Integrative analysis of Lunatic Fringe variants associated with spondylocostal dysostosis type-III.

Lunatic Fringe (LFNG) is required for spinal development. Biallelic pathogenic variants cause spondylocostal dysostosis type-III (SCD3), a rare disease generally characterized by malformed, asymmetrical, and attenuated development of the vertebral column and ribs. However, a variety of SCD3 cases reported have presented with additional features such as auditory alterations and digit abnormalities. There has yet to be a single, comprehensive, functional evaluation of causative LFNG variants and such analyses could unveil molecular mechanisms for phenotypic variability in SCD3. Therefore, nine LFNG missense variants associated with SCD3, c.564C>A, c.583T>C, c.842C>A, c.467T>G, c.856C>T, c.601G>A, c.446C>T, c.521G>A, and c.766G>A, were assessed in vitro for subcellular localization and protein processing. Glycosyltransferase activity was quantified for the first time in the c.583T>C, c.842C>A, and c.446C>T variants. Primarily, our results are the first to satisfy American College of Medical Genetics and Genomics PS3 criteria (functional evidence via well-established assay) for the pathogenicity of c.583T>C, c.842C>A, and c.446C>T, and replicate this evidence for the remaining six variants. Secondly, this work indicates that all variants that prevent Golgi localization also lead to impaired protein processing. It appears that the FRINGE domain is responsible for this phenomenon. Thirdly, our data suggests that variant proximity to the catalytic residue may influence whether LFNG is improperly trafficked and/or enzymatically dysfunctional. Finally, the phenotype of the axial skeleton, but not elsewhere, may be modulated in a variant-specific fashion. More reports are needed to continue testing this hypothesis. We anticipate our data will be used as a basis for discussion of genotype-phenotype correlations in SCD3.

Impact of heterozygous ALK1 mutations on the transcriptomic response to BMP9 and BMP10 in endothelial cells from hereditary hemorrhagic telangiectasia and pulmonary arterial hypertension donors.

Heterozygous activin receptor-like kinase 1 (ALK1) mutations are associated with two vascular diseases: hereditary hemorrhagic telangiectasia (HHT) and more rarely pulmonary arterial hypertension (PAH). Here, we aimed to understand the impact of ALK1 mutations on BMP9 and BMP10 transcriptomic responses in endothelial cells. Endothelial colony-forming cells (ECFCs) and microvascular endothelial cells (HMVECs) carrying loss of function ALK1 mutations were isolated from newborn HHT and adult PAH donors, respectively. RNA-sequencing was performed on each type of cells compared to controls following an 18 h stimulation with BMP9 or BMP10. In control ECFCs, BMP9 and BMP10 stimulations induced similar transcriptomic responses with around 800 differentially expressed genes (DEGs). ALK1-mutated ECFCs unexpectedly revealed highly similar transcriptomic profiles to controls, both at the baseline and upon stimulation, and normal activation of Smad1/5 that could not be explained by a compensation in cell-surface ALK1 level. Conversely, PAH HMVECs revealed strong transcriptional dysregulations compared to controls with > 1200 DEGs at the baseline. Consequently, because our study involved two variables, ALK1 genotype and BMP stimulation, we performed two-factor differential expression analysis and identified 44 BMP9-dysregulated genes in mutated HMVECs, but none in ECFCs. Yet, the impaired regulation of at least one hit, namely lunatic fringe (LFNG), was validated by RT-qPCR in three different ALK1-mutated endothelial models. In conclusion, ALK1 heterozygosity only modified the BMP9/BMP10 regulation of few genes, including LFNG involved in NOTCH signaling. Future studies will uncover whether dysregulations in such hits are enough to promote HHT/PAH pathogenesis, making them potential therapeutic targets, or if second hits are necessary.

Identification of bi-allelic LFNG variants in three patients and further clinical and molecular refinement of spondylocostal dysostosis 3.

Spondylocostal dysostosis (SCD), a condition characterized by multiple segmentation defects of the vertebrae and rib malformations, is caused by bi-allelic variants in one of the genes involved in the Notch signaling pathway that tunes the "segmentation clock" of somitogenesis: DLL3, HES7, LFNG, MESP2, RIPPLY2, and TBX6. To date, seven individuals with LFNG variants have been reported in the literature. In this study we describe two newborns and one fetus with SCD, who were found by trio-based exome sequencing (trio-ES) to carry homozygous (c.822-5C>T) or compound heterozygous (c.[863dup];[1063G>A]) and (c.[521G>T];[890T>G]) variants in LFNG. Notably, the c.822-5C>T change, affecting the polypyrimidine tract of intron 5, is the first non-coding variant reported in LFNG. This study further refines the clinical and molecular features of spondylocostal dysostosis 3 and adds to the numerous investigations supporting the usefulness of trio-ES approach in prenatal and neonatal settings.

Construction of lncRNA-ceRNA networks to reveal the potential role of Lfng/Notch1 signaling pathway in Alzheimer's disease.

BACKGROUND: Alzheimer's disease (AD) develops through a complex pathological process, in which many genes play a synergistic or antagonistic role. LncRNAs represent a kind of non-coding RNA, which can regulate gene expression at the epigenetic, transcriptional and post-transcriptional levels. Multiple lncRNAs have been found to have important regulatory functions in AD. Thus, their expression patterns, targets and functions should be explored as therapeutic targets. METHODS: We used deep RNA-seq analysis to detect the dysregulated lncRNAs in the hippocampus of APP/PS1 mice. We performed Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses to predict the biological roles and potential signaling pathways of dysregulated lncRNAs. Finally, we constructed lncRNA-miRNA-mRNA and lncRNA-mRNA co-expression networks to reveal the potential regulator roles in AD pathogenesis. RESULTS: Our findings revealed 110 significantly dysregulated lncRNAs. GO and KEGG annotations showed the dysregulated lncRNAs to be closely related to the functions of axon and protein digestion and absorption. The lncRNA-mRNA network showed that 19 lncRNAs regulated App, Prnp, Fgf10 and Il33, while 5 lncRNAs regulated Lfng via the lncRNA-miR-3102-3p-Lfng axis. Furthermore, we preliminarily demonstrated the important regulatory role of the Lfng/Notch1 signaling pathway through lncRNA-ceRNA networks in AD. CONCLUSION: We revealed the important regulatory roles of dysregulated lncRNAs in the etiopathogenesis of AD through lncRNA expression profiling. Our results showed that the mechanism involves the regulation of the Lfng/Notch1 signaling pathway.

Fringe family genes and their modulation of Notch signaling in cancer.

Fringes are glycosyltransferases that transfer N-acetylglucosamine to the O-linked fucose of Notch receptors. They regulate the Notch signaling activity that drives tumor formation and progression, resulting in poor prognosis. However, the specific tumor-promoting role of Fringes differs depending on the type of cancer. Although a particular Fringe member could act as a tumor suppressor in one cancer type, it may act as an oncogene in another. This review discusses the tumorigenic role of the Fringe family (lunatic fringe, manic fringe, and radical fringe) in modulating Notch signaling in various cancers. Although the crucial functions of Fringes continue to emerge as more mechanistic studies are being pursued, further translational research is needed to explore their roles and therapeutic benefits in various malignancies.

Altered Cogs of the Clock: Insights into the Embryonic Etiology of Spondylocostal Dysostosis.

Spondylocostal dysostosis (SCDO) is a rare heritable congenital condition, characterized by multiple severe malformations of the vertebrae and ribs. Great advances were made in the last decades at the clinical level, by identifying the genetic mutations underlying the different forms of the disease. These were matched by extraordinary findings in the Developmental Biology field, which elucidated the cellular and molecular mechanisms involved in embryo body segmentation into the precursors of the axial skeleton. Of particular relevance was the discovery of the somitogenesis molecular clock that controls the progression of somite boundary formation over time. An overview of these concepts is presented, including the evidence obtained from animal models on the embryonic origins of the mutant-dependent disease. Evidence of an environmental contribution to the severity of the disease is discussed. Finally, a brief reference is made to emerging in vitro models of human somitogenesis which are being employed to model the molecular and cellular events occurring in SCDO. These represent great promise for understanding this and other human diseases and for the development of more efficient therapeutic approaches.

Bioinformatics and Functional Analyses Implicate Potential Roles for EOGT and L-fringe in Pancreatic Cancers.

Notch signaling receptors, ligands, and their downstream target genes are dysregulated in pancreatic ductal adenocarcinoma (PDAC), suggesting a role of Notch signaling in pancreatic tumor development and progression. However, dysregulation of Notch signaling by post-translational modification of Notch receptors remains poorly understood. Here, we analyzed the Notch-modifying glycosyltransferase involved in the regulation of the ligand-dependent Notch signaling pathway. Bioinformatic analysis revealed that the expression of epidermal growth factor (EGF) domain-specific O-linked N-acetylglucosamine (EOGT) and Lunatic fringe (LFNG) positively correlates with a subset of Notch signaling genes in PDAC. The lack of EOGT or LFNG expression inhibited the proliferation and migration of Panc-1 cells, as observed by the inhibition of Notch activation. EOGT expression is significantly increased in the basal subtype, and low expression of both EOGT and LFNG predicts better overall survival in PDAC patients. These results imply potential roles for EOGT- and LFNG-dependent Notch signaling in PDAC.

Screening of known disease genes in congenital scoliosis.

BACKGROUND: Congenital scoliosis (CS) is defined as a lateral curvature of the spine due to the vertebral malformations and has an incidence of 0.5-1/1,000 births. We previously examined TBX6 in Japanese CS patients and revealed that approximately 10% of CS was caused by TBX6 mutations. However, the genetic cause of remaining CS is unknown. METHODS: We recruited 78 CS patients without TBX6 mutations and major comorbidities, and investigated the genes previously reported to be associated with CS and congenital vertebral malformations by whole-exome sequencing. RESULTS: We identified the compound heterozygous missense variants in LFNG in one patient. No likely disease-causing variants were identified in other patients, however. LFNG encodes a GlcNAc-transferase. The LFNG variants showed loss of their enzyme function. CONCLUSIONS: A LFNG mutation is reported in a case of spondylocostal dysostosis (SCD), a skeletal dysplasia with severe malformations of vertebra and rib. The CS patient with LFNG mutations had multiple vertebral malformations including hemivertebrae, butterfly vertebrae, and block vertebrae, and rib malformations. LFNG mutations may cause a spectrum of phenotypes including CS and SCD. The current list of known disease genes could explain only a small fraction of genetic cause of CS.

Variable developmental delays and characteristic facial features-A novel 7p22.3p22.2 microdeletion syndrome?

Isolated 7p22.3p22.2 deletions are rarely described with only two reports in the literature. Most other reported cases either involve a much larger region of the 7p arm or have an additional copy number variation. Here, we report five patients with overlapping microdeletions at 7p22.3p22.2. The patients presented with variable developmental delays, exhibiting relative weaknesses in expressive language skills and relative strengths in gross, and fine motor skills. The most consistent facial features seen in these patients included a broad nasal root, a prominent forehead a prominent glabella and arched eyebrows. Additional variable features amongst the patients included microcephaly, metopic ridging or craniosynostosis, cleft palate, cardiac defects, and mild hypotonia. Although the patients' deletions varied in size, there was a 0.47 Mb region of overlap which contained 7 OMIM genes: EIP3B, CHST12, LFNG, BRAT1, TTYH3, AMZ1, and GNA12. We propose that monosomy of this region represents a novel microdeletion syndrome. We recommend that individuals with 7p22.3p22.2 deletions should receive a developmental assessment and a thorough cardiac exam, with consideration of an echocardiogram, as part of their initial evaluation.

Reconstitution of TGFBR2 in HCT116 colorectal cancer cells causes increased LFNG expression and enhanced N-acetyl-d-glucosamine incorporation into Notch1.

Transforming growth factor-ß (TGF-ß) signaling plays a key role in regulating normal cell growth and differentiation, and mutations affecting members of this pathway contribute to cancer development and metastasis. In DNA mismatch repair (MMR)-deficient colorectal cancers that exhibit the microsatellite instability (MSI) phenotype, biallelic frameshift mutations in the transforming growth factor ß receptor type 2 (TGFBR2) gene occur at high frequency that lead to altered signal transduction and downstream target gene expression. Although recent evidence suggests that altered TGF-ß signaling can modulate protein glycosylation patterns in MSI-high colorectal tumor cells, affected genes have not been identified. Here, we investigated in a more systematic approach, expression changes of TGFBR2-regulated genes, involved in glycosylation using a TGFBR2-reconstituted colorectal cancer cell line (HCT116-TGFBR2) and Glyco-Gene Chip analysis. Based on this oligonucleotide array of about 1000 human glycosylation-related genes, several candidates including HES1, PDGFB, JUNB and LFNG were found to be upregulated in a TGFBR2-dependent manner and subsequently validated by real-time RT-PCR analyses. Focusing on the glycosyltransferase LFNG and its target signaling protein Notch1, dual labeling with [3H]-N-acetyl-d-glucosamine ([3H]-GlcNAc) and [35S]-l-methionine revealed a significant increase in N-acetyl-d-glucosamine incorporation into immunoprecipitated Notch1 receptor upon TGFBR2 expression whereas the protein level remained unaffected. These data suggest that TGFBR2 signaling can affect Notch1 glycosylation via regulation of glycosyltransferase LFNG expression and provide a first mechanistic example for altered glycosylation in MSI colorectal tumor cells.

Targeting Met and Notch in the Lfng-deficient, Met-amplified triple-negative breast cancer.

Triple negative breast cancer (TNBC) accounts for 15-20% of breast carcinomas and represents one of the most aggressive forms of this disease. Basal and claudin-low are the two main molecular subtypes among TNBCs. We previously reported that deletion of Lfng in mouse mammary gland caused deregulated Notch activation and induced basal-like and claudin-low tumors with co-selection for Met amplification. In human breast cancers, the vast majority of basal tumors and a subset of claudin-low tumors show reduced Lfng expression. Elevated Met expression and activation is associated with basal as well as claudin-low subtypes. To examine roles of Met and Notch in TNBC cells, we established two cell lines that harbor Met amplification as well as Lfng deletion, and possess features of basal and claudin-low breast cancer subtypes. Pharmacological inhibition of Met not only suppressed cell growth, tumorsphere and colony formation, but also reversed epithelial-to-mesenchymal transition and inhibited cell migration in both cell lines. In contrast, inhibition of Notch signaling using a γ-secretase inhibitor (GSI) only suppressed colony formation. Interestingly, GSI had no effect as single agent, but exerted a synergistic effect with Met inhibitor, on cell growth in 2D culture. We found that inhibition of Met resulted in downregulation of Dll ligands and upregulation of Jagged ligands, leading to differential modulation of Notch signaling. Our results suggest that combination targeting of Met and Notch may prove beneficial for TNBC patients with Met overexpression and Notch hyperactivation.

Posterior skeletal development and the segmentation clock period are sensitive to Lfng dosage during somitogenesis.

The segmental structure of the axial skeleton is formed during somitogenesis. During this process, paired somites bud from the presomitic mesoderm (PSM), in a process regulated by a genetic clock called the segmentation clock. The Notch pathway and the Notch modulator Lunatic fringe (Lfng) play multiple roles during segmentation. Lfng oscillates in the posterior PSM as part of the segmentation clock, but is stably expressed in the anterior PSM during presomite patterning. We previously found that mice lacking overt oscillatory Lfng expression in the posterior PSM (Lfng(∆FCE)) exhibit abnormal anterior development but relatively normal posterior development. This suggests distinct requirements for segmentation clock activity during the formation of the anterior skeleton (primary body formation), compared to the posterior skeleton and tail (secondary body formation). To build on these findings, we created an allelic series that progressively lowers Lfng levels in the PSM. Interestingly, we find that further reduction of Lfng expression levels in the PSM does not increase disruption of anterior development. However tail development is increasingly compromised as Lfng levels are reduced, suggesting that primary body formation is more sensitive to Lfng dosage than is secondary body formation. Further, we find that while low levels of oscillatory Lfng in the posterior PSM are sufficient to support relatively normal posterior development, the period of the segmentation clock is increased when the amplitude of Lfng oscillations is low. These data support the hypothesis that there are differential requirements for oscillatory Lfng during primary and secondary body formation and that posterior development is less sensitive to overall Lfng levels. Further, they suggest that modulation of the Notch signaling by Lfng affects the clock period during development.

3'-UTR-dependent regulation of mRNA turnover is critical for differential distribution patterns of cyclic gene mRNAs.

Somite segmentation, a prominent periodic event in the development of vertebrates, is instructed by cyclic expression of several genes, including Hes7 and Lunatic fringe (Lfng). Transcriptional regulation accounts for the cyclic expression. In addition, because the expression patterns vary in a cycle, rapid turnover of mRNAs should be involved in the cyclic expression, although its contribution remains unclear. Here, we demonstrate that 3'-UTR-dependent rapid turnover of Lfng and Hes7 plays a critical role in their dynamic expression patterns. The regions active in the transcription of Lfng and Hes7 are wholly overlapped in the posterior presomitic mesoderm (PSM) of the mouse embryo. However, their distribution patterns are slightly different; Hes7 mRNA shows a broader distribution pattern than Lfng mRNA in the posterior PSM. Lfng mRNA is less stable than Hes7 mRNA, where their 3'-UTRs are responsible for the different stability. Using transgenic mice expressing Venus under the control of the Hes7 promoter, which leads to cyclic transcription in the PSM, we reveal that the Lfng 3'-UTR provides the narrow distribution pattern of Lfng mRNA, whereas the Hes7 3'-UTR contributes the relatively broad distribution pattern of Hes7 mRNA. Thus, we conclude that 3'-UTR-dependent mRNA stability accounts for the differential distribution patterns of Lfng and Hes7 mRNA. Our findings suggest that 3'-UTR-dependent regulation of mRNA turnover plays a crucial role in the diverse patterns of mRNA distribution during development.