Nematodes Are Smarter than You Think

absence of food will move in the same assay without 197–204. main features of the neural circuit controlling thermo-92, 846–849. play antagonistic roles in thermotaxis: AIY activity favors migration to high temperatures and AIZ activity favors low temperatures (Mori and Ohshima, 1995). The paper by Gomez et al. (2001) in this issue of Neuron reports a role for a C. elegans neuronal Ca 2ϩ than You Think sensor protein (NCS-1) in thermotaxis accuracy and plasticity. NCS-1 belongs to a large family of EF hand containing calcium binding proteins and is highly con-Weighing in at about 5 ␮g, with 302 neurons and 5000is expressed in 13 classes of neurons and one muscle havioral complexity is packed into this tiny worm. Worms cell. The neurons are mostly sensory, including the ther-live in a sensory world very different from our own, one mosensory neuron AFD, but they also include the in-dominated by touch, taste, and smell, one in which bac-terneuron AIY. The authors generate a null deletion allele teria are the size of cherries, and Brownian motion and of NCS-1 using reverse genetic methods (Plasterk, 1995). surface tension take the place of wind and gravity. It is ncs-1(null) mutants develop normally and perform nor-difficult for us to intuit what their world is like, but one mally in chemotactic odorant responses, suggesting measure of what the worm cares about is the behavioral that their fine locomotory and taxis systems are unper-and genetic complexity devoted to various sensory turbed. However, their performance in isothermal tracking modes. By this measure, thermotaxis must matter a lot is substantially degraded, resembling that seen when to the worm. This behavior was first described in 1975 the thermosensory neuron AFD is removed. Transgenic by Hedgecock and Russell, who noted, among other experiments with altered ncs-1 genes show that its func-things, two remarkable features. First, worms are capa-tion in thermotaxis depends on its Ca 2ϩ binding sites ble of moving along curving isothermal lines in their and on expression specifically in the interneuron AIY. medium with precision, deviating as little as 0.1ЊC from Up to this point, these results are interesting but, one their preferred temperature. Second, thermal preference might argue, not particularly exceptional: NCS-1 func-is plastic, being conditioned by the presence or absence tions in AIY in its familiar Ca 2ϩ binding role to mediate of food. thermosensory response. However, perhaps inspired by The plasticity in C. elegans thermotaxis is …