Lateral signaling mediated by axon contact and calcium entry regulates asymmetric odorant receptor expression in C-elegans

C. elegans detects several odorants with the bilaterally symmetric pair of AWC olfactory neurons. A stochastic, coordinated decision ensures that the candidate odorant receptor gene str-2 is expressed in only one AWC neuron i n each animal-either the left or the right neuron, but never both. An inter action between the two AWC neurons generates asymmetric str-2 expression in a process that requires normal axon guidance and probably AWC axon contact . This interaction induces str-a expression by reducing calcium signaling t hrough a voltage-dependent Ca2+ channel and the CaM kinase II UNC-43. CaMKI I activity acts as a switch in the initial decision to express str-2; thus, calcium signals can define distinct cell types during neuronal development . A cGMP signaling pathway that is used in olfaction maintains str-2 expres sion after the initial decision has been made.