenfeld-Rieger Syndrome: Clinical presentations, molecular genetics and current/emerging therapies

Aniridia and Axenfeld-Rieger Syndrome are related, human ocular disorders that are typically inherited in an autosomal dominant manner. Both result from incorrect development of the eye and have, as their most serious consequences, elevated risk to develop the blinding condition glaucoma. This review will focus on describing the clinical presentations of Aniridia and Axenfeld-Rieger Syndrome as well as the molecular genetics and current and emerging therapies used to treat patients.

Role of FOXC1 in regulating APSCs self-renewal via STI-1/PrPC signaling

Forkhead box protein C1 (FOXC1) is known to regulate developmental processes in the skull and brain. Methods: The unique multipotent arachnoid-pia stem cells (APSCs) isolated from human and mouse arachnoid-pia membranes of meninges were grown as 3D spheres and displayed a capacity for self-renewal. Additionally, APSCs also expressed the surface antigens as mesenchymal stem cells. By applying the FOXC1 knockout mice and mouse brain explants, signaling cascade of FOXC1-STI-1-PrP^C was investigated to demonstrate the molecular regulatory pathway for APSCs self-renewal. Moreover, APSCs implantation in stroke model was also verified whether neurogenic property of APSCs could repair the ischemic insult of the stroke brain. Results: Activated FOXC1 regulated the proliferation of APSCs in a cell cycle-dependent manner, whereas FOXC1-mediated APSCs self-renewal was abolished in FOXC1 knockout mice (FOXC1^-/- mice). Moreover, upregulation of STI-1 regulated by FOXC1 enhanced cell survival and self-renewal of APSCs through autocrine signaling of cellular prion protein (PrP^C). Mouse brain explants STI-1 rescues the cortical phenotype in vitro and induces neurogenesis in the FOXC1 ^-/- mouse brain. Furthermore, administration of APSCs in ischemic brain restored the neuroglial microenvironment and improved neurological dysfunction. Conclusion: We identified a novel role for FOXC1 in the direct regulation of the STI-1-PrP^C signaling pathway to promote cell proliferation and self-renewal of APSCs.

SOX9 in cartilage development and disease

SOX9 is a pivotal transcription factor in chondrocytes, a lineage essential in skeletogenesis. Its mandatory role in transactivating many cartilage-specific genes is well established, whereas its pioneer role in lineage specification, which along with transactivation defines master transcription factors, remains to be better defined. Abundant, but yet incomplete evidence exists that intricate molecular networks control SOX9 activity during the multi-step chondrogenesis pathway. They include a highly modular genetic regulation, post-transcriptional and post-translational modifications, and varying sets of functional partners. Fully uncovering SOX9 actions and regulation is fundamental to explain mechanisms underlying many diseases that directly or indirectly affect SOX9 activities and to design effective disease treatments. We here review current knowledge, highlight recent discoveries, and propose new research directions to answer remaining questions.