Examples of transgene expression. A: mpeg1:mCherry-CAAX that induced mCherry expression in microglia of the optic tectum. B: mpeg1:Gal4, UAS:YFP-dre-miR-124-1 in microglia of the optic tectum. C: mpeg1:Gal4, UAS:YFP-dre-miR-124-1 (miR-124 expression in microglia) on a ubiquitous mCherry and miR-124 sponge expression background. Note, βactin:mCherry-SP124, mpeg1:eGFP (miR-124 sponge) is identical to this expression with eGFP in place of the YFP-dre-miR-124-1. D: mpeg1:mCherry-CAAX expressing mCherry in microglia of the optic tectum with elavl3 driven YFP-dre-miR-124-1. No clear morphology differences were observed between the transgenic models. Subparts (A) and (B) are maximum intensity projections of the fluorophore channel overlaid on a single slice in the bright field channel at 5 and 6dpf, (C) is a maximum intensity projection of the YFP channel (representing the microglial dre-miR-124-1 and YFP expression) overlaid on a single slice from the mCherry channel (representing βactin driven mCherry and sponge expression) at 5dpf, and (D) is a maximum intensity projection of the microglial mCherry expression and the elavl3 driven dre-miR-124-1 and YFP expression at 6dpf. Scale = 50µm.

Successful microglial scavenging versus left over apoptotic cells. A: Representative region of the optic tectum of an mpeg1:mCherry-CAAX larva at 5dpf. The arrow indicates an apoptotic cell which stands out from the cell layer background, the magenta coloured signal is a microglial process engulfing the cell. B: A representative region of the optic tectum of an mpeg1:Gal4, UAS:YFP-dre-miR-124-1 larvae at 5dpf. Many free-lying apoptotic cells are present on top of the cell layer, the yellow signal is a microglial process in contact with a dead cell. CB, cerebellum, CL, cell layer, Np, neuropil. Scale = 10 µm. C: Residual apoptotic cell body counts for the miR-124 overexpression and rescue in larvae when ≥10 occurred in one or both tectal hemispheres. D: Phagocytic profile of microglia in the optic tectum over the 3-7dpf period. Control microglia, CI: 6.08-6.7; miR-124 overexpressing, CI: 3.01-3.45; miR-124 sponge, CI: 5.7-6.37; rescue, CI: 3.62-4.13.