Meeting Abstract
Mechanisms of neuromuscular plasticity continue to be of interest as new models of integral muscle proteins are presented. We are specifically interesting in Nishikawa et al.’s winding filament theory (2012; Proc R Soc B) and its implications for understanding plastic events like catch tension, which have been difficult to explain at the molecular level. Here we describe our new model for investigating the role of giant sarcomere associated proteins (gSAPs), such as titin, in a simple arthropod model: the larval fruit fly. Much research has shown that among mollusks and arthropods, gSAPs contribute significantly to force production and are modulated by neurotransmitters (e.g. 5-HT), neuromodulators (e.g. octopamine), and divalent cations (i.e. Ca2+). We further suspect many instances of neuromuscular plasticity might be explained by the physiology of gSAPs. We describe here a novel in vivo system to examine the physiological role(s) of gSAPs using an RNAi approach. We utilize temperature sensitive [Gal80(ts)] regulation of the Gal4-UAS system to invoke RNAi against the sallimus gene (sls) while over-expressing Dicer2. sls encodes at least five gSAPs in D. melanogaster, all of which may exist in multiple isoforms. Our expression system allows us to vary the magnitude of sls expression by varying RNAi activation. We report here early findings on the difference between reduced gSAP expression and wildtype neuromuscular physiology; namely, principal components of isometric contraction – amplitude, rise, and decay constants. Lastly, we propose an extension of the winding filament theory; that gSAP wrapping should yield a tether between actin and myosin with progressively increased damping as acto-myosin interaction increases. We hypothesize that in the absence of such a tether (gSAPs), force should vary more widely when driven by a range of motoneuron frequencies.
