Alary muscles and TARMs, a novel type of striated muscles maintaining internal organs positions

Abstract

Alary muscles (AMs) have been described as a component of the cardiac system in various arthropods. Lineage-related thoracic muscles (TARMs), linking the exoskeleton to specific gut regions, have recently been discovered in Drosophila. Asymmetrical attachments of AMs and TARMs, to the exoskeleton on one side, and internal organs on the other, suggested an architectural function in moving larvae. Here, we analysed AMs and TARMs striated organisation, and imaged their atypical deformability in crawling larvae. We then selectively eliminated AMs and TARMs by targeted apoptosis. Elimination of AMs revealed that AMs are required for suspending the heart in proper intra-hemocelic position and opening of the heart lumen, and constrain the curvature of the trachea, the respiratory system, during crawling; TARMs are required for proper positioning of visceral organs and efficient food transit. AM/TARM cardiac versus visceral attachment depends on Hox control, with visceral attachment being the ground state. TARMs and AMs are the first example of multinucleate striated muscles connecting the skeleton to the cardiac and visceral systems in bilaterians, with multiple physiological functions.