Single-cell transcriptomics and proteomics of skeletal muscle: Technology and applications

Skeletal muscle is a heterogeneous organ, composed of different tissues. The properties of skeletal muscle are regulated by myofibers, the contracting cells. Muscles are composed of different types of myofibers that change their phenotypes in response to different stimuli. This makes possible the typical plasticity of skeletal muscle. Each myofiber can be classified according to the expression of myosin heavy-chain isoforms. In mouse muscles, there are four canonical types of myofibers (1, 2A, 2X, and 2B), with the possibility of hybrid composition (1/2A, 2A/2X, 2X/2B). In human type 2B, myofibers do not exist. Interestingly, each myofiber type has specific contractile, metabolic, and resistance to fatigue properties. This chapter will discuss methodological advances to analyze and discover specificities in terms of gene and protein expression of different myofiber types. The advantages of studying single myofibers instead of analyzing whole muscle will also be discussed. Moreover, applications of single-myofiber analysis in healthy and pathological conditions of skeletal muscle will be considered. To conclude the chapter, more recent results on noncoding RNAs of different myofiber types will be presented, evidencing the importance of this new class of genes.