Lack of retinal degeneration in a Dram2 knockout mouse model.

Damage-regulated autophagy modulator 2 (DRAM2) is a homologue of the DRAM family protein, which can induce autophagy process. In the retina, DRAM2 is located to the inner segment of photoreceptors, the apical surface of retinal pigment epithelial (RPE) cells, and the lysosome. Pathogenic variants of DRAM2 lead to autosomal recessive Cone-rod dystrophy 21 (CORD21). Cone-rod dystrophy is characterised by primary cone involvement, or sometimes simultaneous cone and rod loss, thus leading to decreased visual acuity, colour vision deficits, photophobia, and decreased sensitivity of the central visual field. However, the mechanisms underlying DRAM2 related retinal diseases remained unclear. To further explore the role of Dram2 in the retina, we generated Dram2 knockout mice (KO) by CRISPR/Cas-9 technology and demonstrated that expression of DRAM2 was abolished in KO retinas. Dram2 ablation failed to manifest any retinal degenerative phenotypes. Dram2 KO did not exhibit visible defect in photo response and the overt structure of the retinas. Immunostaing analysis using antibodies against cone opsins revealed no detectable loss of cone cells. Moreover, no visible change was observed in the expression and localisation of rhodopsin and other membrane disc proteins in Dram2 KO retinas and no gliosis and apoptosis were detected in KO mice. In summary, these data revealed lack of overt retinal degeneration in Dram2 KO model and emphasized the importance of further investigation of the mechanisms underlying Cone-rod dystrophy 21.