elegans). Many worm strains, including the Hawaiian strain HW, move rapidly, prefer the borders of the lawn, and aggregate in groups, whereas the N2 laboratory strain moves slowly and shows a solitary wandering behavior ( de Bono and Bargmann, 1998). Some elements of this behavior are due to variations in O2 avoidance

behavior. Bacterial lawns consume O2, creating local O2 gradients with low O2 at thick borders and high O2 in the center ( Gray et al., 2004). Under low O2 conditions, HW shows see more solitary behavior rather than aggregates at the borders. Thus, the aggregation behavior is partially explained as an O2 avoidance behavior: most strains avoid high O2 in the presence and absence of food, but N2 avoids high O2

in the absence of food and this avoidance is overridden in the presence of food ( Gray et al., 2004, Cheung et al., 2005 and Rogers et al., 2006). Two genetic differences between N2 and HW have been identified that explain much of the behavioral variation (McGrath et al., 2009). First, changes in a globin www.selleckchem.com/products/MDV3100.html protein GLB-5 modulate the O2-sensing behavior (McGrath et al., 2009 and Persson et al., 2009). Globin domain proteins are heme proteins important for O2 transport and storage (Weber and Vinogradov, 2001). A partial duplication in glb-5 in N2 strains behaves as a recessive mutation, creating a difference in O2 sensing ( McGrath et al., 2009 and Persson et al., 2009). GLB-5 acts in URX neurons that sense increased O2 levels and sensitizes these neurons to small changes in O2. For example, URX

neurons respond to shifts from 20% to 21% O2 in HW but not in N2 ( McGrath et al., 2009 and Persson et al., 2009). Thus, one difference between HW and N2 is that N2 is less sensitive to changes in ambient O2 than HW. However, N2 animals still avoid O2 in the absence of food, consistent with a subtle change in O2 sensing rather than an inability to detect O2. A second major difference is in a neuropeptide receptor (NPR) similar to the neuropeptide F receptor involved in feeding in mammals (de Bono and Bargmann, 1998). N2 animals have a polymorphism in npr (215V) making it more active; other strains have a different polymorphism (215F) making it less active. An npr mutant displays bordering and aggregation similar to the 215F variant. Thus, competing STK38 forces are thought to produce the solitary versus aggregation behavior: aversive cues (including O2) promote aggregation, whereas other cues promote solitary behavior ( de Bono et al., 2002, Gray et al., 2004, Cheung et al., 2005 and Rogers et al., 2006). In the N2 strain, a more active NPR-signaling pathway and a less active O2-sensing pathway promote solitary behavior. In HW, a less active NPR pathway and a more active O2-sensing pathway promote aggregation. Interestingly, N2 likely arose during selection for survival in a laboratory environment: maintaining C.