Figure 4

IMPG2 proteolysis and traffic of its extracellular portion from the matrix inner segment (IS) to outer segment (OS) in an IMPG1-dependent process. (a) Schematic of IMPG2 shows the expected proteolytic and non-proteolytic SEA domains along with extracellular and membrane-portion antibody recognition sites. (b) Representative western blot comparing retina samples from wildtype (WT), IMPG2 knockout (KO), IMPG1 KO, and SKT mice WT and KO. A single band at 32 kDa is present in wildtype, IMPG1 KO, and SKT mice (cyan arrow). (c–h) Immunohistochemistry staining on retina cross-section from wildtype (c,f), IMPG2 KO (d,g), and IMPG1 KO (e,h) mice using a specific antibody against the extracellular portion of IMPG2 (IMPG2ec, green) and membrane portion (IMPG2m, cyan). IMPG2ec antibody stains the outer part of the IS and entire OS (c). IMPG2ec localizes at the outer IS and inner OS region (white bracket), with a substantial reduction in the rest of the OS (e). Outer nuclear layer (ONL) stained with DAPI (blue). Differential interference contrast (DIC) in white. RPE indicates retina pigment epithelium. Scale bar equals 10 µm. N = 3 mice per experiment at postnatal day 45. Scheme of IMPG2m and IMPG2ec localization in wildtype and IMPG1 KO mice according to immunohistochemistry results (c,f,e,h).