The Functional Properties of Human Slow Skeletal Troponin T Isoforms in Cardiac Muscle Regulation

Human slow skeletal troponin T (HSSTnT) shares a high degree of homology with cardiac TnT (CTnT). Although the presence of HSSTnT has not been confirmed in the heart at the protein level, detectable levels of HSSTnT mRNA have been found. Whether HSSTnT isoforms are expressed transiently remains unknown. Because transient re-expression of HSSTnT may be a potential mechanism of regulating function, we explored the effect of HSSTnT on the regulation of cardiac muscle. At least three HSSTnT isoforms have been found to exist in slow skeletal muscle: HSSTnT1 (+exons 5 and 12), HSSTnT2 (+exon 5, −exon 12), and HSSTnT3 (−exons 5 and 12). Another isoform, HSSTnT hypothetical (Hyp) (−exon 5, +exon 12), has only been found at the mRNA level. Compared with HCTnT3 (adult isoform), Tn complexes containing HSSTnT1, -2, and -3 did not alter the actomyosin ATPase activation and inhibition in the presence and absence of Ca²⁺, respectively. HSSTnTHyp was not evaluated as it did not form a Tn complex under a variety of conditions. Porcine papillary skinned fibers displaced with HSSTnT1, -2, or -3 and reconstituted with human cardiac troponin I and troponin C (HCTnI·TnC) complex showed a decrease in the Ca²⁺ sensitivity of force development and an increase in maximal recovered force (HSSTnT1 and -3) compared with HCTnT3. In contrast, HSSTnTHyp showed an increase in the Ca²⁺ sensitivity of force development. This suggests that re- or overexpression of specific SSTnT isoforms might have therapeutic potential in the failing heart because they increase the maximal force of contraction. In addition, circular dichroism and proteolytic digestion experiments revealed structural differences between HSSTnT isoforms and HCTnT3 and that HSSTnT1 is more susceptible to calpain and trypsin proteolysis than the other HSSTnTs. Overall, HSSTnT isoforms despite being homologues of CTnT may display distinct functional properties in muscle regulation.     

Cardiac Muscle Activation Blunted by a Mutation to the Regulatory Component,Troponin T

The striated muscle thin filament comprises actin, tropomyosin, and troponin. The Tn complex consists of three subunits, troponin C (TnC), troponin I (TnI), and troponin T (TnT). TnT may serve as a bridge between the Ca²⁺ sensor (TnC) and the actin filament. In the short helix preceding the IT-arm region, H1(T2), there are known dilated cardiomyopathy-linked mutations (among them R205L). Thus we hypothesized that there is an element in this short helix that plays an important role in regulating the muscle contraction, especially in Ca²⁺ activation. We mutated Arg-205 and several other amino acid residues within and near the H1(T2) helix. Utilizing an alanine replacement method to compare the effects of the mutations, the biochemical and mechanical impact on the actomyosin interaction was assessed by solution ATPase activity assay, an in vitro motility assay, and Ca²⁺ binding measurements. Ca²⁺ activation was markedly impaired by a point mutation of the highly conserved basic residue R205A, residing in the short helix H1(T2) of cTnT, whereas the mutations to nearby residues exhibited little effect on function. Interestingly, rigor activation was unchanged between the wild type and R205A TnT. In addition to the reduction in Ca²⁺ sensitivity observed in Ca²⁺ binding to the thin filament, myosin S1-ADP binding to the thin filament was significantly affected by the same mutation, which was also supported by a series of S1 concentration-dependent ATPase assays. These suggest that the R205A mutation alters function through reduction in the nature of cooperative binding of S1.     

猪骨骼肌快肌肌钙蛋白C2基因的cDNA克隆与表达分析

从人骨骼肌快肌肌钙蛋白C2（TNNC2）基因出发,在dbEST数据库中进行同源性搜索,找到一个有较高同源性且在猪背最长肌中表达EST（BM083186）。通过电子克隆和进一步RT-PCR实验验证,获得猪TNNC2基因全长cDNA序列,其全长843bp,开放阅读框为201～683bp,编码有160个氨基酸。同源性分析结果表明,与人、鼠的骨骼肌快肌肌钙蛋白C2基因cDNA编码区（CDS）同源性分别为93.6％、90.5％,蛋白序列同源性均为97.5%。多种组织的半定量RT-PCR研究表明,该基因在骨骼肌中表达,并且在杜洛克猪背最长肌中的表达比兰塘猪高。     

胰岛素及cAMP对培养人动脉平滑肌细胞HDL受体功能的影响

对胰岛素ｃＡＭＰ对培养人动脉平滑肌细胞（ＳＭＣ）ＨＤＬ受体功能的影响进行了研究,结果发现：胰岛素使ＳＭＣＨＤＬ受体的结合容量Ｂｍａｘ即受体数目显著下降,而对ＳＭＣＨＤＬ受体的Ｋｄ值亲和力无影响;ｃＡＭｐ则ＳＭＣＨＤＬ受体亲和力增加,而对受体数目无影响。     

Pol II–Expressed shRNA Knocks Down Sod2 Gene Expression and Causes Phenotypes of the Gene Knockout in Mice

RNA interference (RNAi) has been used increasingly for reverse genetics in invertebrates and mammalian cells, and has the potential to become an alternative to gene knockout technology in mammals. Thus far, only RNA polymerase III (Pol III)–expressed short hairpin RNA (shRNA) has been used to make shRNA-expressing transgenic mice. However, widespread knockdown and induction of phenotypes of gene knockout in postnatal mice have not been demonstrated. Previous studies have shown that Pol II synthesizes micro RNAs (miRNAs)—the endogenous shRNAs that carry out gene silencing function. To achieve efficient gene knockdown in mammals and to generate phenotypes of gene knockout, we designed a construct in which a Pol II (ubiquitin C) promoter drove the expression of an shRNA with a structure that mimics human miRNA miR-30a. Two transgenic lines showed widespread and sustained shRNA expression, and efficient knockdown of the target gene Sod2. These mice were viable but with phenotypes of SOD2 deficiency. Bigenic heterozygous mice generated by crossing these two lines showed nearly undetectable target gene expression and phenotypes consistent with the target gene knockout, including slow growth, fatty liver, dilated cardiomyopathy, and premature death. This approach opens the door of RNAi to a wide array of well-established Pol II transgenic strategies and offers a technically simpler, cheaper, and quicker alternative to gene knockout by homologous recombination for reverse genetics in mice and other mammalian species.     

Muscle-Specific Splicing of a Heterologous Exon Mediated by a Single Muscle-Specific Splicing Enhancer from the Cardiac Troponin T Gene

The chicken cardiac troponin T (cTNT) gene contains a single 30-nucleotide alternative exon that is included in embryonic striated muscle and skipped in the adult. Transient-transfection analysis of cTNT minigenes in muscle and fibroblast cell cultures previously identified four muscle-specific splicing enhancers (MSEs) that promote exon inclusion specifically in embryonic striated muscle cultures. Three MSEs located in the intron downstream from the alternative exon were sufficient for muscle-specific exon inclusion. In the present study, the boundaries of these MSEs were defined by scanning mutagenesis, allowing analysis of individual elements in gain-of-function experiments. Concatamers of MSE2 were necessary and sufficient to promote muscle-specific inclusion of a heterologous exon, indicating that it is a target for muscle-specific regulation. Sequences present in MSE2 are also found in MSE4, suggesting that these two MSEs act in a similar manner. MSE3 appears to be different from MSE2 and MSE4 yet is able to functionally replace both of these elements, demonstrating functional redundancy of elements that are likely to bind different factors. MSE2 and MSE4 each contain a novel sequence motif that is found adjacent to a number of alternative exons that undergo regulated splicing in striated muscle, suggesting a common role for this element in muscle-specific regulation.     

MappingTNNC1, the Gene That Encodes Cardiac Troponin I in the Human and the Mouse

We have mapped the TNNC1 gene, whose protein product is the cardiac TnI protein. TnI is one of the proteins that makes up the troponin complex, which mediates the response of muscle to calcium ions. The human TNNC1 locus had been assigned to a large region of chromosome 19, and we have refined the mapping position to the distal end of the chromosome by amplification of DNAs from a chromosome 19 mapping panel. We have also mapped the mouse Tnnc1 locus, by following the segregation of an intron sequence through DNAs from the European Interspecific Backcross. Tnnc1 maps close to the centromere on mouse chromosome 7.     

Immunohistochemical Differentiation of Fiber Types in Human Skeletal Muscle Using Monoclonal Antibodies to Slow and Fast Isoforms of Troponin I Subunit

The cDNA sequence of troponin I (TnI), one of the subunits of the skeletal muscle regulatory protein, differs between slow-twitch muscle and fast-twitch muscle. We prepared monoclonal antibodies td the slow and fast isoforms of human TnI for the purpose of differentiating muscle fiber types in human neuromuscular disorders. Slow TnI antibody was labeled with tetramethylrhodamine isothiocyanate while fast TnI antibody was labeled with fluorescein isothiocyanate; then these two antibodies were mixed. This mixture was then used to stain biopsied muscle from patients with neuromuscular disorders. It was possible to differentiate muscle fibers into slow, fast and intermediate fibers having various contents of slow and fast TnI. In tissue composed of small muscle fibers, this method facilitated differentiation of types of muscle fibers by allowing staining of only a single section. The usefulness of our technique using slow and fast TnI antibodies is discussed in comparison with ATPase staining. Because our staining method can distinguish slow and fast fiber components, it is useful for clinical application.     

心肌肌钙蛋白T在病毒性心肌炎心肌组织中的表达及意义

目的:了解病毒性心肌炎心肌组织中肌钙蛋白T的表达情况,探讨病毒性心肌炎时心肌结构蛋白损伤的机制及意义。方法:运用免疫组化和计算机图像分析技术,观察13例明确性病毒性心肌炎和17例界限性病毒性心肌炎尸检心脏标本中心肌肌钙蛋白T的表达与分布。结果:在正常对照的心肌组织中,蛋白成强阳性表达,分布均匀,未见缺染。在明确性心肌炎及14例界限性心肌炎心肌组织中都存在着不同程度的蛋白表达缺染或脱失。缺染的范围及分布与病毒性心肌炎病变特点基本一致,但其范围往往小于炎症细胞浸润范围。计算机图像分析和数据统计结果显示缺染区域的心肌肌钙蛋白T表达量要明显小于其周边区域和正常心肌细胞(P＜0．01)。结论:病毒性心肌炎患者的心肌损害要早于炎症细胞的浸润,病毒的作用可能是心肌肌钙蛋白T脱失的主要因素。心肌肌钙蛋白T的免疫组化检查可以作为一种有效的手段,来辅助病毒性心肌炎的病理学诊断。     

猪肌肉素基因的cDNA克隆与表达

从人肌肉素基因出发, 在dbEST数据库中进行同源性搜索, 找到七个有较高同源性的Expressed Sequence Tag(DY426490, CF787546, AJ660979, AJ664670, AJ663820, AJ680159, DN106254)。通过拼接和进一步RT-PCR实验验证, 获得猪肌肉素基因全长cDNA序列, 其全长651 bp, 开放阅读框为54~452 bp, 编码有132个氨基酸。同源性分析结果表明, 与人、小鼠和大鼠的肌肉素基因cDNA编码区(CDS)同源性分别为87.2%、77.6%和77.9%。利用克隆出的猪肌肉素cDNA, 构建表达载体pGEX-4T-1-musclin, 并在BL21大肠杆菌中成功表达和纯化了分子量为38.59 kD的融合蛋白GST-Musclin, 并运用蛋白印迹技术进行鉴定。     

A Positive GATA Element and a Negative Vitamin D Receptor-Like Element Control Atrial Chamber-Specific Expression of a Slow Myosin Heavy-Chain Gene during Cardiac Morphogenesis

We have used the slow myosin heavy chain (MyHC) 3 gene to study the molecular mechanisms that control atrial chamber-specific gene expression. Initially, slow MyHC 3 is uniformly expressed throughout the tubular heart of the quail embryo. As cardiac development proceeds, an anterior-posterior gradient of slow MyHC 3 expression develops, culminating in atrial chamber-restricted expression of this gene following chamberization. Two cis elements within the slow MyHC 3 gene promoter, a GATA-binding motif and a vitamin D receptor (VDR)-like binding motif, control chamber-specific expression. The GATA element of the slow MyHC 3 is sufficient for expression of a heterologous reporter gene in both atrial and ventricular cardiomyocytes, and expression of GATA-4, but not Nkx2-5 or myocyte enhancer factor 2C, activates reporter gene expression in fibroblasts. Equivalent levels of GATA-binding activity were found in extracts of atrial and ventricular cardiomyocytes from embryonic chamberized hearts. These observations suggest that GATA factors positively regulate slow MyHC 3 gene expression throughout the tubular heart and subsequently in the atria. In contrast, an inhibitory activity, operating through the VDR-like element, increased in ventricular cardiomyocytes during the transition of the heart from a tubular to a chambered structure. Overexpression of the VDR, acting via the VDR-like element, duplicates the inhibitory activity in ventricular but not in atrial cardiomyocytes. These data suggest that atrial chamber-specific expression of the slow MyHC 3 gene is achieved through the VDR-like inhibitory element in ventricular cardiomyocytes at the time distinct atrial and ventricular chambers form.     

Evolution of a Metal-Binding Cluster in the NH2-Terminal Variable Region of Avian Fast Skeletal Muscle Troponin T: Functional Divergence on the Basis of Tolerance to Structural Drifting

This study investigated the evolution of a transition metal ion-binding cluster ([H–X–X–X–H] _n ; Tx) in the alternatively spliced NH₂-terminal variable region of avian pectoral muscle troponin T (TnT). Encoded by avian fast skeletal muscle TnT-specific P exons, Tx-like structures were expressed in the breast muscle TnT's of almost all birds examined. Their presence results in the developmentally up-regulated high molecular weight pectoral muscle TnT. Sequence analysis and metal affinity chromatography revealed that in Galliformes and Craciformes, the Tx structure evolved into multiple H–X–X–X–H pairs with a high-affinity metal-binding capacity. Turkey, chicken, quail, and curassow breast muscle TnT's contain nine, seven, four, and three consecutive or closely located metal-binding sites, respectively, in the NH₂-terminal region. The metal-binding affinity of the Tx element increased as the number of His pairs increased due to the duplication of P exons and the conversion of other exon sequences. The data show two related components of avian pectoral muscle TnT evolution: a larger, more acidic NH₂-terminal segment and a cluster of transition metal-binding sites, both of which may have functional significance for their selection value. The evolution of the Tx segment in the NH₂-terminal variable region of avian pectoral muscle TnT demonstrates a functional divergence on the basis of tolerance to structural drifting. Received: 2 May 2000 / Accepted: 5 September 2000     

Molecular Characterization of a Genomic Fragment Containing Pi-kh Gene from the Genomic Library of Indica Rice Line Tetep

Identification of full length genes along with upstream regulatory elements is important to understand its expression. Here, we report preparation of high titre genomic library and identification of a genomic clone containing Pi-k ^h gene with its complete upstream and downstream sequences from the rice blast resistant line Tetep. Structural analysis of protein revealed that Pi-k ^h has a central nucleotide binding site domain, leucine-rich repeats domain and a unique zinc-finger domain. Comparative analysis of Pi-k ^h protein sequence showed 64% and 45% similarity with the protein sequences of rice blast resistance genes Pi-b and Pi-ta , respectively.     

Down Regulation of Genes Involved in T Cell Polarity and Motility during the Induction of Heart Allograft Tolerance by Allochimeric MHC I

Background

The allochimeric MHC class I molecule [α1h1/u]-RT1.Aa that contains donor-type (Wistar Furth, WF; RT1u) epitopes displayed on recipient-type (ACI, RT1a) administered in conjunction with sub-therapeutic dose of cyclosporine (CsA) induces indefinite survival of heterotopic cardiac allografts in rat model. In vascularized transplantation models, the spleen contributes to graft rejection by generating alloantigen reactive T cells. The immune response in allograft rejection involves a cascade of molecular events leading to the formation of immunological synapses between T cells and the antigen-presenting cells.

Methodology/Principal Findings

To elucidate the molecular pathways involved in the immunosuppressive function of allochimeric molecule we performed microarray and quantitative RTPCR analyses of gene expression profile of splenic T cells from untreated, CsA treated, and allochimeric molecule + subtherapeutic dose of CsA treated animals at day 1, 3 and 7 of post transplantation. Allochimeric molecule treatment caused down regulation of genes involved in actin filament polymerization (RhoA and Rac1), cell adhesion (Catna1, Vcam and CD9), vacuolar transport (RhoB, Cln8 and ATP6v1b2), and MAPK pathway (Spred1 and Dusp6) involved in tubulin cytoskeleton reorganization and interaction between actin and microtubule cytoskeleton. All these genes are involved in T cell polarity and motility, i.e., their ability to move, scan and to form functional immunological synapse with antigen presenting cells (APCs).

Conclusions

These results indicate that the immunosuppressive function of allochimeric molecule may depend on the impairment of T cells'' movement and scanning ability, and possibly also the formation of immunological synapse. We believe that these novel findings may have important clinical implications for organ transplantation.     

Betaine Down Regulates Apelin Gene Expression in Cardiac and Adipose Tissues of Insulin Resistant Diabetic Rats Fed by High-Calorie Diet

Apelin is a newly discovered peptide that its serum level increases in diabetic patients with cardiovascular dysfunction. Recent studies indicate the beneficial actions of betaine in reducing the cardiovascular and metabolic complications, however data related to its effect on adipocytokine expression is limited. The aim of this study was to evaluate the effect of betaine supplementation on Apelin gene expression in cardiac muscle and adipose tissue of insulin resistance, diabetic rats fed by a high calorie diet. To induce insulin resistance rats were fed with high fat/high carbohydrate diet for five weeks and then 30 mg/kg STZ was injected intraperitoneally. After confirming of diabetes incidence (serum glucose above 7.5 mmol/l) the animals were treated with 1 % betaine in drinking water for 28 days. At days 14 and 28 after treatment, animals were euthanized and Apelin gene expression was evaluated by real time PCR and western blot in heart and adipose tissues. Serum levels of insulin, Apelin and glucose and HOMA–IR were also measured. Our results showed that feeding of rats by a high calorie diets caused insulin resistance, which was manifested by elevated plasma insulin, glucose and Apelin levels and also HOMA–IR. Apelin gene expression in heart and adipose tissues were significantly increased simultaneously with the progression of diabetes. Betaine supplementation decreased serum Apelin and down regulated Apelin expression in adipose tissue and cardiac muscle, particularly at day 28 of treatment. We concluded that betaine might improve metabolic and cardiovascular complications in diabetic patients by regulation of Apelin expression and secretion.     

Identification of a Novel Human Gene Containing the Tetratricopeptide Repeat Domain from the Down Syndrome Region of Chromosome 21

The Down syndrome (DS) region on chromosome 21, which is responsiblefor the DS main features, has been defined by analysis of DSpatients with partial trisomy 21. Within the DS region, we constructeda 1.6-Mb P1 contig map previously. To isolate gene fragmentsfrom the 1.6-Mb region, we performed direct cDNA library screeningand exon trapping using the P1 clones and a human fetal braincDNA library, and obtained 67 cDNA fragments and 52 possibleexons. Among them, 23 cDNA fragments and 4 exons were interpretedto be derived from a single gene by localization on P1 clonesand by Northern analysis. To obtain the full-length cDNA sequence,longer cDNA clones were further screened from another humancDNA library which was enriched with longer cDNA species. Theseclones were sequenced and assembled to a sequence of 9045 bp.This transcribed sequence encodes a novel 2025 amino-acid proteincontaining tetratricopeptide repeat (TPR) motifs and thereforethe gene was designated as TPRD (a gene containing the TPR motifson the Down syndrome region). The TPR domain has been foundin a certain protein phosphatase and in other proteins involvedin the regulation of RNA synthesis or mitosis. The TPRD gene,the novel gene which was proved to be in the 1.6-Mb region andto have the interesting features described above, is a candidatefor genes responsible for the DS phenotypes.     

猪流行性腹泻病毒S基因片段的克隆及原核表达

为研究猪流行性腹泻病毒(porcine epidemic diarrhea virus PEDV)S基因片段的原核表达产物是否具有抗原性,分析S基因抗原位点后,用PCR技术扩增S蛋白主要抗原区的核酸序列,经克隆后将目的片段连接到原核表达载体pET-28a(+)中,成功构建了重组质粒pET-28a-PEDV-Sp,其重组菌于37℃、0.5 mmol/L IPTG诱导表达4 h后进行SDS-PAGE分析,在分子质量约为29 kDa处出现一新蛋白带,与预期相符。质谱鉴定表明,已成功表达了目的蛋白。纯化后的重组蛋白免疫兔制备多克隆抗体,抗体效价检测结果显示该蛋白具有良好的抗原性。该研究为猪流行性腹泻基因工程疫苗的研制奠定基础。