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Patsy Nishina, Lihong Zhao, Lisa Stone, Andrew Njaa, Mark P Krebs, LanYing Shi, Wanda Hicks, Juergen Naggert; A new Dpgat1 mutant mouse model for congenital disorder of glycosylation, type Ij, exhibits photoreceptor degeneration and sterility. Invest. Ophthalmol. Vis. Sci. 2017;58(8):4525.
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© ARVO (1962-2015); The Authors (2016-present)
To identify the genetic basis of a rapid photoreceptor degeneration model identified in the Translational Vision Research Models (Tvrm) chemical mutagenesis program.
A mouse mutant (tvrm76) exhibiting a grainy fundus phenotype was discovered in an ENU mutagenesis ocular screen of C57BL/6J mice. The mutation was mapped using an affecteds-only DNA pooling approach, and the candidate region narrowed by recombinational analysis. The high-throughput DNA sequence of a whole-exome capture library from an affected mouse was analyzed using Galaxy software. An allele test with a Dpgat1 null mutant was performed and a rod cell-specific knock-out of Dpagt1 was also generated. Pathological features and progression were probed by fundus imaging, optical coherence tomography and histology. Functional changes were assessed by ERG. Marker and western analyses were carried out.
The tvrm76 mutation is recessive and mapped to Chr 9. Fine mapping and high-throughput sequencing identified a mutation, nt497 A>G, in Dpagt1 (dolichyl phosphate acetylglucosamine transferase 1), encoding an Asp166Gly missense substitution. This mutation co-segregated with the disease phenotype in the mapping backcross and in the segregating colony on the C57BL/6J background. The causative nature of the mutation was confirmed by an allele test against a heterozygous null allele of Dpagt1. Fundus imaging of homozygous Dpagt1tvrm76 and compound heterozygotes - Dpagt1tvrm76/Dpagt1null/+mice confirmed the grainy phenotype and vascular atrophy. OCT and histology indicated a progressive loss of photoreceptor nuclei over 12 months, and ERG confirmed a corresponding decline in function. Loss of Dpagt1 function in rod photoreceptors alone was sufficient to cause degeneration. No change in the levels of overall protein glycosylation or of rhodopsin glycosylation was observed. However, the mutation elevated levels of BiP, an endoplasmic reticulum chaperone, in the retina, indicating ER stress.
A newly identified missense mutation of murine Dpagt1 causes progressive photoreceptor loss and sterility. The affected protein, DPAGT1, catalyzes the committed step in the assembly of carbohydrate chains destined for secretory pathway substrates. Dpagt1tvrm76 mice will be invaluable for understanding the role of Dpagt1 in the adult, as the null allele causes embryonic lethality.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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