The cycle of ciliogenesis and ciliary disassembly is coordinated with cell division. In the unicellular alga Chlamydomonas, the two flagella are maintained at constant and equal length during interphase, and are reabsorbed prior to mitosis. We report that the NIMA-related kinase, Cnk2p, is an axonemal protein that affects flagellar length via effects on disassembly rate and also plays a role in the cellular assessment of size prior to committing to mitosis. This is the second NIMA-related kinase shown to affect ciliary function and cell cycle progression in Chlamydomonas. We speculate that members of the NIMA family have evolved nuanced roles to coordinate cilia/cell cycle regulation.

Reception and interpretation of environmental stimuli is critical for the survival of all organisms. Here, we show that the ablation of BBS1 and BBS4, two genes mutated in Bardet-Biedl syndrome and that encode proteins that localize near the centrioles of sensory neurons, leads to alterations of s.c. sensory innervation and trafficking of the thermosensory channel TRPV1 and the mechanosensory channel STOML3, with concomitant defects in peripheral thermosensation and mechanosensation. The thermosensory phenotype is recapitulated in Caenorhabditis elegans, because BBS mutants manifest deficient thermosensory responses at both physiological and nociceptive temperatures and defective trafficking of OSM-9, a polymodal sensory channel protein and a functional homolog of TRPV1 or TRPV4. Our findings suggest a hitherto unrecognized, but essential, role for mammalian basal body proteins in the acquisition of mechano-and thermosensory stimuli and highlight potentially clinical features of ciliopathies in humans.basal bodies ͉ cilia ͉ thermosensation T he study of sensory organs in both vertebrates and invertebrates has revealed a role for cilia in chemosensation, mechanosensation, and photosensation. In Drosophila, chemosensation and mechanosensation rely specifically on neurons that are ciliated (1). Similarly, a role for cilia in chemosensation is well established in Caenorhabditis elegans, where mutants with compromised function or structure of cilia display defects in sensing odorants or differences in osmolarity (2-4). In mammals, odorant receptors localize to olfactory cilia (5), and the phototransduction apparatus of rod and cone cells in vertebrates localizes to the outer segment, a modified cilium (6). Finally, the kinocilium is essential for cochlear development and, thus, hearing because of its role in stereociliary bundle morphogenesis (7).We and others have shown that loss-of-function mutations in genes underlying the pleiotropic Bardet-Biedl phenotype (8) cause sensory deficits that include vision loss, anosmia, and defective hearing (5, 7, 9, 10). All BBS proteins characterized to date localize near or within basal bodies and in cilia in both mammalian cells (11-13) and in C. elegans sensory neurons (14-16).Here, we show that mammalian peripheral sensory neurons are ciliated and that mouse mutants with targeted loss-of-function mutations in either Bbs1 or Bbs4 exhibit thermosensory phenotypes characterized by significant increases in behavioral response latencies. These defects are unlikely to be caused by higher-order cortical or motor dysfunction but are accompanied by alterations in cutaneous sensory innervation and defective distribution of effector molecules in the sensory neuronal soma. These phenotypes are not unique to mammals, because nematode bbs mutants are also thermosensory-defective. Finally, humans with BBS also manifest some symptoms similar to the ones observed in mice, such as reduced temperature and vibration sensation. Our studies suggest a critical role of basal body and ciliary protein...

BackgroundNIMA-related kinases (Neks) have been studied in diverse eukaryotes, including the fungus Aspergillus and the ciliate Tetrahymena. In the former, a single Nek plays an essential role in cell cycle regulation; in the latter, which has more than 30 Neks in its genome, multiple Neks regulate ciliary length. Mammalian genomes encode an intermediate number of Neks, several of which are reported to play roles in cell cycle regulation and/or localize to centrosomes. Previously, we reported that organisms with cilia typically have more Neks than organisms without cilia, but were unable to establish the evolutionary history of the gene family.Methodology/Principle FindingsWe have performed a large-scale analysis of the Nek family using Bayesian techniques, including tests of alternate topologies. We find that the Nek family had already expanded in the last common ancestor of eukaryotes, a ciliated cell which likely expressed at least five Neks. We suggest that Neks played an important role in the common ancestor in regulating cilia, centrioles, and centrosomes with respect to mitotic entry, and that this role continues today in organisms with cilia. Organisms that lack cilia generally show a reduction in the number of Nek clades represented, sometimes associated with lineage specific expansion of a single clade, as has occurred in the plants.Conclusion/SignificanceThis is the first rigorous phylogenetic analysis of a kinase family across a broad array of phyla. Our findings provide a coherent framework for the study of Neks and their roles in coordinating cilia and cell cycle progression.

The NIMA kinases are an evolutionarily conserved protein family with enigmatic roles in the regulation of mitosis. We report six new members of this family in Chlamydomonas, in addition to the previously identified NIMA-related kinase, Fa2p. Chlamydomonas NIMA-related kinases (CNKs) 1-6 were sequenced from subclones generated by RT-PCR using information from EST libraries and the recently sequenced Chlamydomonas genome. Phylogenetic and bioinformatic approaches were used to determine the relationships of the six new members with known members of the NIMA-related kinase family. Although humans express at least eleven NIMA-related kinases, the eukaryotic microbes that have been studied to date express only one or two members of the family. Thus, the discovery that Chlamydomonas expresses a total of at least seven NIMA-related kinases is intriguing. Our analyses suggest that members of this family may play roles in the assembly and function of cilia.