Frederick Schachat

We are working in three areas. The first focuses on the mechanisms that coordinate contractile protein expression in striated muscle. A variety of approaches, including comparative genomics, cDNA analysis, PCR, and genetic/biochemical analyses of expression in transgenic mice and C. elegans mutants are being used to define the how the expression of different thin filament proteins is coordinated and how the accumulation of thick and thin filament proteins is regulated. As models, we study the troponin-tropomyosin thin filament calcium regulatory complex of mammalian skeletal muscle and uncoordinated mutants of the nematode C. elegans whose phenotypes are consistent with disproportionate synthesis of thick and thin filament proteins.

The second concerns the biomoleuclar interactions involved in the cooperative activation of thin filaments in skeletal muscle contraction. These studies involve the analysis of Ca2+ and rigor crossbridge activation of skeletal muscle fibers in the presence of inhibitory peptides and following the substitution of calmodulin[troponin C] chimeras for troponin C, the Ca2+-binding subunit of the thin filament regulatory complex.

The third centers on the novel proteins and physiological systems responsible for the superfast contractile properties of extraocular muscle. These include extraocular myosin, whose gene we have cloned and mapped, a rare alternative splice variant of troponin T, and selective amplification of the Ca2+-reuptake system.

Overall, we have characterized the troponin T (TnT) and tropomyosin (Tm) species expressed in fast skeletal muscles and identified three programs of TnT-Tm expression in adult and neonatal muscle. Complementing physiological studies show that these different TnT-Tm programs control a muscle fiber's responsiveness to calcium. Strong evidence that posttranscriptional controls are critical to the coordinate expression of myofibrillar proteins has been found; and phylogenetic footprinting provides evidence for hierarchical control of the extraocular muscle specific myosin.