Skip to main page content
Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2018 Jan 2;16(1):e2004218.
doi: 10.1371/journal.pbio.2004218. eCollection 2018 Jan.

An Atlas of Caenorhabditis Elegans Chemoreceptor Expression

Affiliations
Free PMC article

An Atlas of Caenorhabditis Elegans Chemoreceptor Expression

Berta Vidal et al. PLoS Biol. .
Free PMC article

Abstract

One goal of modern day neuroscience is the establishment of molecular maps that assign unique features to individual neuron types. Such maps provide important starting points for neuron classification, for functional analysis, and for developmental studies aimed at defining the molecular mechanisms of neuron identity acquisition and neuron identity diversification. In this resource paper, we describe a nervous system-wide map of the potential expression sites of 244 members of the largest gene family in the C. elegans genome, rhodopsin-like (class A) G-protein-coupled receptor (GPCR) chemoreceptors, using classic gfp reporter gene technology. We cover representatives of all sequence families of chemoreceptor GPCRs, some of which were previously entirely uncharacterized. Most reporters are expressed in a very restricted number of cells, often just in single cells. We assign GPCR reporter expression to all but two of the 37 sensory neuron classes of the sex-shared, core nervous system. Some sensory neurons express a very small number of receptors, while others, particularly nociceptive neurons, coexpress several dozen GPCR reporter genes. GPCR reporters are also expressed in a wide range of inter- and motorneurons, as well as non-neuronal cells, suggesting that GPCRs may constitute receptors not just for environmental signals, but also for internal cues. We observe only one notable, frequent association of coexpression patterns, namely in one nociceptive amphid (ASH) and two nociceptive phasmid sensory neurons (PHA, PHB). We identified GPCRs with sexually dimorphic expression and several GPCR reporters that are expressed in a left/right asymmetric manner. We identified a substantial degree of GPCR expression plasticity; particularly in the context of the environmentally-induced dauer diapause stage when one third of all tested GPCRs alter the cellular specificity of their expression within and outside the nervous system. Intriguingly, in a number of cases, the dauer-specific alterations of GPCR reporter expression in specific neuron classes are maintained during postdauer life and in some case new patterns are induced post-dauer, demonstrating that GPCR gene expression may serve as traits of life history. Taken together, our resource provides an entry point for functional studies and also offers a host of molecular markers for studying molecular patterning and plasticity of the nervous system.

Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Summary of csGPCR reporter expression patterns.
(A) Overall tissue distribution of reporter expression patterns in hermaphrodites. Pie chart showing percentage of GPCR reporters expressed exclusively in neurons, in neurons and other cells types, and exclusively in non-neuronal tissues. Numbers in parentheses represent the absolute number of reporters in each category. (B) Extent of reporter expression within the nervous system. Pie chart showing percentage of neuronal reporters expressed in 1 neuron pair, 2 pairs, 3–4 pairs, 5–10 pairs, or more than 10 pairs. Numbers in parentheses represent the absolute number of reporters in each category. (C) Distribution of reporter gene expression within the nervous system. Pie charts showing percentage of GPCR reporters expressed in amphid neurons, phasmid neurons, other sensory neurons, and inter- or motorneurons. Small pie charts on the upper right represent the percentage of reporters exclusively expressed in amphids, phasmids, other sensory neurons, and inter- or motorneurons. Numbers in parentheses show the absolute number of reporters in each category. (D) Distribution within all sensory neurons of the hermaphrodite. Worm schematics showing the absolute number of GPCR reporters found to be expressed in each sensory neuron class. PHC is a phasmid neuron by name only. See S2 Table for a list of GPCR gene names expressed in the sensory neurons shown here. GPCR, G-protein-coupled receptor.
Fig 2
Fig 2. csGPCR reporters expressed in single sensory neuron classes.
(A) Table showing all GPCR reporters expressed in a single neuron class. Genes in bold are newly identified in this paper. Genes not in bold were previously described (data extracted from www.wormbase.org). * Reporter is also expressed in some non-neuronal tissue (for details, see S1 Table). 1 N. Masoudi, S. Finkelstein, and O. Hobert, in preparation. (B) Representative examples of reporters expressed in a single neuron class identified in this study. Young adult hermaphrodites are shown. Scale bars, 10 μm. GPCR, G-protein-coupled receptor.
Fig 3
Fig 3. csGPCR reporters expressed in non-amphid/non-phasmid sensory neurons, interneurons, and motorneurons.
Examples of GPCR reporters expressed in sensory neurons that are not amphids or phasmids (white font), interneurons (orange font), or motorneurons (blue font). Most examples represented here are from neuron classes that were not previously shown to express any sensory GPCR. Amphid neurons are shown in parentheses. Young adult hermaphrodites are shown. All scale bars, 10 μm, except srsx-30, which is 30 μm. See Table 3 for a complete summary of GPCR reporters expressed in inter- and motorneurons. GPCR, G-protein-coupled receptor.
Fig 4
Fig 4. The only coexpression association of csGPCR reporters is in nociceptive neurons.
(A,B) Graphical representation of ASH, PHA, and PHB coexpression. Green-filled square indicates expression. An asterisk denotes that the gene is exclusively expressed in the indicated neurons. Venn diagram was created with eulerAPE [57]. (C) Hierarchical clustering of neurons by GPCR reporter expression. Red lines show the well-supported ASH, PHA and PHB cluster (AU > 95%). BP values (in green) are listed in percentages.(D) Examples of reporter gene expression profiles in ASH/PHA/PHB. Young adult hermaphrodites are shown. Scale bars, 10 μm. AU, approximately unbiased p-value; BP, bootstrap probability value; GPCR, G-protein-coupled receptor.
Fig 5
Fig 5. Lateralized csGPCR reporter expression in the AWC neuron pair.
(A) Asymmetrically expressed GPCRs, indicated with arrowheads (top row), were all expressed in AWC as assessed by colocalization with the ceh-36p::RFP reporter (middle row). str-130, srd-5, srx-1, srsx-5, and srsx-37 reporters were expressed in AWCOFF while srt-7 was expressed in AWCON as assessed with the str-2p::NLS::RFP reporter, which is an AWCON marker (bottom row). All pictures are dorso-ventral views unless otherwise indicated. srt-13 and srr-9 reporters were also found to be asymmetrically expressed in AWC; however, since these reporters were dim and not very robust, no further analysis was done. Young adult hermaphrodites are shown. Scale bars, 10 μm. (B) AWC asymmetry. Previously known components of genetic pathways that control AWC asymmetries [33]. Not all genes known to be involved are shown. Black and grey gene names indicate whether a gene is more active or more expressed (black) in one neuron compared with the other neuron. Scheme adapted from [63]. (C) Expression of the newly found AWC asymmetric GPCRs is regulated by previously described mechanisms. Representative pictures showing srx-1 reporter expression (AWCOFF) in different mutants of the previously described AWC asymmetry pathway. As expected, in unc-43(n1186lf) mutants, srx-1 reporter is expressed in none of the AWC neurons (2 AWCON phenotype) while in unc-43(n498gf) and nsy-5(ky634) mutants srx-1 is expressed in both AWC neurons (2 AWCOFF phenotype). Scale bars, 10 μm. (D) Expression quantification of AWC asymmetric GPCR reporters in unc-43(n1186lf), unc-43(n498gf), and nsy-5(ky634) mutants. Animals were scored as young adults and show the expected 2 AWCON or 2AWCOFF phenotype. Between 20 and 40 hermaphrodites were scored per genotype. GPCR, G-protein-coupled receptor.
Fig 6
Fig 6. Expression of sex-specifically expressed csGPCR reporters.
Examples of GPCR reporters expressed in hermaphrodite-specific (VCs, HSN) or male-specific neurons (CEMs, CP5, CP6, Rays). Young adult animals are shown. All scale bars,10 μm, except srb-16, which is 30 μm. GPCR, G-protein-coupled receptor; HSN, hermaphrodite-specific neuron.
Fig 7
Fig 7. Expression of non-neuronal csGPCR reporters.
Examples of GPCR reporters expressed in different types of non-neuronal tissue in young adult hermaphrodites. Scale bars, 10 μm. See Table 4 for a complete summary of GPCR reporters expressed in non-neuronal tissues. Amso, amphid socket cells; GPCR, G-protein-coupled receptor; HMC, head mesodermal cell; PHsh, phasmid sheath; PHso, phasmid socket; UV1, uterine/vulval cell 1.
Fig 8
Fig 8. Reporter analysis of entire csGPCR families.
Genomic loci, reporter scheme, and gfp expression images for the srm (A), srr (B), and srn (C) GPCR gene families. Only reporters expressed in the pharynx are shown for the srr family. Young adult hermaphrodites are shown. Scale bars, 10 μm. GPCR, G-protein-coupled receptor.
Fig 9
Fig 9. Temporal regulation of csGPCR reporters.
GFP images showing temporal expression changes (L1 versus young adult) of srh-11, sru-48 and sra-28 reporter genes. Neurons showing temporal changes in expression are outlined with red dotted lines. Scale bars, 10 μm. GFP, green fluorescent protein; GPCR, G-protein-coupled receptor; L1, first larval.
Fig 10
Fig 10. Examples of environment-induced changes in csGPCR expression.
Examples of GPCR reporters that change expression in dauer stage animals. Designations of neuron classes that change expression are highlighted in red. Asterisk indicates posterior gut autofluorescence. Insets for srh-71, sre-43, and srm-4 show enlarged and overexposed images of cells that are too dim to be discernable in main panels. See Table 5 for a complete summary of GPCR expression changes in dauer. Scale bars, 10 μm. GPCR, G-protein-coupled receptor; L3, third larval stage; L4, fourth larval stage.
Fig 11
Fig 11. csGPCR expression patterns as life history traits.
Comparison of GPCR expression in 1-day-old adult hermaphrodite animals that either did pass through the dauer state (right panels) or did not (age-matched fed controls; left panels). Post-dauer animals were in the dauer stage for 5–7 days. Designations of neuron classes that retain dauer-specific expression or acquire post-dauer–specific expression are highlighted in red. Inset for sre-43 shows enlarged and overexposed images of cells that are too dim to be clearly discernable in the main panel. See Table 5 for a complete summary of GPCR expression changes in post-dauer. Scale bars, 10 μm. GPCR, G-protein-coupled receptor.
Fig 12
Fig 12. csGPCR reporter expression in starved L1 animals.
Examples of GPCR reporter expression in starved L1 worms. Eggs isolated by bleach treatment were allowed to hatch and were kept in M9 for 48 hours. Designations of neuron classes that change expression compared to fed L1 worms are highlighted in red. Scale bars, 10 μm. GPCR, G-protein-coupled receptor; L1, first larval stage.

Similar articles

See all similar articles

Cited by 6 articles

See all "Cited by" articles

References

    1. Hobert O, Carrera I, Stefanakis N. The molecular and gene regulatory signature of a neuron. Trends in neurosciences. 2010;33(10):435–45. Epub 2010/07/29. doi: 10.1016/j.tins.2010.05.006 . - DOI - PMC - PubMed
    1. Troemel ER, Chou JH, Dwyer ND, Colbert HA, Bargmann CI. Divergent seven transmembrane receptors are candidate chemosensory receptors in C. elegans. Cell. 1995;83(2):207–18. - PubMed
    1. Chalfie M, Tu Y, Euskirchen G, Ward WW, Prasher DC. Green fluorescent protein as a marker for gene expression. Science. 1994;263(5148):802–5. . - PubMed
    1. Lagerstrom MC, Schioth HB. Structural diversity of G protein-coupled receptors and significance for drug discovery. Nat Rev Drug Discov. 2008;7(4):339–57. Epub 2008/04/03. doi: 10.1038/nrd2518 . - DOI - PubMed
    1. Fredriksson R, Lagerstrom MC, Lundin LG, Schioth HB. The G-protein-coupled receptors in the human genome form five main families. Phylogenetic analysis, paralogon groups, and fingerprints. Mol Pharmacol. 2003;63(6):1256–72. doi: 10.1124/mol.63.6.1256 . - DOI - PubMed

Publication types

MeSH terms

Substances

Feedback