Abstract
Purpose :
Vitamin A is essential for vision, and it is well-established that vitamin A deprivation causes a lack of the light-sensing pigments, severely disrupts the morphology of the photoreceptors, and is the leading cause of preventable childhood blindness. Since chronic vitamin A deprivation in Drosophila melanogaster impairs the synthesis of the visual pigments and damages the photoreceptor morphology, but does not cause photoreceptor death, we hypothesized that an unknown mechanism stabilizes these vitamin A-deficient photoreceptors.
Methods :
To gain insights into this stabilizing mechanism and identify novel factors that respond to vitamin A deficiency, we performed transcriptomics, GeLC-MS/MS mass-spectrometry for global proteomics, and targeted MS-Western for absolute quantification in vitamin A-deficient and vitamin A-sufficient four-day old Drosophila retinas. For functional analysis of our novel protein, we generated null mutants and antibodies. To determine the molecular mechanism of stabilization and identify interaction partners, we performed a yeast-two-hybrid screen and co-immunoprecipitation experiments.
Results :
We identified the novel transmembrane protein Mps (‘Major photoreceptor stabilizer’) as the most upregulated protein (~140-fold) in response to ocular vitamin A deficiency; the corresponding gene also showed the second-strongest transcriptional increase (~25-fold). Using Mps antibodies we found that Mps is dramatically upregulated in the damaged light-sensing compartments, the rhabdomeres. Moreover, vitamin A deficient mps null mutants exhibited completely collapsed rhabdomere membranes with highly abnormal, curtain-like invaginations; these exacerbated morphological defects were rescued by introducing an mps transgene in the mutant background. A yeast-two-hybrid screen and co-immunoprecipitation experiments helped us identify the major photoreceptor scaffolding protein, InaD (Inactivation no afterpotential D), as an interaction partner of Mps.
Conclusions :
In conclusion, we identified the novel transmembrane protein Mps that is highly upregulated in vitamin A-deficient photoreceptors and stabilizes their light-sensing compartments by interacting with the major scaffolding protein InaD. These findings give mechanistic insights into how the eye responds to environmental stresses and could inspire novel therapeutic approaches to treat human eye diseases.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.