Multiple regulators constrain the abundance of Caenorhabditis elegans DLK-1 in ciliated sensory neurons.

The conserved MAP3K DLKs are widely known for their functions in synapse formation, axonal regeneration and degeneration, and neuronal survival, notably under traumatic injury and chronic disease conditions. In contrast, their roles in other neuronal compartments are much less explored. Through an unbiased forward genetic screening in C. elegans for altered patterns of GFP-tagged DLK-1 expressed from the endogenous locus, we have recently uncovered a mechanism by which the abundance of DLK-1 is tightly regulated by intraflagellar transport in ciliated sensory neurons. Here, we report additional mutants identified from the genetic screen. Most mutants exhibit increased accumulation of GFP::DLK-1 in sensory endings, and the levels of misaccumulated GFP::DLK-1 are exacerbated by loss of function in cebp-1, the b-Zip transcription factor acting downstream of DLK-1. We identify several new mutations in genes encoding proteins functioning in intraflagellar transport and cilia assembly, in components of BBSome, MAPK-15, and DYF-5 kinases. We report a novel mutation in the chaperone HSP90 that causes misaccumulation of GFP::DLK-1 and up-regulation of CEBP-1 selectively in ciliated sensory neurons. We also find that the guanylate cyclase ODR-1 constrains GFP::DLK-1 abundance throughout cilia and dendrites of AWC neurons. Moreover, in odr-1 mutants, AWC cilia display distorted morphology, which is ameliorated by loss of function in dlk-1 or cebp-1. These data expand the landscape of DLK-1 signaling in ciliated sensory neurons and underscore a high degree of cell- and neurite- specific regulation.