Behavioral Effects of a Chemorepellent Receptor Knockout Mutation in <named-content content-type="genus-species">Tetrahymena thermophila</named-content>

ABSTRACT A conditioned supernatant from Tetrahymena thermophila contains a powerful chemorepellent for wild-type cells, and a gene called G37 is required for this response. This is the first genomic identification of a chemorepellent receptor in any eukaryotic unicellular organism. This conditioned...

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Autores principales:	Dianxiong Zou, Todd M. Hennessey
Formato:	article
Lenguaje:	EN
Publicado:	American Society for Microbiology 2017
Materias:	GPCR knockout mutation behavioral bioassay chemorepellent receptor chemosensory transduction excitability Microbiology QR1-502
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spelling	oai:doaj.org-article:d2012bd2814d4048834a9806a62b57892021-11-15T15:22:04ZBehavioral Effects of a Chemorepellent Receptor Knockout Mutation in <named-content content-type="genus-species">Tetrahymena thermophila</named-content>10.1128/mSphere.00182-172379-5042https://doaj.org/article/d2012bd2814d4048834a9806a62b57892017-08-01T00:00:00Zhttps://journals.asm.org/doi/10.1128/mSphere.00182-17https://doaj.org/toc/2379-5042ABSTRACT A conditioned supernatant from Tetrahymena thermophila contains a powerful chemorepellent for wild-type cells, and a gene called G37 is required for this response. This is the first genomic identification of a chemorepellent receptor in any eukaryotic unicellular organism. This conditioned supernatant factor (CSF) is small (<1 kDa), and its repellent effect is resistant to boiling, protease treatment, and nuclease digestion. External BAPTA eliminated the CSF response, suggesting that Ca2+ entry is required for the classical avoiding reactions (AR) used for chemorepulsion. A macronuclear G37 gene knockout (G37-KO) mutant is both nonresponsive to the CSF and overresponsive to other repellents such as quinine, lysozyme, GTP, and high potassium concentrations. All of these mutant phenotypes were reversed by overexpression of the wild-type G37 gene in a G37 overexpression mutant. Overexpression of G37 in the wild type caused increased responsiveness to the CSF and underresponsiveness to high K+ concentrations. Behavioral adaptation (by prolonged exposure to the CSF) caused decreases in responsiveness to all of the stimuli used in the wild type and the overexpression mutant but not in the G37-KO mutant. We propose that the constant presence of the CSF causes a decreased basal excitability of the wild type due to chemosensory adaptation through G37 and that all of the G37-KO phenotypes are due to an inability to detect the CSF. Therefore, the G37 protein may be the CSF receptor. The physiological role of these G37-mediated responses may be to both moderate basal excitability and detect the CSF as an indicator of high cell density growth. IMPORTANCE Although many single-cell eukaryotes have served as classical model systems for chemosensory studies for decades, the major emphasis has been on chemoattraction and no chemorepellent receptor gene has been identified in any unicellular eukaryote. This is the first description of a gene that codes for a chemorepellent receptor in any protozoan. Integration of both depolarizing chemorepellent pathways and hyperpolarizing chemoattractant pathways is as important to chemoresponses of motile unicells as excitatory and inhibitory neurotransmitter pathways are to neurons. Therefore, both chemoattractant and chemorepellent pathways should be represented in a useful unicellular model system. Tetrahymena cells provide such a model system because simple behavioral bioassays, gene knockouts, biochemical analysis, and other approaches can be used with these eukaryotic model cells. This work can contribute to the basic understanding of unicellular sensory responses and provide insights into the evolution of chemoreceptors and possible chemorepellent approaches for preventing infections by some pathogenic protozoa.Dianxiong ZouTodd M. HennesseyAmerican Society for MicrobiologyarticleGPCRknockout mutationbehavioral bioassaychemorepellent receptorchemosensory transductionexcitabilityMicrobiologyQR1-502ENmSphere, Vol 2, Iss 4 (2017)
institution	DOAJ
collection	DOAJ
language	EN
topic	GPCR knockout mutation behavioral bioassay chemorepellent receptor chemosensory transduction excitability Microbiology QR1-502
spellingShingle	GPCR knockout mutation behavioral bioassay chemorepellent receptor chemosensory transduction excitability Microbiology QR1-502 Dianxiong Zou Todd M. Hennessey Behavioral Effects of a Chemorepellent Receptor Knockout Mutation in <named-content content-type="genus-species">Tetrahymena thermophila</named-content>
description	ABSTRACT A conditioned supernatant from Tetrahymena thermophila contains a powerful chemorepellent for wild-type cells, and a gene called G37 is required for this response. This is the first genomic identification of a chemorepellent receptor in any eukaryotic unicellular organism. This conditioned supernatant factor (CSF) is small (<1 kDa), and its repellent effect is resistant to boiling, protease treatment, and nuclease digestion. External BAPTA eliminated the CSF response, suggesting that Ca2+ entry is required for the classical avoiding reactions (AR) used for chemorepulsion. A macronuclear G37 gene knockout (G37-KO) mutant is both nonresponsive to the CSF and overresponsive to other repellents such as quinine, lysozyme, GTP, and high potassium concentrations. All of these mutant phenotypes were reversed by overexpression of the wild-type G37 gene in a G37 overexpression mutant. Overexpression of G37 in the wild type caused increased responsiveness to the CSF and underresponsiveness to high K+ concentrations. Behavioral adaptation (by prolonged exposure to the CSF) caused decreases in responsiveness to all of the stimuli used in the wild type and the overexpression mutant but not in the G37-KO mutant. We propose that the constant presence of the CSF causes a decreased basal excitability of the wild type due to chemosensory adaptation through G37 and that all of the G37-KO phenotypes are due to an inability to detect the CSF. Therefore, the G37 protein may be the CSF receptor. The physiological role of these G37-mediated responses may be to both moderate basal excitability and detect the CSF as an indicator of high cell density growth. IMPORTANCE Although many single-cell eukaryotes have served as classical model systems for chemosensory studies for decades, the major emphasis has been on chemoattraction and no chemorepellent receptor gene has been identified in any unicellular eukaryote. This is the first description of a gene that codes for a chemorepellent receptor in any protozoan. Integration of both depolarizing chemorepellent pathways and hyperpolarizing chemoattractant pathways is as important to chemoresponses of motile unicells as excitatory and inhibitory neurotransmitter pathways are to neurons. Therefore, both chemoattractant and chemorepellent pathways should be represented in a useful unicellular model system. Tetrahymena cells provide such a model system because simple behavioral bioassays, gene knockouts, biochemical analysis, and other approaches can be used with these eukaryotic model cells. This work can contribute to the basic understanding of unicellular sensory responses and provide insights into the evolution of chemoreceptors and possible chemorepellent approaches for preventing infections by some pathogenic protozoa.
format	article
author	Dianxiong Zou Todd M. Hennessey
author_facet	Dianxiong Zou Todd M. Hennessey
author_sort	Dianxiong Zou
title	Behavioral Effects of a Chemorepellent Receptor Knockout Mutation in <named-content content-type="genus-species">Tetrahymena thermophila</named-content>
title_short	Behavioral Effects of a Chemorepellent Receptor Knockout Mutation in <named-content content-type="genus-species">Tetrahymena thermophila</named-content>
title_full	Behavioral Effects of a Chemorepellent Receptor Knockout Mutation in <named-content content-type="genus-species">Tetrahymena thermophila</named-content>
title_fullStr	Behavioral Effects of a Chemorepellent Receptor Knockout Mutation in <named-content content-type="genus-species">Tetrahymena thermophila</named-content>
title_full_unstemmed	Behavioral Effects of a Chemorepellent Receptor Knockout Mutation in <named-content content-type="genus-species">Tetrahymena thermophila</named-content>
title_sort	behavioral effects of a chemorepellent receptor knockout mutation in <named-content content-type="genus-species">tetrahymena thermophila</named-content>
publisher	American Society for Microbiology
publishDate	2017
url	https://doaj.org/article/d2012bd2814d4048834a9806a62b5789
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Behavioral Effects of a Chemorepellent Receptor Knockout Mutation in <named-content content-type="genus-species">Tetrahymena thermophila</named-content>

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