Sakurai, Yuki et al. (2011) International Worm Meeting "Genetic analysis of food-associated salt concentration memory."

Sakurai, Yuki, Iino, Yuichi, Kunitomo, Hirofumi

[International Worm Meeting, 2011]

Caenorhabditis elegans is usually attracted to NaCl if grown on standard culture conditions. On the other hand, it avoids the salt after exposure to salt under starvation (salt chemotaxis learning). We have reported that the insulin/PI3-kinase signaling regulates salt chemotaxis learning in ASER, one of the major taste neurons of the organism (Tomioka et al. 2006, Adachi et al, 2010). To examine how preference for salt is modified by experiences, we exploited a novel behavioral test, salt preference assay. Briefly, adult animals grown under standard culture conditions (50 mM NaCl with E. coli as food) are transferred to a conditioning plate that contains a defined concentration, 0-100 mM, of NaCl with food. After 6 hours of conditioning, worms are washed out from the plates and tested for chemotaxis to 35-95 mM of NaCl. Through this analysis, we found that wild-type C. elegans is attracted to the NaCl concentrations at which it has been fed (food-associated salt preference), indicating that the behavior on salt gradient is based on salt concentration memory. Mutants of PI3-kinase pathway didnt show significant defects in this assay. This result suggests that the mechanisms for salt preference is distinct, at least in part, from that of salt chemotaxis learning. To elucidate the mechanisms of food-associated salt preference, we screened for mutants of food-associated NaCl concentration preference. 30,000 EMS-mutagenized F2 animals were divided into 30 independent groups and screened by the salt preference assay after 0 or 100 mM NaCl conditioning with food. Animals that were attracted to high or low concentrations of NaCl after 0 or 100 mM conditioning, respectively, were collected and bred for next generation. In this screen we isolated several independent mutant strains JN572-JN577. JN574 showed no food-associated salt preference, whereas JN572 and JN577 showed defects only after conditioning at low concentrations of salt. These mutants are not likely chemosensory mutants because they showed normal salt chemotaxis after starvation. Characterization of these mutants will clarify the molecular mechanisms as to how the animals adapt to ambient salt conditions.

Park, Chanhyun et al. (2017) International Worm Meeting "Roles of the CLC chloride channel clh-1 in food-associated salt chemotaxis learning of Caenorhabditis elegans."

Park, Chanhyun, Kunitomo, Hirofumi, Iino, Yuichi, Sakurai, Yuki

[International Worm Meeting, 2017]

Animals modulate their chemotaxis behavior to seek preferred conditions by memorizing experienced environmental conditions and subsequently modifying navigation strategies. For instance, they show an experience-dependent behavioral plasticity in NaCl chemotaxis in which preference of NaCl is regulated by food availability. Worms are attracted to the salt concentration at which they have been fed, while avoiding it if they have been starved. The insulin/PI3-kinase signaling in ASER salt-sensing neuron regulates starvation-induced behavioral changes (Tomioka et al. 2006, Ohno et al. 2014). However, PI3-kinase pathway mutants showed no discernable defect in the food-associated salt preference behavior, suggesting that the mechanism of food-associated learning is different from that of starvation-induced learning (Kunitomo et al. 2013). Through a genetic screen for mutants that show defects in the food-associated learning but not in the starvation-induced learning, we obtained two mutants JN572 and JN577. Further, we found that each of the two mutants has a point mutation in clh-1, which encodes a CLC chloride channel. CLH-1 is known to function as a HCO3- transporter in pH homeostasis of the amphid sheath glia (Grant et al. 2015). Four out of 9 CLC proteins in human are implicated in neurologic disorders. Interestingly, clh-1 deletion mutants that are expected to eliminate clh-1 functions, did not show behavioral defects in the food-associated learning. This result suggested that the mutations were neomorphic. Tissue-specific rescue of the clh-1 mutants indicated that CLH-1 acts in the salt sensing neuron ASER in the food-associated learning. In addition, measurement of ciliary length of ASER implicated a role of clh-1 in ciliary formation or maintenance.