scholarly journals The exocyst complex and intracellular vesicles mediate soluble protein trafficking to the primary cilium

2021 ◽  
Author(s):  
Sylwia M Niedziółka ◽  
Sampurna Datta ◽  
Tomasz Uśpieński ◽  
Brygida Baran ◽  
Eric W Humke ◽  
...  
Keyword(s):  
Primary Cilium ◽  
Protein Trafficking ◽  
Developmental Disorders ◽  
Soluble Proteins ◽  
Signaling Cascades ◽  
Transport Mechanisms ◽  
Exocyst Complex ◽  
Gli Transcription Factors ◽  
Intracellular Vesicles ◽  
Intracellular Vesicle Transport

Efficient transport of proteins into the primary cilium is a crucial step for many signaling pathways. Dysfunction of this process can lead to the disruption of signaling cascades or cilium assembly, resulting in developmental disorders and cancer. Previous studies on ciliary trafficking were mostly focused on the membrane-embedded receptors. In contrast, how soluble proteins are delivered into the cilium is poorly understood. In our work, we identify the exocyst complex as a key player in the ciliary trafficking of soluble Gli transcription factors. Considering that the exocyst mediates intracellular vesicle transport, we demonstrate that soluble proteins, including Gli2/3 and Lkb1, can use the endosome recycling machinery for their delivery to the primary cilium. Finally, we identify GTPases: Rab14, Rab18, Rab23, and Arf4 involved in vesicle-mediated Gli protein ciliary trafficking. Our data pave the way for a better understanding of ciliary transport and uncover novel transport mechanisms inside the cell.

Hedgehog-induced ciliary trafficking of kinesin-4 motor KIF7 requires intraflagellar transport but not KIF7’s microtubule binding

2021 ◽  
Author(s):  
Yang Yue ◽  
Martin F. Engelke ◽  
T. Lynne Blasius ◽  
Kristen J. Verhey
Keyword(s):  
Transcription Factors ◽  
Signaling Pathway ◽  
Primary Cilium ◽  
Hedgehog Signaling ◽  
Intraflagellar Transport ◽  
Hedgehog Signaling Pathway ◽  
Microtubule Binding ◽  
Pathway Activation ◽  
Gli Transcription Factors ◽  
Ciliary Localization

The kinesin-4 motor KIF7 is a conserved regulator of the Hedgehog signaling pathway. In vertebrates, Hedgehog signaling requires the primary cilium, and KIF7 and Gli transcription factors accumulate at the cilium tip in response to Hedgehog activation. Unlike conventional kinesins, KIF7 is an immotile kinesin and its mechanism of ciliary accumulation is unknown. We generated KIF7 variants with altered microtubule binding or motility. We demonstrate that microtubule binding of KIF7 is not required for the increase in KIF7 or Gli localization at the cilium tip in response to Hedgehog signaling. In addition, we show that the immotile behavior of KIF7 is required to prevent ciliary localization of Gli transcription factors in the absence of Hedgehog signaling. Using an engineered kinesin-2 motor that enables acute inhibition of intraflagellar transport (IFT), we demonstrate that kinesin-2 KIF3A/KIF3B/KAP mediates the translocation of KIF7 to the cilium tip in response to Hedgehog pathway activation. Together, these results suggest that KIF7’s role at the tip of the cilium is unrelated to its ability to bind to microtubules.

scholarly journals Defective organellar membrane protein trafficking in Ap3b1-deficient cells

2000 ◽  
Vol 113 (22) ◽  
pp. 4077-4086 ◽  
Author(s):  
W. Yang ◽  
C. Li ◽  
D.M. Ward ◽  
J. Kaplan ◽  
S.L. Mansour
Keyword(s):  
Membrane Protein ◽  
Protein Trafficking ◽  
Coat Color ◽  
Causal Gene ◽  
Alternate Pathway ◽  
Intracellular Vesicle ◽  
Membrane Protein Trafficking ◽  
Lysosomal Membrane Proteins ◽  
Intracellular Vesicle Transport ◽  
Compound Heterozygotes

AP-3 is a heterotetrameric protein complex involved in intracellular vesicle transport. Molecular analyses show that Ap3b1, which encodes the AP-3 (β)3A subunit, is altered in pearl mice. To provide genetic evidence that mutation of Ap3b1 is responsible for the pearl phenotype and to determine the null phenotype, the Ap3b1 gene was disrupted by homologous recombination. Mice homozygous for the resulting allele, Ap3b1(LN), or compound heterozygotes with pearl, displayed phenotypes similar to those of pearl mice, confirming that Ap3b1 is the causal gene for pearl. Moreover, pearl is likely to be a hypomorph as the Ap3b1(LN) homozygotes had a lighter coat color and accumulated fewer of the μ3 and (Δ)3 subunits of AP-3 than did pearl mice. Finally, immunofluorescence analysis of fibroblasts and melanocytes cultured from Ap3b1(LN) homozygotes revealed that the lysosomal membrane proteins Lamp I and Lamp II and the melanosomal membrane protein tyrosinase were mislocalized. In particular, the Lamp proteins were clustered on the cell surface. These findings strengthen the evidence for an alternate pathway via the plasma membrane for cargo normally transported to organelles by AP-3.

scholarly journals The primary cilium dampens proliferative signaling and represses a G2/M transcriptional network in quiescent myoblasts

2020 ◽  
Author(s):  
Nisha Venugopal ◽  
Ananga Ghosh ◽  
Hardik Gala ◽  
Ajoy Aloysius ◽  
Neha Vyas ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Primary Cilium ◽  
Developmental Disorders ◽  
Adult Stem Cells ◽  
Primary Cilia ◽  
Translational Repressor ◽  
Elevated Protein ◽  
Proliferative Signaling

Abstract Background Reversible cell cycle arrest (quiescence/G0) is characteristic of adult stem cells and is actively controlled at multiple levels. Quiescent cells also extend a primary cilium, which functions as a signaling hub. Primary cilia have been shown to be important in multiple developmental processes, and are implicated in numerous developmental disorders. Although the association of the cilium with G0 is established, the role of the cilium in the control of the quiescence program is still poorly understood. Results Primary cilia are dynamically regulated across different states of cell cycle exit in skeletal muscle myoblasts: quiescent myoblasts elaborate a primary cilium in vivo and in vitro , but terminally differentiated myofibers do not. Myoblasts where ciliogenesis is ablated using RNAi against a key ciliary assembly protein (IFT88) can exit the cell cycle but display an altered quiescence program and impaired self-renewal. Specifically, the G0 transcriptome in IFT88 knockdown cells is aberrantly enriched for G2/M regulators, suggesting a focused repression of this network by the cilium. Cilium-ablated cells also exhibit features of activation including enhanced activity of Wnt and mitogen signaling and elevated protein synthesis via inactivation of the translational repressor 4E-BP1. Conclusions Taken together, our results show that the primary cilium integrates and dampens proliferative signaling, represses translation and G2/M genes, and is integral to the establishment of the quiescence program.

scholarly journals Lipid Modifications in Cilia Biology

2019 ◽  
Vol 8 (7) ◽  
pp. 921 ◽  
Author(s):  
Kasturi Roy ◽  
Ethan P. Marin
Keyword(s):  
Protein Stability ◽  
Signaling Pathways ◽  
Protein Trafficking ◽  
Specific Protein ◽  
Signaling Cascades ◽  
Cellular Structures ◽  
Future Studies ◽  
Lipid Modifications ◽  
Ciliary Protein

Cilia are specialized cellular structures with distinctive roles in various signaling cascades. Ciliary proteins need to be trafficked to the cilium to function properly; however, it is not completely understood how these proteins are delivered to their final localization. In this review, we will focus on how different lipid modifications are important in ciliary protein trafficking and, consequently, regulation of signaling pathways. Lipid modifications can play a variety of roles, including tethering proteins to the membrane, aiding trafficking through facilitating interactions with transporter proteins, and regulating protein stability and abundance. Future studies focusing on the role of lipid modifications of ciliary proteins will help our understanding of how cilia maintain specific protein pools strictly connected to their functions.

scholarly journals The primary cilium dampens proliferative signaling and represses a G2/M transcriptional network in quiescent myoblasts

2019 ◽  
Author(s):  
Nisha Venugopal ◽  
Ananga Ghosh ◽  
Hardik Gala ◽  
Ajoy Aloysius ◽  
Neha Vyas ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Primary Cilium ◽  
Developmental Disorders ◽  
Adult Stem Cells ◽  
Primary Cilia ◽  
Translational Repressor ◽  
Elevated Protein ◽  
Proliferative Signaling

Abstract Background: Reversible cell cycle arrest (quiescence/G0) is characteristic of adult stem cells and is actively controlled at multiple levels. Quiescent cells also extend a primary cilium, which functions as a signaling hub. Primary cilia have been shown to be important in multiple developmental processes, and are implicated in numerous developmental disorders. Although the association of the cilium with G0 is established, the role of the cilium in the control of the quiescence program is still poorly understood.Results: Primary cilia are dynamically regulated across different states of cell cycle exit in skeletal muscle myoblasts: quiescent myoblasts elaborate a primary cilium in vivo and in vitro , but terminally differentiated myofibers do not. Myoblasts where ciliogenesis is ablated using RNAi against a key ciliary assembly protein (IFT88) can exit the cell cycle but display an altered quiescence program and impaired self-renewal. Specifically, the G0 transcriptome in IFT88 knockdown cells is aberrantly enriched for G2/M regulators, suggesting a focused repression of this network by the cilium. Cilium-ablated cells also exhibit features of activation including enhanced activity of Wnt and mitogen signaling and elevated protein synthesis via inactivation of the translational repressor 4E-BP1.Conclusions: Taken together, our results show that the primary cilium integrates and dampens proliferative signaling, represses translation and G2/M genes, and is integral to the establishment of the quiescence program.

scholarly journals Primary Cilium Formation and Ciliary Protein Trafficking Is Regulated by the Atypical MAP Kinase MAPK15 in Caenorhabditis elegans  and Human Cells

Genetics ◽  
2017 ◽  
pp. genetics.300383.2017 ◽  
Author(s):  
Anna Kazatskaya ◽  
Stefanie Kuhns ◽  
Nils J. Lambacher ◽  
Julie E. Kennedy ◽  
Andrea G. Brear ◽  
...  
Keyword(s):  
Caenorhabditis Elegans ◽  
Map Kinase ◽  
Primary Cilium ◽  
Protein Trafficking ◽  
Human Cells ◽  
Cilium Formation ◽  
Ciliary Protein

Distinct intracellular vesicle transport mechanisms are selectively modified by spastin and spastin mutations

2010 ◽  
Vol 226 (2) ◽  
pp. 362-368 ◽  
Author(s):  
Julia C. Fuerst ◽  
Andreas W. Henkel ◽  
Armin Stroebel ◽  
Oliver Welzel ◽  
Teja W. Groemer ◽  
...  
Keyword(s):  
Vesicle Transport ◽  
Transport Mechanisms ◽  
Intracellular Vesicle ◽  
Intracellular Vesicle Transport

scholarly journals Deficiency of U4atac snRNA secondarily results in ciliary defects

2021 ◽  
Author(s):  
Deepak Khatri ◽  
Audrey Putoux ◽  
Audric Cologne ◽  
Sophie Kaltenbach ◽  
Alicia Besson ◽  
...  
Keyword(s):  
Intellectual Disability ◽  
Primary Cilium ◽  
Growth Retardation ◽  
Skeletal Dysplasia ◽  
Developmental Disorders ◽  
Retinal Dystrophy ◽  
Joubert Syndrome ◽  
Zebrafish Model ◽  
Splicing Defects ◽  
Cilium Function

In the human genome, about 700 genes contain usually one intron excised by the minor spliceosome. This spliceosome comprises its own set of snRNAs, among which U4atac. Its non-coding gene, RNU4ATAC, has been found mutated in Taybi-Linder (MOPD1/TALS), Roifman (RFMN) and Lowry-Wood syndromes (LWS). These rare developmental disorders, whose physiopathological mechanisms remain unsolved, associate ante- and post-natal growth retardation, microcephaly, skeletal dysplasia, intellectual disability, retinal dystrophy and immunodeficiency. Here, we report a homozygous RNU4ATAC mutation in the Stem II domain, n.16G>A, in two unrelated patients presenting with both typical traits of the Joubert syndrome (JBTS), a well-characterized ciliopathy, and of TALS/RFMN/LWS, thus widening the clinical spectrum of RNU4ATAC-associated disorders and indicating ciliary dysfunction as a mechanism downstream of minor splicing defects. This finding is supported by alterations of primary cilium function in TALS and JBTS/RFMN fibroblasts, as well as by u4atac zebrafish model, which exhibit ciliopathy-related phenotypes and ciliary defects. Altogether, our data indicate that alteration of cilium biogenesis is part of the physiopathological mechanisms of TALS/RFMN/LWS, secondarily to defects of minor intron splicing.

scholarly journals Investigating Primary Cilia during Peripheral Nervous System Formation

2021 ◽  
Author(s):  
Elkhan Yusifov ◽  
Alexandre Dumoulin ◽  
Esther T. Stoeckli
Keyword(s):  
Central Nervous System ◽  
Nervous System ◽  
Neural Crest ◽  
Peripheral Nervous System ◽  
Primary Cilium ◽  
Developmental Disorders ◽  
Neural Crest Cells ◽  
Neuronal Cultures ◽  
System Formation

The primary cilium plays a pivotal role during embryonic development of vertebrates. It acts as a somatic signaling hub for specific pathways, such as sonic hedgehog signaling. In humans, mutations in genes that cause dysregulation of ciliogenesis or ciliary function lead to severe developmental disorders called ciliopathies. Beyond its obvious role in early morphogenesis, growing evidence points towards an essential function of the primary cilium in neural circuit formation in the central nervous system. However, very little is known about a potential role in the formation of the peripheral nervous system. Here, we investigated the presence of the primary cilium in neural crest cells and their derivatives in the trunk of the developing chicken embryo in vivo. We found that neural crest cells, sensory neurons, and boundary cap cells all bear a primary cilium during key stages of early peripheral nervous system formation. Moreover, we described differences in the ciliation of neuronal cultures of different populations from the peripheral and central nervous system. Our results offer a framework for further in vivo and in vitro investigations on specific roles that the primary cilium might play during peripheral nervous system formation.

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