Targeting of β-Arrestin2 to the Centrosome and Primary Cilium: Role in Cell Proliferation Control

International audienceBackground: The primary cilium is a sensory organelle generated from the centrosome in quiescent cells and found at the surface of most cell types, from where it controls important physiological processes. Specific sets of membrane proteins involved in sensing the extracellular milieu are concentrated within cilia, including G protein coupled receptors (GPCRs). Most GPCRs are regulated by b-arrestins, barr1 and barr2, which control both their signalling and endocytosis, suggesting that barrs may also function at primary cilium.Methodology/Principal Findings: In cycling cells, βarr2 was observed at the centrosome, at the proximal region of the centrioles, in a microtubule independent manner. However, βarr2 did not appear to be involved in classical centrosome-associated functions. In quiescent cells, both in vitro and in vivo, βarr2 was found at the basal body and axoneme of primary cilia. Interestingly, βarr2 was found to interact and colocalize with 14-3-3 proteins and Kif3A, two proteins known to be involved in ciliogenesis and intraciliary transport. In addition, as suggested for other centrosome or cilia-associated proteins, βarrs appear to control cell cycle progression. Indeed, cells lacking βarr2 were unable to properly respond to serum starvation and formed less primary cilia in these conditions.Conclusions/Significance: Our results show that βarr2 is localized to the centrosome in cycling cells and to the primary cilium in quiescent cells, a feature shared with other proteins known to be involved in ciliogenesis or primary cilium function. Within cilia, βarr2 may participate in the signaling of cilia-associated GPCRs and, therefore, in the sensory functions of this cell “antenna”

Seaweed extracts inhibit invasion of Salmonella Enteritidis into avian epithelial cells

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Optimisation of the expression of a fluorescent marker in <em>Cryptosporidium parvum</em> transgenic lines

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Functional characterization of tektin-1 in motile cilia and evidence for TEKT1 as a new candidate gene for motile ciliopathies

International audienceA child presenting with Mainzer-Saldino syndrome (MZSDS), characterized by renal, retinal and skeletal involvements, was also diagnosed with lung infections and airway ciliary dyskinesia. These manifestations suggested dysfunction of both primary and motile cilia, respectively. Targeted exome sequencing identified biallelic mutations in WDR19, encoding an IFT-A subunit previously associated with MZSDS-related chondrodysplasia, Jeune asphyxiating thoracic dysplasia and cranioectodermal dysplasia, linked to primary cilia dysfunction, and in TEKT1 which encodes tektin-1 an uncharacterized member of the tektin family, mutations of which may cause ciliary dyskinesia. Tektin-1 localizes at the centrosome in cycling cells, at basal bodies of both primary and motile cilia and to the axoneme of motile cilia in airway cells. The identified mutations impaired these localizations. In addition, airway cells from the affected individual showed severe motility defects without major ultrastructural changes. Knockdown of tekt1 in zebrafish resulted in phenotypes consistent with a function for tektin-1 in ciliary motility, which was confirmed by live imaging. Finally, experiments in the zebrafish also revealed a synergistic effect of tekt1 and wdr19. Altogether, our data show genetic interactions between WDR19 and TEKT1 likely contributing to the overall clinical phenotype observed in the affected individual and provide strong evidence for TEKT1 as a new candidate gene for primary ciliary dyskinesia

Septins 2, 7 and 9 and MAP4 colocalize along the axoneme in the primary cilium and control ciliary length

Septins are a large, evolutionarily conserved family of GTPases that form hetero-oligomers and interact with the actin-based cytoskeleton and microtubules. They are involved in scaffolding functions, and form diffusion barriers in budding yeast, the sperm flagellum and the base of primary cilia of kidney epithelial cells. We investigated the role of septins in the primary cilium of retinal pigmented epithelial (RPE) cells, and found that SEPT2 forms a 1:1:1 complex with SEPT7 and SEPT9 and that the three members of this complex colocalize along the length of the axoneme. Similar to observations in kidney epithelial cells, depletion of cilium-localized septins by siRNA-based approaches inhibited ciliogenesis. MAP4, which is a binding partner of SEPT2 and controls the accessibility of septins to microtubules, was also localized to the axoneme where it appeared to negatively regulate ciliary length. Taken together, our data provide new insights into the functions and regulation of septins and MAP4 in the organization of the primary cilium and microtubule-based activities in cells

Nephrocystins play a crucial role in renal epithelial morphogenesis via the regulation of Wnt/PCP components Dishevelled and Rho GTPases

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