TMEM67, TMEM237, and Embigin in Complex With Monocarboxylate Transporter MCT1 Are Unique Components of the Photoreceptor Outer Segment Plasma Membrane

Abstract

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Antisense oligonucleotide therapy for the common Stargardt disease type 1-causing variant in ABCA4

“…ABCA4 protein was clearly expressed in wild-type ROs and its localization was confined to the outer segments of retinal photoreceptors, as observed in the human retina. ABCA4 was much less present in the outer segment when compared to rhodopsin, which is in line with earlier observations conducted in mouse rod cells where the molar ratio of ABCA4 to rhodopsin was 1:300 (Skiba et al 2021). The protein assays in STGD1 ROs that underwent the AON treatment confirmed the utility of ROs as in vitro model for STGD1; we confirmed that the rescued protein is trafficked and co-localizes in outer segments of photoreceptor cells.…”

Super-resolution microscopy reveals photoreceptor-specific subciliary location and function of ciliopathy-associated protein CEP290

“…Some essential CC-resident proteins, such as RPGR orf15 ( 73 ) and RPGRIP1 ( 74 ), localize to centrioles in other cell types ( 75 ), and others, such as SPATA7 ( 36 ), are missing or nonessential in TZ of other cilia. It was recently reported ( 76 ) that MKS3/TMEM67, which is considered a marker of the TZ in primary cilia ( 18 , 49 , 50 ), is found at the base of and throughout the plasma membrane of rod outer segments, suggesting photoreceptor-specific location and function, which bears further investigation. We show here that the well-characterized TZ marker, NPHP8, locates to a narrow region at the base of the CC, as in other cilia, and not throughout the entire CC length ( Figure 5 ).…”

Absolute quantification of photoreceptor outer segment proteins

“…The goal of this study was to determine the absolute amounts of proteins that perform phototransduction or otherwise uniquely reside in the photoreceptor disc membranes where phototransduction takes place. We only included proteins that were documented to produce at least two unique tryptic peptides confidently identified by mass spectrometry in our previous studies (10,22,25,26). This allowed us to analyze 16 proteins directly engaged in phototransduction (entries 1-16 in Supplementary Table 1) and four additional disc-specific proteins (entries [17][18][19][20].…”

“…A more accurate mass spectrometry-based approach for absolute protein quantification involves the use of commercially synthesized isotope labeled peptide standards corresponding to tryptic fragments of a protein of interest. To our knowledge, this technique has only been applied to quantifying a handful of outer segment proteins in a single study (10). The limited use of this approach is due, at least in part, to the high costs of labeled peptide standards, potential issues with the stability and solubility of these peptides and the fact that concentrations of many commercial peptide standards are not easy to independently verify in a quantitatively consistent manner (11).…”