ASEL, ASER

Type: Sensory neuron (chemosensory (gustatory), CO2-sensory)
In MoW: ASE
Male Wiring Project: ASEL, ASER
In Wormbase: ASE, ASEL, ASER
Lineage: AB alppppppaa, AB praaapppaa
Location: Lateral ganglia of head
Description: Amphid neurons, single (AsE) ciliated endings. Like all other amphid neurons, ASE are born near the presumptive nose of the embryo during development. They then anchor a short projection there, after which the cell body migrates away, stretching the dendrite out behind it. This process is dependent on DEX-1 or DYF-7, secreted extracellular matrix proteins which act cooperatively for anchoring. In mutants lacking these proteins, the dendrite fails to anchor at the nose and is dragged along with the migrating cell body, giving rise to a short dendritic stub (Heiman and Shaham, 2010). ASE axon projects into ring via amphid commissure from ventral ganglion, makes diverse synaptic connections in ring neuropil. Although these neurons are left–right homologs anatomically, they exhibit marked asymmetries in gene expression and function (Cochella and Hobert, 2012) .
Neurotransmitter/ Neuropeptide:
- Glutamate
- FLP-4; expressed in ASEL only. FMRFamide-like neuropeptide
- FLP-6; FMRFamide-like neuropeptide
- FLP-13; FMRFamide-like neuropeptide
- FLP-20; expressed in ASEL only. FMRFamide-like neuropeptide




- FLP-25; FMRFamide-like neuropeptide
- INS-1; insulin-like peptide, orthologous to human insulin
- INS-22; insulin-like peptide
- INS-26; insulin-like peptide
- INS-32; expressed in ASEL only. Insulin-like peptide
- NLP-3; neuropeptide-like peptide
- NLP-5; expressed in ASER only. Neuropeptide-like peptide
- NLP-7; bilaterally expressed (Nathoo et al., 2001) vs only in ASER (Takayama et al., 2010). Neuropeptide-like peptide
- NLP-14; neuropeptide-like peptide
(N.B. Despite earlier reports suggesting FLP-5 and FLP-21 are expressed in ASE neurons, later studies indicate they are not; see Li and Kim, 2008-table 2.)
(Pereira et al., 2015; Takayama et al., 2010; Li and Kim, 2008; Etchberger et al, 2007; Johnston et al., 2005; Kim and Li, 2004; Rogers et al., 2003; Nathoo et al., 2001; Pierce et al, 2001; O. Hobert, pers. comm.)
Innexin expression:
ASE neurons have no gap junctions in the adult (MoW), and no innexin expression was observed in ASE neurons through L1 to adult stages (Altun et al., 2009)
Receptor expression:
- DEL-3; degenerin-like , amiloride-sensitive channel
- DEL-4; degenerin-like , amiloride-sensitive channel
- DAF-2; functional studies suggest DAF-2 (RTK ins/IGF rec ortholog) is possibly expressed in ASER
- DOP-3; mammalian D2-like dopamine receptor
- DOP-5; homolog of mammalian dopamine and serotonin receptors
- GCY-1; expressed in ASER only. Transmembrane receptor guanylate cyclase
- GCY-3; expressed in ASER only. Transmembrane receptor guanylate cyclase
- GCY-4; expressed in ASER only. Transmembrane receptor guanylate cyclase
- GCY-5; expressed in ASER only. Transmembrane receptor guanylate cyclase
- GCY-6; expressed in ASEL only. Transmembrane receptor guanylate cyclase
- GCY-7; expressed in ASEL only. Transmembrane receptor guanylate cyclase
- GCY-14; expressed in ASEL only. Transmembrane receptor guanylate cyclase
- GCY-19; bilaterally expressed (faint) (Ortiz et al., 2006) vs only in ASER (Takayama et al., 2010). Transmembrane receptor guanylate cyclase
- GCY-20; expressed in ASEL only. Transmembrane receptor guanylate cyclase
- GCY-22; expressed in ASER only. Transmembrane receptor guanylate cyclase
- GCY-29; bilaterally expressed. Transmembrane receptor guanylate cyclase
- MGL-3 ; metabotropic glutamate receptor
- NPR-1; receptor for flp-18- and flp-21-encoded peptides
- NPR-5; receptor for flp-3 and flp-18 encoded peptides
- NPR-15; neuropeptide receptor
- OSM-9; TRPV (transient receptor potential channel, vanilloid subfamily; mammalian capsaicin receptor-like channel)
- SRAB-14 ; G-protein-coupled seven transmembrane receptor
- SRD-33 ; G-protein-coupled seven transmembrane receptor
- SRG-30 ; G-protein-coupled seven transmembrane receptor
- SRX-76 ; G-protein-coupled seven transmembrane receptor
- TMC-1; putative cation channel, salt-sensing receptor
- TRPA-2 ; transient receptor potential ion channel (TRPA, TRPM and TRPV ion channel families are considered "thermoTRPs" that sense temperature")
- TRP-2 ; expressed in ASER only. Transient receptor potential ion channel (TRPC family)
- TYRA-2; tyramine receptor
(Wormbase; Chatzigeorgiou et al., 2013; Mills et al., 2012; Altun, 2011; Takayama et al., 2010; Etchberger et al., 2007; Ortiz et al., 2006; Tomiaka et al 2006; Coates and de Bono , 2002; Colbert et al., 1997; Yu et al., 1997).
Function:
- Chemotaxis to water soluble attractants including Na+, Cl-, cAMP, biotin and lysine. Simultaneous ablation of all amphid and phasmid neurons except ASE spares chemotaxis, indicating that the role of ASE in water-soluble chemotaxis is the most important. In the absence of ASE neurons, ADF, ASG, ASI, ASK, and ASJ carry out a weak residual response (Bargmann, 2006). ASE neurons respond to stepwise changes in NaCl concentration rather than absolute concentration. ASEL is primarily sensitive to Na+, whereas ASER is primarily sensitive to Cl- and K+ (Bargmann, 2006; Pierce-Shimomura et al., 2001; Bargmann and Horvitz, 1991). Opposite intacellular Ca2+ transients are generated in ASEL and ASER in response to changes in salt concentration; ASEL is an ON-cell, activated by increases in NaCl concentration, whereas ASER is an OFF-cell, i.e, it is tonically active at baseline and becomes deactivated by increases in NaCl concentration (Suzuki et al., 2008; Suzuki et al., 2004). ASE responses are likely mediated by cGMP signalling. Behaviorally, increases in NaCl concentration increase the probability of forward locomotion and decrease the probability of turning, whereas decreases in NaCl concentration have the opposite effect resulting in a biased random walk towards the chemoattractant. Activation of ASEL inhibits reversals and lengthens bouts of forward locomotion (runs), whereas activation of ASER promotes reversals and direction changes (turns) (Appelby, 2012; Suzuki et al., 2008)
- ASH, ADL, ASK and ASE sensory neurons are responsible for the detection of certain chemical repellents. ASH neurons play a major role in this avoidance, whereas ADL, ASK and ASE play minor roles that are only evident when ASH neurons are missing (Hiliard et al., 2002; Sambongi et al., 1999; Bargmann et al, 1990.) ASE neurons mediate avoidance behavior from Cd2+ and Cu2+ (Sambongi et al., 1999)
- Functions in adaptive food-leaving behavior (leaving a food patch as it is becoming depleted to start foraging); the ASE neurons promote food-leaving behavior via a cGMP pathway as food becomes limited; in well-fed animals ASE neurons mediate chemoattraction to water-soluble cues as noted above. However, food withdrawal or gradual depletion of food turns this attraction to salt into repulsion. This switch in preference involves signaling by the DAF-2 insulin receptor in ASER as well as INS-1-dependent feedback from AIA to ASER (Milward et al., 2011; Tomioka et al., 2006).
- AFD, BAG and ASE are primary CO2 sensors while oxygen-sensing neurons AQR, PQR and URX are also weakly CO2 responsive. As opposed to their asymmetric NaCl response, both ASEL and ASER become activated when CO2 rises (Bretscher et al., 2011).


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To see quicktime movie of ASER, click on the image.


 
 

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ASEL (AB alppppppaa) development in the embryo.
Dorsal view. Bottom is left side of the embryo. Spheres indicate individual nuclei. Black sphere: ancestors of ASEL (since last ASEL ancestor has not yet gone through its final division, the black sphere seen at the end of this movie is still AB alppppppa); dark grey spheres: apoptotic cells; other cells follow the WA color code (after they acquire specific cell or tissue identities). 0 min is fertilization. Click on the movie for higher resolution rendition (by A. Santella & Z. Bao).

 
 

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ASER (AB praaapppaa) development in the embryo.
Dorsal view. Bottom is left side of the embryo. Spheres indicate individual nuclei. Black sphere: ancestors of ASER (since last ASER ancestor has not yet gone through its final division, the black sphere seen at the end of this movie is still AB praaapppa); dark grey spheres: apoptotic cells; other cells follow the WA color code (after they acquire specific cell or tissue identities). 0 min is fertilization. Click on the movie for higher resolution rendition (by A. Santella & Z. Bao).


 
 

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3D reconstruction of the anterior sensory endings (cilia and dendrites) from high resolution serial section transmission electron micrographs (ssTEMs).
Bar 1 μm. Color code for the sensory endings is shown on the right-colors do not follow the WA color code. To expand, double click on the video, to return to original size, click "esc" (Doroquez et al., 2014)

 
 
 

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3D reconstruction of all amphid neuron cilia and associated socket and sheath cell processes.
Modeled from serial section transmission electron micrographs
(ssTEMs). Bar 1 μm. Color code for the sensory endings is shown on the left-colors do not follow the WA color code. To expand, double click on the video, to return to original size, click "esc" (Doroquez et al., 2014)

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