AUTHOR=Brandwine Tal , Ifrah Reut , Bialistoky Tzofia , Zaguri Rachel , Rhodes-Mordov Elisheva , Mizrahi-Meissonnier Liliana , Sharon Dror , Katanaev Vladimir L. , Gerlitz Offer , Minke Baruch 

TITLE=Knockdown of Dehydrodolichyl Diphosphate Synthase in the Drosophila Retina Leads to a Unique Pattern of Retinal Degeneration

JOURNAL=Frontiers in Molecular Neuroscience

VOLUME=14

YEAR=2021

URL=https://www.frontiersin.org/journals/molecular-neuroscience/articles/10.3389/fnmol.2021.693967

DOI=10.3389/fnmol.2021.693967

ISSN=1662-5099

ABSTRACT=<p>Dehydrodolichyl diphosphate synthase (DHDDS) is a ubiquitously expressed enzyme that catalyzes <italic>cis</italic>-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 <italic>DHDDS</italic> gene are presented with non-syndromic retinitis pigmentosa with unknown underlying mechanism. We have used the <italic>Drosophila</italic> model to compromise <italic>DHDDS</italic> ortholog gene (<italic>CG10778</italic>) 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 <italic>CG10778</italic> 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 <italic>CG10778</italic>-mRNA in the early embryo using the actin promoter or in the developing wings using the <italic>nub</italic> promoter resulted in lethality, or wings loss, respectively. Targeted expression of <italic>CG10778</italic>-RNAi using the <italic>glass multiple reporter</italic> (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.</p>