The C. elegans Regulatory Factor X (RFX) DAF-19M Module: A Shift From General Ciliogenesis to Ciliary and Behavioral Specialization

In animals, cilia are important for the interaction with environments and the proper function of tissues and organs. While the basic structure of cilia is well conserved, ciliated cells have a variety of functions. To understand the distinctive identities of each type of ciliated cell, the identification of cell-specific proteins and their regulation is essential. Here, we report the mechanism that confers a specific identity on IL2 neurons in C. elegans, neurons important for the dauer larva-specific nictation behavior. We show that DAF-19M, an isoform of the sole C. elegans RFX transcription factor DAF-19, heads a regulatory subroutine, regulating target genes including CWP-4, a novel nictation regulator protein, through X-box motif variants under the overall control of terminal selector proteins UNC-86 and CFI-1 in IL2 neurons. Considering the conservation of this DAF-19M module in IL2 neurons for nictation and in male-specific neurons for mating behavior, we propose the existence of an evolutionarily adaptable, hard-wired genetic module for distinct behaviors that share the feature “recognizing the environment.”