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See detailPhosphoinositides Regulate Ciliary Protein Trafficking to Modulate Hedgehog Signaling.
Garcia-Gonzalo, F. R.; Phua, S. C.; Roberson, E. C. et al

in Developmental Cell (2015), 34

Primary cilia interpret vertebrate Hedgehog (Hh) signals. Why cilia are essential for signaling is unclear. One possibility is that some forms of signaling require a distinct membrane lipid composition ... [more ▼]

Primary cilia interpret vertebrate Hedgehog (Hh) signals. Why cilia are essential for signaling is unclear. One possibility is that some forms of signaling require a distinct membrane lipid composition, found at cilia. We found that the ciliary membrane contains a particular phosphoinositide, PI(4)P, whereas a different phosphoinositide, PI(4,5)P2, is restricted to the membrane of the ciliary base. This distribution is created by Inpp5e, a ciliary phosphoinositide 5-phosphatase. Without Inpp5e, ciliary PI(4,5)P2 levels are elevated and Hh signaling is disrupted. Inpp5e limits the ciliary level s of inhibitors of Hh signaling, including Gpr161 and the PI(4,5)2-binding protein Tulp3. Increasing ciliary PI(4,5)P2levels or conferring the ability to bind PI(4)P on Tulp3 increases the ciliary localization of Tulp3. Lowering Tulp3 in cells lacking Inpp5e [less ▲]

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See detailModulation of ciliary phosphoinositide content regulates trafficking and Sonic hedgehog signaling output
Chavez, M; Van Sande, J; de Kerchove d'Exaerde, A et al

in Developmental Cell (2015), 34

Ciliary transport is required for ciliogenesis, signal transduction, and trafficking of receptors to the primary cilium. Mutations in inositol polyphosphate 5-phosphatase E (INPP5E) have been associated ... [more ▼]

Ciliary transport is required for ciliogenesis, signal transduction, and trafficking of receptors to the primary cilium. Mutations in inositol polyphosphate 5-phosphatase E (INPP5E) have been associated with ciliary dysfunction; however, its role in regulating ciliary phosphoinositides is unknown. Here we report that in neural stem cells, phosphatidylinositol 4-phosphate (PI4P) is found in high levels in cilia whereas phosphatidylinositol (4,5)-bisphosphate (PI(4,5)P2) is not detectable. Upon INPP5E inactivation, PI(4,5)P2 accumulates at the ciliary tip whereas PI4P is depleted. This is accompanied by recruitment of the PI(4,5)P2-interacting protein TULP3 to the ciliary membrane, along with Gpr161. This results in an increased production of cAMP and a repression of the Shh transcription gene Gli1. Our results reveal the link between ciliary regulation of phosphoinositides by INPP5E and Shh regulation via ciliary trafficking of TULP3/Gpr161 and also provide mechanistic insight into ciliary alterations found in Joubert and MORM syndromes resulting from INPP5E mutations. [less ▲]

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See detailp27(Kip1) Is a Microtubule-Associated Protein that Promotes Microtubule Polymerization during Neuron Migration.
Godin, Juliette ULg; Thomas, Noemie; Laguesse, Sophie ULg et al

in Developmental Cell (2012), 23(4), 729-44

The migration of cortical interneurons is characterized by extensive morphological changes that result from successive cycles of nucleokinesis and neurite branching. Their molecular bases remain elusive ... [more ▼]

The migration of cortical interneurons is characterized by extensive morphological changes that result from successive cycles of nucleokinesis and neurite branching. Their molecular bases remain elusive, and the present work describes how p27(Kip1) controls cell-cycle-unrelated signaling pathways to regulate these morphological remodelings. Live imaging reveals that interneurons lacking p27(Kip1) show delayed tangential migration resulting from defects in both nucleokinesis and dynamic branching of the leading process. At the molecular level, p27(Kip1) is a microtubule-associated protein that promotes polymerization of microtubules in extending neurites, thereby contributing to tangential migration. Furthermore, we show that p27(Kip1) controls actomyosin contractions that drive both forward translocation of the nucleus and growth cone splitting. Thus, p27(Kip1) cell-autonomously controls nucleokinesis and neurite branching by regulating both actin and microtubule cytoskeletons. [less ▲]

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See detailProneural bHLH and Brn proteins coregulate a neurogenic program through cooperative binding to a conserved DNA motif.
Castro, Diogo S; Skowronska-Krawczyk, Dorota; Armant, Olivier et al

in Developmental Cell (2006), 11(6), 831-44

Proneural proteins play a central role in vertebrate neurogenesis, but little is known of the genes that they regulate and of the factors that interact with proneural proteins to activate a neurogenic ... [more ▼]

Proneural proteins play a central role in vertebrate neurogenesis, but little is known of the genes that they regulate and of the factors that interact with proneural proteins to activate a neurogenic program. Here, we demonstrate that the proneural protein Mash1 and the POU proteins Brn1 and Brn2 interact on the promoter of the Notch ligand Delta1 and synergistically activate Delta1 transcription, a key step in neurogenesis. Overexpression experiments in vivo indicate that Brn2, like Mash1, regulates additional aspects of neurogenesis, including the division of progenitors and the differentiation and migration of neurons. We identify by in silico screening a number of additional candidate target genes, which are recognized by Mash1 and Brn proteins through a DNA-binding motif similar to that found in the Delta1 gene and present a broad range of activities. We thus propose that Mash1 synergizes with Brn factors to regulate multiple steps of neurogenesis. [less ▲]

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