Alternative titles; symbols
HGNC Approved Gene Symbol: MFAP2
Cytogenetic location: 1p36.13 Genomic coordinates (GRCh38): 1:16,974,502-16,981,583 (from NCBI)
The extracellular matrix (ECM) contains a heterogeneous population of 3- to 20-nanometer filaments that Low (1962) termed microfibrils. Microfibrils 10 nm in diameter are present in elastic and nonelastic tissues and have a similar, if not identical, structure and composition. Gibson et al. (1986) identified an acidic glycoprotein of 31 kD, termed microfibril-associated glycoprotein (MAGP), as a major antigen of elastin-associated microfibrils in fetal bovine nuchal ligament extracts. Other elastin-associated microfibril components include fibrillin (see FBN1; 134797) and emilin (see 130660).
Chen et al. (1993) cloned mouse Mfap2, which they called Magp. The deduced 185-amino acid protein has an N-terminal half rich in glutamine, proline, aspartic acid, and glutamic acid and a C-terminal half with 13 conserved cysteines. In situ hybridization demonstrated widespread expression of the mouse Magp transcript in mesenchymal/connective tissue cells throughout mouse development.
A human MFAP2 cDNA was cloned by Faraco et al. (1995) from a human lung cDNA library using a human probe initially identified with primers from the bovine Mfap2 gene. The deduced 183-amino acid protein is highly similar to bovine and murine proteins, including a conserved stretch of 5 glutamines and 13 conserved cysteines in the C-terminal half that are predicted to form intermolecular and intramolecular disulfide bonds.
By EST database analysis, Segade et al. (2000) identified 4 splice variants of human MAGP1. The most abundant variant, MAGP1A, corresponds to that identified by Faraco et al. (1995). The MAGP1B variant skips exon 3 and encodes a deduced 153-amino acid intracellular protein lacking the C-terminal end of the signal peptide and the signal peptidase site found in the full-length protein. MAGP1C includes 102 bp of intronic sequence, which introduces a premature stop codon after residue 58. MAGP1A-prime uses an alternate splice site at exon 3, resulting in deletion of ala13 within the putative MAGP1 signal peptide. PCR analysis detected variable expression of MAGP1A and MAGP1B in most of the 23 human tissues examined. MAGP1A was the most abundant splice variant in most tissues. MAGP1B was the only variant detected in spleen, liver, colon, and peripheral leukocytes, and MAGP1A and MAGP1B showed similar expression in placenta. MAGP1C was detected in placenta following extended amplification. Magp1 was also expressed in all mouse tissues examined; however, mouse displayed a different complement of splice variants, including Magp1d, which was not detected in human tissues.
Segade et al. (2002) found that full-length, fluorescence-tagged human MAGP1A was secreted from transfected RFL-6 rat lung fibroblasts and decorated fibrils of the ECM. Both fluorescence-tagged MAGP1B and mouse Magp1d were retained intracellularly.
Chen et al. (1993) demonstrated that the mouse Magp gene has 9 exons with the initiator codon located in exon 2.
Faraco et al. (1995) determined that the human MFAP2 gene, like the bovine and murine homologs, contains 8 coding exons. However, it also contains 2 alternatively used 5-prime untranslated exons, compared with 1 in each of the other species.
Segade et al. (2000) determined that the MFAP2 gene contains 9 exons and spans at least 6.1 kb. The 5-prime region contains no TATA box, but it has an 800-bp CG-rich section and a single transcription start site within a loose consensus initiator element. There are 4 binding sites for SP1 (189906) and several binding sites for inducible factors. The upstream region also contains several repetitive elements, including total and partial SINE sequences, 2 partial LINE-2 elements, and 2 solitary retroviral long terminal repeats. Segade et al. (2000) found no evidence for an alternative first exon.
Faraco et al. (1995) mapped the MFAP2 gene to chromosome 1p36.1-p35 using rodent-human somatic cell hybrids and fluorescence in situ hybridization. They used a polymorphism in intron 7 to demonstrate tight linkage to the marker D1S170 with a physical distance between the 2 of under 100 kb.
Chen et al. (1993) demonstrated that the mouse Magp gene is on chromosome 4 by analysis of somatic cell hybrid lines and by fluorescence in situ hybridization. This region of mouse chromosome 4 is syntenic to human chromosome 1p36.1-p35.
By mutation analysis, Segade et al. (2002) identified a 54-amino acid C-terminal domain within full-length human MAGP1A that was required for binding of MAGP1A to ECM. Deletion of this domain or mutation of any of its 7 cysteines abrogated binding of fluorescence-tagged MAGP1A to ECM. Mutation of other residues had no effect on MAGP1A secretion or binding to ECM. In contrast, fluorescence-tagged MAGP2 (MFAP5; 601103) was secreted from transfected cells but did not bind ECM. Segade et al. (2002) noted that MAGP2 contains only 6 cysteines within its putative ECM-binding domain. They found that substitution of val101 with cys in MAGP2 permitted association of MAGP2 with ECM. Segade et al. (2002) concluded that the presence of an odd number of cysteines in the ECM-binding domain of MAGP1A may permit disulfide bond formation between MAGP1A and its ligand in the ECM.
Using solid-phase binding assays, Hanssen et al. (2004) found that purified fetal bovine Magp1 and Magp2 showed distinct patterns of binding to recombinant human FBN1 and FBN2 (612570). Both bound the same central region of FBN1, but they also bound distinct N-terminal sites of FBN1. Immunogold labeling of developing bovine nuchal ligament revealed regular covalent and periodic association of Magp2 with fibrillin-containing microfibrils and that Magp2 was attached at 2 distinct points. In contrast, Magp1 had only a single attachment site.
Using bovine and human constructs in protein interaction assays, Werneck et al. (2004) found that the cysteine-rich matrix-binding domain of MAGP1 interacted with a central 8-cysteine motif of FBN2. The matrix-binding domain, but not full-length MAGP1, also bound to several other regions of FBN2.
Using a gene expression array, Segade et al. (2007) found that stable expression of intracellular MAGP1B in SAOS-2 cells caused significant upregulation of 67 genes and downregulation of 8 genes. The most highly upregulated gene was CSPG2 (VCAN; 118661), which encodes a protein involved in the structure and function of extracellular matrix, and the most significantly downregulated gene was CSTF2 (300907), which encodes a factor required for 3-prime end cleavage of pre-mRNAs. RT-PCR analysis of SAOS-2 cells overexpressing MAGP1B revealed upregulation of all 4 CSPG2 splice variants.
Weinbaum et al. (2008) found that Magp1 -/- mice were viable and largely fertile with normal litter size. However, a complex spectrum of phenotypes developed that were variably penetrant and dependent on genetic background. On a mixed genetic background, Magp1 -/- mice showed variable penetrance of increased body size, several bone abnormalities, and male sterility associated with testicular hydrocele and inverted seminal vesicles. On the C57 background, Magp1 -/- mice showed normal body size and no bone abnormalities. On either background, Magp1 -/- mice showed reduced platelet number, bleeding diathesis, and delayed wound healing. Elastin-rich tissues showed normal structure and function in all Magp1 -/- animals, and Magp1 -/- skin fibroblasts assembled a normal elastin matrix in culture.
Chen, Y., Faraco, J., Yin, W., Germiller, J., Francke, U., Bonadio, J. Structure, chromosomal localization, and expression pattern of the murine Magp gene. J. Biol. Chem. 268: 27381-27389, 1993. [PubMed: 8262979]
Faraco, J., Bashir, M., Rosenbloom, J., Francke, U. Characterization of the human gene for microfibril-associated glycoprotein (MFAP2), assignment to chromosome 1p36.1-p35, and linkage to D1S170. Genomics 25: 630-637, 1995. [PubMed: 7759096] [Full Text: https://doi.org/10.1016/0888-7543(95)80004-6]
Gibson, M. A., Hughes, J. L., Fanning, J. C., Cleary, E. G. The major antigen of elastin-associated microfibrils is a 31-kDa glycoprotein. J. Biol. Chem. 261: 11429-11436, 1986. [PubMed: 3015971]
Hanssen, E., Hew, F. H., Moore, E., Gibson, M. A. MAGP-2 has multiple binding regions on fibrillins and has covalent periodic association with fibrillin-containing microfibrils. J. Biol. Chem. 279: 29185-29194, 2004. [PubMed: 15131124] [Full Text: https://doi.org/10.1074/jbc.M313672200]
Low, F. N. Microfibrils: fine filamentous components of the tissue space. Anat. Rec. 142: 131-137, 1962. [PubMed: 14466918] [Full Text: https://doi.org/10.1002/ar.1091420205]
Segade, F., Broekelmann, T. J., Pierce, R. A., Mecham, R. P. Revised genomic structure of the human MAGP1 gene and identification of alternate transcripts in human and mouse tissues. Matrix Biol. 19: 671-682, 2000. [PubMed: 11102756] [Full Text: https://doi.org/10.1016/s0945-053x(00)00115-3]
Segade, F., Suganuma, N., Mychaleckyj, J. C., Mecham, R. P. The intracellular form of human MAGP1 elicits a complex and specific transcriptional response. Int. J. Biochem. Cell Biol. 39: 2303-2313, 2007. [PubMed: 17692555] [Full Text: https://doi.org/10.1016/j.biocel.2007.06.017]
Segade, F., Trask, B. C., Broekelmann, T. J., Pierce, R. A., Mecham, R. P. Identification of a matrix-binding domain in MAGP1 and MAGP2 and intracellular localization of alternative splice forms. J. Biol. Chem. 277: 11050-11057, 2002. [PubMed: 11796718] [Full Text: https://doi.org/10.1074/jbc.M110347200]
Weinbaum, J. S., Broekelmann, T. J., Pierce, R. A., Werneck, C. C., Segade, F., Craft, C. S., Knutsen, R. H., Mecham, R. P. Deficiency in microfibril-associated glycoprotein-1 leads to complex phenotypes in multiple organ systems. J. Biol. Chem. 283: 25533-25543, 2008. [PubMed: 18625713] [Full Text: https://doi.org/10.1074/jbc.M709962200]
Werneck, C. C., Trask, B. C., Broekelmann, T. J., Trask, T. M., Ritty, T. M., Segade, F., Mecham, R. P. Identification of a major microfibril-associated glycoprotein-1-binding domain in fibrillin-2. J. Biol. Chem. 279: 23045-23051, 2004. [PubMed: 15044481] [Full Text: https://doi.org/10.1074/jbc.M402656200]