The mouse synemin gene encodes three intermediate filament proteins generated by alternative exon usage and different open reading frames.

We have previously cloned and characterized the human synemin gene, which encodes two intermediate filament proteins (IFPs). We now show that the mouse synemin gene encodes three different synemin isoforms through an alternative splicing mechanism. Two of them, synemin H and M are similar to human alpha and beta synemin, and the third isoform, L synemin, constitutes a new form of IFP. It has a typical rod domain and a short tail (49 residues) with a novel sequence that is produced by a different open reading frame. The synthesis of H/M synemins starts in the embryo, whereas the synemin L isoform is present in adult muscles. The H/M isoforms are bound to desmin or vimentin in the muscle cells of wild-type mice. Using desmin- and vimentin-deficient mice, we have obtained direct evidence that synemin is associated with muscle intermediate filaments in vivo. The organization of the synemin fibril is disrupted in skeletal and cardiac muscle when desmin is absent and in smooth muscle when vimentin is absent. The fact that the three synemin isoforms differ in the sequences of their tail domains as well as in their developmental patterns suggests that they fulfill different functions.

Human synemin gene generates splice variants encoding two distinct intermediate filament proteins.

Intermediate filament (IF) proteins are constituents of the cytoskeleton, conferring resistance to mechanical stress, and are encoded by a dispersed multigene family. In man we have identified two isoforms (180 and 150 kDa) of the IF protein synemin. Synemin alpha and beta have a very short N-terminal domain of 10 amino acids and a long C-terminal domain consisting of 1243 amino acids for the alpha isoform and 931 amino acids for the beta isoform. An intronic sequence of the synemin beta isoform is used as a coding sequence for synemin alpha. Both mRNA isoforms (6.5 and 7.5 kb) result from alternative splicing of the same gene, which has been assigned to human chromosome 15q26.3. Analyses by Northern and Western blot revealed that isoform beta is the predominant isoform in striated muscles, whereas both isoforms (alpha and beta) are present in almost equal quantities in smooth muscles. Co-transfection and immunolabeling experiments indicate that both synemin isoforms are incorporated with desmin to form heteropolymeric IFs. Furthermore synemin and desmin are found aggregated together in certain pathological situations.

Cardiac functional improvement by a human Bcl-2 transgene in a mouse model of ischemia/reperfusion injury.

BACKGROUND: Apoptosis has been shown to contribute to myocardial reperfusion injury. It has been suggested that, in reducing the apoptotic component within the ischemic area at risk, Bcl-2 overexpression could lead to a ventricular function improvement. METHODS: Transgenic mice overexpressing the anti-apoptotic human Bcl-2 cDNA in heart were subjected to a 1-h left coronary artery occlusion followed by a 24-h reperfusion. At the end of the experiment, left ventricular function was assessed by two-dimensional echocardiography. After sacrifice, the area at risk (AR) and the infarct area (IA) were determined by Evans blue and triphenyltetrazolium chloride staining, respectively. The extent of apoptosis was assessed by the TUNEL method. Non-transgenic littermates served as controls. RESULTS: Baseline AR was not different between Bcl-2 transgenic mice and their wild-type littermates. In contrast, left ventricular ejection fraction was significantly improved in the transgenic mice line (61.25 +/- 4.0%) compared to non-transgenic littermates (43.2 +/- 5.0%, p < 0.01). This functional amelioration was correlated with a significant reduction of infarct size in transgenic animals (IA/AR 18.51 +/- 3.4% vs 50.83 +/- 8.4% in non-transgenic littermates). Finally, apoptotic nuclei were less numerous in transgenic mice than in controls as quantified by TUNEL analysis (8.1 +/- 2.2% vs 20.6 +/- 4.4%). CONCLUSIONS: Bcl-2 overexpression is effective in reducing myocardial reperfusion injury and improving heart function. This benefit correlates with a reduction of cardiomyocyte apoptosis. The apoptotic component of ischemia/reperfusion injury could therefore constitute a new therapeutic target in the acute phase of myocardial infarction.

Characterization of the dystrophin-syntrophin interaction using the two-hybrid system in yeast.

The carboxy-terminal region of dystrophin has previously been shown to interact directly with alpha1 syntrophin, a cytoplasmic component of the dystrophin-glycoprotein complex, by in vitro biochemical studies such as overlay assay or immunoprecipitation. Using the two-hybrid system, we have isolated from a human heart cDNA library the entire coding sequence of human alpha1 syntrophin, therefore confirming for the first time this interaction via an in vivo approach. In addition, we have reduced the interaction domain to the distal half of alpha1 syntrophin.