Biology subjects

Koelle, M. R.

Publications and source records attributed to Koelle, M. R..

4 recordsLinked to original sources

bioRxiv2022

A neuron that regulates locomotion makes a potential sensory cilium lying over the C. elegans egg-laying apparatus

The neural circuit for C. elegans egg laying has been studied intensively for decades, yet it is not clear that its known components can account for how egg-laying and locomotion behaviors are coordinated. We found that the two PVP neurons, which release neuropeptides that promote roaming locomotion, make previously-undescribed branches that terminate in large wing-shaped endings directly over the egg-laying apparatus. The PVP branches occur in hermaphrodites but not males and develop during the L4 larval stage when the egg-laying system also develops. The PVP wing is located at the junction between the uterus and the vulva, adjacent to neurons that control egg laying, and surrounded by cells that we found label with a glial marker. The morphology of the PVP wing and its envelopment within possible glial cells are consistent with the hypothesis that the PVP wing is a sensory cilium. Although PVP is reported to express sensory receptor homologs, we have been unable to detect PVP expression of more specific markers of neural cilia, and we have also not detected strong PVP defects in the daf-19 mutant, which does show defects in known neural cilia. The PVPs are extraordinarily sensitive to expression of transgenes, which cause developmental and possibly functional defects in these neurons. This has prevented us from recording or manipulating PVP activity to determine its functional roles. Thus, the intriguing hypothesis that PVP is a sensory neuron that might coordinate egg laying and locomotion will remain speculative until better methods to manipulate PVP can be developed.

neuroscience↗

bioRxiv2022

Subthreshold serotonin signals combined by the G proteins Gαq and Gαs activate the C. elegans egg-laying muscles

Individual neuron or muscle cells express many G protein coupled receptors (GPCRs) for neurotransmitters and neuropeptides. It remains unclear how these cells integrate multiple GPCR signals that all must act through the same few G proteins. We investigated how two serotonin GPCRs, Gq-coupled SER-1 and Gs-coupled SER-7, function together on the C. elegans egg-laying muscles to promote contraction and thus cause eggs to be laid. Using receptor null mutations and cell-specific knockdowns, we found that serotonin signaling through either SER-1/Gq or SER-7/Gs alone does not induce egg laying, but these subthreshold signals can combine to promote egg laying. However, using designer receptors or optogenetics to artificially induce high levels of either Gq signaling or Gs signaling in the muscles was sufficient to induce egg laying. Conversely, knocking down both Gq and Gs in the egg-laying muscle cells induced egg-laying defects stronger than those of a ser-7 ser-1 double knockout. These results suggest that, in the egg-laying muscles, multiple GPCRs for serotonin and other signals each produce weak effects that individually do not result in strong behavioral outcomes. However, they can combine to produce sufficient levels of Gq and Gs signaling to promote muscle activity and egg laying.

neuroscience↗

bioRxiv2021

The neural G protein Gαo tagged with GFP at an internal loop is functional in C. elegans

Go is the alpha subunit of the major heterotrimeric G protein in neurons and mediates signaling by every known neurotransmitter, yet the signaling mechanisms activated by Go remain to be fully elucidated. Genetic analysis in Caenorhabditis elegans has shown that Go signaling inhibits neuronal activity and neurotransmitter release, but studies of the molecular mechanisms underlying these effects have been limited by lack of tools to complement genetic studies with other experimental approaches. Here we demonstrate that inserting the green fluorescent protein (GFP) into an internal loop of the Go protein results in a tagged protein that is functional in vivo and that facilitates cell biological and biochemical studies of Go. Transgenic expression of Go-GFP rescues the defects caused by loss of endogenous Go in assays of egg laying and locomotion behaviors. Defects in body morphology caused by loss of Go are also rescued by Go-GFP. The Go-GFP protein is localized to the plasma membrane of neurons, mimicking localization of endogenous Go. Using GFP as an epitope tag, Go-GFP can be immunoprecipitated from C. elegans lysates to purify Go protein complexes. The Go-GFP transgene reported in this study enables studies involving in vivo localization and biochemical purification of Go to complement the already well-developed genetic analysis of Go signaling.

neuroscience↗

bioRxiv2020

Cellular expression and functional roles of all 26 neurotransmitter GPCRs in the C. elegans egg-laying circuit

Maps of the synapses made and neurotransmitters released by all neurons in model systems such as C. elegans have left still unresolved how neural circuits integrate and respond to neurotransmitter signals. Using the egg-laying circuit of C. elegans as a model, we mapped which cells express each of the 26 neurotransmitter G protein coupled receptors (GPCRs) of this organism and also genetically analyzed the functions of all 26 GPCRs. We found that individual neurons express many distinct receptors, epithelial cells often express neurotransmitter receptors, and receptors are often positioned to receive extrasynaptic signals. The egg-laying circuit appears to use redundancy and compensation to achieve functional robustness, as receptor knockouts reveal few defects; however, increasing receptor signaling through overexpression more efficiently reveals receptor functions. This map of neurotransmitter GPCR expression and function in the egg-laying circuit provides a model for understanding GPCR signaling in other neural circuits.

neuroscience↗