Kim, Daeyeon et al. (2011) International Worm Meeting "Biomechanical analysis of C. elegans locomotion."

Kim, Daeyeon, Weitz, David, Park, Jin-Sung, Shin, Jennifer H.

[International Worm Meeting, 2011]

The characteristics of C. elegans' locomotion are sensitively regulated by mechanical environments. For example, the worm's wavelength and amplitude were shown to be altered in different gelatin concentrations and swimming velocity of a worm was enhanced in a granular medium compared to that in a simple fluid [1, 2]. Therefore, understanding the mechanism behind the differential responses of C. elegans in mechanically different environments is an intriguing problem to gain insight on mechano-sensation of the worm. In this study, we investigate the surface rigidity dependent crawling motion of a worm as well as swimming motion in colloidal suspensions. In crawling gait, the wild-type worm adaptively changes the shapes of its sinusoidal waveform when the surface rigidity of solid agar plates is varied. However, mechanosensation-defective worms (mec-4 and mec-10 mutants) show insensitivity to the changes in the surface rigidity. The wild-type worm modifies its waveform by decreasing the interval of muscle contractions and increasing the extent of them as the surface rigidity increases. This modulation pattern of the muscle contraction provides more propulsive force to the worm against the environments of higher loads. In swimming gait, worms changed their swimming speeds in different volume percents of colloidal suspensions of 600 nm sized polystyrene beads. In low volume percents of colloids (0.4 ~ 8 %), the swimming speed was similar to that in the water whereas it significantly increased in 12 and 16 % of colloids. Through a detailed biomechanical analysis, we suggest that this enhancement in swimming speed results from the interplay between the shear thinning fluid properties of 12 and 16 % colloids and the unique stroke pattern of the worm. This work was supported by the National Research Foundation (NRF) grant 2010-0016886. [1] Berri et al., HFSP J. 3, 186 (2009). [2] Jung et al., Chaos 18, 041106 (2008).

Monika Tzoneva et al. (2001) International C. elegans Meeting "UNC-58 IS AN UNUSUAL POTASSIUM CHANNEL OF THE TWIK FAMILY"

James H Thomas, Monika Tzoneva

[International C. elegans Meeting, 2001]

unc-58 was first identified by dominant mutations that cause hypercontracted body-wall and egg-laying muscle in C. elegans . unc-58(dm) animals are rigidly paralyzed and egg-laying constitutive. unc-58(dm) animals also frequently flip around their longitudinal axis. Putative loss-of-function unc-58 alleles have been isolated as revertants of the unc-58(dm) phenotype. These alleles have a much milder and distinct phenotype, suggesting that unc-58(dm) mutants result in an inappropriately activated gene product. We have cloned unc-58 and found that it encodes a member of the TWIK potassium channel family. TWIKs are a distinct family of potassium channels having four transmembrane domains (M1 to M4) and two pore domains. Potassium-selective currents have been recorded from TWIKs from both mammals and worms. The hypercontracted phenotype of unc-58(dm) is in sharp contrast to that of all other activated potassium channel mutants, which lead to muscle relaxation caused by excessive inhibitory currents. Two scenarios can explain this hypercontraction. First, UNC-58(dm) may produce excessive potassium currents in the inhibitory motorneurons. However, this does not account for the hypercontraction of the egg-laying muscle, which is not innervated by inhibitory motorneurons. Second,, UNC-58(dm) may act in excitatory neurons and/or muscle to conduct an excitatory current. A precedent for that is the Ih channel from the human heart, which is related to potassium channels by sequence, but is permeable to both potassium and sodium [Ludwig et al, Nature 393, 587-591]. To distinguish between these two possibilities, we are expressing UNC-58(dm) in Xenopus laevis oocytes to determine its ion selectivity and using GFP fusions to determine the UNC-58 site of action. Both the flipping and the hypercontarction phenotypes of unc-58(dm) are partially rescued by the drug endosulfan, best known as an antagonist of GABA-gated chloride channels (B. Wightman and G. Garriga, personal communication; our unpublished data). This rescue is allele specific, and is not affected by mutants in GABA-ergic neurotransmission. We plan to use electrophysiology to determine whether this rescue is by direct channel block.