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ARL13B regulates Sonic hedgehog signaling from outside primary cilia.

ABSTRACT: ARL13B is a regulatory GTPase highly enriched in cilia. Complete loss of Arl13b disrupts cilia architecture, protein trafficking and Sonic hedgehog signaling. To determine whether ARL13B is required within cilia, we knocked in a cilia-excluded variant of ARL13B (V358A) and showed it retains all known biochemical function. We found that ARL13B^V358A protein was expressed but could not be detected in cilia, even when retrograde ciliary transport was blocked. We showed Arl13b^V358A/V358A mice are viable and fertile with normal Shh signal transduction. However, in contrast to wild type cilia, Arl13b^V358A/V358A cells displayed short cilia and lacked ciliary ARL3 and INPP5E. These data indicate that ARL13B's role within cilia can be uncoupled from its function outside of cilia. Furthermore, these data imply that the cilia defects upon complete absence of ARL13B do not underlie the alterations in Shh transduction, which is unexpected given the requirement of cilia for Shh transduction.

SUBMITTER: Gigante ED

PROVIDER: S-EPMC7075693 | biostudies-literature | 2020 Mar

REPOSITORIES: biostudies-literature

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ARL13B regulates Sonic hedgehog signaling from outside primary cilia.

Gigante Eduardo D ED Taylor Megan R MR Ivanova Anna A AA Kahn Richard A RA Caspary Tamara T

eLife 20200304

ARL13B is a regulatory GTPase highly enriched in cilia. Complete loss of Arl13b disrupts cilia architecture, protein trafficking and Sonic hedgehog signaling. To determine whether ARL13B is required within cilia, we knocked in a cilia-excluded variant of ARL13B (V358A) and showed it retains all known biochemical function. We found that ARL13BV358A protein was expressed but could not be detected in cilia, even when retrograde ciliary transport was blocked. We showed Arl13b<su ...[more]

PMID: 32129762

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Project description:Background:Primary cilia are small non-motile microtubule and cell membrane protrusions expressed on most vertebrate cells, including cortical and hippocampal neurons. These small organelles serve as sensory structures sampling the extracellular environment and reprogramming the transcriptional machinery in response to environmental change. Primary cilia are decorated with a variety of receptor proteins and are necessary for specific signaling cascades such as the Sonic hedgehog (Shh) pathway. Disrupting cilia structure or function results in a spectrum of diseases collectively referred to as ciliopathies. Common to human ciliopathies is cognitive impairment, a symptom also observed in Alzheimer's disease (AD). One hallmark of AD is accumulation of senile plaques composed of neurotoxic Amyloid-? (A?) peptide. The A? peptide is generated by the proteolytic cleavage of the amyloid precursor protein (APP). We set out to determine if A? affects primary cilia structure and the Shh signaling cascade. Methods:We utilized in vitro cell-based assays in combination with fluorescent confocal microscopy to address our study goals. Shh signaling and cilia structure was studied using two different cell lines, mouse NIH3T3 and human HeLa cells. To investigate how A? levels affect Shh signaling and cilia structure in these cells, we utilized naturally secreted A? as well as synthetic A?. Effects on Shh signaling were assessed by luciferase activity while cilia structure was analyzed by fluorescent microscopy. Results:Here, we report that APP localizes to primary cilia and A? treatment results in distorted primary cilia structure. In addition, we demonstrate that A? treatment interrupts canonical Shh signal transduction. Conclusions:Overall, our study illustrates that A? can alter primary cilia structure suggesting that elevated A? levels, like those observed in AD patients, could have similar effects on neuronal primary cilia in the brain. Additionally, our study suggests that A? impairs the Shh signaling pathway. Together our findings shed light on two novel targets for future AD therapeutics.

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ARL13B regulates Sonic hedgehog signaling from outside primary cilia.

Publications

ARL13B regulates Sonic hedgehog signaling from outside primary cilia.

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