The broad aim of this research proposal is to gain insights into the cellular mechanisms that direct the development and the adaptive growth of the heart. An important aspect of both processes is the "remodeling" of cellular systems through qualitative as well as quantitative changes in gene expression. Thus, in this proposal, we will examine the molecular mechanisms that regulate the expression of contractile protein genes, and specifically, the genes for the cardiac alpha and Beta myosin heavy chains (HC). These proteins are major structural and enzymatic protein of muscle, and their expression is regulated both during development and in adaptive growth resulting in hypertrophy. It is postulated that the control of cardiac myosin HC gene expression is likely to involve of multiple regulatory elements that specify various facets of regulation in a combinatoral manner. Thus, to define the molecular mechanisms directing the changes in gene expression, our approach will be hierarchical-- primarily focusing on those aspects relating to tissue-specific regulation, then relating these mechanisms to modulation of these genes by thyroid hormones, and to the changes in gene expression problems experimentally, we will extend our initial analysis on the transcriptional regulation of the rabbit cardiac myosin HC genes to heart muscle. Tissue-specific expression of the genes will be evaluated in vitro by DNA-mediated gene transfer into cultured cardiac myocytes and in vivo in transgenic mice. The latter approach also may reveal the effects of distant gene sequences on tissue specific regulation. Cis-regulatory sequences that modulate expression in cardiac muscle then will be defined by mutational analyses in DNA-mediated gene transfer experiments. The role of putative trans-acting factors will be established by their DNA-binding properties, and selected protein factors will be characterized through the cloning of their cDNAs. Finally, we will evaluate whether tissue-specific effectors are also involved in controlling the expression of these gene in different physiologic and pathologic states by examining alternations in the expression and binding of nuclear proteins. The identification and characterization of relevant controlling regions of these genes and associated regulatory effector molecules would provide insights into the cellular pathways that may modulate gene expression, and are involved in controlling the growth the heart in normal and pathologic states.