Locally expressed IGF1 propeptide improves mouse heart function in induced dilated cardiomyopathy by blocking myocardial fibrosis and SRF-dependent CTGF induction.

Cardiac fibrosis is critically involved in the adverse remodeling accompanying dilated cardiomyopathies (DCMs), which leads to cardiac dysfunction and heart failure (HF). Connective tissue growth factor (CTGF), a profibrotic cytokine, plays a key role in this deleterious process. Some beneficial effects of IGF1 on cardiomyopathy have been described, but its potential role in improving DCM is less well characterized.

Srf-dependent paracrine signals produced by myofibers control satellite cell-mediated skeletal muscle hypertrophy.

Adult skeletal muscles adapt their fiber size to workload. We show that serum response factor (Srf) is required for satellite cell-mediated hypertrophic muscle growth. Deletion of Srf from myofibers and not satellite cells blunts overload-induced hypertrophy, and impairs satellite cell proliferation and recruitment to pre-existing fibers.

Premature aging in skeletal muscle lacking serum response factor.

Aging is associated with a progressive loss of muscle mass, increased adiposity and fibrosis that leads to sarcopenia. At the molecular level, muscle aging is known to alter the expression of a variety of genes but very little is known about the molecular effectors involved. SRF (Serum Response Factor) is a crucial transcription factor for muscle-specific gene expression and for post-natal skeletal muscle growth.

Mosaic inactivation of the serum response factor gene in the myocardium induces focal lesions and heart failure.

Background And Aims: Regional alterations in ventricular mechanical functions are a primary determinant for the risk of myocardial injuries in various cardiomyopathies. The serum response factor (SRF) is a transcription factor regulating contractile and cytoskeletal genes and may play an important role in the remodelling of myocardium at the cellular level.

Methods: Using Desmin-Cre transgenic mice, we generated a model of mosaic inactivation of a floxed-Srf allele in the heart to analyze the consequence of regional alterations of SRF-mediated functions in the myocardium.

Delayed liver regeneration in mice lacking liver serum response factor.

Various immediate early genes (IEGs) upregulated during the early process of liver regeneration are transcriptional targets of the serum response factor (SRF). We show here that the expression of SRF is rapidly induced in rodent liver after partial hepatectomy. Because the inactivation of the SRF gene in mice is embryonic lethal, the in vivo role of SRF in liver regeneration after partial hepatectomy was analyzed in mutant mice conditionally deleted for SRF in the liver.

New role for serum response factor in postnatal skeletal muscle growth and regeneration via the interleukin 4 and insulin-like growth factor 1 pathways.

Serum response factor (SRF) is a crucial transcriptional factor for muscle-specific gene expression. We investigated SRF function in adult skeletal muscles, using mice with a postmitotic myofiber-targeted disruption of the SRF gene. Mutant mice displayed severe skeletal muscle mass reductions due to a postnatal muscle growth defect resulting in highly hypotrophic adult myofibers.

Conditional inactivation of the murine serum response factor in the pancreas leads to severe pancreatitis.

The Serum Response Factor (SRF) is widely expressed transcription factor acting at the confluence of multiple signaling pathways and has been implicated in the control of differentiation, growth, and cell death. In the present study, we found that SRF is expressed in the developing and adult pancreas. To explore the possible role of SRF in this organ, we have generated mutant mice with conditional disruption of the Srf gene.

Temporally controlled onset of dilated cardiomyopathy through disruption of the SRF gene in adult heart.

Background: Serum response factor (SRF) is a cardiac transcription factor involved in cell growth and differentiation. We have shown, using the Cre/loxP system, that cardiac-specific disruption of SRF gene in the embryonic heart results in lethal cardiac defects. The role of SRF in adult heart is unknown.

Targeted inactivation of serum response factor in the developing heart results in myocardial defects and embryonic lethality.

Serum response factor (SRF) is at the confluence of multiple signaling pathways controlling the transcription of immediate-early response genes and muscle-specific genes. There are active SRF target sequences in more than 50 genes expressed in the three muscle lineages including normal and diseased hearts. However, the role of SRF in heart formation has not been addressed in vivo thus far due to the early requirement of SRF for mesoderm formation.

Muscle electrotransfer as a tool for studying muscle fiber-specific and nerve-dependent activity of promoters.

Muscle electrotransfer has recently become a promising tool for efficient delivery of plasmids and transgene expression in skeletal muscle. This technology has been mainly applied to use of muscle as a bioreactor for production of therapeutic proteins. However, it remains to be determined whether muscle electrotransfer may also be accurately used as an alternative tool to transgenesis for studying aspects of muscle-specific gene control that must be explored in fully mature muscle fibers in vivo, such as fiber specificity and nerve dependence.

High-efficiency gene transfer into adult fish: a new tool to study fin regeneration.

Zebrafish represents an excellent model to study the function of vertebrate genes (e.g., well-developed genetics, large number of mutants, and genomic sequencing in progress), inasmuch as we have tools to manipulate gene expression.

RhoA GTPase and serum response factor control selectively the expression of MyoD without affecting Myf5 in mouse myoblasts.

MyoD and Myf5 belong to the family of basic helix-loop-helix transcription factors that are key operators in skeletal muscle differentiation. MyoD and Myf5 genes are selectively activated during development in a time and region-specific manner and in response to different stimuli. However, molecules that specifically regulate the expression of these two genes and the pathways involved remain to be determined.

Growth and differentiation of C2 myogenic cells are dependent on serum response factor.

In order to study to what extent and at which stage serum response factor (SRF) is indispensable for myogenesis, we stably transfected C2 myogenic cells with, successively, a glucocorticoid receptor expression vector and a construct allowing for the expression of an SRF antisense RNA under the direction of the mouse mammary tumor virus long terminal repeat. In the clones obtained, SRF synthesis is reversibly down-regulated by induction of SRF antisense RNA expression by dexamethasone, whose effect is antagonized by the anti-hormone RU486. Two kinds of proliferation and differentiation patterns have been obtained in the resulting clones.

Expression and activity of serum response factor is required for expression of the muscle-determining factor MyoD in both dividing and differentiating mouse C2C12 myoblasts.

To understand the mechanism by which the serum response factor (SRF) is involved in the process of skeletal muscle differentiation, we have assessed the effect of inhibiting SRF activity or synthesis on the expression of the muscle-determining factor MyoD. Inhibition of SRF activity in mouse myogenic C2C12 cells through microinjection of either the SRE oligonucleotide (which acts by displacing SRF proteins from the endogenous SRE sequences), purified SRF-DB (a 30-kDa portion of SRF containing the DNA-binding domain of SRF, which acts as a dominant negative mutant in vivo), or purified anti-SRF antibodies rapidly prevents the expression of MyoD. Moreover, the rapid shutdown of MyoD expression after in vivo inhibition of SRF activity is observed not only in proliferating myoblasts but also in myoblasts cultured under differentiating conditions.

The serum response factor (SRF) is needed for muscle-specific activation of CArG boxes.

CArG boxes, whose consensus sequence is CC(A/T)6GG, are involved in two very different types of transcriptional responses: response of immediate early genes to serum, mediated by so-called Serum Response Elements (SRE), and transcriptional activation of muscle-specific genes during muscle differentiation. Although previous studies have shown that the Serum Response Factor (SRF) binds to muscular CArG boxes, the role of such a binding in muscle-specific activation of CArG box-dependent genes was not directly demonstrated. Here, by transient co-transfection experiments, we demonstrate that intact SRF is required for muscle-specific transcriptional activation through CArG boxes.

Muscle-specific transcriptional activation by CArG box requires either homophilic or heterophilic interactions of the CArG box binding factors.

CArG boxes (CC(A/T)6GG sequences) are present in various promoters and are able to confer two different types of transcriptional responsiveness: serum inducibility and muscle-specific activation. Inserted upstream from the ubiquitous HSV thymidine kinase promoter, multimerized HCA1 boxes (human cardiac alpha-actin proximal CArG box) behave as strong muscle-specific activating elements. Transient expression assay was used to determine whether the muscle-specific transcriptional activation by the CArG boxes depends on the presence in the vicinity of other specific cis-acting DNA elements.

Activation of gene expression via CArG boxes during myogenic differentiation.

We have studied gene activation via CArG boxes in the context of myogenesis. The proximal CArG box of the human cardiac actin gene (HCA1) stimulates transcription from the herpes simplex virus thymidine kinase (TK) promoter in a tissue-specific fashion. Thus in transient transfection assays, when the expression of chloramphenicol acetyltransferase (CAT) from p(HCA1)4 TKCAT is compared to that derived from p(M1)4 TKCAT which contains an inactive mutated version (M1) of the HCA1 element, high levels of expression are seen in C2 mouse myoblasts and myotubes, and in the T4 myoblast cell line derived from the C3H10T1/2 cell line by 5-azacytidine treatment, whereas only low levels of expression are seen in the mouse L fibroblast cell line.

CC Ar GG boxes, cis-acting elements with a dual specificity. Muscle-specific transcriptional activation and serum responsiveness.

The influence of different CC Ar GG boxes derived from either muscle-specific or serum-responsive genes, on the specificity of different promoters has been investigated. Inserted upstream from an 85 base-pair long minimal promoter of the human cardiac alpha-actin gene, a single copy of both the cognate CC Ar GG element (HCA1) and the c-fos gene serum response element (SRE) stimulate transcription four- to fivefold more efficiently in C2 myogenic cells than in L fibroblastic cells, SRE being two- to threefold more active than HCA1. Inserted upstream from the ubiquitous Herpes simplex thymidine kinase (HSV-tk) promoter, multimerized CC Ar GG boxes behave as strong muscle-specific activating elements, about 20-fold more active in myogenic C2 cells than in L fibroblasts and hepatoma HepG2 cells.

The 'CC.Ar.GG' box. A protein-binding site common to transcription-regulatory regions of the cardiac actin, c-fos and interleukin-2 receptor genes.

We have previously suggested that a repeated sequence motif in the upstream region of the human cardiac actin gene 'CC.Ar.GG', where Ar is an (A + T)-rich six-base-pair-sequence, may be important in the muscle-specific expression of this gene [Minty, A.

Transferrin gene expression in choroid plexus of the adult rat brain.

Transferrin immunoreactivity and transferrin messenger RNA (mRNA) were recently found to be present in oligodendrocytes of the adult rat brain by using immunohistochemistry and in situ hybridization procedure. The present study demonstrates, in the same way, that epithelial cells of the choroid plexus also contain transferrin together with transferrin mRNA. Choroid plexus of the lateral and the third ventricle are rich in transferrin mRNA, while choroid plexus of the fourth ventricle contain few if any transferrin mRNA.

In vivo developmental modifications of the expression of genes encoding muscle-specific enzymes in rat.

cDNA clones for rat muscle-type creatine kinase and glycogen phosphorylase and aldolase A were isolated from a rat muscle cDNA library. An additional clone recognizing an unidentified 2.7-kilobase pair mRNA species was also isolated.

Transferrin gene expression visualized in oligodendrocytes of the rat brain by using in situ hybridization and immunohistochemistry.

The presence and production of transferrin in the adult rat brain have been investigated using both immunohistochemistry and in situ hybridization in tissue sections. Indirect immunofluorescence with four distinct antisera against rat and human transferrin and one monoclonal antibody against human transferrin demonstrated labeling of the cytoplasm of oligodendrocytes (a category of glial cells) in most parts of the brain, especially in the white matter. In situ hybridization using rat transferrin 32P-labeled cDNA as a probe revealed the presence of transferrin mRNA in glial cells whose appearance, distribution, and organization exactly matched those of the cells decorated with the transferrin antibodies.

Transient transcriptional inhibition of the transferrin gene by cyclic AMP.

Transferrin mRNA content and gene transcription rate were measured in the liver of rats submitted to iron overload or depletion, castration, treatment with sexual steroid hormones, glucagon and cyclic AMP. The influence of puberty in males and females and of pregnancy was also analysed. Glucagon and cyclic AMP reduced mRNA level by about 50% at the 12th hour of treatment and transferrin gene transcription by as much as 95% at the 30th minute of drug infusion, with a secondary increase of the transcription rate for a protracted treatment.

Expression of the transferrin gene during development of non-hepatic tissues: high level of transferrin mRNA in fetal muscle and adult brain.

Using a cloned rat transferrin cDNA probe, we looked for transferrin mRNA in the various rat tissues during development. In all the cases the mRNA detected seemed to be the same and to be product of a single gene. The transferrin gene is early expressed at a high level during liver differentiation.