Centrosome Loss in Embryonic Development Disrupts Axonal Pathfinding and Muscle Integrity

Centrosomes, the primary microtubule-organizing centres (MTOCs), are crucial for early neuronal development, particularly in establishing polarity and promoting axon formation. Once thought dispensable in many terminally differentiated cells, growing evidence shows that many cells retain active centrosomes, while others do not, highlighting context-dependent roles in specialized functions. In some mammalian neurons, centrosome-mediated microtubule (MT) remodelling is essential for axon elongation, with centrosome dysfunction leading to axonal misrouting and growth defects. Although active centrosomes have been detected in embryonic tracheal terminal cells of Drosophila melanogaster , their activity in neurons in vivo has not been observed. Their gradual loss during embryogenesis has been reported as non-essential for organogenesis, as adult flies can eclose without centrioles.

To investigate centrosome activity in neurons, we revisited Drosophila Sas-4 mutants, which exhibit centrosome loss (CL), and observed that 50% of homozygous mutant individuals fail to hatch as larvae. We analysed their development, focusing on the expressivity and penetrance of nervous system phenotypes, and examined centrosome localization in neurons. Our findings confirm the presence of centrosomes in wild-type motor and sensory neurons in Drosophila and their localization near the nascent axon in motor neurons. CL conditions resulted in axonal misrouting and muscle developmental abnormalities. Targeted downregulation of Sas-4 in the pioneer motor neurons aCC, pCC and RP2 induced axon guidance errors, indicating an autonomous role for centrosomes in axonal navigation. Colocalization of acetylated- and γ-tubulin with centrosomes in motor neurons and MT repolymerization analysis further confirmed the presence of active centrosomes in these cells. Analysis of motor axons revealed that CL leads to motor axon tortuosity, a characteristic associated with neurodegeneration. This is the first direct association of CL with axonal morphological phenotypes, highlighting the role of centrosomes in neuronal development and their broader influence on nervous system structure and function.