Abstract
Dehydrodolichyl diphosphate synthase (DHDDS) is a ubiquitously expressed enzyme that catalyzes cis-prenyl chain elongation to produce the poly-prenyl backbone of dolichol. It appears in all tissues including the nervous system and it is a highly conserved enzyme that can be found in all animal species. Individuals who have biallelic missense mutations in the DHDDS gene are presented with non-syndromic retinitis pigmentosa with unknown underlying mechanism. We have used the Drosophila model to compromise DHDDS ortholog gene (CG10778) in order to look for cellular and molecular mechanisms that, when defective, might be responsible for this retinal disease. The Gal4/UAS system was used to suppress the expression of CG10778 via RNAi-mediated-knockdown in various tissues. The resulting phenotypes were assessed using q-RT-PCR, transmission-electron-microscopy (TEM), electroretinogram, antibody staining and Western blot analysis. Targeted knockdown of CG10778-mRNA in the early embryo using the actin promoter or in the developing wings using the nub promoter resulted in lethality, or wings loss, respectively. Targeted expression of CG10778-RNAi using the glass multiple reporter (GMR)-Gal4 driver (GMR-DHDDS-RNAi) in the larva eye disc and pupal retina resulted in a complex phenotype: (a) TEM retinal sections revealed a unique pattern of retinal-degeneration, where photoreceptors R2 and R5 exhibited a nearly normal structure of their signaling-compartment (rhabdomere), but only at the region of the nucleus, while all other photoreceptors showed retinal degeneration at all regions. (b) Western blot analysis revealed a drastic reduction in rhodopsin levels in GMR-DHDDS-RNAi-flies and TEM sections showed an abnormal accumulation of endoplasmic reticulum (ER). To conclude, compromising DHDDS in the developing retina, while allowing formation of the retina, resulted in a unique pattern of retinal degeneration, characterized by a dramatic reduction in rhodopsin protein level and an abnormal accumulation of ER membranes in the photoreceptors cells, thus indicating that DHDDS is essential for normal retinal formation.
Highlights
The identification of a founder mutation in the dehydrodolichyl diphosphate synthase (DHDDS) gene in Ashkenazi Jews (AJ) with non-syndromic retinitis pigmentosa (RP) was reported a decade ago (Zelinger et al, 2011; Züchner et al, 2011)
To study the effect of compromising DHDDS on retinal structure and function in a model animal, we examined the consequences of targeted expression of CG10778-RNAi (DHDDS-RNAi) using the glass multiple reporter (GMR)-Gal4 driver and other tissuespecific promoters
Mutations in the human DHDDS have been associated with RP, a disease resulting in retinal degeneration and blindness
Summary
The identification of a founder mutation in the dehydrodolichyl diphosphate synthase (DHDDS) gene in Ashkenazi Jews (AJ) with non-syndromic retinitis pigmentosa (RP) was reported a decade ago (Zelinger et al, 2011; Züchner et al, 2011). The p.K42E mutation affects a highly conserved region of the DHDDS protein, which is located in close proximity to a binding site of farnesyl diphosphate. This mutation has subsequently been confirmed in other similar patients and is found in 10–20% of autosomal recessive RP in AJ population (Zelinger et al, 2011). Patients harboring mutations in DHDDS demonstrated fundus findings at a relatively early age. They demonstrated waxy appearance of the optic nerve head, attenuation of retinal blood vessels and retinal atrophy in the mid and far periphery combined with significant bone spiculelike pigmentation, starting already in their 20s. An additional study describing a patient with a severe multisystem disease associated with DHDDS deficiency shows that RP is not the only clinical sign in cases of DHDDS deficiency (Sabry et al, 2016)
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