Cofilin Loss in Drosophila Muscles Contributes to Muscle Weakness through Defective Sarcomerogenesis during Muscle Growth

Abstract

SUMMARY Sarcomeres, the fundamental contractile units of muscles, are conserved structures composed of actin thin filaments and myosin thick filaments. How sarcomeres are formed and maintained is not well understood. Here, we show that knockdown of Drosophila cofilin ( DmCFL ), an actin depolymerizing factor, disrupts both sarcomere structure and muscle function. The loss of DmCFL also results in the formation of sarcomeric protein aggregates and impairs sarcomere addition during growth. The activation of the proteasome delays muscle deterioration in our model. Furthermore, we investigate how a point mutation in CFL2 that causes nemaline myopathy (NM) in humans affects CFL function and leads to the muscle phenotypes observed in vivo . Our data provide significant insights to the role of CFLs during sarcomere formation, as well as mechanistic implications for disease progression in NM patients.

Analyzing muscle structure and function throughout the larval instars in live Drosophila

“…Quantification of larval crawling velocity by tracking larval movement serves as a proxy for muscle function and can help understand how mutations in genes involved in muscle development and function can affect muscle contraction, thereby impairing larval movement. In control larvae, larval locomotion velocity increases as the larvae progress through the instars [ Figure 5 I, ( Balakrishnan et al., 2020 )]. This increase in locomotion velocity throughout larval stages is consistent with an increase in muscle size that occurs during the instars ( Balakrishnan et al., 2020 , Demontis and Perrimon, 2009 , Bawa et al., 2020 ).…”

“…In control larvae, larval locomotion velocity increases as the larvae progress through the instars [ Figure 5 I, ( Balakrishnan et al., 2020 )]. This increase in locomotion velocity throughout larval stages is consistent with an increase in muscle size that occurs during the instars ( Balakrishnan et al., 2020 , Demontis and Perrimon, 2009 , Bawa et al., 2020 ). Mutations in genes affecting larval locomotion thus far have predominantly decreased locomotion, with very few mutations identified that increase locomotion of the larva ( Camuglia et al., 2018 ).…”

“…Examining muscle structure in control larvae highlights that both sarcomere and muscle structure, which are established in the late embryonic stages, are maintained throughout the larval stages with an increase in sarcomere number as muscles grow ( Balakrishnan et al., 2020 ). In control muscles, sarcomere size remains the same as muscles increase in size ( Balakrishnan et al., 2020 ).…”

“…Here, we present a workflow for systematically analyzing muscle structure and function at discrete larval stages, as well as throughout the larval instars, using both newly developed and adapted methods. For complete details on the use and execution of this protocol, please refer to Balakrishnan et al. (2020) .…”

“…For complete details on the use and execution of this protocol, please refer to Balakrishnan et al. (2020) .…”