Intraflagellar transport in Caenorhabditis elegans: identification of novel proteins and behavioural functions

Intraflagellar transport (IFT) is the dynamic bidirectional process required for the biogenesis and maintenance of eukaryotic cilia. Landmark studies exploiting the model organism Chlamydomonas reinhardtii have provided a basic mechanism for the process, although recent research examining IFT in the nematode Caenorhabditis elegans has revealed a greater complexity to the original model of IFT described in Chlamydomonas, which includes the orthologues of several human proteins involved in cilium-associated diseases. The wealth of genomic, bioinformatic, and molecular tools available to C. elegans researchers is exploited in this thesis to uncover and characterise a number of novel proteins involved in the process of IFT, namely DYF-11, MKS-1, MKSR-1, and MKSR-2. DYF-11 localises throughout nematode ciliary structures and acts as a key component of the core IFT subcomplex B. The latter three proteins are members of a previously uncharacterised family of B9-domain containing polypeptides, all of which appear to localise at the base of cilia (basal body/transition zone), where they are found to regulate a cilium-based insulin signalling pathway. The results of this study contribute to the growing realisation in C. elegans cilia research that a network of transition-zone-specific proteins are participating in ciliary processes ranging from subtle modulation of ciliary signalling pathways to the actual biogenesis and maintenance of the organelle. Next, we examine previously isolated nematode strains that are defective in paraquat resistance for impaired retrograde IFT. We identify a retrograde-IFT deficient strain that likely represents a mutation in an IFT component that has not been previously characterised in C. elegans; the mutation maps closely to a highly conserved protein identified as a core component of IFT subcomplex A. Finally, we examine the role played by the IFT-associated Bardet-Biedl syndrome (BBS) proteins in C. elegans thermosensation. bbs mutant worms appear to be slightly defective in responding to both noxious and physiological temperatures. Furthermore, the nature of the physiological temperature defect correlates with a decreased roaming ability that is not the result of impaired locomotion. Altogether, the studies presented in this thesis offer novel insights into both the molecular makeup and physiological functions of IFT in C. elegans.