Olfaction
Volatile organic molecules are sensed through olfaction. C. elegans can distinguish and respond to many volatile odorants through attractive or repulsive chemotactic behaviors. In some instances volatile compounds can induce both behaviors depending on its concentration. Olfaction studies in C. elegans has revealed a complex sensory system where only three types of neurons (AWC, AWA, and AWB) have been found to be responsible for processing over seven classes of volatile odorants, including alcohols, ketones, organic acids, sulfhydrals, and heterocyclic compounds. Detailed study of the molecular machinery behind odor reception has shown that each neuron controls a particular attractive or repulsive behavioral response, for example, AWC controls attractive chemotaxis responses and AWB controls repulsive chemotaxis responses. One distinguishing feature of C. elegans sensory system is that the sensory neurons are polymodal in their stimulus detecting ablility; that is, individual neurons in C. elegans express multiple odorant receptors allowing multiple sensory functions, whereas vertebrate neurons express a single receptor limiting their function to detecting a single odorant.
Wnt signaling pathway
Wnt glycoproteins are signaling molecules that control a wide range of developmental processes and is a conserved feature of metazoan development. In C. elegans Wnt signaling has been shown to play a role in cell fate specification and determination of cell polarity, cell migration, and axis determination during axon outgrowth. A 'canonical' Wnt signaling pathway has been elucidated in vertebrate and invertebrate model systems where Wnt binding leads to the stabilization of the transcription factor beta-catenin, which then enters the nucleus to regulate Wnt pathway target genes. Like other species, the C. elegans genome encodes multiple genes for Wnt ligands, EGL-20, LIN-44, MOM-2, CWN-1, CWN-2) and Wnt receptors (LIN-17, MOM-5, MIG-1, CFZ-2, LIN-18). Canonical Wnt signaling in C. elegans, utilizes the beta-catenin BAR-1 to convert POP-1 into an activator and controls the expression of several homeobox genes. However, unlike vertebrates or Drosophila, the C. elegans genome encodes multiple beta-catenin genes (HMP-2, BAR-1, SYS-1, WRM-1), which give rise to noncanonical Wnt signalling pathways: for example, the endoderm induction pathway requires the beta-catenin WRM-1 and parallel input from a mitogen-activated kinase (MAPK) pathway to downregulate POP-1.