Visualization of the Cytoskeleton in Fixed Drosophila Embryos

Abstract Embryogenesis necessitates the precise orchestration of cellular events to establish tissue patterning, developmental robustness, and viability. Syncytial embryogenesis, as in Drosophila melanogaster , poses added challenges as the synchronous and rapid nuclear divisions prior to cellularization occur within a shared cytoplasm. While the first several rounds of nuclear divisions occur within the center of the embryo, the nuclei progressively migrate peripherally, giving rise to the syncytial blastoderm. This spatial choreography hinges upon the dynamic interplay of actin and microtubules. Actin and microtubules coordinate nuclear division and position while preventing deleterious nuclear collisions. Additionally, the cytoskeleton also facilitates the segregation of organelles and molecular cargoes, including cell fate determinants required for cellular differentiation. As development progresses, actin and microtubules drive cellularization events for both germline and somatic cell lineages. Cytoskeletal disruption causes developmental arrest and embryonic lethality, underscoring its importance for embryogenesis. Given the significance of the cytoskeleton to these events, its visualization remains a cornerstone of cell and developmental biology research. Indeed, studies of the Drosophila embryo cytoskeleton have yielded valuable insights into cell biological mechanisms and developmental pathways conserved in various systems. Nevertheless, achieving optimal preservation of filamentous cytoskeletal structures poses technical challenges. Here, we present an embryo fixation method tailored to enhance the visualization of actin and microtubules via standard light microscopy approaches. This protocol complements immunofluorescence and molecular labeling techniques, including the direct labeling of fluorescently tagged proteins or mRNAs. By enabling detailed analysis of the cytoskeleton, this method expands opportunities to investigate the molecular mechanisms underlying embryo development and related processes. © 2025 Wiley Periodicals LLC. Basic Protocol 1 : Preparation of embryos for immunofluorescence of actin or microtubules Basic Protocol 2 : Coupling immunofluorescence of the cytoskeleton with visualization of mRNAs via smFISH