Figure 1. Loss of Vps26 in the eye causes PR degeneration.

(A) Schematic showing the retromer complex associated with an endosomal membrane. Snx3 and Rab7A recruit the Vps35-29-26 trimer to endosomes. Vps35 is one of the protein partners of Vps26 in the retromer. The arrestin-like domain of Vps26 and the α-solenoid domain of Vps35 are aligned with the human homologs. (B) ERG traces of control (iso) and Vps26¹ mosaic eyes at day 0, kept in LD (light intensity = 1,800 lux) for 2, 10, and 21 d; Vps26¹ rescued by an EGFP-tagged genomic rescue construct (GR, Vps26-gEGFP) kept in LD for 21 d; and Vps26¹ kept in DD for 21 d. A UAS-RNAi against the w gene product is expressed in the eyes of the rescued animals (Vps26¹ GR or Vps26² GR) to remove red pigments. On- and off-transients disappear and the amplitude decreases upon 2 d in LD, but remain unchanged upon keeping the flies in DD for 3 wk. The loss of on- and off-transients and reduced depolarization can be fully rescued by the Vps26-gEGFP rescue construct. (C) Quantification of ERG amplitudes of flies kept in LD or DD. Ten ERG traces were recorded for each genotype at the indicated time points. ERG amplitudes are normalized to control PRs recorded at day 0. Light responses of Vps26¹ (or Vps26²) are compared between the mutants kept in LD and those in DD at indicated time points. Student's t test; error bars represent SEM; **p<0.01. (D) Bright field sections of control, Vps26¹, and rescued Vps26¹ flies kept in LD for the indicated periods, or Vps26¹ kept in DD for 21 d. The UAS-w RNAi is expressed in the rescued animals. Newly eclosed Vps26¹ mutants are mostly normal but exhibit an occasional loss of a rhabdomere. The PRs of Vps26¹ are severely impaired after 21 d in LD but remain largely intact in DD. The Vps26-gEGFP rescue construct rescues the PR degeneration of Vps26¹ mutants. Scale bar, 2 µm. (E) Quantification of intact rhabdomere numbers in (D). Thirty ommatidia from three animals were examined for each genotype. Student's t test; error bars are SEM; ** p<0.01; ns, no significance. (F) Molecular lesions in Vps26. Mutations in both alleles alter highly conserved amino acid residues in an arrestin-like domain.