Smilja Jakovcic

Control of myosin heavy chain expression in cardiac hypertrophy

The control of myosin expression by thyroid hormone is analyzed as an example of compensatory mechanisms of the heart. Two topics are discussed in detail: polymorphism of cardiac myosin heavy chains in the mammalian heart, and effect of thyroid hormone on myosin heavy chain expression by thyroid hormone. Our current knowledge about the identity of heavy chains and their corresponding isomyosins myosins is summarized and the dynamic nature of the myosin phenotype of the heart is discussed. The data on the thyroid hormones role include studies in which the synthesis rate of the 2 classes of heavy chains (alpha and beta) was compared with their respective messenger RNA levels. A close correlation was observed and is consistent with pretranslational control. Transcription of myosin heavy chain genes was examined using isolated nuclei in a run-off experiment The rate of gene transcription was found to be the principal determinant of the cytoplasmic level of messenger RNA and of the isomyosin composition of the heart.

Structural and phylogenetic analysis of the chicken ventricular myosin heavy chain rod

SummaryWe have isolated and characterized five overlapping clones that encompass 3.2 kb and encode a part of the short subfragment 2, the hinge, and the light meromyosin regions of the myosin heavy chain rod as well as 143 bp of the 3′ untranslated portion of the mRNA. Northern blot analysis showed expression of this mRNA mainly in ventricular muscle of the adult chicken heart, with trace levels detected in the atrium. Transient expression was seen in skeletal muscle during development and in regenerating skeletal muscle following freeze injury. To our knowledge, this is the first report of an avian ventricular myosin heavy chain sequence. Phylogenetic analysis indicated that this isoform is a distant homolog of other ventricular and skeletal muscle myosin heavy chains and represents a distinct member of the multigene family of sarcomeric myosin heavy chains. The ventricular myosin heavy chain of the chicken is either paralogous to its counterpart in other vertebrates or has diverged at a significantly higher rate.

Characterization of monoclonal antibodies directed against determinants on cardiac myosin heavy chain.

Summary Monoclonal antibodies against cardiac myosin from chicken (18d embryos) and rabbit were produced in vitro by fusion of mouse myeloma cells (P3-X63-Ag8) with spleen cells from immunized BALB/c mice and Lewis rats. Three antibodies were examined and found to react with different antigenic determinants in the myosin heavy chain subunit. Antibody RCM-79 reacted specifically with heavy meromyosin. Antibodies CCM-13 and RCM-79 reacted with equal affinities to cardiac myosin from chicken, rabbit, rat, and man, but with lower affinities to skeletal muscle myosins from chicken and rabbit. Antibody CCM-31A reacted only to chicken cardiac myosin and not to other cardiac or skeletal myosins tested. Our results show that monoclonal antibodies can be produced that are either specific for sequences common to all of the cardiac myosins examined or unique to the immunizing type.