| Summary: | Loss of muscle homeostasis can lead to muscle atrophy, the severe wasting of muscle mass associated with clinical conditions such as cancer, diabetes and heart failure and which occurs progressively in the elderly increasing morbidity and mortality. Several extracellular signals are known to be associated with muscle atrophy in humans; however the regulatory intramuscular signalling mechanisms are incompletely understood. To identify new regulators of muscle homeostasis and to gain insight into the global regulation of a single tissue in vivo, the effect of knockdown of 401 kinase-encoding genes (kinome) and 193 phosphatase-encoding genes (phosphatome) by RNAi was examined. A strain containing a muscle lacZ reporter established to read out on cytosolic muscle protein degradation and two GFP strains established to identify dystrophies of myofibres, mitochondria and nuclei were employed. This screen identified 161 kinases and 98 phosphatases which appear to negatively regulate cytosolic protein degradation, mitochondrial dynamics or sarcomere assembly. Functional clustering of genes identified to induce cytosolic protein degradation upon RNAi knockdown into known proteolytic signalling mechanisms demonstrated that half appear to contribute to autophagy-mediated degradation and two thirds signal through MPK-1. Construction of predicted interaction networks between the genes identified illustrated testable models of regulation. In summary, this study quantified the complexity of the regulation of muscle homeostasis and specific subcellular processes by the kinome and phospatome and provides a platform for further study of individual kinases and phosphatases within a single tissue in vivo. As 70% of the genes identified have human orthologues or homologues of which 60% are known to be expressed in human skeletal muscle, knowledge about these genes may be transferred to humans for further study of muscle atrophy. Identification of potential signalling mechanisms and coordinate regulation of different subcellular processes may provide opportunities for the application of specific inhibitory drugs for use in clinical practice.
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