Actin-dependent astrocytic infiltration is a key step for axon defasciculation during remodeling

Astrocytes are essential for synapse formation, maturation, and plasticity; however, their function during developmental neuronal remodeling is largely unknown. To identify astrocytic molecules required for axon pruning of mushroom body (MB) γ neurons in Drosophila, we profiled astrocytes before (larva) and after (adult) remodeling. Focusing on genes enriched in larval astrocytes, we identified 12 astrocytic genes that are required for axon pruning, including the F-actin regulators Actin-related protein 2/3 complex, subunit 1 (Arpc1) and formin3 (form3). Interestingly, perturbing astrocytic actin dynamics does not affect their gross morphology, migration, or transforming growth factor β (TGF-β) secretion. In contrast, actin dynamics is required for astrocyte infiltration into the axon bundle at the onset of pruning. Remarkably, decreasing axonal adhesion facilitates infiltration by Arpc1 knockdown (KD) astrocytes and promotes axon pruning. Conversely, increased axonal adhesion reduces lobe infiltration by wild-type (WT) astrocytes. Together, our findings suggest that actin-dependent astrocytic infiltration is a key step in axon pruning, thus promoting our understanding of neuron-glia interactions during remodeling. [Display omitted] •Larval and adult astrocytic transcriptome reveals potential neuro-glia interactions•Astrocytic F-actin regulating genes are required for neuronal remodeling•Arpc1-KD astrocytes show reduced infiltration into the axon bundle before pruning•Interplay between astrocytic infiltration and axonal adhesion regulate axon pruning Marmor-Kollet et al. profile Drosophila larval and adult astrocytes to identify astrocytic genes potentially important for neuronal remodeling of mushroom body neurons. Astrocytic Arpc1, a branched F-actin nucleator, is required for infiltration into the axon bundle prior to pruning. The interplay between astrocytic infiltration and axonal adhesion governs axon pruning.