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Ciliary tip actin dynamics regulate the cadence of photoreceptor disc formation

ABSTRACT: As signalling organelles, primary cilia regulate their membrane G protein-coupled receptor (GPCR) content by ectocytosis, a process requiring localised actin dynamics at their tip to alter membrane shape.1,2 Mammalian photoreceptor outer segments comprise an expanse of folded membranes (discs) at the tip of highly-specialised connecting cilia (CC), in which photosensitive GPCRs like rhodopsin are concentrated. In an extraordinary feat of biology, outer segment discs are shed and remade daily.3 Defects in this process, due to genetic mutations, cause retinitis pigmentosa (RP), an untreatable, blinding disease. The mechanism by which photoreceptor cilia generate outer segments is therefore fundamental for vision yet poorly understood. Here, we show the membrane deformation required for outer segment disc genesis is driven by dynamic changes in the actin cytoskeleton in a process akin to ectocytosis. Further, we show RPGR, a leading causal RP gene, regulates activity of actin binding proteins crucial to this process. Disc genesis is compromised in Rpgr mouse models, slowing the actin dynamics required for timely disc formation, leading to aborted membrane shedding as ectosome-like vesicles, photoreceptor death and visual loss. Manipulation of actin dynamics partially rescues the phenotype, suggesting this pathway could be targeted therapeutically. These findings help define how actin-mediated dynamics control outer segment turnover.

INSTRUMENT(S): Orbitrap Fusion Lumos

ORGANISM(S): Mus Musculus (mouse)

SUBMITTER: Alex von kriegsheim

LAB HEAD: a von kiregshiem

PROVIDER: PXD038015 | Pride | 2024-05-08

REPOSITORIES: Pride

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Project description:NeuroD1 encodes a basic helix-loop-helix transcription factor involved in the development of neural and endocrine structures. NeuroD1 mRNA is highly abundant in the adult mammalian pineal gland and exhibits a developmental expression pattern similar to the retina. This is consistent with the common evolutionary origin of pinealocytes and retinal photoreceptors. Pinealocytes and retinal photoreceptors express a shared set of phototransduction genes and submammalian pinealocytes are photosensitive. In contrast to the retina, the pineal gland is a relatively homogeneous structure, composed 95% of pinealocytes. This makes the pineal gland a particularly useful model for understanding photoreceptor cell biology. The loss of NeuroD1 in the retina results in progressive photoreceptor degeneration and the molecular mechanisms underlying this retinal degeneration phenotype remain unknown. Similarly, the role that NeuroD1 plays in the pineal gland is unknown. To determine the function of NeuroD1 in the pineal gland and retina, a Cre/loxP recombination strategy was used to selectively target a NeuroD1 floxed allele and generate NeuroD1 conditional knockout (cKO) mice. Tissue specificity was conferred using Cre recombinase expressed under the control of the promoter of Crx, a transcription factor selectively expressed in the pineal gland and retina. Pineal and retinal tissues from two-month-old NeuroD1 cKO and control animals were used in microarray studies to identify candidate genes responsible for the photoreceptor degeneration phenotype. The Cre/loxP recombination strategy was used to target a NeuroD1 floxed allele and generate NeuroD1 conditional knockout mice (NeuroD1floxed::Crx-Cre+/-). NeuroD1 floxed mice (NeuroD1floxed::Crx-Cre-/-) served as the controls. Pineal glands and retinas from two-month-old control and conditional knockout mice were collected at ZT6 and ZT20. 3 pools of 6 pineal glands per genotype and respective time of day were collected for each sample. Similarly, 3 pools of 6 retinas each were also collected. RNA from each pool was extracted and hybridized on the Affymetrix Mouse 430 2.0 array.

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Ciliary tip actin dynamics regulate the cadence of photoreceptor disc formation

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