Complex Locomotion Behavior Changes Are Induced in Caenorhabditis elegans by the Lack of the Regulatory Leak K+ Channel TWK-7

Abstract

The change of locomotion activity in response to external cues is a considerable achievement of animals and is required for escape responses, foraging, and other complex behaviors. Little is known about the molecular regulators of such an adaptive locomotion. The conserved eukaryotic two-pore domain potassium (K 2 P) channels have been recognized as regulatory K + channels that modify the membrane potential of cells, thereby affecting, e.g., rhythmic muscle activity. By using the Caenorhabditis elegans system combined with cell-type-specific approaches and locomotion in-depth analyses, here, we found that the loss of K 2 P channel TWK-7 increases the locomotor activity of worms during swimming and crawling in a coordinated mode. Moreover, loss of TWK-7 function results in a hyperactive state that (although less pronounced) resembles the fast, persistent, and directed forward locomotion behavior of stimulated C. elegans. TWK-7 is expressed in several head neurons as well as in cholinergic excitatory and GABAergic inhibitory motor neurons. Remarkably, the abundance of TWK-7 in excitatory B-type and inhibitory D-type motor neurons affected five central aspects of adaptive locomotion behavior: velocity/frequency, wavelength/amplitude, direction, duration, and straightness. Hence, we suggest that TWK-7 activity might represent a means to modulate a complex locomotion behavior at the level of certain types of motor neurons.L OCOMOTION is a fundamental aspect of life, because it is required for escape responses, foraging, and other behaviors. In both invertebrates and vertebrates, rhythmic and patterned locomotion is usually controlled by specific motor circuits with autonomous rhythmic activities called central pattern generators (Marder and Calabrese 1996). The overall output of the motor network depends on the interplay of premotor interneurons, motor neurons, muscle cells, and the intrinsic membrane properties of the involved cells. For example, in insects, motor activity appears to increase during walking by tonic depolarization of interneurons and/or motor neurons (Ludwar et al. 2005). In response to environmental cues, animals often adjust their locomotion activity, which, in principle, can be regulated at the level of central pattern generators, interneurons, motor neurons, or muscle cells. Two-pore domain potassium (K 2 P) channels are evolutionarily conserved eukaryotic membrane proteins (Enyedi and Czirjak 2010). They contain two pore domains per subunit and function as dimers building one conductance pore. K 2 P channels operate as regulatory K + channels to stabilize the negative membrane potential and to counterbalance membrane depolarization. Closure of their potassium pore usually induces membrane depolarization and facilitates the excitability of cells. K 2 P channels are specifically regulated by a variety of factors, including temperature, pH, membrane stretch, fatty acids, and signaling-pathway-dependent phosphorylation. The physiological function of most K 2 P channels remains to be elucid...

Locomotion Behavior Is Affected by the GαS Pathway and the Two-Pore-Domain K+ Channel TWK-7 Interacting in GABAergic Motor Neurons in Caenorhabditis elegans

“…For B-type neuron-specific rescue, we exchanged the unc-47p fragment for 4.12 kb of the acr-5 promoter region, leading to an acr5p::KIN-2 construct. The transgenic acr-5p::TWK-7::mCherry::let-858(39UTR) and unc-47p::TWK-7::mCherry::let-858(39UTR) have been previously generated (Lüersen et al 2016). The transgenic strains were generated by biolistic bombardment following the protocol of Wilm et al (1999).…”

“…Locomotion analyses on NGM agar plates were carried out as described in Lüersen et al (2016). The assay was set up by placing 500 late L3-or early L4-stage larvae on locomotion assay plates spread with a thin lawn of OP50 bacteria (100 ml of an OP50 overnight culture per plate, incubated for 20 hr at 37°).…”

“…The activity of K 2 P channels can be modulated by a variety of factors including pH, temperature, membrane stretch, G proteincoupled receptor pathways, polyunsaturated fatty acids, and medicinal agents such as volatile anesthetics (Gray et al 2000;Yost 2000;Patel and Honore 2001;Aryal et al 2015;Zhang et al 2015). Accordingly, we suggested that TWK-7 may be involved in the regulation of locomotor activity and behavior of C. elegans (Lüersen et al 2016).…”

“…Remarkably, spontaneous forward locomotion is not prevented (McIntire et al 1993). However, modulation of D-type motor neuron function has been demonstrated to significantly alter wave parameters and to impair coordinated crawling (Donnelly et al 2013;Lüersen et al 2016).…”

“…Recently, we found that the two-pore-domain potassium (K 2 P) channel TWK-7 is required in motor neurons to maintain the normal spontaneous locomotion behavior of C. elegans (Lüersen et al 2016). Inactivation of TWK-7 in B-type motor neurons led to accelerated but still coordinated spontaneous crawling with slightly flattened amplitudes, whereas twk-7(null) worms rescued by overexpressing twk-7 specifically in B-type or D-type motor neurons exhibited slower and less directed spontaneous locomotion with altered amplitudes and wavelengths.…”