Prior studies from our laboratory and others have demonstrated two layers of transcriptional regulation of the serotonin-biosynthesis enzyme tryptophan hydroxylase
tph-1 in the ciliated chemosensory neurons ADF. The OCR-2/OSM-9 TRPV channel regulates the basal
tph-1 expression under optimal growth conditions (Zhang et al., 2004). Stress conditions or mutations of the sensory cilia further upregulate
tph-1 expression in ADFs (Zhang et al., 2005; Chang et al., 2006; Moussaif and Sze, 2009; Shivers et al., 2009). To identify new genes involved in the regulation of
tph-1 expression in the ADF neurons, two genetic screens were carried out. We identified that
yz58, a gain-of-function allele of the Toll-interleukin 1 receptor domain protein TIR-1, restored
tph-1 expression in the
ocr-2 mutant background. Characterization of mutations that suppress
tph-1 upregulation by
tir-1 (
yz58) led to the identification of two
daf-19 alleles. Interestingly, both mutations are located in the DAF-19 dimerization domain. Mutations in DAF-19 do not affect the expression of CAT-1/VMAT, indicating that the mutations do not transform the ADF serotonergic cell fate. Further analysis suggests that DAF-19 also interacts with TIR-1 signaling in other cellular and physiological functions. References Chang AJ, Chronis N, Karow DS, Marletta MA, Bargmann CI. 2006. A distributed chemosensory circuit for oxygen preference in C. elegans. PLoS Biol 4:
e274. Moussaif M, Sze JY. 2009. Intraflagellar transport/Hedgehog-related signaling components couple sensory cilium morphology and serotonin biosynthesis in Caenorhabditis elegans. J Neurosci 29:4065-75. Shivers RP, Kooistra T, Chu SW, Pagano DJ, Kim DH. 2009. Tissue-specific activities of an immune signaling module regulate physiological responses to pathogenic and nutritional bacteria in C. elegans. Cell Host Microbe 6:321-30. Zhang S, Sokolchik I, Blanco G, Sze JY. 2004. Caenorhabditis elegans TRPV ion channel regulates 5HT biosynthesis in chemosensory neurons. Development 131:1629-38. Zhang Y, Lu H, Bargmann CI. 2005. Pathogenic bacteria induce aversive olfactory learning in Caenorhabditis elegans. Nature 438:179-84.