| Summary: | We previously identified a homozygous G178R mutation in human <i>ASRGL1</i> (<i>hASRGL1</i>) through whole-exome analysis responsible for early onset retinal degeneration (RD) in patients with cone–rod dystrophy. The mutant G178R ASRGL1 expressed in Cos-7 cells showed altered localization, while the mutant ASRGL1 in <i>E. coli</i> lacked the autocatalytic activity needed to generate the active protein. To evaluate the effect of impaired ASRGL1 function on the retina in vivo, we generated a mouse model with c.578_579insAGAAA (NM_001083926.2) mutation (<i>Asrgl1<sup>mut/mut</sup></i>) through the CRISPR/Cas9 methodology. The expression of ASGRL1 and its asparaginase activity were undetectable in the retina of <i>Asrgl1<sup>mut/mut</sup></i> mice. The ophthalmic evaluation of <i>Asrgl1<sup>mut/mut</sup></i> mice showed a significant and progressive decrease in scotopic electroretinographic (ERG) response observed at an early age of 3 months followed by a decrease in photopic response around 5 months compared with age-matched wildtype mice. Immunostaining and RT-PCR analyses with rod and cone cell markers revealed a loss of cone outer segments and a significant decrease in the expression of <i>Rhodopsin</i>, <i>Opn1sw</i>, and <i>Opn1mw</i> at 3 months in <i>Asrgl1<sup>mut/mut</sup></i> mice compared with age-matched wildtype mice. Importantly, the retinal phenotype of <i>Asrgl1<sup>mut/mut</sup></i> mice is consistent with the phenotype observed in patients harboring the G178R mutation in <i>ASRGL1</i> confirming a critical role of ASRGL1 in the retina and the contribution of <i>ASRGL1</i> mutations in retinal degeneration.
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