Investigating the correlation of muscle function tests and sarcomere organization in C. elegans

Leila Lesanpezeshki,Masoud Norouzi Darabad,Nathaniel J. Szewczyk,Hiroshi Qadota,Karishma Kashyap,Guy M. Benian,Carla M. R. Lacerda,Siva A. Vanapalli

doi:10.1186/s13395-021-00275-4

Abstract

BackgroundCaenorhabditis elegans has been widely used as a model to study muscle structure and function. Its body wall muscle is functionally and structurally similar to vertebrate skeletal muscle with conserved molecular pathways contributing to sarcomere structure, and muscle function. However, a systematic investigation of the relationship between muscle force and sarcomere organization is lacking. Here, we investigate the contribution of various sarcomere proteins and membrane attachment components to muscle structure and function to introduce C. elegans as a model organism to study the genetic basis of muscle strength.MethodsWe employ two recently developed assays that involve exertion of muscle forces to investigate the correlation of muscle function to sarcomere organization. We utilized a microfluidic pillar-based platform called NemaFlex that quantifies the maximum exertable force and a burrowing assay that challenges the animals to move in three dimensions under a chemical stimulus. We selected 20 mutants with known defects in various substructures of sarcomeres and compared the physiological function of muscle proteins required for force generation and transmission. We also characterized the degree of sarcomere disorganization using immunostaining approaches.ResultsWe find that mutants with genetic defects in thin filaments, thick filaments, and M-lines are generally weaker, and our assays are successful in detecting the functional changes in response to each sarcomere location tested. We find that the NemaFlex and burrowing assays are functionally distinct informing on different aspects of muscle physiology. Specifically, the burrowing assay has a larger bandwidth in phenotyping muscle mutants, because it could pick ten additional mutants impaired while exerting normal muscle force in NemaFlex. This enabled us to combine their readouts to develop an integrated muscle function score that was found to correlate with the score for muscle structure disorganization.ConclusionsOur results highlight the suitability of NemaFlex and burrowing assays for evaluating muscle physiology of C. elegans. Using these approaches, we discuss the importance of the studied sarcomere proteins for muscle function and structure. The scoring methodology we have developed enhances the utility of C. elegans as a genetic model to study muscle function.

Highlights

Caenorhabditis elegans has been widely used as a model to study muscle structure and function
Selection of muscle mutants and prior assessment of muscle function To investigate the relationship between muscle structure and function in C. elegans, we selected 18 muscle proteins (Fig. 1)
This selection was based on (i) proteins that were located at different structural components of the sarcomere, (ii) mutants that have been previously characterized in terms of locomotion (Table 1), (iii) whether these proteins are involved in generating muscle forces versus transmitting them

Summary

Introduction

Caenorhabditis elegans has been widely used as a model to study muscle structure and function. We investigate the contribution of various sarcomere proteins and membrane attachment components to muscle structure and function to introduce C. elegans as a model organism to study the genetic basis of muscle strength. The contractile force generation occurs by the sliding of two filaments composed primarily of the two most abundant muscle proteins—actin and myosin [1]. The contractile force generation and functional performance of the skeletal muscle can be significantly influenced by genetic defects in the contractile apparatus [2]. Mutations such as in ACTN3 and ACE have been shown to improve muscle contractile performance in elite power athletes [3]. Since muscle strength is a useful predictor of all-cause mortality [8], there is a significant interest in uncovering the genetic basis for improved muscle mass [9] and strength [2] with age

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Conclusion