Fig. 1.

Liprin-α is required for R7 photoreceptor targeting. (A–C) Horizontal sections of adult heads carrying glass-lacZ to label all photoreceptors, stained with anti-β-gal. (A) WT. Photoreceptors project to the lamina (la) and medulla (me). R7 and R8 terminate in two distinct layers in the medulla (arrowheads). (B and C) In Liprin-α^oos homozygous mutants (B) and in LAR null mutants (C), only one layer of termini is present in the medulla (arrowhead). (D) oos flies have a nonsense mutation predicted to truncate the Drosophila Liprin-α gene within the N-terminal coiled-coil domain. The C-terminal liprin homology domain (LHD) of Liprin-α binds to the PTP-D2 domain of LAR. The extracellular domain of LAR, containing three Ig domains and nine fibronectin type III domains, is not shown. Three tyrosine residues (Y) within the LHD of Liprin-α are highly conserved throughout evolution. (E) Tangential section of a retina containing a small Liprin-α^oos mutant clone. The central R7 rhabdomere is present in both pigmented WT regions (yellow arrows) and unpigmented, mutant regions (red arrows). (F) Horizontal section of an adult head with Liprin-α^oos mutant clones carrying the PanR7-lacZ reporter to label all R7 photoreceptors, stained with X-Gal. Liprin-α^oos mutant R7 axons (brackets) terminate more superficially than surrounding WT R7 photoreceptors. (G and H) R1–R6 project from the retina (re) to the lamina (la) in both WT (G) and Liprin-α^oos (H) horizontal sections of adult heads carrying the Rh1-lacZ reporter and stained with anti-β-gal. (I) shows a Liprin-α^oos mutant whole-mount optic lobe at 24 h after puparium formation stained with anti-β-gal to reveal glass-lacZ expression. At this stage, most R7 termini are clearly separated from the R8 layer. A maximum intensity projection of six optical sections spanning ≈3 μm along the z axis is shown. (J) Horizontal head sections of the indicated genotypes carrying glass-lacZ were stained with anti-β-gal and scored for R7-targeting defects. In Liprin-α^oos homozygous mutants, only 37% of R7 axons project beyond the R8 layer. Expression of HA-tagged Liprin-α from two independent transgene insertions (#21 and #43) in all neurons with elav-GAL4 or in R7 with sev-GAL4 rescued R7 targeting to almost the WT level. HA-Liprin-α expression driven in R8 by 109.68-GAL4 did not improve R7 targeting. Number of cartridges counted are given in parentheses in this and subsequent figures.