Alternative titles; symbols
HGNC Approved Gene Symbol: CFL2
Cytogenetic location: 14q13.1 Genomic coordinates (GRCh38) : 14:34,709,113-34,714,593 (from NCBI)
| Location | Phenotype |
Phenotype MIM number |
Inheritance |
Phenotype mapping key |
|---|---|---|---|---|
| 14q13.1 | Nemaline myopathy 7, autosomal recessive | 610687 | Autosomal recessive | 3 |
Cofilin is a widely distributed intracellular actin-modulating protein that binds and depolymerizes filamentous F-actin and inhibits the polymerization of monomeric G-actin in a pH-dependent manner. (Gillett et al., 1996). Cofilin-2 is a member of the AC group of proteins that also includes cofilin-1 (CFL1; 601442) and destrin (DSTN; 609114), all of which regulate actin-filament dynamics (Bamburg et al., 1999; Maciver and Hussey, 2002). The CFL2 gene encodes a skeletal muscle-specific isoform (Vartiainen et al., 2002) localized to the thin filaments, where it exerts its effect on actin, in part through interactions with tropomyosins (Ono and Ono, 2002).
Ono et al. (1994) cloned mouse Cfl2, which they called M-type cofilin. The deduced protein contains 166 amino acids and has a calculated molecular mass of 18.7 kD. It shares 81.3% amino acid identity with mouse brain cofilin (CFL1). Cfl2 has an N-terminal nuclear localization signal, followed by an actin- and phosphoinositide-binding site and a region homologous to the N-terminal sequence of tropomyosin (see 191010). Northern blot analysis of mouse tissues detected Cfl2 transcripts of 1.8 and 3.0 kb in heart, skeletal muscle, and testis. Among mouse cell lines, high expression was detected in 3Y1 fibroblasts, C2 myogenic cells, and A10 smooth muscle cells. The amount of Cfl2 expressed in C2 cells increased during differentiation from myoblasts to myotubes.
By RT-PCR using primers based on murine Cfl2, Thirion et al. (2001) cloned 4 CFL2 variants from human fetal and adult myoblasts. The transcripts differ in their 5-prime and 3-prime ends, but have identical coding regions, due to alternative splicing of the first exon and the use of alternative polyadenylation signals. The deduced 166-amino acid CFL2 protein has a calculated molecular mass of 19 kD and shares 99% and 81% identity with mouse Cfl2 and human CFL1, respectively. Northern blot analysis detected 2 major CLF2 transcripts that were highly expressed in heart and skeletal muscle, with weaker expression in all other tissues examined. Primary human myoblasts and myotubes expressed transcripts of 1.55, 1.65, and 3.2 kb. Immunohistochemical analysis of murine and human skeletal muscle localized CFL2 in a uniform cytoplasmic distribution characteristic of sarcomeric proteins. Western blot analysis of healthy mouse muscle showed that 30 to 50% of Cfl2 was phosphorylated.
Agrawal et al. (2012) stated that mouse Cfl2 is expressed as 1.8- and 3.0-kb transcripts that differ in their 3-prime UTRs only and are alternately expressed during striated muscle development. The 1.8-kb transcript is expressed at embryonic day 13, peaks in skeletal and cardiac muscle at birth, and decreases thereafter. The 3.0-kb transcript is expressed in skeletal muscle only, and its expression increases as expression of the 1.8-kb transcript decreases.
By RT-PCR analysis, Rosen et al. (2020) identified 3 Cfl2 splice variants in mouse: a predominantly expressed full-length transcript, and 2 shorter transcripts that were expressed at low levels.
Thirion et al. (2001) determined that the CFL2 gene contains 5 exons, including alternative first exons (exons 1a and 1b) that encode the initiating methionine only. Identification of transcription factor-binding sites upstream of exons 1a and 1b suggested the presence of 2 promoters. CFL2 has 2 polyadenylation signals.
Gillett et al. (1996) mapped CFL2, the human muscle-type (M-type) cofilin, to chromosome 14 by analysis of a somatic cell hybrid panel using an expressed sequence tag (EST) with homology to the mouse muscle-type cofilin and chicken cofilin.
Agrawal et al. (2012) stated that the CFL2 gene maps to chromosome 14q12.
By Western blot analysis of 2-dimensional gels, Thirion et al. (2001) found that expression of Clf2 decreased sharply and that phosphorylated Cfl2 became undetectable following acute muscle damage in mice. Skeletal muscle of Duchenne muscular dystrophy (310200) patients and dystrophin (DMD; 300377)-deficient mdx mice, where continuous muscle degeneration and regeneration occurs, showed a similar phenomenon.
Agrawal et al. (2007) used genomic PCR and DNA sequencing to screen the CFL2 gene in 113 unrelated patients with nemaline myopathy and 58 patients with clinical pathologic diagnoses of other congenital myopathies. None of the patients had known mutations in previously identified genes. In 2 sibs with nemaline myopathy (NEM7; 610687) in a large family of Middle Eastern origin, Agrawal et al. (2007) identified a homozygous mutation in the CFL2 gene (A35T; 601443.0001). The proband's muscle contained characteristic nemaline bodies, as well as occasional fibers with minicores, concentric laminated bodies, and areas of F-actin accumulation. Cofilin-2 levels were significantly lower in the proband's muscle, and the mutant protein was less soluble when expressed in Escherichia coli, suggesting that deficiency of cofilin-2 may result in reduced depolymerization of actin filaments, causing their accumulation in nemaline bodies, minicores, and, possibly concentric laminated bodies.
In 2 Iraqi sisters, born of consanguineous parents, with nemaline myopathy-7, Ockeloen et al. (2012) identified a homozygous missense mutation in the CFL2 gene (V7M; 601443.0002). The mutation was found by homozygosity mapping followed by candidate gene sequencing.
Agrawal et al. (2012) found that Cfl2 -/- mice were indistinguishable from wildtype at birth. However, by postnatal day 3, Cfl2 -/- mice showed reduced size and activity, followed by rapid deterioration and death by postnatal day 8. Presence of milk in stomachs of Cfl2 -/- mice at postnatal day 3, but not at postnatal day 7, suggested that the older animals had lost the ability to suckle. Targeted disruption of Cfl2 to skeletal or cardiac muscle resulted in a phenotype that was only modestly less severe. Electron microscopic analysis revealed ballooning degeneration of skeletal muscle fibers, core-like lesions, extensive sarcomeric disruption, nemaline bodies, and actin accumulation. Cardiac muscle fibers did not show evidence of degeneration. Muscle degeneration and weakness in Cfl2 -/- mice coincided with normal developmental depletion of Cfl1 in myofibers. Agrawal et al. (2012) hypothesized that Cfl1 may initiate myofibrillogenesis, whereas Cfl2 is required for myofiber maintenance.
Rosen et al. (2020) found that knockin mice homozygous for the A35T mutation in Cfl2 associated with congenital myopathy in human were born at the expected mendelian ratio and were indistinguishable from wildtype. However, mutant mice began to display growth defects by postnatal day-3 (P3), and all died by P9. Mutant mice had lower body weight and shorter average length than controls and displayed disrupted early postnatal muscle maintenance and abnormal muscle structure. Western blot analysis revealed that Cfl2 protein was absent in several organs of mutant mice, including skeletal muscle, heart, brain, lung, and kidney, whereas skeletal actin (see 102610) was increased in skeletal muscle and heart. Further analysis demonstrated that a splicing defect in mutant mice resulted in significant upregulation of the short Cfl2 splice variant with concomitant and marked reduction of the full-length transcript. Similar alternative splicing was observed in human, with patients with the A35T mutation displaying marked reduction of the full-length CFL2 transcript.
In 2 sisters in a family of Middle Eastern origin, Agrawal et al. (2007) found that nemaline myopathy with some unusual histopathologic and clinical features (NEM7; 610687) was related to homozygous mutation of the CFL2 gene, 103G-A, predicted to result in an alanine-to-threonine substitution at residue 35 (A35T). An unaffected sib, both unaffected parents, and a number of other members of the extended family were heterozygous for this change. Extensive intermarriage, with multiple consanguinity loops, strongly suggested identity by descent for the 2 mutant alleles, a supposition that was supported by linkage studies using flanking markers. The mutation was ruled out in 282 unaffected control individuals, including 91 originating from the same geographic region and ethnic group as the family.
In 2 Iraqi sisters, born of consanguineous parents, with nemaline myopathy-7 (NEM7; 610687), Ockeloen et al. (2012) identified a homozygous c.19G-A transition in exon 2 of the CFL2 gene, resulting in a val7-to-met (V7M) substitution at a highly conserved residue. The mutation was found by homozygosity mapping followed by candidate gene sequencing. The unaffected parents were heterozygous for the mutation, which was not found in 250 controls or in dbSNP. Functional studies were not performed. The girls had delayed walking and proximal and axial muscle weakness; muscle biopsy showed nemaline rods and abnormal protein aggregates.
Agrawal, P. B., Greenleaf, R. S., Tomczak, K. K., Lehtokari, V.-L., Wallgren-Pettersson, C., Wallefeld, W., Laing, N. G., Darras, B. T., Maciver, S. K., Dormitzer, P. R., Beggs, A. H. Nemaline myopathy with minicores caused by mutation of the CFL2 gene encoding the skeletal muscle actin-binding protein, cofilin-2. Am. J. Hum. Genet. 80: 162-167, 2007. [PubMed: 17160903] [Full Text: https://doi.org/10.1086/510402]
Agrawal, P. B., Joshi, M., Savic, T., Chen, Z., Beggs, A. H. Normal myofibrillar development followed by progressive sarcomeric disruption with actin accumulations in a mouse Cfl2 knockout demonstrates requirement of cofilin-2 for muscle maintenance. Hum. Molec. Genet. 21: 2341-2356, 2012. [PubMed: 22343409] [Full Text: https://doi.org/10.1093/hmg/dds053]
Bamburg, J. R., McGough, A., Ono, S. Putting a new twist on actin: ADF/cofilins modulate actin dynamics. Trends Cell Biol. 9: 364-370, 1999. [PubMed: 10461190] [Full Text: https://doi.org/10.1016/s0962-8924(99)01619-0]
Gillett, G. T., Fox, M. F., Rowe, P. S. N., Casimir, C. M., Povey, S. Mapping of human non-muscle type cofilin (CFL1) to chromosome 11q13 and muscle-type cofilin (CFL2) to chromosome 14. Ann. Hum. Genet. 60: 201-211, 1996. [PubMed: 8800436] [Full Text: https://doi.org/10.1111/j.1469-1809.1996.tb00423.x]
Maciver, S. K., Hussey, P. J. The ADF/cofilin family: actin-remodeling proteins. Genome Biol. 3: reviews3007, 2002. Note: Electronic Article. [PubMed: 12049672] [Full Text: https://doi.org/10.1186/gb-2002-3-5-reviews3007]
Ockeloen, C. W., Gilhuis, H. J., Pfundt, R., Kamsteeg, E. J., Agrawal, P. B., Beggs, A. H., Dara Hama-Amin, A., Diekstra, A., Knoers, N. V. A. M., Lammens, M., van Alfen, N. Congenital myopathy caused by a novel missense mutation in the CFL2 gene. Neuromusc. Disord. 22: 632-639, 2012. [PubMed: 22560515] [Full Text: https://doi.org/10.1016/j.nmd.2012.03.008]
Ono, S., Minami, N., Abe, H., Obinata, T. Characterization of a novel cofilin isoform that is predominantly expressed in mammalian skeletal muscle. J. Biol. Chem. 269: 15280-15286, 1994. [PubMed: 8195165]
Ono, S., Ono, K. Tropomyosin inhibits ADF/cofilin-dependent actin filament dynamics. J. Cell Biol. 156: 1065-1076, 2002. Note: Erratum: J. Cell Biol. 157: 727 only, 2002. [PubMed: 11901171] [Full Text: https://doi.org/10.1083/jcb.200110013]
Rosen, S. M., Joshi, M., Hitt, T., Beggs, A. H., Agrawal, P. B. Knockin mouse model of the human CFL2 p.A35T mutation results in a unique splicing defect and severe myopathy phenotype. Hum. Molec. Genet. 29: 1996-2003, 2020. [PubMed: 32160286] [Full Text: https://doi.org/10.1093/hmg/ddaa035]
Thirion, C., Stucka, R., Mendel, B., Gruhler, A., Jaksch, M., Nowak, K. J., Binz, N., Laing, N. G., Lochmuller, H. Characterization of human muscle type cofilin (CFL2) in normal and regenerating muscle. Europ. J. Biochem. 268: 3473-3482, 2001. [PubMed: 11422377] [Full Text: https://doi.org/10.1046/j.1432-1327.2001.02247.x]
Vartiainen, M. K., Mustonen, T., Mattila, P. K., Ojala, P. J., Thesleff, I., Partanen, J., Lappalainen, P. The three mouse actin-depolymerizing factor/cofilins evolved to fulfill cell-type-specific requirements for actin dynamics. Molec. Biol. Cell 13: 183-194, 2002. [PubMed: 11809832] [Full Text: https://doi.org/10.1091/mbc.01-07-0331]