Abstract
Astrocytes have diverse, remarkably complex shapes in different brain regions. Their branches closely associate with neurons. Despite the importance of this heterogeneous glial cell type for brain development and function, the molecular cues controlling astrocyte branch morphogenesis and positioning during neural circuit assembly remain largely unknown. We found that in the Drosophila visual system, astrocyte-like medulla neuropil glia (mng) variants acquire stereotypic morphologies with columnar and layered branching patterns in a stepwise fashion from mid-metamorphosis onwards. Using knockdown and loss-of-function analyses, we uncovered a previously unrecognized role for the transmembrane leucine-rich repeat protein Lapsyn in regulating mng development. lapsyn is expressed in mng and cell-autonomously required for branch extension into the synaptic neuropil and anchoring of cell bodies at the neuropil border. Lapsyn works in concert with the fibroblast growth factor (FGF) pathway to promote branch morphogenesis, while correct positioning is essential for mng survival mediated by gliotrophic FGF signaling.
Highlights
Astrocytes have diverse, remarkably complex shapes in different brain regions
To visualize mng in the Drosophila visual system, we tested several Gal[4] insertions for specific activity (Fig. 1b–c and Supplementary Fig. 1a–d). mng were identified by co-expression of membranebound green fluorescent protein (GFP) and the glial-specific homeodomain transcription factor reversed polarity (Repo)[34], and cell body position at the medulla neuropil border
We found that lapsyn knockdown in astrocyte-like mng severely impaired the infiltration of the adult medulla neuropil by glial processes of dmng, pmng, and lmng (Fig. 3c–e)
Summary
Astrocytes have diverse, remarkably complex shapes in different brain regions In addition to providing tensile strength and metabolic support to neurons, astrocytes influence neuronal activity by regulating extracellular ion and neurotransmitter concentrations at synapses[9, 10] To fulfill these roles, their processes closely associate with neuronal cell bodies, dendritic and axonal arbors and synaptic contacts[10, 11]. The question as to how astrocytes acquire their characteristic shapes at specific locations has so far received little attention Like their vertebrate counterparts, glia in the central nervous system (CNS) of Drosophila melanogaster comprise several populations[10]. In the visual system, we and others previously described an astrocyte-like subtype among medulla neuropil glia (mng) with a columnar branching pattern[29,30,31,32]
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