Cilia are widespread eukaryotic subcellular organelles that function in cell motility, movement of extracellular fluids and sensory reception. While structure and function of cilia are well known, there are many questions with regard to cilia formation and development. The gene
daf-19, encoding an RFX-family transcription factor, is crucial for the formation of cilia of sensory neurons. DAF-19 regulates the activity of its target genes by binding to the x-box promoter motif. The C. elegans genome has more than 200 candidate x-box genes. We have initiated expression analysis of these candidate genes. Our results suggest that only genes with x-boxes of a certain nucleotide composition will be expressed in most or all ciliated neurons. Using this consensus sequence we have identified new genes such as the dynein-complex gene
xbx-1 that is involved in retrograde cilium transport, and genes D1009.5 and F20D12.3 that are also thought to be very important for cilium structure and function. The roles of new cilium genes are being determined by using RNAi, by generating knockouts and by interaction screens with already known cilium components. Based on the data obtained so far we conclude that DAF-19 typically regulates genes for cilium structure and transport machinery, whereas genes for signal reception and transduction do not require its function. Thus, the x-box search strategy represents a powerful tool for discovering new cilium genes in C. elegans. The knowledge of cilium genes and their function is very important for understanding human pathologies that are caused by defects in cilia.