A transcriptomics resource reveals a transcriptional transition during ordered sarcomere morphogenesis in flight muscle

Abstract

Muscles organise pseudo-crystalline arrays of actin, myosin and titin filaments to build force-producing sarcomeres. To study sarcomerogenesis, we have generated a transcriptomics resource of developing Drosophila flight muscles and identified 40 distinct expression profile clusters. Strikingly, most sarcomeric components group in two clusters, which are strongly induced after all myofibrils have been assembled, indicating a transcriptional transition during myofibrillogenesis. Following myofibril assembly, many short sarcomeres are added to each myofibril. Subsequently, all sarcomeres mature, reaching 1.5 µm diameter and 3.2 µm length and acquiring stretch-sensitivity. The efficient induction of the transcriptional transition during myofibrillogenesis, including the transcriptional boost of sarcomeric components, requires in part the transcriptional regulator Spalt major. As a consequence of Spalt knock-down, sarcomere maturation is defective and fibers fail to gain stretch-sensitivity. Together, this defines an ordered sarcomere morphogenesis process under precise transcriptional control – a concept that may also apply to vertebrate muscle or heart development.

Dissection of <em>Drosophila melanogaster</em> Flight Muscles for Omics Approaches

“…IFMs are the largest muscles in the fly, spanning nearly 1 mm across the entire length of the thorax in adults 31,32 . However, this small size generates the challenge of obtaining enough sample to apply omics technologies in Drosophila in a tissue-type specific manner.…”

“…The myofibers then grow to span the entire length of the thorax, with myofibrils undergoing an initial growth phase focused on sarcomere addition until about 48 h APF, and then transitioning to a maturation phase, in which sarcomeres grow in length and width and are remodeled to establish stretch-activation by 72 h APF ( Figure 1A-D) 32,35 . The onset of fiber maturation is at least partially controlled by Salm and E2F 32,36,37 , and multiple IFM-specific sarcomere protein isoforms whose splicing is controlled by Bru1 are incorporated during this phase 16,17 . Mature flies eclose from 90-100 h APF.…”

Matrix metalloproteinase 1 modulates invasive behavior of tracheal branches during ingression intoDrosophilaflight muscles

“…In Drosophila, two sets of IFMs, the dorsal-longitudinal muscles (DLMs) and the perpendicularly oriented dorso-ventral muscles (DVMs) are anchored to the thoracic cuticle and move the wings indirectly by deforming the thoracic exoskeleton rather than by acting directly on the wings. Each adult IFM is approximately 1 mm long and 100 µm wide (Spletter et al, 2018) and contains about 1000 nuclei (Rai & Nongthomba, 2013). To supply these large muscles with sufficient oxygen, an extensive network of gas-filled tracheal tubes not only superficially enwraps the IFMs, but also invades the myotube interior.…”

RNA Interference Screening for Genes Regulating Drosophila Muscle Morphogenesis

“…Depending on which structure should be observed this preparation is suitable for fast imaging, including laser micro-lesions followed by imaging with a spinning disc confocal [19], long-term imaging over several hours observing myoblast fusion or attachment, or high resolution imaging observing myofibrillogenesis using a two-photon microscope [19,20]. It can also be used to quantify spontaneous muscle contractions using a regular scanning confocal microscope with a fast scanning option [21] 4 Notes 1. In the GAL4 stock, using a Y-heat-shock-hid virginizer chromosome facilitates virgin collection [22].…”

“…7. The ImageJ plugin MyofibrilJ (https://imagej.net/MyofibrilJ) can be used for detailed analysis of sarcomere phenotypes as it allows measuring sarcomere length and width automatically using Phalloidin labelled-muscles [21]. 8.…”