Figure 6. InsPs are present in the vertebrate retina and bind Arr1.

(A) PAGE analysis shows the presence of InsP₅ and InsP₆ in bovine retina homogenates. Amounts of standards (nmol) are noted at the top. 25% of the sample extracted from 25 bovine retinas was loaded in the “retina” lane. (B-C) Single cell RNA-sequencing (scRNA-seq) heat map depicting absolute (unscaled, B) and relative (scaled as a fraction of the absolute expression value in the retinal cell type with maximal expression for each gene, C) expression values of PP-InsP enzymes by cell type in wild-type (WT) murine retina (Hoang et al., 2020). MC, Müller cell; BC, bipolar cell; AC, amacrine cell; HC, horizontal cell; As, astrocyte; EC, endothelial cell; RPE, retinal pigment epithelium. (D) In situ hybridization analyses of WT murine retinal cryo-sections showing Ppip5k1 and Ip6k2 message throughout the retina with strongest signals in the photoreceptor outer nuclear layer (ONL) (n = 3, representative image shown). The section is co-stained with peanut agglutinin (PNA) and DAPI to demarcate cone photoreceptors and nuclei, respectively. INL, inner nuclear layer; GCL, ganglion cell layer. Scale bar, 50 μm. (E-F) Affinity measurements of natural (E) and synthetic (F) InsPs for Arr1 performed using a fluorescence quenching assay (n=3, mean ± SD). The data in E and F were corrected to account for ligand depletion and the curves based on a one-site binding model.