Alternative titles; symbols
Other entities represented in this entry:
HGNC Approved Gene Symbol: MN1
Cytogenetic location: 22q12.1 Genomic coordinates (GRCh38) : 22:27,748,277-27,801,756 (from NCBI)
| Location | Phenotype |
Phenotype MIM number |
Inheritance |
Phenotype mapping key |
|---|---|---|---|---|
| 22q12.1 | CEBALID syndrome | 618774 | Autosomal dominant | 3 |
| Meningioma | 607174 | Autosomal dominant | 3 |
The MN1 gene encodes a transcription cofactor (summary by Miyake et al., 2020). MN1 received its name because it was first identified as an oncogene in a meningioma (Lekanne Deprez et al., 1995).
Using a balanced translocation t(4;22) found in a meningioma (607174), Lekanne Deprez et al. (1995) isolated a gene, which they designated MN1, that was disrupted by the translocation. The cDNA encoded a protein of 1,319 amino acids when the first methionine in the open reading frame was used. The MN1 cDNA contained 2 sets of CAG repeats, one of which coded for a string of 28 glutamines.
Miyake et al. (2020) found high expression of the MN1 gene in human fetal brain and fetal and adult skeletal muscle. The MN1 protein has an N-terminal nuclear localization signal, proline-rich sequences, and 2 polyglutamine stretches. Miyake et al. (2020) found that MN1 contains a large intrinsically disordered region (IDR) with a prion-like structure, suggesting that the majority of the MN1 protein does not form a fixed tertiary structure. In HeLa cells, MN1 localized to the nucleus and tended to form aggregated patterns.
Lekanne Deprez et al. (1995) determined that the MN1 gene spans about 70 kb and has at least 2 large exons of approximately 4.7 kb and 2.8 kb.
Lekanne Deprez et al. (1995) reported that the MN1 gene maps to chromosome 22q11.
Miyake et al. (2020) stated that the MN1 gene maps to chromosome 22q12.1.
Using immunoprecipitation and mass spectrometry, Miyake et al. (2020) found that MN1 interacts with several transcription factors or regulators, including PBX1 (176310), PKNOX1 (602100), E2F7 (612046), and ZBTB24 (614064), as well as other proteins, such as RING1 (602045) and KIF11 (148760).
In the meningioma analyzed by Lekanne Deprez et al. (1995), the t(4;22) translocation disrupted the 5-prime exon within the open reading frame. No expression of the MN1 mRNA was observed in the tumor. The translocation in this case represented a germline change in a patient with multiple meningiomas (607174) (Lekanne Deprez et al., 1991).
Buijs et al. (1995) showed that the MN1 gene is fused to the TEL gene (600618) in the translocation t(12;22)(p13;q11) that is observed in some patients with acute myeloid leukemia.
In 22 probands with CEBALID syndrome (618774), Mak et al. (2020) identified germline de novo heterozygous nonsense or frameshift mutations in the MN1 gene (see, e.g., 156100.0001; 156100.0003-156100.0005). In addition, 2 affected sibs (patients 5 and 6) inherited a heterozygous nonsense mutation (Q1273X; 156100.0002) from their mildly affected father (patient 7), who was somatic mosaic for the mutation. The patients, ascertained for syndromic intellectual disability or developmental disorders, underwent whole-exome, whole-genome, or Sanger sequencing from 15 independent research or diagnostic laboratories. The first group of variants, which accounted for most of the mutations, occurred in the C terminus at the end of exon 1 or in exon 2, and all were predicted to escape nonsense-mediated mRNA decay. This was confirmed by RNA analysis of fibroblasts derived from 3 of these patients (patient 2, 10, and 21), which showed expression of the mutant transcripts at levels similar to wildtype, indicating escape of nonsense-mediated mRNA decay. Although additional functional studies were not performed, Mak et al. (2020) postulated that a truncated protein is produced in these patients, which may have a dominant-negative or gain-of-function effect. In contrast, 3 patients (patients 24, 25, and 26) had nonsense or frameshift mutations in the N-terminal third of the protein, which were predicted to result in nonsense-mediated mRNA decay, and 2 further patients (patients 27 and 28) had de novo heterozygous deletions of the whole MN1 gene found by array analysis. The mutations or deletions in this second group of patients were predicted to cause MN1 haploinsufficiency, and the phenotype was somewhat different than that observed in the first group of patients.
In 3 unrelated patients with CEBALID syndrome, Miyake et al. (2020) identified de novo heterozygous frameshift or nonsense mutations in the C-terminal region of the MN1 gene (R1295X, 156100.0003; Q1279X, 156100.0006; and c.3846_3849del, 156100.0007). The mutations, which were found by whole-exome sequencing and confirmed by Sanger sequencing, were not found in the Exome Variant Server, ExAC, or gnomAD databases, or in an in-house database of 575 controls. In vitro functional expression studies in HeLa cells showed that mutant MN1 formed larger and more insoluble aggregates compared to wildtype. The mutant proteins were more stable and resistant to ubiquitin-proteasome degradation compared to wildtype, suggesting that the C terminus is required for degradation. The mutant proteins, which maintained transactivation activity, also showed a trend towards stronger inhibition of cell proliferation compared to wildtype, which would be consistent with a gain-of-function effect. The deletion of the C terminus would likely increase the fraction of IDRs and possibly alter phase separation. Immunoprecipitation studies showed that the R1295X mutant protein had impaired interaction with ZBTB24 and no binding to RING1 or E2F7 compared to wildtype, although it showed binding to certain partners that wildtype MN1 did not, including MEIS1 (601739) and PBX2 (176311). Transcriptome analysis of lymphoblastoid cells derived from the patient with the R1295X mutation showed both up- and down-regulation of genes compared to wildtype, suggesting dysregulated transcription of MN1 target genes.
Meester-Smoor et al. (2005) found that Mn1 -/- mice and a small percentage of Mn1 +/- mice died immediately after birth due to cleft secondary palate. The majority of Mn1 +/- mice had no obvious defects and had a normal lifespan. Skulls of Mn1 -/- mice exhibited severe bone abnormalities, with several bones completely absent or hypoplastic. The severity of bone abnormalities was intermediate in Mn1 +/- mice compared with Mn1 -/- and wildtype mice.
By in situ hybridization, Liu et al. (2008) showed that Mn1 expression started around embryonic day 9.5 (E9.5) in mice and persisted throughout early embryogenesis. During palate development, Mn1 exhibited differential expression along the anterior-posterior axis of developing secondary palate, with preferential expression in the middle and posterior regions during palatal outgrowth. Histologic analysis revealed that palatal development required Mn1 function after E13.5, and that Mn1 -/- mice exhibited palatal retardation and failure of palatal shelf elevation starting at E14.5. Mn1 was required for proper palatal shelf growth, with absence of Mn1 resulting in dramatic degeneration of posterior palatal shelves due to decreased proliferation and increased apoptosis of palatal cells. The palatal shelf growth defect in Mn1 -/- mice was accompanied by decreased cyclin D2 (CCND2; 123833) expression at E13.5, indicating that Mn1 regulated palatal shelf growth, at least in part, by maintaining cyclin D2 expression. Mn1 functioned as a transcriptional activator of Tbx22 (300307). Tbx22 exhibited an expression pattern similar to that of Mn1 in wildtype mice, but Tbx22 expression was dramatically reduced in middle and posterior palatal shelves of Mn1 -/- embryos.
In a 7-year-old girl (patient 2) with CEBALID syndrome (618774), Mak et al. (2020) identified a germline heterozygous c.3745G-T transversion (c.3745G-T, NM_002430.2) at the end of exon 1 of the MN1 gene, resulting in a glu1249-to-ter (E1249X) substitution. The mutation, which was found by direct Sanger sequencing, was not present in the unaffected father or in the gnomAD database. DNA from the unaffected mother was not available. RNA analysis of patient fibroblasts showed expression of the mutant transcript at levels similar to wildtype, indicating that it escaped nonsense-mediated mRNA decay. Although additional functional studies were not performed, Mak et al. (2020) postulated that a truncated protein is produced, which may have a dominant-negative or gain-of-function effect.
In 2 brothers (patients 5 and 6) with CEBAID syndrome (618774), Mak et al. (2020) identified a heterozygous c.3817C-T transition (c.3817C-T, NM_002430.2) in exon 2 of the MN1 gene, resulting in a gln1273-to-ter (Q1273X) substitution. The mutation, which was found by trio-based whole-exome sequencing and confirmed by Sanger sequencing, was inherited from the mildly affected father (patient 7), who was somatic mosaic for the mutation. An unrelated patient (patient 4) with a similar phenotype as the brothers, also carried a de novo Q1273X mutation by trio-based whole-exome sequencing. The variant was not found in the gnomAD database. Although functional studies of the variant and studies of patient cells were not performed, it was predicted to escape nonsense-mediated mRNA decay and result in production of a truncated protein with either a dominant-negative or gain-of-function effect.
In 8 unrelated patients (patients 11 through 18) with CEBALID syndrome (618774), Mak et al. (2020) identified a de novo heterozygous c.3883C-T transition (c.3883C-T, NM_002430.2) in exon 2 of the MN1 gene, resulting in an arg1295-to-ter (R1295X) substitution. The mutation, which was found by trio-based whole-exome sequencing and confirmed by Sanger sequencing, was not found in the gnomAD database. Although functional studies of the variant and studies of patient cells were not performed, it was predicted to escape nonsense-mediated mRNA decay and result in production of a truncated protein with either a dominant-negative or gain-of-function effect.
Miyake et al. (2020) identified a de novo heterozygous R1295X mutation in a 6-year-old Japanese boy (patient 1) with CEBALID syndrome. The mutation was found by whole-exome sequencing and confirmed by Sanger sequencing, was not found in the Exome Variant Server, ExAC, or gnomAD databases, or in an in-house database of 575 controls. In vitro functional expression studies in HeLa cells showed that mutant MN1 formed larger and more insoluble aggregates compared to wildtype. The mutant protein was more stable and resistant to ubiquitin-proteasome degradation compared to wildtype, suggesting that the C terminus is required for degradation. The mutant protein, which maintained transactivation activity, also showed a trend towards stronger inhibition of cell proliferation compared to wildtype, which would be consistent with a gain-of-function effect. Immunoprecipitation studies showed that the R1295X mutant protein had impaired interaction with ZBTB24 (614064) and no binding to RING1 (602045) or E2F7 (612046) compared to wildtype, although it showed binding to certain partners that wildtype MN1 did not, including MEIS1 (601739) and PBX2 (176311). Transcriptome analysis of lymphoblastoid cells derived from the patient with the R1295X mutation showed both up- and downregulation of genes compared to wildtype, suggesting dysregulated transcription of MN1 target genes.
In a 10-year-old girl of Han Chinese origin (patient 10) with CEBALID syndrome (618774), Mak et al. (2020) identified a de novo heterozygous 10-bp duplication (c.3870_3879dup, NM_002430.2) in exon 2 of the MN1 gene, resulting in a frameshift and premature termination (Ala1294Ter). The mutation, which was found by whole-exome sequencing and confirmed by Sanger sequencing, was not found in the gnomAD database. RNA analysis of patient fibroblasts showed expression of the mutant transcript at levels similar to wildtype, indicating that it escaped nonsense-mediated mRNA decay. Although additional functional studies were not performed, Mak et al. (2020) postulated that a truncated protein is produced, which may have a dominant-negative or gain-of-function effect.
In 3 unrelated patients (patients 20, 21, and 22) with CEBALID syndrome (618774), Mak et al. (2020) identified a de novo heterozygous c.3903G-A transition (c.3903G-A, NM_002430.2) in exon 2 of the MN1 gene, resulting in a trp1301-to-ter (W1301X) substitution. The mutation, which was found by whole-exome sequencing and confirmed by Sanger sequencing, was not found in the gnomAD database. RNA analysis of fibroblasts derived from patient 21 showed expression of the mutant transcript at levels similar to wildtype, indicating that it escaped nonsense-mediated mRNA decay. Although additional functional studies were not performed, Mak et al. (2020) postulated that a truncated protein is produced, which may have a dominant-negative or gain-of-function effect. Patient 21 had previously been reported by Tully et al. (2012) and Ishak et al. (2012).
In a 5-year-old French girl (patient 2) with CEBALID syndrome (618774), Miyake et al. (2020) identified a de novo heterozygous c.3835C-T transition in exon 2 of the MN1 gene, resulting in a gln1279-to-ter (Q1279X) substitution. The mutation, which was found by whole-exome sequencing and confirmed by Sanger sequencing, was not found in the Exome Variant Server, ExAC, or gnomAD databases, or in an in-house database of 575 controls. In vitro functional expression studies in HeLa cells showed that mutant MN1 formed larger and more insoluble aggregates compared to wildtype. The mutant protein was more stable and resistant to ubiquitin-proteasome degradation compared to wildtype, suggesting that the C terminus is required for degradation. The mutant protein, which maintained transactivation activity, also showed a trend towards stronger inhibition of cell proliferation compared to wildtype, which would be consistent with a gain-of-function effect.
In an 18-year-old Japanese woman (patient 3) with CEBALID syndrome (618774), Miyake et al. (2020) identified a de novo heterozygous 4-bp deletion (c.3846_3849del) in exon 2 of the MN1 gene, resulting in a frameshift and premature termination (Val1283ThrfsTer36). The mutation, which was found by whole-exome sequencing and confirmed by Sanger sequencing, was not found in the Exome Variant Server, ExAC, or gnomAD databases, or in an in-house database of 575 controls. In vitro functional expression studies in HeLa cells showed that mutant MN1 formed larger and more insoluble aggregates compared to wildtype. The mutant protein was more stable and resistant to ubiquitin-proteasome degradation compared to wildtype, suggesting that the C terminus is required for degradation. The mutant protein, which maintained transactivation activity, also showed a trend towards stronger inhibition of cell proliferation compared to wildtype, which would be consistent with a gain-of-function effect.
Buijs, A., Sherr, S., van Baal, S., van Bezouw, S., van der Plas, D., Geurts van Kessel, A., Riegman, P., Lekanne Deprez, R., Zwarthoff, E., Hagemeijer, A., Grosveld, G. Translocation (12;22)(p13;q11) in myeloproliferative disorders results in fusion of the ETS-like TEL gene on 12q13 to the MN1 gene on 22q11. Oncogene 10: 1511-1519, 1995. Note: Erratum: Oncogene 11: 809 only, 1995. [PubMed: 7731705]
Ishak, G. E., Dempsey, J. C., Shaw, D. W. W., Tully, H., Adam, M. P., Sanchez-Lara, P. A., Glass, I., Rue, T. C., Millen, K. J., Dobyns, W. B., Doherty, D. Rhombencephalosynapsis: a hindbrain malformation associated with incomplete separation of midbrain and forebrain, hydrocephalus and a broad spectrum of severity. Brain 135: 1370-1386, 2012. [PubMed: 22451504] [Full Text: https://doi.org/10.1093/brain/aws065]
Lekanne Deprez, R. H., Groen, N. A., van Biezen, N. A., Hagemeijer, A., van Drunen, E., Koper, J. W., Avezaat, C. J. J., Bootsma, D., Zwarthoff, E. C. A t(4;22) in a meningioma points to the localization of a putative tumor-suppressor gene. Am. J. Hum. Genet. 48: 783-790, 1991. [PubMed: 2014801]
Lekanne Deprez, R. H., Riegman, P. H. J., Groen, N. A., Warringa, U. L., van Biezen, N. A., Molijn, A. C., Bootsma, D., de Jong, P. J., Menon, A. G., Kley, N. A., Seizinger, B. R., Zwarthoff, E. C. Cloning and characterization of MN1, a gene from chromosome 22q11, which is disrupted by a balanced translocation in a meningioma. Oncogene 10: 1521-1528, 1995. [PubMed: 7731706]
Liu, W., Lan, Y., Pauws, E., Meester-Smoor, M. A., Stanier, P., Zwarthoff, E. C., Jiang, R. The Mn1 transcription factor acts upstream of Tbx22 and preferentially regulates posterior palate growth in mice. Development 135: 3959-3968, 2008. [PubMed: 18948418] [Full Text: https://doi.org/10.1242/dev.025304]
Mak, C. C. Y., Doherty, D., Lin, A. E., Vegas, N., Cho, M. T., Viot, G., Dimartino, C., Weisfeld-Adams, J. D., Lessel, D., Joss, S., Li, C., Gonzaga-Jauregui, C., and 71 others. MN1 C-terminal truncation syndrome is a novel neurodevelopmental and craniofacial disorder with partial rhombencephalosynapsis. Brain 143: 55-68, 2020. Note: Erratum: Brain 143: e24, 2020. [PubMed: 31834374] [Full Text: https://doi.org/10.1093/brain/awz379]
Meester-Smoor, M. A., Vermeij, M., van Helmond, M. J. L., Molijn, A. C., van Wely, K. H. M., Hekman, A. C. P., Vermey-Keers, C., Riegman, P. H. J., Zwarthoff, E. C. Targeted disruption of the Mn1 oncogene results in severe defects in development of membranous bones of the cranial skeleton. Molec. Cell. Biol. 25: 4229-4236, 2005. [PubMed: 15870292] [Full Text: https://doi.org/10.1128/MCB.25.10.4229-4236.2005]
Miyake, N., Takahashi, H., Nakamura, K., Isidor, B., Hiraki, Y., Koshimizu, E., Shiina, M., Sasaki, K., Suzuki, H., Abe, R., Kimura, Y., Akiyama, T., and 11 others. Gain-of-function MN1 truncation variants cause a recognizable syndrome with craniofacial and brain anomalies. Am. J. Hum. Genet. 106: 13-25, 2020. [PubMed: 31839203] [Full Text: https://doi.org/10.1016/j.ajhg.2019.11.011]
Tully, H. M., Dempsey, J. C., Ishak, G. E., Adam, M. P., Curry, C. J. R., Sanchez-Lara, P., Hunter, A., Gripp, K. W., Allanson, J., Cunniff, C., Glass, I., Millen, K. J., Doherty, D., Dobyns, W. B. Beyond Gomez-Lopez-Hernandez syndrome: recurring phenotypic themes in rhombencephalosynapsis. Am. J. Med. Genet. 158A: 2393-2406, 2012. [PubMed: 22965664] [Full Text: https://doi.org/10.1002/ajmg.a.35561]