| *605906 | |||||||||||||||||||||||||||||||||
| LIM DOMAIN-BINDING 3; LDB3 | |||||||||||||||||||||||||||||||||
| Alternative titles; symbols | |||||||||||||||||||||||||||||||||
| Z-BAND ALTERNATIVELY SPLICED PDZ MOTIF-CONTAINING PROTEIN; ZASP CYPHER, MOUSE, HOMOLOG OF; CYPHER KIAA0613 | |||||||||||||||||||||||||||||||||
| HGNC Approved Gene Symbol: LDB3 | |||||||||||||||||||||||||||||||||
| Cytogenetic location: 10q23.2 Genomic coordinates (GRCh37): 10:88,428,205 - 88,495,824 (from NCBI) | |||||||||||||||||||||||||||||||||
| Gene Phenotype Relationships | |||||||||||||||||||||||||||||||||
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| TEXT | |||||||||||||||||||||||||||||||||
| For general information on LIM domain-binding factors, see LDB2 (603450). | |||||||||||||||||||||||||||||||||
| Cloning | |||||||||||||||||||||||||||||||||
| By screening a muscle cDNA library using a muscle EST sequence as the probe, Faulkner et al. (1999) obtained cDNAs encoding mouse and human ZASP. The deduced 283-amino acid human ZASP protein has an 85-residue N-terminal PDZ domain and shares significant similarity with the 734-amino acid protein encoded by the KIAA0613 cDNA isolated by Ishikawa et al. (1998). Database, PCR, and genomic DNA analyses indicated the presence of alternatively spliced isoforms of ZASP that encode proteins of 470, 617, and 727 (KIAA0613) amino acids. Northern blot analysis detected a major 1.9-kb ZASP transcript that was most abundant in skeletal muscle and heart but absent in other tissues tested. Additional transcripts of 4.0 and 5.4 kb were detected when using a 5-prime rather than a 3-prime probe. RT-PCR analysis detected wide expression of KIAA0613, with weak or undetectable expression in liver, pancreas, and spleen (Ishikawa et al., 1998). Western blot analysis showed expression of 32- and 78-kD proteins in heart and muscle. Immunofluorescence microscopy demonstrated that ZASP was expressed in pseudopodia and in the cytoplasm around the nucleus, and that it colocalized with actin in the I-band. Immunoelectron microscopy localized ZASP within the Z-band. Zhou et al. (1999) identified splice variants of the mouse homolog of ZASP, which they termed termed Cypher1 (723 residues) and Cypher2 (288 residues). The longer variant has a LIM domain that interacts with protein kinase C (see 176982). Huang et al. (2003) identified 6 isoforms of mouse Cypher, including the 2 isoforms identified by Zhou et al. (1999). The 6 isoforms could be divided into skeletal- or cardiac-specific classes based on the inclusion of skeletal- or cardiac-specific domains following the common N-terminal PDZ domain. Each class contains a short isoform and 2 long isoforms. The long isoforms in each class differ from one another in the sequence following the cardiac- or skeletal-specific domain, but both have 3 C-terminal LIM domains. Huang et al. (2003) found that expression of the Cypher isoforms was developmentally regulated. One long isoform predominated in mouse heart throughout development, but in skeletal muscle, the predominant long isoform switched during maturation of embryonic to neonatal skeletal muscle. The skeletal- and cardiac-specific short isoforms were only expressed postnatally. | |||||||||||||||||||||||||||||||||
| Gene Structure | |||||||||||||||||||||||||||||||||
| Vatta et al. (2003) determined that the LDB3 gene consists of 16 exons and spans approximately 70 kb. Huang et al. (2003) determined that the mouse Cypher gene contains 17 exons. The cardiac-specific region is encoded by exon 4, and the skeletal muscle-specific region is encoded by exons 5 through 7. Exon 7 is skipped in one of the skeletal muscle splice variants. | |||||||||||||||||||||||||||||||||
| Mapping | |||||||||||||||||||||||||||||||||
| By radiation hybrid analysis, Ishikawa et al. (1998) mapped the KIAA01613 gene, or ZASP, to chromosome 10. Using PCR and radiation hybrid analysis, Faulkner et al. (1999) localized the ZASP gene to 10q22.2-q23.3, near the locus for infantile-onset spinocerebellar ataxia (IOSCA; 271245). | |||||||||||||||||||||||||||||||||
| Gene Function | |||||||||||||||||||||||||||||||||
| PDZ domain-containing proteins interact with each other in cytoskeletal assembly or with other proteins involved in targeting and clustering of membrane proteins. By yeast 2-hybrid analysis, Faulkner et al. (1999) determined that the PDZ domain of ZASP interacts with the C terminus of alpha-actinin-2 (ACTN2; 102573). By yeast 2-hybrid analysis, Frey and Olson (2002) showed that ZASP interacted strongly with MYOZ1 (605603), MYOZ2 (605602), and MYOZ3 (610735). Coimmunoprecipitation studies in COS-7 cells showed that both the longest and shortest ZASP splice variants bind all 3 members of the myozenin family, suggesting that the interaction is not isoform specific. | |||||||||||||||||||||||||||||||||
| Molecular Genetics | |||||||||||||||||||||||||||||||||
| In 11 of 54 unrelated patients with myofibrillar myopathy (609452), Selcen and Engel (2005) identified 3 different heterozygous mutations in the ZASP gene (605906.0001-605906.0003). Vatta et al. (2003) evaluated the role of Cypher/ZASP in the pathogenesis of dilated cardiomyopathy with or without noncompaction of the left ventricular myocardium (see CMD1C, 601493). They screened 100 probands with left ventricular dysfunction and identified heterozygosity for 5 missense mutations in the LDB3 gene (605906.0004-605096.0008) in 6 probands (6%), 2 of whom had CMD alone and 4 of whom also had left ventricular noncompaction. None of the mutations were found in 200 ethnically matched controls. By in vitro studies, they showed cytoskeleton disarray in cells transfected with mutated Cypher/ZASP. Arimura et al. (2004) searched for LDB3 mutations in 96 unrelated Japanese patients with dilated cardiomyopathy who were negative for mutation in 11 other cardiomyopathy-related genes. A heterozygous missense mutation (D626N; 605906.0009) was identified in a late-onset familial case. The authors demonstrated that the D626N mutation increased the affinity of the LIM domain for protein kinase C, suggesting a novel biochemical mechanism of the pathogenesis of dilated cardiomyopathy. In 4 affected members of 2 unrelated Japanese families with left ventricular noncompaction (LVNC3; see 601493), Xing et al. (2006) identified heterozygosity for the D626N substitution. | |||||||||||||||||||||||||||||||||
| Animal Model | |||||||||||||||||||||||||||||||||
| Huang et al. (2003) found that Cypher-null mice died within the first week of birth. Knockin of either a short or long skeletal muscle-specific isoform rescued the lethal phenotype, although the surviving mice exhibited muscle pathology. Zhou et al. (2001) found that homozygous Cypher-null mice were either not viable or died by postnatal day 5 from respiratory insufficiency. The mice also showed limb weakness, inability to suckle, and right and left cardiac ventricular dilatation. Ultrastructural examination showed that active skeletal and cardiac muscle of the mutant mice displayed disorganized and fragmented Z lines, whereas noncontracting embryonic muscles had normal Z line structure. The findings were consistent with a myopathy, not a muscular dystrophy, suggesting that Cypher is required for striated muscle function and maintenance during the stress of contraction, but not for initial formation of the Z line. In vitro studies showed that individual domains within Cypher localize independently to the Z line. Targeted deletion studies showed that the Cypher PDZ domain binds to the last 3 amino acids of the ACTN2 C terminus. Zhou et al. (2001) concluded that Cypher acts as a linker-strut in muscle and suggested that mutations in the human ZASP gene could result in congenital myopathies with cardiac involvement. Zheng et al. (2009) showed that cardiac-specific Cypher knockout (CKO) mice developed a severe form of dilated cardiomyopathy (DCM) with disrupted cardiomyocyte ultrastructure and decreased cardiac function, which eventually led to death before 23 weeks of age. A similar phenotype was observed in inducible cardiac-specific CKO mice in which Cypher was specifically ablated in adult myocardium. In both cardiac-specific CKO models, ERK (EPHB2; 600997) and Stat3 (102582) signaling pathways were augmented. Yeast 2-hybrid assay and Western blot analysis demonstrated specific binding of the Cypher PDZ domain to the C-terminal region of both calsarcin-1 (MYOZ2; 605602) and myotilin (TTID; 604103) within the Z line. Zheng et al. (2009) suggested that Cypher plays a pivotal role in maintaining adult cardiac structure and cardiac function through protein-protein interactions with other Z-line proteins, and specific signaling pathways participate in Cypher mutant-mediated dysfunction of the heart, and may in concert facilitate the progression to heart failure. | |||||||||||||||||||||||||||||||||
| ALLELIC VARIANTS (Selected Examples): | |||||||||||||||||||||||||||||||||
| Table View | |||||||||||||||||||||||||||||||||
| .0001 MYOPATHY, MYOFIBRILLAR, ZASP-RELATED | |||||||||||||||||||||||||||||||||
| LDB3, ALA147THR [dbSNP:rs121908333] | |||||||||||||||||||||||||||||||||
| In 7 unrelated patients with myofibrillar myopathy (609452), Selcen and Engel (2005) identified a heterozygous 464G-A transition in exon 6 of the LDB3 gene, resulting in an ala147-to-thr (A147T) substitution in a conserved region immediately before the ZM motif needed for interaction with alpha-actinin (see, e.g., ACTN1, 102575). Five patients had a family history of the disorder; the A147T mutation was identified in affected family members of 1 proband. All patients had progressive proximal and/or distal weakness, 3 patients had cardiac involvement, and 2 had evidence of peripheral neuropathy. The mutation was not identified in 220 control alleles. | |||||||||||||||||||||||||||||||||
| .0002 MYOPATHY, MYOFIBRILLAR, ZASP-RELATED | |||||||||||||||||||||||||||||||||
| LDB3, ALA165VAL [dbSNP:rs121908334] | |||||||||||||||||||||||||||||||||
| In 3 unrelated patients with myofibrillar myopathy (609452), Selcen and Engel (2005) identified a heterozygous 519C-T transition in exon 6 of the LDB3 gene, resulting in an ala165-to-val (A165V) substitution within the ZM motif needed for interaction with alpha-actinin (see, e.g., ACTN1, 102575). Two patients had a family history of the disorder. All had progressive weakness that was more severe distally, 1 had cardiac involvement, and 2 had evidence of peripheral neuropathy. The mutation was not identified in 220 control alleles. | |||||||||||||||||||||||||||||||||
| .0003 MYOPATHY, MYOFIBRILLAR, ZASP-RELATED | |||||||||||||||||||||||||||||||||
| LDB3, ARG268CYS [dbSNP:rs121908335] | |||||||||||||||||||||||||||||||||
| In a patient with myofibrillar myopathy (609452), Selcen and Engel (2005) identified a heterozygous 827C-T transition in exon 9 of the LDB3 gene, resulting in an arg268-to-cys (R268C) substitution. Exon 9 is only present in the short muscle transcript of the gene. This patient had a late-onset at age 73 years and had no cardiac involvement, suggesting that the longer LDB3 isoforms may have partially compensated for the defect. | |||||||||||||||||||||||||||||||||
| .0004 CARDIOMYOPATHY, DILATED, 1C | |||||||||||||||||||||||||||||||||
| LDB3, ILE352MET [dbSNP:rs121908336] | |||||||||||||||||||||||||||||||||
| In 3 affected members of a family with 'pure' dilated cardiomyopathy (601493) and an autosomal dominant inheritance pattern, Vatta et al. (2003) identified heterozygosity for a 1056C-G transversion in exon 10 of the LDB3 gene, resulting in an ile352-to-met (I352M) substitution. The proband and her affected brother and father also had left ventricular hypertrophy by electrocardiography. The mutation was not found in her unaffected sister or in 200 ethnically matched controls. | |||||||||||||||||||||||||||||||||
| .0005 CARDIOMYOPATHY, DILATED, WITH LEFT VENTRICULAR NONCOMPACTION | |||||||||||||||||||||||||||||||||
| LDB3, SER196LEU [dbSNP:rs45487699] | |||||||||||||||||||||||||||||||||
| In a 40-year-old man with dilated cardiomyopathy associated with severe left ventricular hypertrophy and a trabeculated left ventricle on echocardiogram (see 601493), Vatta et al. (2003) identified heterozygosity for a 587C-T transition in exon 4 of the LDB3 gene, resulting in a ser196-to-leu (S196L) substitution. Four other family members were affected: the proband's 68-year-old mother; his 2 brothers, 1 of whom died with severe dilated cardiomyopathy at age 41 years; and the deceased brother's 7-year-old daughter, who presented with a mildly dilated left ventricle. The proband's mother and living brother both also had severe left ventricular hypertrophy. The mutation was not found in 200 ethnically matched controls. | |||||||||||||||||||||||||||||||||
| .0006 CARDIOMYOPATHY, DILATED, WITH LEFT VENTRICULAR NONCOMPACTION | |||||||||||||||||||||||||||||||||
| LDB3, THR213ILE [dbSNP:rs121908337] | |||||||||||||||||||||||||||||||||
| In a 15-month-old Latin American male with profound bradycardia, atrial ventricular block, and depressed ventricular function with mild left ventricular dilation (see 601493), Vatta et al. (2003) identified heterozygosity for a 638C-T transition in exon 4 of the LDB3 gene, resulting in a thr213-to-ile (T213I) substitution. Thr213 is conserved in mouse and rat. Neither parent had the substitution. | |||||||||||||||||||||||||||||||||
| .0007 CARDIOMYOPATHY, DILATED, WITH LEFT VENTRICULAR NONCOMPACTION | |||||||||||||||||||||||||||||||||
| LDB3, ASP117ASN [dbSNP:rs121908338] | |||||||||||||||||||||||||||||||||
| In 2 unrelated sporadic cases of dilated cardiomyopathy with left ventricular noncompaction (see 601493), Vatta et al. (2003) identified heterozygosity for a 349G-A transition in exon 6 of the LDB3 gene, resulting in an asp117-to-asn (D117N) mutation. One patient was a 44-year-old female, diagnosed at 41 years of age with DCM, heart failure, left bundle branch block, and dilated left ventricle with deep trabeculations. The other was a 33-year-old male, diagnosed with DCM at 30 years of age during a family echocardiographic screen after sudden death had occurred within the family. Echocardiographic and MRI screening identified both left and right ventricular trabeculations, with severe left ventricular hypertrophy, an intraventricular conduction delay, and ventricular bigeminy on electrocardiogram, as well as echocardiographic evidence of borderline systolic function and a dilated left ventricle. In the other family members, neither DCM nor isolated noncompaction of the left ventricular myocardium was identified. | |||||||||||||||||||||||||||||||||
| .0008 CARDIOMYOPATHY, DILATED, 1C | |||||||||||||||||||||||||||||||||
| LDB3, LYS136MET [dbSNP:rs121908339] | |||||||||||||||||||||||||||||||||
| In a 16-year-old Caucasian male with the diagnosis of dilated cardiomyopathy (CMD1C; 601493) by echocardiography and left ventricular hypertrophy on electrocardiography, Vatta et al. (2003) identified heterozygosity for a 407A-T transversion in exon 6 of the LDB3 gene, resulting in a lys136-to-met (K136M) substitution. | |||||||||||||||||||||||||||||||||
| .0009 CARDIOMYOPATHY, DILATED, 1C | |||||||||||||||||||||||||||||||||
| LEFT VENTRICULAR NONCOMPACTION 3, INCLUDED | |||||||||||||||||||||||||||||||||
| LDB3, ASP626ASN [dbSNP:rs45514002] | |||||||||||||||||||||||||||||||||
| In a Japanese family with dilated cardiomyopathy (601493), Arimura et al. (2004) found heterozygosity for a G-to-A transition in exon 15 of the LDB3 gene, resulting in an asp626-to-asn (D626N) substitution at a conserved residue within the third LIM domain. All affected sibs had the same mutation, which was not found in 400 healthy controls; 1 sister, aged 65, had the mutation but did not have dilated cardiomyopathy. Clinical information suggested that cardiomyopathy was of late onset. The mutation was not found in 400 unrelated healthy controls. In 4 affected members of 2 unrelated Japanese families with left ventricular noncompaction (see 601493), Xing et al. (2006) identified heterozygosity for a 1876G-A transition in exon 15 of LDB3, resulting in the D626N substitution. The mutation was not found in 200 controls. In the first family, twin sisters presented with isolated LVNC shortly after birth; their father and paternal grandfather were reportedly diagnosed with LVNC and dilated cardiomyopathy, but DNA was not available for study. In the second family, the male proband was diagnosed with isolated LVNC and Wolff-Parkinson-White syndrome (WPW; 194200) on routine physical examination at 13 years of age; his asymptomatic mutation-positive mother was found to have LVNC on echocardiography. A maternal aunt died at 10 years of age of indistinct cardiac disease. | |||||||||||||||||||||||||||||||||
| REFERENCES | |||||||||||||||||||||||||||||||||
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