Glia instruct developmental neuronal remodeling through TGF-β signaling

Abstract

We found that glia secrete myoglianin, a TGF-β ligand, to instruct developmental neural remodeling in Drosophila. Glial myoglianin upregulated neuronal expression of an ecdysone nuclear receptor that triggered neurite remodeling following the late-larval ecdysone peak. Thus glia orchestrate developmental neural remodeling not only by engulfment of unwanted neurites but also by enabling neuron remodeling.

Figure 1. Expression of myo transcripts in the larval brain

(a-d) Expression of myo transcripts detected by in situ hybridization in brains of early third (a), middle third (b) and wandering third instar larvae (c-d). Cortex layer (c) and inner brain region (d) are shown. (e-h) Signals of myo transcripts (arrows) co-localized with the cell bodies of cortex glia (f) and astrocyte-like glia (h), which were labeled with nuclear-lacZ (NZ, magenta). Scale bars = 50 μm.

Figure 2. Effect of glial silencing of myo on MB remodeling

(a-d) Remodeling of MB axonal lobes during metamorphosis. MB lobes labeled with anti-Fas2 (b,d) and their schematic illustration (a,c) in control (a,b) and repo>myo-RNAi (dsRNA) (c,d) at WL, 18h APF and adult. Arrows show larval lobes of γ neurons (b,d). Note that, in repo>myo-RNAi (d), larval γ lobes persist at 18h APF (arrows with asterisk) and adult (γ*). (e-m) Expression of EcR-B1 in wandering larva of control (e,h,k), repo>myo- miRNA (f,g,i,j,l,m). The myo-miRNA resistant myo was co-expressed in glia (g,j,m). Arrows show bi-lateral clusters of MB γ neurons (e-g). High magnification view of larval MB neurons stained with anti-EcR-B1 antibody (h-m). Cell bodies of MB neurons were counter-labeled with MB247>rCD2::GFP in lower panels (k-m). Scale bars = 50 μm.

Figure 3. Effect of loss of function mutation of myo on MB remodeling

(a) Genome organization of myo deletion mutant. (b) RT-PCR of myo transcript in the myo^Δ1 mutant. (c-h) Expression of EcR-B1 in MB γ neurons in myo^Δ1 white pupa (c,f) and prepupa (d,g) and control prepupa (e,h). Counter-labeling of cell bodies of MB neurons with MB247>rCD2::GFP are shown (f-h). (i-n) Effect of myo overexpression in the myo^Δ1 mutant with (i-k) and without (l-n) glial expression. Expression of EcR-B1 in MB γ neurons in white pupae (i,l). MB lobes of 18h APF (j,m) and adult brain (k,n) labeled with anti-Fas2. The myo overexpression was induced by myo-GAL4 (i-n) and glial expression was suppressed with repo-GAL80 (l-n). Scale bars = 50 μm.