Alternative titles; symbols
HGNC Approved Gene Symbol: LFNG
Cytogenetic location: 7p22.3 Genomic coordinates (GRCh38): 7:2,512,529-2,529,177 (from NCBI)
| Location | Phenotype |
Phenotype MIM number |
Inheritance |
Phenotype mapping key |
|---|---|---|---|---|
| 7p22.3 | Spondylocostal dysostosis 3, autosomal recessive | 609813 | Autosomal recessive | 3 |
Notch (see NOTCH1, 190198) signaling is an evolutionarily conserved mechanism that determines cell fate in a variety of developmental contexts. LFNG encodes a fucose-specific beta-1,3-N-acetylglucosaminyltransferase that modifies Notch receptors and alters Notch signaling activity. LFNG is 1 of 3 mammalian homologs of the Drosophila Fringe gene (review by Dunwoodie, 2009).
The Drosophila melanogaster fringe gene encodes a secreted signaling protein that participates in the formation of boundaries between groups of cells during development. The fringe protein acts by modulating the activation of the Notch signal transduction pathway at the dorsal-ventral boundary of the Drosophila wing imaginal disc. Johnston et al. (1997) identified 3 human ESTs with homology to fringe and used them to clone the corresponding genes from mouse. They named the genes lunatic fringe (LFNG), manic fringe (MFNG; 602577), and radical fringe (RFNG; 602578). The predicted 378-amino acid mouse Lfng protein has a putative signal peptide and an internal proteolytic processing site. Unlike the other 2 homologs, Lfng did not have an effect when misexpressed in the Drosophila wing disc; Johnston et al. (1997) suggested that this may result from an inability of Drosophila cells to process the mature form of Lfng. Expression studies of the fringe homologs in mouse embryos by in situ hybridization suggested that all 3 homologs participate in the Notch signaling pathway in determining boundaries during segmentation and cell fates during neurogenesis.
Moran et al. (1999) characterized the genomic loci of the fringe gene family members, revealing a conserved genomic organization of 8 exons. Comparative analysis of mammalian fringe genomic organization suggested that the first exon is evolutionarily labile and that the fringe genes have a genomic structure distinct from those of previously characterized glycosyltransferases.
By somatic cell hybridization, radiation hybrid analysis, and FISH, Egan et al. (1998) mapped the human LFNG gene to chromosome 7p22. By interspecific backcross analysis, Moran et al. (1999) mapped the Lfng gene in the mouse to chromosome 5.
Dale et al. (2003) demonstrated that the Lfng protein product oscillates in the chick presomitic mesoderm (PSM). Overexpressing Lfng in the paraxial mesoderm abolishes the expression of cyclic genes including endogenous Lfng and leads to defects in segmentation. This effect on cyclic genes phenocopies inhibition of Notch signaling in the PSM. Dale et al. (2003) therefore proposed that Lfng establishes a negative feedback loop that implements periodic inhibition of Notch, which in turn controls rhythmic expression of cyclic genes in the chick PSM. This feedback loop provides a molecular basis for the oscillator underlying the avian segmentation clock.
Using transgenic mouse studies and comparative sequence analysis, Cole et al. (2002) identified 2 distinct regulatory elements in the Lfng promoter that direct both cyclic expression and anterior PSM expression of Lfng during somitogenesis in the mouse. In an independent study using deletion constructs, Morales et al. (2002) identified an evolutionarily conserved region in the mouse Lfng promoter that drives periodic expression of Lfng in the PSM. The region includes conserved blocks required for enhancing and repressing cyclic Lfng transcription and for preventing continued expression in formed somites. Using mouse embryos with deficient Notch signaling, Morales et al. (2002) observed that dynamic expression of Lfng in the cycling PSM is lost in the absence of Notch signaling. They concluded that cyclic initiation of transcription is the principal mechanism responsible for generating dynamic expression of Lfng in the PSM.
Visan et al. (2006) found that developmental stage-specific expression of Lfng was required for coordinating access of mouse T-cell progenitors to intrathymic niches supporting Notch1-dependent phases of T-cell development. Progenitors lacking Lfng generated few thymocytes in competitive assays, whereas overexpression of Lfng resulted in 'supercompetitive' thymocytes that showed enhanced binding to delta-like ligands (e.g., DLL1; 606582) and blocked T lymphopoiesis by normal progenitors. Visan et al. (2006) proposed that LFNG and NOTCH1 control of progenitor competition for cortical niches that suppress the B-cell potential of progenitors is important in regulation of thymus size.
Dunwoodie (2009) reviewed the role of LFNG in somite formation and vertebral column development in mice and humans.
Yoshioka-Kobayashi et al. (2020) established a live-imaging system in which a fluorescent reporter was fused to Hes7 (608059) to monitor synchronous oscillations in Hes7 expression in mouse PSM at single-cell resolution. They found that wildtype PSM cells could rapidly correct for phase fluctuations in Hes7 oscillations, whereas loss of Lfng led to loss of synchrony between PSM cells. Moreover, Hes7 oscillations were severely dampened in individual cells of Lfng-null PSM. When Lfng-null PSM cells were completely dissociated, the amplitude and periodicity of Hes7 oscillations were almost normal, suggesting that Lfng is involved mostly in cell-cell coupling. Mixed cultures of wildtype and Lfng-null PSM cells, and an optogenetic Notch signaling reporter assay, revealed that Lfng delayed the signal-sending process of intercellular Notch signaling transmission. These results, as well as mathematical modeling, suggested that Lfng-null PSM cells shortened the coupling delay, thereby approaching oscillation or amplitude death of coupled oscillators. A small compound that lengthened the coupling delay partially rescued the amplitude and synchrony of Hes7 oscillations in Lfng-null PSM cells. The findings revealed a delay control mechanism of the oscillatory networks involved in somite segmentation and showed that intercellular coupling with the correct delay is essential for synchronized oscillation.
Matsuda et al. (2020) used human induced pluripotent stem cells for in vitro induction of PSM and its derivatives to model human somitogenesis, with a focus on the human segmentation clock. The authors observed oscillatory expression of core segmentation clock genes, including HES7 and DKK1 (605189), determined the period of the human segmentation clock to be around 5 hours, and demonstrated the presence of dynamic traveling wave-like gene expression in in vitro-induced human PSM. Identification and comparison of oscillatory genes in human and mouse PSM derived from pluripotent stem cells revealed species-specific and shared molecular components and pathways associated with the putative mouse and human segmentation clocks. Knockout of genes mutated in patients with segmentation defects of vertebrae, including HES7, LFNG, DLL3 (602768), and MESP2 (605195), followed by analysis of patient-like and patient-derived induced pluripotent stem cells revealed gene-specific alterations in oscillation, synchronization, or differentiation properties.
Fringe proteins can positively and negatively modulate the ability of Notch ligands to activate the Notch receptor. Moloney et al. (2000) established the biochemical mechanism of Fringe action. Drosophila and mammalian Fringe proteins possess a fucose-specific beta-1,3 N-acetylglucosaminyltransferase activity that initiates elongation of O-linked fucose residues attached to epidermal growth factor (EGF; 131530)-like sequence repeats of Notch. They obtained biologic evidence that Fringe-dependent elongation of O-linked fucose on Notch modulates Notch signaling by using coculture assays in mammalian cells and by expression of an enzymatically inactive Fringe mutant in Drosophila.
Bruckner et al. (2000) showed that Fringe acts in the Golgi as a glycosyltransferase enzyme that modifies the EGF modules of Notch and alters the ability of Notch to bind its ligand Delta (602768). The authors demonstrated that Fringe catalyzes the addition of N-acetylglucosamine to fucose, which is consistent with a role in the elongation of O-linked fucose O-glycosylation that is associated with EGF repeats.
Arboleda-Velasquez et al. (2005) showed that Notch3 mutations resulting in CADASIL (125310) did not affect the addition of O-fucose but did impair carbohydrate chain elongation by Fringe. Notch3 mutations induced aberrant heterodimerization with Fringe. They suggested that Fringe may play a role in CADASIL pathophysiology.
The spondylocostal dysostoses are a heterogeneous group of vertebral malsegmentation disorders that arise during embryonic development by a disruption of somitogenesis. Mutations causing autosomal recessive forms of spondylocostal dysostosis were identified in 2 genes in the Notch signaling pathway: DLL3 (602768) and MESP2 (605195). Sparrow et al. (2006) used a candidate-gene approach to identify a mutation in a third Notch pathway gene, LFNG, in a family with autosomal recessive spondylocostal dysostosis (SCDO3; 609813). LFNG encodes a glycosyltransferase that modifies the Notch family of cell-surface receptors, a key step in the regulation of this signaling pathway. A missense mutation (F188L; 602576.0001) was identified in a highly conserved residue close to the active site of the enzyme. Functional analysis demonstrated that the mutant LFNG was not localized to the correct compartment of the cell, was unable to modulate Notch signaling in a cell-based assay, and was enzymatically inactive. The finding reinforces the hypothesis that proper regulations of the Notch signaling pathway is an absolute requirement for the correct patterning of the axial skeleton.
In a 9-month-old Japanese boy with SCDO3, Otomo et al. (2019) found compound heterozygosity for a missense (D201N; 602576.0002) and a frameshift (602576.0003) mutation in the LFNG gene. Each parent was heterozygous for 1 of the mutations. Neither mutation was found in the ExAC, ESP6500, or iJGVD databases.
Zhang and Gridley (1998) found that mice homozygous for a targeted mutation in the signal peptide and proprotein region of Lfng had defects in somite formation and anterior-posterior patterning of somites. The mutation was often fatal in homozygous neonates due to malformed rib cages, but some survived to adulthood. In mutant mice, the somites were irregular in size and shape. Marker analysis revealed that, in the PSM of mutant embryos, sharply demarcated domains of expression of several components of the Notch signaling pathway were replaced by even gradients of gene expression. Zhang and Gridley (1998) concluded that Lfng encodes an essential component of the Notch signaling pathway during somitogenesis in mice.
Independently, Evrard et al. (1998) generated mice with a targeted mutation in the first exon of Lfng and presented findings similar to those of Zhang and Gridley (1998). They concluded that Lfng is required for somite segmentation and rostral-caudal patterning and vertebrate boundary formation.
In affected members of a Lebanese family with autosomal recessive spondylocostal dysostosis (SCDO3; 609813), Sparrow et al. (2006) found a homozygous missense mutation, 564C-A, in exon 3 of the LFNG gene, predicted to result in substitution of leucine for phenylalanine (F188L) at a highly conserved residue. The proband had extensive congenital vertebral anomalies and hand anomalies. Both parents with normal spinal and hand anatomy were heterozygous for the mutant allele. Functional analysis demonstrated that the mutant LFNG was not localized to the correct compartment of the cell, was unable to modulate Notch signaling in a cell-based assay, and was enzymatically inactive.
In a 9-month-old Japanese boy with spondylocostal dysostosis (SCDO3; 609813), Otomo et al. (2019) identified compound heterozygosity for 2 mutations in the LFNG gene: a c.601G-A transition (c.601G-A, NM_001040167.1) in exon 4, resulting in an asp201-to-asn (D201N) substitution in the DxD motif, and a 1-bp deletion (c.372delG) in exon 1, resulting in a frameshift and a premature termination codon (Lys124AsnfsTer21; 602576.0003). The missense mutation was inherited from his father and the frameshift mutation from his mother. Neither mutation was found in the ExAC, ESP6500, or iJGVD databases. Functional analysis showed that the mutant D201N protein had significantly reduced GlcNAc-transferase activity compared to wildtype, indicating a loss of enzyme function.
For discussion of the 1-bp deletion (c.372delG, NM_001040167.1) in exon 1 of the LFNG gene, resulting in a frameshift and premature termination (Lys124AsnfsTer), that was found in compound heterozygous state in a patient with spondylocostal dysostosis-3 (SCDO3; 609813) by Otomo et al. (2019), see 602576.0002.
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Cole, S. E., Levorse, J. M., Tilghman, S. M., Vogt, T. F. Clock regulatory elements control cyclic expression of lunatic fringe during somitogenesis. Dev. Cell 3: 75-84, 2002. [PubMed: 12110169] [Full Text: https://doi.org/10.1016/s1534-5807(02)00212-5]
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Dunwoodie, S. L. Mutation of the fucose-specific beta-1,3 N-acetylglucosaminyltransferase LFNG results in abnormal formation of the spine. Biochim. Biophys. Acta 1792: 100-111, 2009. [PubMed: 19061953] [Full Text: https://doi.org/10.1016/j.bbadis.2008.11.003]
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Morales, A. V., Yasuda, Y., Ish-Horowicz, D. Periodic lunatic fringe expression is controlled during segmentation by a cyclic transcriptional enhancer responsive to Notch signaling. Dev. Cell 3: 63-74, 2002. [PubMed: 12110168] [Full Text: https://doi.org/10.1016/s1534-5807(02)00211-3]
Moran, J. L., Johnston, S. H., Rauskolb, C., Bhalerao, J., Bowcock, A. M., Vogt, T. F. Genomic structure, mapping, and expression analysis of the mammalian lunatic, manic, and radical fringe genes. Mammalian Genome 10: 535-541, 1999. [PubMed: 10341080] [Full Text: https://doi.org/10.1007/s003359901039]
Otomo, N., Mizumoto, S., Lu, H.-F., Takeda, K., Campos-Xavier, B., Mittaz-Crettol, L., Guo, L., Takikawa, K., Nakamura, M., Yamada, S., Matsumoto, M., Watanabe, K., Ikegawa, S. Identification of novel LFNG mutations in spondylocostal dysostosis. J. Hum. Genet. 64: 261-264, 2019. [PubMed: 30531807] [Full Text: https://doi.org/10.1038/s10038-018-0548-2]
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Visan, I., Tan, J. B., Yuan, J. S., Harper, J. A., Koch, U., Guidos, C. J. Regulation of T lymphopoiesis by Notch1 and lunatic fringe-mediated competition for intrathymic niches. Nature Immun. 7: 634-643, 2006. [PubMed: 16699526] [Full Text: https://doi.org/10.1038/ni1345]
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