Michael Koelle, PhD
Research & Publications
Overview of Research in the Koelle Lab
The Koelle lab is interested in the molecular mechanisms by which neurons respond to neurotransmitters, and also how neurotransmission is used to control the dynamic activities of neural circuits.
The human brain has ~80,000,000,000 neurons; but underlying all this complexity there are simpler units called neural circuits, small sets of neurons which are physically connected at synaptic junctions. These neurons communicate with each other using chemical signals called neurotransmitters and neuropeptides, and induce dynamic patterns of circuit activity. In this way, neural circuits are the functional units of the brain, and the circuit activity induced by neurotransmitter and neuropeptide signaling is what constitutes thoughts and controls behaviors.
Neurotransmitter Signaling: Molecular Mechanisms
Some neurotransmitters act by binding ion channel receptors, but these neurotransmitters also have G protein coupled receptors (GPCRs), and many neurotransmitters and essentially all neuropeptides act exclusively via GPCRs. Our lab uses a combination of C. elegans genetics along with biochemical experiments carried out in both C. elegans and mouse brain lysates to study the proteins that mediate GPCR signaling in neurons. A current focus is to identify the effector proteins that mediate signaling downstream of the major neural G protein, Gαo, to inhibit neural function. These effectors have remained elusive despite 35 years of effort by many labs to find them. Through a combination of biochemical and genetic efforts, we are characterizing a set of proteins through which Gαo signals.
Neurotransmitter Signaling in Neural Circuits
Why are there so many neurotransmitters and neuropeptides, and why does each neurotransmitter have so many different receptors? How is all this signaling used to set up the dynamic pattern of activity within neural circuits to allow these circuits to think thoughts and control behaviors? Currently, there is not a single neural circuit in any organism in which we know how all the signals and receptors are used to control activity of the circuit. We aim to change this by studying a single simple model circuit in C. elegans, the egg-laying circuit. We are also generating a map of what cells express every G protein coupled neurotransmitter and neuropeptide receptor in C. elegans, so that our analysis of the egg-laying circuit can eventually be broadened to analyzing all neural circuits in C. elegans. By understanding first one and then a few neural circuits in great depth, we hope to uncover general principals that apply to all neural circuits in all organisms.
Extensive Research Description
Biochemical and Genetic Studies of the Gαo Signaling Mechanism
Gαo is by far the most abundant Gα protein in the brain, and every neurotransmitter has receptors that activate this G protein. Gαo was discovered over 35 years ago, yet we still do not know what “effector” proteins this G protein directly binds and regulates to carry out its functions. We do know from C. elegans genetics that Gαo directly opposes Gαq signaling, and ultimately Gαo signaling inactivates neurons, preventing them from carrying out neurotransmitter release.
We have recently carried out rapid, gentle immunopurifications of Gαo protein complexes from both mouse brain and C. elegans lysates, and identified the proteins in these complexes by mass spectrometry. We found a number of proteins that copurify with Gαo in both mouse and worms, and verified the association of Gαo with these proteins by co-immunoprecipitation/Western blots. Intriguingly, several of these proteins are regulators of Gαq signaling and/or neurotransmitter release, exactly the types of proteins that could plausibly mediate Gαo signaling. We are carrying out further biochemical studies of the association of Gαo with these proteins, analyzing how Gαo may regulate activity of these proteins, and are using C. elegans genetics to analyze the functional significance of these proteins in Gαo signaling.
Organization of G protein coupled receptors in neural circuits
C. elegans has 27 G protein coupled neurotransmitter receptors and about 150 G protein coupled neuropeptide receptors, which together facilitate signaling among the 302 neurons (of 118 types) found in the worm. Interestingly, humans have about the same number of G protein coupled neurotransmitter and neuropeptide receptors, even though we have ~80-100 billion neurons. In C. elegans, if each receptor is expressed in 20-30 types of neurons (a reasonable estimate based on existing data), that means the average neuron expresses about 6 neurotransmitter and 32 neuropeptide receptors. As one of the first steps to understanding how a neural circuit functions, we need to know which neurons in the circuit express which receptors.
We are undertaking a large-scale project to map which cells in C. elegans express each of its 27 G protein coupled neurotransmitter receptors. For every receptor, we have created fosmid-based GFP reporter transgenes that cause all cells expressing that receptor to fluoresce green. We are currently mapping out which cells express each receptor within the egg-laying circuit, and then we will broaden our analysis to map neurotransmitter receptor expression in the entire nervous system. We have also begun work mapping the cellular expression patterns of the neuropeptide receptors. The neural signaling maps we produce will be essential tools for future work analyzing any neural circuit or behavior in C. elegans.
An egg-laying circuit as a model for understanding neural circuits in general
Much of what is known about neural circuits comes from past studies of very simple circuits in crustaceans, in which their large neurons could be impaled with electrodes to study their activity. Unfortunately, modern genetic methods cannot be applied to crustaceans, limiting what we can learn from them. Conversely, the nematode C. elegans is readily amenable to genetic manipulation via mutations and transgenes and has one of the best-characterized nervous systems of any organism.
The egg-laying circuit of C. elegans consists of 12 neurons of three types and 16 muscle cells of four types. The circuit is silent most of the time, but about every 20 minutes it becomes rhythmically active for 2-3 minutes, in which a few eggs are laid. Activity of the circuit is controlled by two “command neurons” called the HSNs, whose release of a combination of serotonin and a neuropeptide is sufficient to activate the rest of the circuit. This provides us with an opportunity to study signaling by serotonin, a neurotransmitter involved in human mood disorders.
We (and others before us) have studied the egg-laying circuit for decades, and as a result we now have a large collection of C. elegans mutants in which the functions of individual cells within the circuit have been specifically altered. We also have developed methods to express the calcium-sensitive fluorescent protein GCaMP in individual cells of the circuit so that we can optically record activity of these cells within freely-behaving animals. Further, we have expressed ion channels in individual cells of the circuit that can be controlled by light or chemicals so that we can activate or silence these cells at will. By combining these experimental approaches, we now have a virtually unlimited ability to manipulate the egg-laying circuit and measure the consequent effects on circuit activity and egg-laying behavior.
Our goal is to use this approach to understand all the neurotransmitter and neuropeptide signals used within the egg-laying circuit that set up its dynamic pattern of activity. Because the egg-laying circuit has several features common with other circuits that have been studied in the past, we expect that the insights we gain from studying the egg-laying circuit will give us broad insights into the function of neural circuits in general.
Biochemistry; Biophysics; Molecular Biology; Neurobiology; Serotonin; Caenorhabditis elegans; Neurotransmitter Agents; RGS Proteins
- The neural G protein Gαo tagged with GFP at an internal loop is functional in Caenorhabditis elegansKumar S, Olson AC, Koelle MR. The neural G protein Gαo tagged with GFP at an internal loop is functional in Caenorhabditis elegans G3: Genes, Genomes, Genetics 2021, 11: jkab167. PMID: 34003969, PMCID: PMC8496287, DOI: 10.1093/g3journal/jkab167.
- Cellular Expression and Functional Roles of All 26 Neurotransmitter GPCRs in the C. elegans Egg-Laying CircuitFernandez RW, Wei K, Wang EY, Mikalauskaite D, Olson A, Pepper J, Christie N, Kim S, Weissenborn S, Sarov M, Koelle MR. Cellular Expression and Functional Roles of All 26 Neurotransmitter GPCRs in the C. elegans Egg-Laying Circuit Journal Of Neuroscience 2020, 40: 7475-7488. PMID: 32847964, PMCID: PMC7511189, DOI: 10.1523/jneurosci.1357-20.2020.
- Serotonin and neuropeptides are both released by the HSN command neuron to initiate C. elegans egg layingBrewer JC, Olson AC, Collins KM, Koelle MR. Serotonin and neuropeptides are both released by the HSN command neuron to initiate C. elegans egg laying PLOS Genetics 2019, 15: e1007896. PMID: 30677018, PMCID: PMC6363226, DOI: 10.1371/journal.pgen.1007896.
- Neurotransmitter signaling through heterotrimeric G proteins: insights from studies in C. elegans.Koelle MR. Neurotransmitter signaling through heterotrimeric G proteins: insights from studies in C. elegans. WormBook 2018, 2018: 1-52. PMID: 26937633, PMCID: PMC5010795, DOI: 10.1895/wormbook.1.75.2.
- Neural Architecture of Hunger-Dependent Multisensory Decision Making in C. elegansGhosh DD, Sanders T, Hong S, McCurdy LY, Chase DL, Cohen N, Koelle MR, Nitabach MN. Neural Architecture of Hunger-Dependent Multisensory Decision Making in C. elegans Neuron 2016, 92: 1049-1062. PMID: 27866800, PMCID: PMC5147516, DOI: 10.1016/j.neuron.2016.10.030.
- Activity of the C. elegans egg-laying behavior circuit is controlled by competing activation and feedback inhibitionCollins KM, Bode A, Fernandez RW, Tanis JE, Brewer JC, Creamer MS, Koelle MR. Activity of the C. elegans egg-laying behavior circuit is controlled by competing activation and feedback inhibition ELife 2016, 5: e21126. PMID: 27849154, PMCID: PMC5142809, DOI: 10.7554/elife.21126.
- Evolutionary Conservation of a GPCR-Independent Mechanism of Trimeric G Protein ActivationColeman BD, Marivin A, Parag-Sharma K, DiGiacomo V, Kim S, Pepper JS, Casler J, Nguyen LT, Koelle MR, Garcia-Marcos M. Evolutionary Conservation of a GPCR-Independent Mechanism of Trimeric G Protein Activation Molecular Biology And Evolution 2015, 33: 820-837. PMID: 26659249, PMCID: PMC4760084, DOI: 10.1093/molbev/msv336.
- RNA ligation in neurons by RtcB inhibits axon regenerationKosmaczewski SG, Han SM, Han B, Meyer B, Baig HS, Athar W, Lin-Moore AT, Koelle MR, Hammarlund M. RNA ligation in neurons by RtcB inhibits axon regeneration Proceedings Of The National Academy Of Sciences Of The United States Of America 2015, 112: 8451-8456. PMID: 26100902, PMCID: PMC4500288, DOI: 10.1073/pnas.1502948112.
- An Evolutionarily Conserved Switch in Response to GABA Affects Development and Behavior of the Locomotor Circuit of Caenorhabditis elegansHan B, Bellemer A, Koelle MR. An Evolutionarily Conserved Switch in Response to GABA Affects Development and Behavior of the Locomotor Circuit of Caenorhabditis elegans Genetics 2015, 199: 1159-1172. PMID: 25644702, PMCID: PMC4391577, DOI: 10.1534/genetics.114.173963.
- Postsynaptic ERG Potassium Channels Limit Muscle Excitability to Allow Distinct Egg-Laying Behavior States in Caenorhabditis elegansCollins KM, Koelle MR. Postsynaptic ERG Potassium Channels Limit Muscle Excitability to Allow Distinct Egg-Laying Behavior States in Caenorhabditis elegans Journal Of Neuroscience 2013, 33: 761-775. PMID: 23303953, PMCID: PMC3542984, DOI: 10.1523/jneurosci.3896-12.2013.
- LIN-12/Notch signaling instructs postsynaptic muscle arm development by regulating UNC-40/DCC and MADD-2 in Caenorhabditis elegansLi P, Collins KM, Koelle MR, Shen K. LIN-12/Notch signaling instructs postsynaptic muscle arm development by regulating UNC-40/DCC and MADD-2 in Caenorhabditis elegans ELife 2013, 2: e00378. PMID: 23539368, PMCID: PMC3601818, DOI: 10.7554/elife.00378.
- Receptors and Other Signaling Proteins Required for Serotonin Control of Locomotion in Caenorhabditis elegansGürel G, Gustafson MA, Pepper JS, Horvitz HR, Koelle MR. Receptors and Other Signaling Proteins Required for Serotonin Control of Locomotion in Caenorhabditis elegans Genetics 2012, 192: 1359-1371. PMID: 23023001, PMCID: PMC3512144, DOI: 10.1534/genetics.112.142125.
- The G protein regulator AGS-3 allows C. elegans to alter behaviors in response to food deprivationHofler C, Koelle MR. The G protein regulator AGS-3 allows C. elegans to alter behaviors in response to food deprivation Worm 2012, 1: 56-60. PMID: 24058824, PMCID: PMC3670173, DOI: 10.4161/worm.19042.
- AGS-3 Alters Caenorhabditis elegans Behavior after Food Deprivation via RIC-8 Activation of the Neural G Protein GαoHofler C, Koelle MR. AGS-3 Alters Caenorhabditis elegans Behavior after Food Deprivation via RIC-8 Activation of the Neural G Protein Gαo Journal Of Neuroscience 2011, 31: 11553-11562. PMID: 21832186, PMCID: PMC3161416, DOI: 10.1523/jneurosci.2072-11.2011.
- Two types of chloride transporters are required for GABAA receptor‐mediated inhibition in C. elegansBellemer A, Hirata T, Romero MF, Koelle MR. Two types of chloride transporters are required for GABAA receptor‐mediated inhibition in C. elegans The EMBO Journal 2011, 30: 1852-1863. PMID: 21427702, PMCID: PMC3101993, DOI: 10.1038/emboj.2011.83.
- A Conserved Protein Interaction Interface on the Type 5 G Protein β Subunit Controls Proteolytic Stability and Activity of R7 Family Regulator of G Protein Signaling Proteins*Porter MY, Xie K, Pozharski E, Koelle MR, Martemyanov KA. A Conserved Protein Interaction Interface on the Type 5 G Protein β Subunit Controls Proteolytic Stability and Activity of R7 Family Regulator of G Protein Signaling Proteins* Journal Of Biological Chemistry 2010, 285: 41100-41112. PMID: 20959458, PMCID: PMC3003408, DOI: 10.1074/jbc.m110.163600.
- RSBP-1 Is a Membrane-targeting Subunit Required by the Gαq-specific But Not the Gαo-specific R7 Regulator of G protein Signaling in Caenorhabditis elegansPorter MY, Koelle MR. RSBP-1 Is a Membrane-targeting Subunit Required by the Gαq-specific But Not the Gαo-specific R7 Regulator of G protein Signaling in Caenorhabditis elegans Molecular Biology Of The Cell 2009, 21: 232-243. PMID: 19923320, PMCID: PMC2808233, DOI: 10.1091/mbc.e09-07-0642.
- Chapter 2 Insights into RGS Protein Function from Studies in Caenorhabditis elegansPorter MY, Koelle MR. Chapter 2 Insights into RGS Protein Function from Studies in Caenorhabditis elegans 2009, 86: 15-47. PMID: 20374712, DOI: 10.1016/s1877-1173(09)86002-x.
- The Potassium Chloride Cotransporter KCC-2 Coordinates Development of Inhibitory Neurotransmission and Synapse Structure in Caenorhabditis elegansTanis JE, Bellemer A, Moresco JJ, Forbush B, Koelle MR. The Potassium Chloride Cotransporter KCC-2 Coordinates Development of Inhibitory Neurotransmission and Synapse Structure in Caenorhabditis elegans Journal Of Neuroscience 2009, 29: 9943-9954. PMID: 19675228, PMCID: PMC2737711, DOI: 10.1523/jneurosci.1989-09.2009.
- Regulation of Serotonin Biosynthesis by the G Proteins Gαo and Gαq Controls Serotonin Signaling in Caenorhabditis elegansTanis JE, Moresco JJ, Lindquist RA, Koelle MR. Regulation of Serotonin Biosynthesis by the G Proteins Gαo and Gαq Controls Serotonin Signaling in Caenorhabditis elegans Genetics 2008, 178: 157-169. PMID: 18202365, PMCID: PMC2206068, DOI: 10.1534/genetics.107.079780.
- Biogenic amine neurotransmitters in C. elegans.Chase DL, Koelle MR. Biogenic amine neurotransmitters in C. elegans. WormBook 2007, 1-15. PMID: 18050501, PMCID: PMC4781333, DOI: 10.1895/wormbook.1.132.1.
- A Specific Subset of Transient Receptor Potential Vanilloid-Type Channel Subunits in Caenorhabditis elegans Endocrine Cells Function as Mixed Heteromers to Promote Neurotransmitter ReleaseJose AM, Bany IA, Chase DL, Koelle MR. A Specific Subset of Transient Receptor Potential Vanilloid-Type Channel Subunits in Caenorhabditis elegans Endocrine Cells Function as Mixed Heteromers to Promote Neurotransmitter Release Genetics 2007, 175: 93-105. PMID: 17057248, PMCID: PMC1774992, DOI: 10.1534/genetics.106.065516.
- C. elegans G Protein Regulator RGS-3 Controls Sensitivity to Sensory StimuliFerkey DM, Hyde R, Haspel G, Dionne HM, Hess HA, Suzuki H, Schafer WR, Koelle MR, Hart AC. C. elegans G Protein Regulator RGS-3 Controls Sensitivity to Sensory Stimuli Neuron 2007, 53: 39-52. PMID: 17196529, PMCID: PMC1855255, DOI: 10.1016/j.neuron.2006.11.015.
- Heterotrimeric G Protein Signaling: Getting inside the CellKoelle MR. Heterotrimeric G Protein Signaling: Getting inside the Cell Cell 2006, 126: 25-27. PMID: 16839871, DOI: 10.1016/j.cell.2006.06.026.
- Caenorhabditus elegans Arrestin Regulates Neural G Protein Signaling and Olfactory Adaptation and Recovery*Palmitessa A, Hess HA, Bany IA, Kim YM, Koelle MR, Benovic JL. Caenorhabditus elegans Arrestin Regulates Neural G Protein Signaling and Olfactory Adaptation and Recovery* Journal Of Biological Chemistry 2005, 280: 24649-24662. PMID: 15878875, DOI: 10.1074/jbc.m502637200.
- Domains, Amino Acid Residues, and New Isoforms of Caenorhabditis elegans Diacylglycerol Kinase 1 (DGK-1) Important for Terminating Diacylglycerol Signaling in Vivo *Jose AM, Koelle MR. Domains, Amino Acid Residues, and New Isoforms of Caenorhabditis elegans Diacylglycerol Kinase 1 (DGK-1) Important for Terminating Diacylglycerol Signaling in Vivo * Journal Of Biological Chemistry 2004, 280: 2730-2736. PMID: 15563467, PMCID: PMC2048986, DOI: 10.1074/jbc.m409460200.
- RGS-7 Completes a Receptor-Independent Heterotrimeric G Protein Cycle to Asymmetrically Regulate Mitotic Spindle Positioning in C. elegansHess HA, Röper JC, Grill SW, Koelle MR. RGS-7 Completes a Receptor-Independent Heterotrimeric G Protein Cycle to Asymmetrically Regulate Mitotic Spindle Positioning in C. elegans Cell 2004, 119: 209-218. PMID: 15479638, DOI: 10.1016/j.cell.2004.09.025.
- Activation of EGL-47, a Gαo-Coupled Receptor, Inhibits Function of Hermaphrodite-Specific Motor Neurons to Regulate Caenorhabditis elegans Egg-Laying BehaviorMoresco JJ, Koelle MR. Activation of EGL-47, a Gαo-Coupled Receptor, Inhibits Function of Hermaphrodite-Specific Motor Neurons to Regulate Caenorhabditis elegans Egg-Laying Behavior Journal Of Neuroscience 2004, 24: 8522-8530. PMID: 15456826, PMCID: PMC6729914, DOI: 10.1523/jneurosci.1915-04.2004.
- Mechanism of extrasynaptic dopamine signaling in Caenorhabditis elegansChase DL, Pepper JS, Koelle MR. Mechanism of extrasynaptic dopamine signaling in Caenorhabditis elegans Nature Neuroscience 2004, 7: 1096-1103. PMID: 15378064, DOI: 10.1038/nn1316.
- Genetic Analysis of RGS Protein Function in Caenorhabditis elegansChase DL, Koelle MR. Genetic Analysis of RGS Protein Function in Caenorhabditis elegans 2004, 389: 305-320. PMID: 15313573, DOI: 10.1016/s0076-6879(04)89018-9.
- Genetic and Cellular Basis for Acetylcholine Inhibition of Caenorhabditis elegans Egg-Laying BehaviorBany IA, Dong MQ, Koelle MR. Genetic and Cellular Basis for Acetylcholine Inhibition of Caenorhabditis elegans Egg-Laying Behavior Journal Of Neuroscience 2003, 23: 8060-8069. PMID: 12954868, PMCID: PMC6740490, DOI: 10.1523/jneurosci.23-22-08060.2003.
- An N-terminal Region of Caenorhabditis elegans RGS Proteins EGL-10 and EAT-16 Directs Inhibition of Gαo VersusGαq Signaling*Patikoglou GA, Koelle MR. An N-terminal Region of Caenorhabditis elegans RGS Proteins EGL-10 and EAT-16 Directs Inhibition of Gαo VersusGαq Signaling* Journal Of Biological Chemistry 2002, 277: 47004-47013. PMID: 12354761, DOI: 10.1074/jbc.m208186200.