The ability to sense environmental stimuli is indispensable for the proper response and survival of an organism. For the reception of external signals, organisms have developed a variety of sensory organs and organelles, among them cilia, antenna-like structures emanating from the surface of specialized sensory cells. In many animals including humans, cilia serve a crucial role in the perception of sensory information critical for survival. Regulatory Factor X transcription factors (RFX TFs) are master regulators of genes important for ciliogenesis, cilia structure and function. RFX TFs regulate cilia genes through recognizing and binding to X-box promoter motifs. This module, RFX TF, X-box motif and downstream cilia genes, is well conserved across all animals, including in the nematode C. elegans. The gene
daf-19encodes the sole RFX TF in worms and thereby the master regulator of sensory cilia formation. However,
daf-19consists of a few isoforms that govern additional roles:
daf-19cencodes the pan-ciliary factor, and
daf-19a/bis important for synaptic protein homeostasis.
daf-19mis expressed in only a few ciliated neurons: the male-specific CEM, RnB, and HOB neurons and the IL2 neurons, present in both hermaphrodites and males. In a previous study,
daf-19mwas connected to male mating behavior, but its specific role in IL2 neurons and its regulatory relationship with other
daf-19isoforms remain to be discovered.IL2 neurons regulate nictation, the dauer-specific dispersal behavior. In the wild, nematodes exist mainly in the dauer stage, the diapause stage resistant to harsh conditions, and produce progeny only during their encounters of good conditions. Nictation is a crucial sensory behavior for the successful interaction with carrier organisms during these cycles of boom and bust. The factors controlling development, differentiation and then specialized, functional activation of IL2 are unknown. Our forward genetic screening established that
daf-19m - under the umbrella of IL2 terminal selector genes - controls a regulatory subroutine for the activation of functional genes in IL2 neurons, important for nictation. Interestingly, this regulation is mediated through a non-classical type of X-box motif. We propose a novel function for RFX TFs, contributing to species dispersal behavior in the wild.