Visual system function requires translational regulation of ATF4 by Hbs1-Pelo

Deletion mutations in the translation termination factor HBS1L result in progressive loss of vision in human patients, amongst other developmental anomalies. The etiology of vision defects seen with HBS1L deletion remains unknown. Here, we use the Drosophila visual system to demonstrate that the HBS1L ortholog, Hbs1, and its interaction partner, Pelo, are required for proper phototransduction. Hbs1 mutants showed 'vacuolization' of the lamina layer, indicative of defective synapse transmission between photoreceptors and lamina neurons. Depleting Hbs1 in lamina neurons replicated the phototransduction defects seen in Hbs1 mutants, suggesting that Hbs1-Pelo is required for proper lamina neuron function. Mechanistically, we found that loss of HBS1L in both Drosophila and cultured human cells results in reduced levels of the stress responsive Activating Transcription Factor 4 (ATF4). Strikingly, restoring ATF4 expression in the lamina partially rescues ERG defects in Hbs1 mutants, indicating that ATF4 is likely a relevant mRNA target regulated by Hbs1-Pelo in these cells. Together, we propose a model wherein Hbs1-Pelo-mediated translation regulation of ATF4 in lamina neurons underlies the inherited retinal disease caused by HBS1L deletion.