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 RFX-transcription factor DAF-19 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. We conducted a genome-wide search for X-boxes in promoters of C. elegans with subsequent expression and some mutant analyses of the group of positive matches in wild-type and
daf-19 mutant backgrounds. Of the more than 30 transcriptional fusions tested so far in worms, we identified 18 X-box genes that function in the development of ciliated sensory neurons. We found that DAF-19 regulates not only genes for the cilium structure and transport machinery (
che-2,
che-13,
osm-1,
osm-5,
osm-6,
bbs-1,
bbs-2,
bbs-7,
bbs-8,
xbx-1) but also possible receptors (M04D8.6, T24A11.2) and other factors (
odr-4,
nhr-44). Most of them have homologous X-box sequences in promoters of C. briggsae, D. melanogaster and humans. We also observed that the actual X-box and it's position within the promoter can help us to predict expression patterns in ciliated neurons (in most or all / in some / in none). We propose a model where the gene
daf-19 controls the expression of a "ciliary module" which leads to the formation of functional ciliated endings in sensory neurons in C. elegans. Different structural and functional parts of the "ciliary module" correspond to certain X-box compositions.