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The primary cilium is an antenna-like projection from the plasma membrane that serves as a sensor of the extracellular environment and a crucial signaling hub. Primary cilia are generated in most mammalian cells, and their physiological significance is highlighted by the large number of severe developmental disorders or ciliopathies that occur when primary ciliogenesis is impaired. Primary ciliogenesis is a tightly regulated process, and a central early regulatory step is the removal of a key mother centriole capping protein, CP110 (also known as CCP110). This uncapping allows vesicles docked on the distal appendages of the mother centriole to fuse to form a ciliary vesicle, which is bent into a ciliary sheath as the microtubule-based axoneme grows and extends from the mother centriole. When the mother centriole migrates toward the plasma membrane, the ciliary sheath fuses with the plasma membrane to form the primary cilium. In this Review, we outline key early steps of primary ciliogenesis, focusing on several novel mechanisms for removal of CP110. We also highlight examples of ciliopathies caused by genetic variants that encode key proteins involved in the early steps of ciliogenesis. [ABSTRACT FROM AUTHOR]

Endosomes play crucial roles in the cell, serving as focal and 'triage' points for internalized lipids and receptors. As such, endosomes are a critical branching point that determines whether receptors are sorted for degradation or recycling. This Viewpoint aims to highlight recent advances in endosome research, including key endosomal functions such as sorting and fission. Moreover, the Viewpoint addresses key technical and conceptual challenges in studying endosomes. [ABSTRACT FROM AUTHOR]

The mammalian retromer consists of subunits VPS26 (either VPS26A or VPS26B), VPS29 and VPS35, and a loosely associated sorting nexin (SNX) heterodimer or a variety of other SNX proteins. Despite involvement in yeast and mammalian cell trafficking, the role of retromer in development is poorly understood, and its impact on primary ciliogenesis remains unknown. Using CRISPR/Cas9 editing, we demonstrate that vps-26-knockout worms have reduced brood sizes, impaired vulval development and decreased body length, all of which have been linked to ciliogenesis defects. Although preliminary studies did not identify worm ciliary defects, and impaired development limited additional ciliogenesis studies, we turned to mammalian cells to investigate the role of retromer in ciliogenesis. VPS35 localized to the primary cilium of mammalian cells, and depletion of VPS26, VPS35, VPS29, SNX1, SNX2, SNX5 or SNX27 led to decreased ciliogenesis. Retromer also coimmunoprecipitated with the centriolar protein, CP110 (also known as CCP110), and was required for its removal from the mother centriole. Herein, we characterize new roles for retromer in C. elegans development and in the regulation of ciliogenesis in mammalian cells, suggesting a novel role for retromer in CP110 removal from the mother centriole. [ABSTRACT FROM AUTHOR]

The endocytic protein EHD1 plays an important role in ciliogenesis by facilitating fusion of the ciliary vesicle and removal of CP110 (also known as CCP110) from the mother centriole, as well as removal of Cep215 (also known as CDK5RAP2) from centrioles to permit disengagement and duplication. However, the mechanism of its centrosomal recruitment remains unknown. Here, we address the role of the EHD1 interaction partner MICAL-L1 in ciliogenesis. MICAL-L1 knockdown impairs ciliogenesis in a similar manner to EHD1 knockdown, and MICAL-L1 localizes to cilia and centrosomes in both ciliated and non-ciliated cells. Consistent with EHD1 function, MICAL-L1- depletion prevents CP110 removal from the mother centriole. Moreover, upon MICAL-L1-depletion, EHD1 fails to localize to basal bodies. Since MICAL-L1 localizes to the centrosome even in nonciliated cells, we hypothesized that it might be anchored to the centrosome via an interaction with centrosomal proteins. By performing mass spectrometry, we identified several tubulins as potential MICAL-L1 interaction partners, and found a direct interaction between MICAL-L1 and both α-tubulin–β-tubulin heterodimers and γ-tubulin. Our data support the notion that a pool of centriolar γ-tubulin and/or α-tubulin–β-tubulin heterodimers anchor MICAL-L1 to the centriole, where it might recruit EHD1 to promote ciliogenesis. [ABSTRACT FROM AUTHOR]