Yuichi Iino et al. (2008) C.elegans Neuronal Development Meeting "Behavioral Strategy for Salt Chemotaxis and Underlying Neurons"

Kazushi Yoshida, Yuichi Iino, Takanobu Tagawa

[C.elegans Neuronal Development Meeting, 2008]

C. elegans shows chemotaxis to water-soluble chemoattractants such as sodium chloride. How this behavior is achieved was previously addressed by several investigators. Among them, Jon Pierce-Shimomura analyzed the behavior of animals during chemotaxis using computerized worm-tracking system and proposed a pirouette strategy (1). Worms often change the direction of locomotion by a stereotyped behavior called pirouette, a bout of reversals coupled to sharp turns. It was proposed that worms show pirouettes more often when the concentration of salt decreases, biasing their movement towards salt concentration peak. This response was directly tested and confirmed by applying salt concentration change to restricted worms, making this strategy widely accepted (2-4). We reexamined the chemotaxis behavior by using a worm-tracking system, and found another strategy called weather-vane strategy. We focused on the behavior during run, the period in which worms move forward without displaying pirouette. Quantitative analysis reveals that during run, worms tend to curve towards the side with higher concentration of salt. The average curving rate is roughly proportional to the geometrical gradient of salt concentration in the direction perpendicular to the orientation of locomotion. This strategy in principle drives the worm to orient towards the peak of salt concentration. We are further analyzing the statistical nature of the behavior. By computer simulation, neither pirouette strategy alone nor weather-vane strategy alone generates chemotaxis as efficient as real worms, but combination of the two leads to chemotaxis quantitatively similar to real worms, suggesting that worms employ the two strategies in parallel during chemotaxis. To understand the neural basis of the behavior, we laser-ablated several candidate neurons and performed worm-tracking analysis on treated animals. So far, some neurons important for both pirouette and weather-vane strategies have been identified. The neural and behavioral mechanism of chemotaxis will be discussed.

Kazushi Yoshida et al. (2010) East Asia Worm Meeting "Neural and behavioral mechanisms of response to an odorant depending on its concentration"

Takeshi Ishihara, Takanobu Tagawa, Shigekazu Oda, Kazushi Yoshida, Yuichi Iino, Takaaki Hirotsu

[East Asia Worm Meeting, 2010]

Odor perception can differ depending on its concentration in many species. In C. elegans, it was reported that several odorants such as benzaldehyde and 2, 4, 5-trimethylthiazole, act as attractants at low concentrations, but as repellents at high concentrations. We found that this dose-dependent behavioral change was also observed in chemotaxis to all the odorants tested (isoamyl alcohol, diacetyl, and 2,4-pentanedione). To examine the underlying neural circuit, we performed laser ablation of individual neurons and found that avoidance of high concentration of isoamyl alcohol is regulated by multiple sensory neurons. In addition, we identified some interneurons which positively mediate this avoidance. It was previously reported that AWC sensory neurons regulate attraction to diluted isoamyl alcohol and are activated by the removal of isoamyl alcohol. Using calcium imaging, we showed that AWB olfactory neurons and ASH polymodal neurons, which are both known to mediate an avoidance behavior, respond to the removal and addition of isoamyl alcohol, respectively. Recently, we reported that worms employ two strategies (the pirouette and weathervane strategies) for efficient chemotaxis. To investigate the behavioral mechanisms of avoidance of isoamyl alcohol at the high concentration, we analyzed this behavior by using multi-worm tracking system. The avoidance behavior was mainly regulated by the pirouette mechanism. Interestingly, the weathervane mechanism was employed to curve toward isoamyl alcohol. Computer simulation showed that behaviors of model animals using both strategies are quantitatively similar to those of real worms.

Lyczak R et al. (2000) West Coast Worm Meeting "Got the blues? Try another genetic screen!"

Aroian RV, Bowerman BA, Lyczak R, Rappleye CA

[West Coast Worm Meeting, 2000]

To better understand the process by which cell polarity is established, we are analyzing genes required for the characteristic asymmetries of the early C. elegans embryo. Recently, we showed that the pod-1 locus represents a new class of polarity genes as mutation of pod loci results in osmosensitive embryos in addition to loss of polarity ('pod'=polarity and osmotic defective). The identification of pod-2 by our lab (see abstract by A. Tagawa) further underscores the importance of the pod class of mutants. The osmosensitivity of pod mutants appears to result from permeability of the egg shell surrounding the embryo. Understanding the connection between polarity establishment and egg shell formation should begin to reveal the molecular mechanisms underlying cellular asymmetry. To further identify the set of components responsible for this aspect of polarity establishment, we have initiated a study of mutants that have osmosensitive phenotypes. Among previously identified osmotically sensitive mutants, emb-8 and emb-30 mutants also exhibit the 'Pod' phenotype. In these, as well as a pod-1 null mutant, the polarity defect is not completely penetrant suggesting that multiple, parallel pathways might contribute to overall cell polarity. However, analysis of double mutants between pod-1 and emb-8 or emb-30 indicate that these three function in a common genetic pathway. Through two different genetic screens, one of which directly identifies osmosensitive embryos, we have isolated a number of other mutations that represent new loci of the pod class. This collection includes genes which when mutated cause near 100% penetrant loss of polarity. We are currently pursuing the molecular identities of these loci which will enable us to refine our models for how cellular asymmetry is controlled.