Sterile Alpha Motif Containing 7 (Samd7) Is a Novel Crx-Regulated Transcriptional Repressor in the Retina

Abstract

Inherited retinal diseases are mainly caused by mutations in genes that are highly expressed in photoreceptors of the retina. The majority of these genes is under the control of the transcription factor Cone rod homeobox (Crx), that acts as a master transcription factor in photoreceptors. Using a genome-wide chromatin immunoprecipitation dataset that highlights all potential in vivo targets of Crx, we have identified a novel sterile alpha motif (SAM) domain containing protein, Samd7. mRNA Expression of Samd7 was confined to the late postnatal and adult mouse retina as well as the pineal gland. Using immunohistochemistry and Western blot, we could detect Samd7 protein in the outer nuclear layer of adult mouse retina. Ectopic over-expression in HEK293 cells demonstrated that Samd7 resides in the cytoplasm as well as the nucleus. In vitro electroporation of fluorescent reporters into living mouse retinal cultures revealed that transcription of the Samd7 gene depends on evolutionary conserved Crx motifs located in the first intron enhancer. Moreover, Crx knock-down with shRNA strongly reduced Samd7 reporter activity and endogenous Samd7 protein, indicating that Crx is required for retinal expression of Samd7. Finally, using co-transfections in luciferase reporter assays we found that Samd7 interferes with Crx-dependent transcription. Samd7 suppressed luciferase activity from a reporter plasmid with five Crx consensus repeats in a dose dependent manner and reduced Crx-mediated transactivation of regulatory sequences in the retinoschisin gene and the Samd7 gene itself. Taken together, we have identified a novel retinal SAM domain protein, Samd7, which could act as a transcriptional repressor involved in fine-tuning of Crx-regulated gene expression.

Samd7 is a cell type-specific PRC1 component essential for establishing retinal rod photoreceptor identity

“…Samd7 expression levels were confirmed by Northern blot analysis. Consistent with the results of in situ hybridization and the previous RT-qPCR study (37), we observed that the Samd7 expression level in the retina peaked between P6 and P14 ( Fig. S1A).…”

“…Samd7 (4930597A01Rik) was first reported to be expressed predominantly in the photoreceptor layer of the developing retina (36). Although Samd7 was shown to suppress the Crx-mediated transactivation of Retinoschisin and Samd7 promoters in a reporter assay (37), neither the molecular machinery of transcriptional suppression by Samd7 nor its in vivo function in the retina have yet been reported. Samd7 and Samd11 proteins contain a single SAM domain bearing high similarities to those of Polyhomeotic homologs (Phc).…”

Progressive Retinal Degeneration and Glial Activation in the CLN6nclf Mouse Model of Neuronal Ceroid Lipofuscinosis: A Beneficial Effect of DHA and Curcumin Supplementation

“…Measurements were performed in duplicates. Results were analyzed with an ABI sequence detector software version 2.3 using the ΔΔCt method for relative quantification and ATP5B as stable reference gene [24]. A Ct (cycle threshold) value of 35 was used as a cutoff for estimating significantly expressed transcripts.…”

Early-onset autosomal recessive cerebellar ataxia associated with retinal dystrophy: new human hotfoot phenotype caused by homozygous GRID2 deletion

“…Human and mouse retinal sections were used for immunofluorescence analysis, which was performed as previously described 22 (see Supplementary Text S1 online).…”