The C. elegans touch response facilitates escape from predacious fungi

The microarchitecture of C. elegans behavior during lethargus: homeostatic bout dynamics, a typical body posture, and regulation by a central neuron

STUDY OBJECTIVES

The nematode C. elegans develops through four larval stages before it reaches adulthood. At the transition between stages and before it sheds its cuticle, it exhibits a sleep-like behavior during a stage termed lethargus. The objectives of this study were to characterize in detail behavioral patterns and physiological activity of a command interneuron during lethargus.

MEASUREMENTS AND RESULTS

We found that lethargus behavior was composed of bouts of quiescence and motion. The duration of individual bouts ranged from 2 to 100 seconds, and their dynamics exhibited local homeostasis: the duration of bouts of quiescence positively correlated with the duration of bouts of motion that immediately preceded them in a cAMP-dependent manner. In addition, we identified a characteristic body posture during lethargus: the average curvature along the body of L4 lethargus larvae was lower than that of L4 larvae prior to lethargus, and the positions of body bends were distributed non-uniformly along the bodies of quiescent animals. Finally, we found that the AVA interneurons, a pair of backward command neurons, mediated locomotion patterns during L4 lethargus in similar fashion to their function in L4 larvae prior to lethargus. Interestingly, in both developmental stages backward locomotion was initiated and terminated asymmetrically with respect to AVA intraneuronal calcium concentration.

CONCLUSIONS

The complex behavioral patterns during lethargus can be dissected to quantifiable elements, which exhibit rich temporal dynamics and are actively regulated by the nervous system. Our findings support the identification of lethargus as a sleep-like state.

CITATION

Iwanir S; Tramm N; Nagy S; Wright C; Ish D; Biron D. The microarchitecture of C. elegans behavior during lethargus: homeostatic bout dynamics, a typical body posture, and regulation by a central neuron. SLEEP 2013;36(3):385-395.

The neuroethology of C. elegans escape

Escape behaviors are crucial to survive predator encounters. Touch to the head of Caenorhabditis elegans induces an escape response where the animal rapidly backs away from the stimulus and suppresses foraging head movements. The coordination of head and body movements facilitates escape from predacious fungi that cohabitate with nematodes in organic debris. An appreciation of the natural habitat of laboratory organisms, like C. elegans, enables a comprehensive neuroethological analysis of behavior. In this review we discuss the neuronal mechanisms and the ecological significance of the C. elegans touch response.

Bending amplitude - a new quantitative assay of C. elegans locomotion: identification of phenotypes for mutants in genes encoding muscle focal adhesion components

The nematode Caenorhabditis elegans uses striated muscle in its body wall for locomotion. The myofilament lattice is organized such that all the thin filament attachment structures (dense bodies, analogous to Z-disks) and thick filament organizing centers (M-lines) are attached to the muscle cell membrane. Thus, the force of muscle contraction is transmitted through these structures and allows locomotion of the worm. Dense bodies and M-lines are compositionally similar to focal adhesions and costameres, and are based on integrin and associated proteins. Null mutants for many of the newly discovered dense body and M-line proteins do not have obvious locomotion defects when observed casually, or when assayed by counting the number of times a worm moves back and forth in liquid. We hypothesized that many of these proteins, located as they are in muscle focal adhesions, function in force transmission, but we had not used an appropriate or sufficiently sensitive assay to reveal this function. Recently, we have developed a new quantitative assay of C. elegans locomotion that measures the maximum bending amplitude of an adult worm as it moves backwards. The assay had been used to reveal locomotion defects for null mutants of genes encoding ATN-1 (α-actinin) and PKN-1 (protein kinase N). Here, we describe the details of this method, and apply it to 21 loss of function mutants in 17 additional genes, most of which encode components of muscle attachment structures. As compared to wild type, mutants in 11 genes were found to have less ability to bend, and mutants in one gene were found to have greater ability to bend. Loss of function mutants for eight proteins had been reported to have normal locomotion (ZYX-1 (zyxin), ALP-1 (Enigma), DIM-1, SCPL-1), or locomotion that was not previously investigated (FRG-1 (FRG1), KIN-32 (focal adhesion kinase), LIM-8), or had only slightly decreased locomotion (PFN-3 (profilin)).