Disease relevance of Myl2

• Ventricular expression of a MLC-2v-ras fusion gene induces cardiac hypertrophy and selective diastolic dysfunction in transgenic mice [1].
• In conclusion, this model system with the 2.1-kb ventricle-specific MLC-2 promoter sequence should facilitate the overexpression of gene products in the developing and mature heart muscle and further elucidate molecular mechanisms of myocardial diseases such as cardiomyopathies [2].
• MLC2v/ras transgenic mice display a phenotype characteristic of hypertrophic cardiomyopathy, with septal hypertrophy and focal myocyte disarray [3].
• To study the transcriptional regulatory mechanisms which mediate cardiac-specific and inducible expression during myocardial cell hypertrophy, we have extensively characterized the rat cardiac myosin light-chain-2 (MLC-2) gene as a model system [4].
• For treating ischemic heart diseases, a cardiac-specific MLC-2v promoter is used to deliver transgenes specifically to the heart [5].

High impact information on Myl2

• In another transgenic strain, carrying the rat MLC2 gene and a modified rat skeletal muscle actin gene (actin-globin chimeric gene), transcripts of the rat MLC2 gene were detected in skeletal muscle only, whereas the actin-globin transcripts were detected in skeletal muscle as well as in the heart [6].
• Crt(-/-) EBs exhibited a severe decrease in expression and a lack of phosphorylation of ventricular myosin light chain 2 (MLC2v), resulting in an impaired organization of myofibrils [7].
• An imposed ionomycin-triggered cystolic-free Ca(2+) concentration ([Ca(2+)](c)) elevation restored the expression, phosphorylation, and insertion of MLC2v into sarcomeric structures and in turn the myofibrillogenesis [7].
• METHODS AND RESULTS: Postnatal transgenic cardiac-specific overexpression of MLC2v was achieved by use of the alpha-myosin heavy chain promoter [8].
• Accordingly, we designed the present experiment to define the cardiac chamber-specific functional effects of the ventricular isoform of the regulatory myosin light chain (MLC2v) [8].

Biological context of Myl2

• Analysis of this panel has located the CR hairless rat's hypotrichosis-generating mutation on chromosome 1, near Myl2, where only the fuzzy mutation in rat (fz) and the frizzy mutation in mouse (fr) have been previously localized [9].
• Taken together, this provides evidence for early positional specification of MLC-2v gene expression in the primitive heart tube and indicates regional specification of part of the ventricular muscle gene program can precede ventricular septation during mammalian cardiogenesis [10].
• Transgenic mice harboring a 250-base-pair MLC-2v promoter fragment fused to a luciferase reporter gene demonstrate reporter gene activity from at least day 9 pc [10].
• To study the process of ventricular specification during cardiogenesis, we examined the in situ expression of cardiac ventricular myosin light chain 2 (MLC-2v) mRNA during murine embryogenesis [10].
• However, if the transgene encodes the isoform that is normally present (e.g., MLC2v expressed in the ventricle), the protein levels remain unaffected, although the transgenic transcript accumulates to very high levels [11].

Anatomical context of Myl2

• The cardiac myosin light-chain 2v (MLC-2v) gene has served as a model system to identify the pathways which restrict the expression of cardiac muscle genes to particular chambers of the heart during cardiogenesis [12].
• Treatment with nifedipine altered the mRNA expression of the transcription factor Gata4, which was absent in the developing ventricles, and the sarcomeric protein Mylpc (myosin light chain 2V), which was decreased distal to the left ventricle and was absent at the site of the developing right ventricle [13].
• To begin to explore these issues, we used transgenesis to determine the feasibility of effecting a complete or partial replacement of the cardiac regulatory light chains with the isoform that is normally expressed in fast skeletal muscle fibers (fast muscle-specific MLC2) [14].
• This result suggests that the 2.1-kb DNA fragment of the 5' flanking region of the cardiac MLC-2 gene contains the regulatory elements required for selective gene expression in cardiac myocytes in vivo [2].
• A 2.1-kb DNA fragment of the 5' flanking region of the rat cardiac MLC-2 gene was fused to the firefly luciferase reporter gene and introduced into fertilized mouse oocytes [2].

Associations of Myl2 with chemical compounds

• This study provides direct evidence that USF, a member of the basic helix-loop-helix leucine zipper family, binds to MLE1, HF-1a, and PRE B sites and suggests that it is a component of protein complexes that may coordinately control the expression of MLC-2v and alpha-myosin heavy-chain genes [15].
• Statins concentration- and time-dependently downregulated basal as well as angiotensin-induced expression of ANF by 86+/-2.3% and 89+/-1.7%, as well as MLC-2 by 75+/-4.1% and 84+/-6%, respectively [16].
• We have established a CGR8 embryonic stem (ES) cell clone (MLC2ECFP) which expresses the enhanced cyan variant of Aequorea victoria green fluorescent protein (ECFP) under the transcriptional control of the ventricular myosin light chain 2 (MLC2v) promoter [17].
• Nonetheless, the CVB3 mutant was found to induce a cytopathic effect in transfected myocytes, which was demonstrated by inhibition of cotransfected MLC-2v luciferase reporter activity and an increase in release of lactate dehydrogenase from transfected cells [18].
• These cells expressed cardiomyocyte-specific genes such as alpha-skeletal actin, beta-myosin heavy chain, MLC-2v, and CaV1.2 and incorporated bromodeoxyuridine for 5 days [19].

Regulatory relationships of Myl2

• MLC2v is strongly expressed in the ventricular myocardium and distinctly lower in the outflow tract and atrioventricular canal [20].

Other interactions of Myl2

• As assessed by hybridization with a specific MLC-2v riboprobe, mRNA expression can be found in the ventricular region at day 8.0 postcoitum (pc) [10].
• With development, myocardial cells are observed in the lower endocardial ridges that share MLC2a and MLC2v expression with the myocardial cells of the outflow tract [20].
• We have recently reported that cardiac lineage protein-1 (CLP-1), a nuclear protein with an acidic region that constitutes a potential protein-protein interaction domain, regulates transcription of the cardiac myosin light chain-2v (MLC-2v) gene promoter in a manner consistent with its being a transcriptional co-activator or regulator [21].
• However, its function in striated muscle remains obscure, and the different functional activities of the various isoforms that are expressed in the mammalian heart (ventricle- and atrium-specific MLC2) remain undefined [14].

Analytical, diagnostic and therapeutic context of Myl2

• Using epifluorescence imaging of vital embryoid bodies (EB) and reverse transcription-polymerase chain reaction (RT-PCR), we found that the MLC2v promoter is switched on as early as day 7 and is accompanied by formation of cell clusters featuring a bright ECFP blue fluorescence [17].
• Based on in situ hybridization studies that indicated the expression of the cardiac myosin-light-chain-2 (MLC-2) gene in ventricular myocardium and in the lower outflow tract, a model system for selective targeting of foreign genes to the heart of transgenic mice has been developed [22].

References