Ray development
C. elegans male tail contains four types of male-specific sensilla, the most prominent of which are the rays. These 18 sensory rays convey mechano- and chemosensory information critical to male mating. Each ray is composed of three cells: RnA: A-type sensory neuron; RnB: B-type sensory neuron; and Rnst: ray structural cell, which are derived from one neuroblast, the ray precursor cell called Rn. Each ray is morphologically and molecularly distinct from each other. Most all ray identity follows a determinate cell lineage model where cell identity is established based on the pattern of cell division; ray 5 does require external cues from a TGF-beta signalling pathway to adopt its final fate.
Chemosensation
Chemosensation is the process of detecting, processing, and responding to volatile and water-soluble stimuli in the environment. C. elegans has a sophisticated chemosensory system, with much of its nervous system devoted to this process. Detection of these stimuli can result in behavioral outputs such as avoidance of or attraction to the chemical. While physiological responses can include a switch in developmental programs to a dauer stage rather than continuing to reproductive maturity. The amphid (anterior) and phasmid (posterior) chemosensory organs mediate chemosensation. On a cellular level, detection and activation of the chemosensory systems occurs through G-protein coupled receptors (GPCRs), of which different combinations are expressed in each amphid sensory neuron. The combination of GPCRs direct the type of chemical sensed and the response of the animal to the stimulus.
RTK/Ras/MAPK signaling pathway
Receptor Tyrosine Kinase (RTK)/Ras GTPase/MAP kinase (MAPK) activated signaling pathways are used repeatedly during metazoan development to control many different biological processes. C. elegans contains two different RTKs (LET-23/EGFR and EGL-15 /FGFR) that are known to stimulate LET-60/Ras and a MAPK cascade consisting of the kinases LIN-45/Raf, MEK-2/MEK and MPK-1/ERK. This Ras/MAPK cascade is required for multiple developmental events, including induction of vulval, uterine, spicule, P12 and excretory duct cell fates, control of sex myoblast migration and axon guidance, and promotion of germline meiosis. Studies in C. elegans have provided much insight into the basic framework of this RTK/Ras/MAPK signaling pathway, its regulation, how it elicits cell-type specific responses, and how it interacts with other signaling pathways such as the Wnt and Notch pathways.