Architecture of distal tips of motile cilia is shaped by the pseudoenzyme Jhc1 in non-mammalian vertebrates.

Stereotypical interciliary contacts in a C. elegans sense organ

Physical interactions among cells and their processes are critical for intercellular communication and the generation of ordered tissue patterns. Primary cilia projecting from the cell surface have recently been shown to form contacts with the processes of diverse cell types, as well as with other cilia, in the brain and other organs. Whether these ciliary contacts are established in an instructive manner or are formed passively due to physical proximity is unclear. Ultrastructural analyses previously showed that the cilia of a subset of sensory neurons in the head amphid organs of C. elegans exhibit interciliary contacts within a glia-defined channel. Here we show that these ciliary contact patterns are stereotyped and can be established in the absence of neighboring cilia, indicating that these associations may not simply reflect relative positioning within the amphid channel. We show that mutations in genes implicated in ciliary protein trafficking, ciliary membrane phospholipid composition, and cilia-cell interactions disrupt cilia structure and/or interciliary contacts, and that in a subset of mutants, cilia with altered morphologies can nevertheless establish correct contacts. Together, our findings suggest that cilia-cilia interactions within a sense organ are established via instructive mechanisms, and raise the possibility that cellular functions may be modulated by cilia-mediated intercellular communication. Summary This work investigates how primary cilia, structures that detect and transmit signals, form contacts with one another in a head sensory organ of the nematode Caenorhabditis elegans. The authors found that these contacts follow consistent patterns and can form even when neighboring cilia are absent, suggesting they are actively established rather than occurring due to physical proximity. The authors identified mutations in genes that regulate cilia protein content, membrane composition, and cellular adhesion that disrupt cilia structure or contacts. These findings suggest that cilia-cilia interactions are regulated, raising the possibility that they play important roles in cell communication.

RNAseK is vital for epithelial function in Drosophila melanogaster.

The transporting epithelial tissues comprising the Drosophila melanogaster alimentary and renal systems are known to share a common set of enriched genes sometimes referred to as the "epitheliome", reflecting their shared transport functions. Core amongst these genes are the vha genes, which encode subunits of the large Vacuolar-type ATPase (V-ATPase) proton pump complex. However, many of the non-vha components of the epitheliome remain broadly uncharacterised. Here, we explore the role of RNAseK, a gene identified during unbiased epithelial screens in Drosophila whose function within insects is not yet known, though evidence from mammalian systems suggest a role in supporting proton pump activity. We demonstrate computationally that RNAseK is strongly conserved across evolutionary history, and that expression is regulated by the highly epithelial-specific dCLEAR motif. Seeking to understand why epithelial expression is so emphasised, we have assayed the effects of RNAseK knockdown in different epithelia throughout the fly. Across hindgut, midgut, and Malpighian tubules, we note profound defects in gross tissue morphology, transport activity, and fly survival. Mechanistically, RNAseK co-localises apically with the V-ATPase subunit Vha55, and RNAseK knockdown phenotypes overlap with those caused by V-ATPase perturbation. These findings are consistent with a role for RNAseK in acidification-dependent epithelial transport and membrane homeostasis, although direct effects on V-ATPase biochemical activity or on other epithelial transport and junctional pathways remain to be tested.

The dynamics of ciliogenesis in prepubertal mouse meiosis reveals new clues about testis maturation

Primary cilia have recently been identified in mammalian spermatocytes, but their developmental regulation during testicular maturation remains poorly understood. Here, we investigate the dynamics of ciliogenesis during mouse puberty and show that primary cilia are not an intrinsic feature of spermatocytes during the first wave of meiosis, initiated at 8 days post partum (dpp). Ciliogenesis begins only at day 20 dpp, where cilia are detected across all stages of prophase I, indicating no direct association with synapsis or desynapsis. We further found that Aurora kinase A is associated with cilia disassembly in late diplotene and that spermatocytes retaining a polymerized cilium fail to assemble a bipolar spindle. In addition, proteomic analysis defined the 19–21 dpp period as a key developmental window associated with ciliogenesis and flagellogenesis. We also identified ciliated spermatocytes in the human testis, providing the first evidence of meiotic cilia in human meiocytes. This work reveals that ciliogenesis is a developmentally regulated process during testicular maturation in mouse.

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Rotational asymmetry is required to position centrioles at the base of the primary cilium

GRAF1-dependent endocytotic processes and the Golgi apparatus contribute to previously unrecognized intermediate stages of early ciliogenesis

The intracellular cilia assembly pathway is a complex, multistep process that requires the continuous and coordinated incorporation of membrane material. However, how membrane remodeling occurs during early ciliogenesis is not yet understood. Moreover, the identity of the organelle(s) that supply membrane material for the nascent cilium has yet to be determined. Here, we extend the current model of primary cilia formation by showing that randomly attached distal appendage vesicles and tubules fuse laterally to generate a doughnut-shaped membrane structure. Centripetal fusion events follow to close the central hole. Our data demonstrate that both the Golgi apparatus and endocytotic pathways independently contribute to ciliogenesis. We identify the endocytotic protein GRAF1 as being essential during the early stages of ciliogenesis and for the delivery of plasma membrane-derived material to the developing ciliary membrane. Our three-dimensional ultrastructural analysis uncovers previously unrecognized intermediate stages in the intracellular cilia assembly pathway with GRAF1 as a regulator of ciliogenesis. A three-dimensional ultrastructural analysis reveals previously unrecognized intermediate stages in the formation of primary cilia. It is demonstrated that both the endocytotic protein GRAF1 and the Golgi apparatus contribute to the intracellular pathway of ciliogenesis.