Identifying novel molecular players involved in patterning the dorsal longitudinal muscles of Drosophila melanogaster

Abstract

Pattern formation, a fundamental concept in developmental biology, describes how living systems organise complex structures from initially undifferentiated cells. This process, influenced by genetic information, underpins the spatial and temporal organisation of tissues and organs. Muscles, particularly in Drosophila melanogaster, serve as a model for understanding these mechanisms due to their evolutionary significance and relevance to congenital disorders. The development of Drosophila muscles showcases pattern formation through two phases: embryonic and adult myogenesis. Adult muscles like the indirect flight muscles (IFMs), including the dorsal longitudinal muscles (DLMs), arise in specific spatial arrangements, enabling essential functions like flight. This study utilised Drosophila to explore the molecular players regulating DLM patterning, focusing on RNA-binding Fox protein 1 (Rbfox1), a conserved splicing factor. Rbfox1, critical for muscle differentiation, exhibits a bimodal expression pattern during flight muscle development, with peaks corresponding to myoblast fusion and myofibrillogenesis. Investigations revealed its essential role, during late stage of adult myogenesis, in fibre-type specificity, alternative splicing, and transcriptional regulation. Specifically, Rbfox1 modulates the production of fibrillar muscle-specific isoforms, such as those of Wings up A, influencing sarcomere contraction. Its interaction with other splicing factors, like Bruno 1, underscores a coordinated mechanism of muscle differentiation. During early myogenesis, Rbfox1 and the conserved microRNA mir-33 regulate the JAK/STAT signalling pathway, controlling stem cell maintenance and actin dynamics. Misregulation of several players leads to developmental defects, highlighting that that their expression be optimum for their context-dependent roles. Studies also identified regulators like E(spl)m8-HLH, an effector of Notch signalling, and the conserved microRNA mir-9a, which modulate Rbfox1 expression via feedback loops, revealing layers of transcriptional and post-transcriptional control. Further research identified genetic interactions between Rbfox1 and microtubule star, which encodes the catalytic subunit of Protein phosphatase 2A, linked to signalling pathways like Hedgehog and Wingless, influencing muscle patterning. Explorations of CRISPR-based mutants affecting flight muscles and systemic aging further underscored broad implications of muscle development. In conclusion, this study elucidates the dual roles Rbfox1 in early and late myogenesis, offering insights into the temporal and spatial control of gene expression during muscle development. By integrating genetic, molecular, and developmental approaches, these findings contribute to a deeper understanding of pattern formation, and its evolutionary and clinical significance.