Presynaptic Gαo (GOA-1) signals to depress command neuron excitability and allow stretch-dependent modulation of egg laying in Caenorhabditis elegans

Abstract

Egg laying in the nematode worm Caenorhabditis elegans is a two-state behavior modulated by internal and external sensory input. We have previously shown that homeostatic feedback of embryo accumulation in the uterus regulates bursting activity of the serotonergic HSN command neurons that sustains the egg-laying active state. How sensory feedback of egg release signals to terminate the egg-laying active state is less understood. We find that Gαo, a conserved Pertussis Toxin-sensitive G protein, signals within HSN to inhibit egg-laying circuit activity and prevent entry into the active state. Gαo signaling hyperpolarizes HSN, reducing HSN Ca2+ activity and input onto the postsynaptic vulval muscles. Loss of inhibitory Gαo signaling uncouples presynaptic HSN activity from a postsynaptic, stretch-dependent homeostat, causing precocious entry into the egg-laying active state when only a few eggs are present in the uterus. Feedback of vulval opening and egg release activates the uv1 neuroendocrine cells which release NLP-7 neuropeptides which signal to inhibit egg laying through Gαo-independent mechanisms in the HSNs and Gαo-dependent mechanisms in cells other than the HSNs. Thus, neuropeptide and inhibitory Gαo signaling maintains a bi-stable state of electrical excitability that dynamically controls circuit activity in response to both external and internal sensory input to drive a two-state behavior output.

Serotonin signals through postsynaptic Gαq, Trio RhoGEF, and diacylglycerol to promoteC. elegansegg-laying circuit activity and behavior

“…4B and 4C). This elevated vulval muscle Ca 2+ activity was reminiscent of that observed in egl-1(n986dm) animals lacking the HSNs (Collins et al, 2016) as these animals still enter and leave infrequent egg-laying active states, possibly driven by the stretch-dependent feedback of egg accumulation in the uterus (Ravi et al, 2018a) which does not appear to act by modulating HSN activity (Ravi et al, 2021). These data further indicate that the egg-laying defects of PLCβ mutants are not caused by a loss of vulval muscle Ca 2+ activity.…”

“…Like PLCβ, DGK-1 is expressed in neurons (Nurrish et al, 1999), suggesting alterations of IP 3 and/or DAG levels in neurons may affect the frequency of egg-laying active states without altering the overall pattern or strength of vulval muscle Ca 2+ activity within those active states. Indeed, goa-1(n1134) mutants that reduce inhibitory Gα o signaling have hyperactive egg-laying behavior defects that strongly resemble dgk-1(nu62) mutants without a significant increase in vulval muscle Ca 2+ activity (Ravi et al, 2021). Together, these results indicate Gα q and Trio RhoGEF, but not PLCβ, are required for vulval muscle activity that drives twitching and egg-laying Ca 2+ transients during egg-laying active states.…”

“…In C. elegans , 2-AG activates the NPR-19 endocannabinoid receptor ortholog that couples to Gα o to modulate serotonin transmission, pharyngeal, feeding, and locomotory behaviors (Oakes et al, 2019; Oakes et al, 2017; Pastuhov et al, 2016). We have recently shown that feedback of egg accumulation alters vulval muscle Ca 2+ activity, which subsequently signals to regulate bursts of Ca 2+ transients in the HSNs that accompany the onset of the egg-laying active state (Ravi et al, 2018a; Ravi et al, 2021). These results support a model where stretch-dependent feedback of egg accumulation stimulates postsynaptic vulval muscle Ca 2+ signaling.…”

Muscle-directed mechanosensory feedback activates egg-laying circuit activity and behavior inC. elegans

“…hermaphrodites (Collins et al, 2016;Ravi et al, 2021). mCherry(+) vsIs165/+ male cross-progeny were then crossed with RB1546 tmc-1(ok1859) X hermaphrodites.…”

“…The VC neurons are mechanically activated by the contraction and opening of the vulval muscles, releasing acetylcholine to enhance vulval opening for egg release (Kopchock et al, 2021). The uv1 neuroendocrine cells sit between the vulval canal and uterus, are mechanically deformed and activated in response to passage of eggs through the vulval canal (Collins et al, 2016; Jose et al, 2007), and provide inhibitory feedback following egg laying through the release of tyramine and neuropeptides that inhibit HSN activity (Alkema et al, 2005; Banerjee et al, 2017; Ravi et al, 2021; Zhang et al, 2010). Whether other cells in the egg-laying circuit are mechanosensitive and how their feedback signals to modulate discrete steps in egg laying is not clear.…”