Figure 6. Dscam4 acts in the same pathway as Dscam2 to direct L4 dendritic targeting.

(A) Diagram of Dscam4 locus and mutant allele. Dscam4 allele is a MiMIC insertion bearing a splice acceptor (SA), followed by translational (red octagon) and transcriptional stops (pA). Translation start site and sequences encoding transmembrane domain are denoted with an arrow and orange band, respectively. Genomic sequence contained within a BAC is also indicated.

(B) MARCM analysis of Dscam4 mutant L4 neurons showing that the BAC rescues the dendritic patterning phenotype.

(C) Constitutive Dscam4 reporter (left panel) driving myr-tdTom (red) at 24 h APF. Scale bar, 15 μm. Dscam4 expression in each lamina neuron subtype was confirmed with a conditional reporter (right panels) with L1–L5 identified by their unique cell body positions, dendritic and axonal morphologies. This conditional reporter is only expressed in lamina neurons where the presence of a lamina-specific recombinase induces excision of an FRT-cassette, which otherwise prevents its expression. See Figure S7F for reporters. Scale bar, 5 μm.

(D) Constitutive Dscam4 reporter driving nuc-GFP reveals expression in R3 cells in the retina at 24 h APF (left panel). At 48 h APF, sporadic expression in R7 cells is seen in addition to R3 (right panel). mδ-GAL4 driving myr-tdTom and anti-ELAV staining are in red and magenta, respectively. Scale bar, 5 μm.

(E,F) MARCM analysis of Dscam4 in adults (E) and at 24 h APF (F). Data for control and Dscam2 samples are the same as in Figure 1G (for adults) and Figure 3B (for 24 h APF) as these were collected at the same time.