Morphological Diversity of C. elegans Sensory Cilia Instructed by the Differential Expression of an Immunoglobulin Domain Protein

Cilia on dendritic endings of sensory neurons organize distinct types of sensory machinery [1]. Ciliated endings display neuron-type-specific patterns of membrane elaborations [1–3], but it is not well understood how such neuron-type-specific morphologies are generated and whether they are coupled to the specification of other identity aspects of a terminally differentiated sensory neuron. In the course of a genome-wide analysis of members of a small family of immunoglobulin domain proteins, we found that OIG-8, a previously uncharacterized transmembrane protein with a single immunoglobulin (Ig) domain, instructs the distinct, neuron-type-specific elaboration of ciliated endings of different olfactory neuron types in the nematode C. elegans. OIG-8 protein localizes to ciliated endings of these sensory neurons, and is transcribed at different levels in distinct olfactory neuron types. oig-8 expression levels correlate with the extent of sensory cilia growth and branching patterns. Loss of oig-8 leads to a reduction in the branching patterns of cilia, whereas raising the levels of oig-8 results in an increase in elaborations. Levels of OIG-8 expression are controlled by the specific combination of a terminal selector type of transcription factors that also specify other identity features of distinct olfactory neuron types. •OIG-8, a transmembrane Ig domain protein, localizes to cilia of sensory neurons•oig-8 is expressed at different levels in distinct olfactory neuron types•oig-8 expression levels correlate with the extent of cilia membrane elaborations•Lowering of oig-8 expression decreases, and raising oig-8 increases, cilia elaborations Howell and Hobert identify a transmembrane protein involved in determining the neuron-type-specific morphology of ciliated sensory endings of C. elegans olfactory neurons. This protein is expressed at different levels in different olfactory neurons and its dosage determines the extent of cilia elaborations in these distinct neuron types.