Development 139, 2234-2245 (2012) doi:10.1242/dev.075184
© 2012. Published by The Company of Biologists Ltd
UNC-4 antagonizes Wnt signaling to regulate synaptic choice
in the C. elegans motor circuit
Nervous system function is defined by connections between
specific neurons. These links include chemical synapses that utilize
neurotransmitters to evoke postsynaptic responses and gap
junctions that regulate ion flow between coupled neurons.
Although some progress has been made towards understanding the
molecular basis of chemical synaptic specificity (Sanes and
Yamagata, 2009; Shen and Scheiffele, 2010), little is known about
how neurons choose partners for gap junction assembly (Bennett
and Zukin, 2004; Hestrin and Galarreta, 2005). Both types of
synapses are active in motor circuits that regulate body movements
(Charlton and Gray, 1966; Westerfield and Frank, 1982; Van Der
Giessen et al., 2008; Li et al., 2009). The key role of transcription
factor codes in motor circuit neuron fate suggests that genetic
programs define the specificity of these connections (Briscoe et al.,
2000; Shirasaki and Pfaff, 2002). Downstream targets with roles in
synaptic specificity are largely unknown but probably include a
combination of diffusible cues and cell-surface proteins that
regulate synaptogenic responses (Pecho-Vrieseling et al., 2009).
Wnt signaling functions as a key regulator of synaptic assembly
in the brain and at the neuromuscular junction (Budnik and Salinas,
2011). For example, in cerebellar neurons, Wnt7a activates a
cytoplasmic pathway that promotes local assembly of presynaptic
components whereas Wnt-dependent synaptic assembly at the
Drosophilaneuromuscular junction can also depend on
transcriptional regulation (Packard et al., 2002; Ahmad-Annuar et
al., 2006; Ataman et al., 2006; Miech et al., 2008). Wnts might also
function as antagonistic cues to limit synapse formation (Inaki et
al., 2007; Klassen and Shen, 2007) and, in at least one case, adopt
opposing roles that either promote or inhibit synaptogenesis (Davis
et al., 2008). Although multiple members of the Wnt family are
expressed in the developing spinal cord and have been shown to
regulate axon trajectory and neuron fate, explicit roles in
synaptogenesis have not been uncovered (Lyuksyutova et al., 2003;
Liu et al., 2005; Agalliu et al., 2009). Here, we describe our finding
that opposing Wnt signaling pathways regulate the specificity of
synaptic inputs in a nematode motor circuit.
In C. elegans, backward movement depends on connections
between AVA interneurons and VA class motor neurons, whereas
forward locomotion requires AVB input to VB motor neurons (Fig.
1) (Chalfie et al., 1985; Ben Arous et al., 2010; Haspel et al., 2010).
The specificity of these connections is controlled by the UNC-4
homeodomain transcription factor, which functions in VA motor
neurons (Miller et al., 1992). In unc-4 mutants, AVA inputs to VAs
are replaced with gap junctions from AVB and backward locomotion
is disrupted. The characteristic anterior polarity of VA motor neurons
is not perturbed, however, which suggests that UNC-4 regulates the
specificity of synaptic inputs but not other traits that distinguish VAs
from sister VB motor neurons (White et al., 1992; Miller and
Niemeyer, 1995). UNC-4 functions as a transcriptional repressor
with the conserved Groucho-like protein UNC-37 to block
expression of VB-specific genes (Pflugrad et al., 1997; Winnier et
al., 1999) (Fig. 3). We have shown that one of these VB proteins, the
HB9 (MNX1) homolog CEH-12, is sufficient to rewire VA motor
neurons with VB-type inputs (Von Stetina et al., 2007b). Thus, these
findings revealed a regulatory switch in which differential expression
1Department of Cell and Developmental Biology, Vanderbilt University, Nashville, TN
37232, USA. 2Hubrecht Institute, KNAW, University Medical Center Utrecht,
Uppsalalaan 8, 3584 CT, Utrecht, The Netherlands. 3Departments of Physics and
Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
4Neuroscience Program, Program in Developmental Biology and Vanderbilt Kennedy
Center, Vanderbilt University Nashville, TN 37232, USA.
*These authors contributed equally to this work
‡Present address: Department of Molecular and Cellular Biology, Harvard University,
Cambridge, MA 02138, USA
§Author for correspondence (email@example.com)
Accepted 3 April 2012
Coordinated movement depends on the creation of synapses between specific neurons in the motor circuit. In C. elegans, this
important decision is regulated by the UNC-4 homeodomain protein. unc-4 mutants are unable to execute backward locomotion
because VA motor neurons are mis-wired with inputs normally reserved for their VB sisters. We have proposed that UNC-4
functions in VAs to block expression of VB genes. This model is substantiated by the finding that ectopic expression of the VB
gene ceh-12 (encoding a homolog of the homeodomain protein HB9) in unc-4 mutants results in the mis-wiring of posterior VA
motor neurons with VB-like connections. Here, we show that VA expression of CEH-12 depends on a nearby source of the Wnt
protein EGL-20. Our results indicate that UNC-4 prevents VAs from responding to a local EGL-20 cue by disabling a canonical Wnt
signaling cascade involving the Frizzled receptors MIG-1 and MOM-5. CEH-12 expression in VA motor neurons is also opposed by
a separate pathway that includes the Wnt ligand LIN-44. This work has revealed a transcriptional mechanism for modulating the
sensitivity of specific neurons to diffusible Wnt ligands and thereby defines distinct patterns of synaptic connectivity. The
existence of comparable Wnt gradients in the vertebrate spinal cord could reflect similar roles for Wnt signaling in vertebrate
motor circuit assembly.
KEY WORDS: C. elegans, Wnt signaling, Gap junction, Motor circuit, Synaptic specificity, unc-4
Judsen Schneider1,*, Rachel L. Skelton1,*, Stephen E. Von Stetina1,*,‡, Teije C. Middelkoop2,
Alexander van Oudenaarden2,3, Hendrik C. Korswagen2and David M. Miller, III1,4,§
Wnt pathways control synaptic choice
of the transcription factors, UNC-4 versus CEH-12, in VAs results in
alternate sets of presynaptic inputs. This mechanism, however, shows
regional specificity along the length of the ventral nerve cord.
Ectopic expression of ceh-12 in unc-4 mutants is limited to posterior
VA motor neurons and VA input specificity in this location depends
on ceh-12. These findings suggest that UNC-4 might regulate
multiple targets that function in parallel to specify inputs to selected
VA motor neurons in different ventral cord domains (Von Stetina et
al., 2007b). Here, we report the discovery that ceh-12 expression in
posterior VA motor neurons is activated by a specific Wnt protein,
EGL-20, that is secreted from adjacent cells in this region. We
propose that UNC-4 normally prevents VAs from responding to
EGL-20 by antagonizing a canonical Wnt signaling pathway
utilizing the Frizzled (Frz) receptors MOM-5 and MIG-1. We have
also identified a separate Wnt pathway, involving the Frz receptor
LIN-17 and the Wnt ligands LIN-44 and CWN-1, that preserves VA
inputs by blocking CEH-12 expression in anterior VAs. Our results
have uncovered a key role for the UNC-4 transcription factor in
modulating the relative strengths of Wnt signaling pathways with
opposing roles in synaptic choice. The widespread occurrence of
regional Wnt signaling cues in the developing spinal cord could be
indicative of similar functions for transcription factors in regulating
synaptic specificity in the vertebrate motor circuit.
MATERIALS AND METHODS
Nematode strains and genetics
Nematodes were cultured as described (Brenner, 1974). Mutants were
obtained from the Caenorhabditis Genetics Center (CGC) or by generous
donations from other laboratories (supplementary material Tables S1, S2).
Transgenic strains and primer sequences used for building constructs are
listed in supplementary material Table S3.
Punc-4::DNT-BAR-1 was generated by overlap PCR from plasmid
pHCK19 (supplementary material Table S3) (Gleason et al., 2002),
microinjected (Fire et al., 1991) with pMH86 (dpy-20[+]) to produce
NC1847 [wdEx636[Punc-4::DNT-BAR-1, dpy-20(+)]] and crossed into
wdIs85 (see below). Punc-4::MIG-1::YFP was generated by overlap PCR
(supplementary material Table S3) and microinjected to produce NC1870
A spontaneous integrant, wdIs85 (LGIII), of wdEx310 was used to assay
ceh-12::GFP expression. L2 larval VAs and VBs were scored for the
presence or absence of ceh-12::GFP expression (n>10 for each neuron).
Animals were anesthetized with either 0.25% tricaine/0.025% tetramisole
or 10 mM levamisole. Supplementary material Table S6 shows results used
in pie charts (supplementary material Fig. S8).
Detecting AVB gap junctions with ventral cord motor neurons
The AVB gap junction marker strain NC1694 [wdIs54[Punc-7::UNC-
7S::GFP, col-19::GFP] unc-7(e5) X] was integrated by irradiation
(4000 Rads) of EH578 (Starich et al., 2009) and backcrossed into wild
type ten times. AVB gap junctions in the ventral cord were detected
by anti-GFP immunostaining in L4 larvae and specific motor neurons
were identified as described (Von Stetina et al., 2007b). n≥10 for each
neuron. Supplementary material Table S7 shows values used in pie
charts (supplementary material Fig. S8).
Single molecule mRNA FISH
In situ hybridization assays were performed (Raj et al., 2008; Harterink et
al., 2011) in wild type, unc-4(e120) and unc-37(e262) with unc-4::GFP to
mark DA and VA neurons. Synchronized worms were fixed in 4%
formaldehyde, 70% ethanol.
(www.singlemoleculefish.com) were coupled to Alexa 594 (mig-1) or Cy5
(mom-5). Nuclei were stained with DAPI. z-stacks (0.5 m per slice) were
collected using a Leica DM6000 microscope with 100? objective and Tx2
(Alexa594) or Y5 (Cy5) filter cube. 1024?1024 images were subjected to
2?2 binning. Each VA neuron was identified by its position in the ventral
nerve cord and its cell soma was delineated by the outside edge of unc-
4::GFP staining (Leica AF Lite). Individual fluorescent puncta (mRNA)
from this region were counted by direct inspection of the z-stack. n≥5 for
GRASP assay of AVA to VA10 synapses
The GFP reconstitution across synaptic partners (GRASP) marker wdIs65
was integrated by irradiation (4000 Rads) of wyEx1845 (Feinberg et al.,
2008) and used to label AVA to A-class motor neuron synapses. z-stacks
were collected with identical microscope settings. Line scans in the GFP
channel were collected in the VA10 to DA7 interval (Feinberg et al., 2008).
An equivalent length scan was obtained from the posterior dorsal nerve
cord (devoid of GFP puncta) to obtain an average background signal in the
GFP channel for each animal. The intensity score for each experimental
sample was calculated from the percentage of measurements from the
VA10 to DA7 interval that exceeded this background signal. n≥10 for each
wdIs85(ceh-12::GFP) and wdIs54(Punc-7::UNC-7S::GFP) were scored
with a 100? objective in a Zeiss Axioplan microscope with a
Hammamatsu Orca camera. Images of wdIs85 were obtained using a Leica
TCS SP5 confocal microscope. Images of wdIs54 were obtained using an
Olympus FV-1000 confocal microscope with a 60?/1.45 Plan-Apochromat
lens. Pseudocolors and image overlays were generated using Olympus
software and Adobe Photoshop.
A movement assay (‘tapping assay’) detected effects of specific mutants
on backward locomotion (Von Stetina et al., 2007b). For each genotype,
n>50 L4-young adults were tapped on the head with a platinum wire.
Backward movement was scored as either Unc (coiled instantly, no net
backward movement) or Suppressed (detectable backward movement of
posterior region or entire body in locomotory sinusoidal waves).
Embryos were placed on nematode growth media (NGM) plates streaked
with OP50 bacteria, covered with pyrvinium palmoate dissolved in
soybean oil, and allowed to hatch. Tapping assays were performed on
young adults (n50).
Lithium chloride treatment
Lithium chloride was added to NGM media before pouring plates to yield
a final concentration of 10 mM LiCl. Synchronized L1 larvae were grown
on LiCl plates for 3 days at 20°C and tapping assays performed on young
AVA, AVD, AVE
Fig. 1. Diagram of the C. elegans motor neuron circuit.
Interneurons from the head and tail extend axons into the ventral nerve
cord to synapse with specific motor neurons. The forward circuit (red)
includes AVB and PVC interneurons and DB (not shown) and VB motor
neurons. The backward circuit (blue) includes AVA, AVD and AVE
interneurons and DA (not shown) and VA motor neurons. VAs and VBs
arise from a common progenitor but are connected to separate sets of
interneurons (AVA and AVB shown for simplicity).
2244 RESEARCH ARTICLE
Development 139 (12)
Frizzled-2 during synapse development requires the PDZ protein dGRIP. Proc.
Natl. Acad. Sci. USA 103, 7841-7846.
Ben Arous, J., Tanizawa, Y., Rabinowitch, I., Chatenay, D. and Schafer, W. R.
(2010). Automated imaging of neuronal activity in freely behaving
Caenorhabditis elegans. J. Neurosci. Methods 187, 229-234.
Bennett, M. V. and Zukin, R. S. (2004). Electrical coupling and neuronal
synchronization in the Mammalian brain. Neuron 41, 495-511.
Brenner, S. (1974). The genetics of Caenorhabditis elegans. Genetics 77, 71-94.
Briscoe, J., Pierani, A., Jessell, T. M. and Ericson, J. (2000). A homeodomain
protein code specifies progenitor cell identity and neuronal fate in the ventral
neural tube. Cell 101, 435-445.
Broihier, H. and Skeath, J. (2002). Drosophila homeodomain protein dHb9
directs neuronal fate via crossrepressive and cell-nonautonomous mechanisms.
Neuron 35, 39-50.
Budnik, V. and Salinas, P. C. (2011). Wnt signaling during synaptic development
and plasticity. Curr. Opin. Neurobiol. 21, 151-159.
Calvo, D., Victor, M., Gay, F., Sui, G., Luke, M. P., Dufourcq, P., Wen, G.,
Maduro, M., Rothman, J. and Shi, Y. (2001). A POP-1 repressor complex
restricts inappropriate cell type-specific gene transcription during Caenorhabditis
elegans embryogenesis. EMBO J. 20, 7197-7208.
Cerpa, W., Godoy, J. A., Alfaro, I., Farias, G. G., Metcalfe, M. J., Fuentealba,
R., Bonansco, C. and Inestrosa, N. C. (2008). Wnt-7a modulates the synaptic
vesicle cycle and synaptic transmission in hippocampal neurons. J. Biol. Chem.
Chalfie, M., Sulston, J. E., White, J. G., Southgate, E., Thompson, J. N. and
Brenner, S. (1985). The neural circuit for touch sensitivity in Caenorhabitis
elegans. J. Neurosci. 5, 956-964.
Charlton, B. T. and Gray, E. G. (1966). Comparative electron microscopy of
synapses in the vertebrate spinal cord. J. Cell Sci. 1, 67-80.
Ciani, L. and Salinas, P. C. (2005). WNTs in the vertebrate nervous system: from
patterning to neuronal connectivity. Nat. Rev. Neurosci. 6, 351-362.
Ciani, L., Boyle, K. A., Dickins, E., Sahores, M., Anane, D., Lopes, D. M.,
Gibb, A. J. and Salinas, P. C. (2011). Wnt7a signaling promotes dendritic spine
growth and synaptic strength through Ca2+/Calmodulin-dependent protein
kinase II. Proc. Natl. Acad. Sci. USA 108, 10732-10737.
Coudreuse, D. Y., Roel, G., Betist, M. C., Destree, O. and Korswagen, H. C.
(2006). Wnt gradient formation requires retromer function in Wnt-producing
cells. Science 312, 921-924.
Davis, E. K., Zou, Y. and Ghosh, A. (2008). Wnts acting through canonical and
noncanonical signaling pathways exert opposite effects on hippocampal synapse
formation. Neural Dev. 3, 32.
Eisenmann, D. M. (2005). Wnt signaling. WormBook 1-17. www.wormbook.org.
Eisenmann, D. M., Maloof, J. N., Simske, J. S., Kenyon, C. and Kim, S. K.
(1998). The beta-catenin homolog BAR-1 and LET-60 Ras coordinately regulate
the Hox gene lin-39 during Caenorhabditis elegans vulval development.
Development 125, 3667-3680.
Esmaeili, B., Ross, J. M., Neades, C., Miller, D. M., 3rd. and Ahringer, J.
(2002). The C. elegans even-skipped homologue, vab-7, specifies DB
motoneurone identity and axon trajectory. Development 129, 853-862.
Feinberg, E. H., Vanhoven, M. K., Bendesky, A., Wang, G., Fetter, R. D.,
Shen, K. and Bargmann, C. I. (2008). GFP reconstitution across synaptic
partners (GRASP) defines cell contacts and synapses in living nervous systems.
Neuron 57, 353-363.
Fire, A., Albertson, D., Harrison, S. W. and Moerman, D. G. (1991). Production
of antisense RNA leads to effective and specific inhibition of gene expression in
C. elegans muscle. Development 113, 503-514.
Fisher, R. A. (1925). Statistical Methods for Research Workers. Edinburgh: Oliver
Fox, R. M., Von Stetina, S. E., Barlow, S. J., Shaffer, C., Olszewski, K. L.,
Moore, J. H., Dupuy, D., Vidal, M. and Miller, D. M., 3rd (2005). A gene
expression fingerprint of C. elegans embryonic motor neurons. BMC Genomics
Fradkin, L. G., Garriga, G., Salinas, P. C., Thomas, J. B., Yu, X. and Zou, Y.
(2005). Wnt signaling in neural circuit development. J. Neurosci. 25, 10376-
Gleason, J. E., Korswagen, H. C. and Eisenmann, D. M. (2002). Activation of
Wnt signaling bypasses the requirement for RTK/Ras signaling during C. elegans
vulval induction. Genes Dev. 16, 1281-1290.
Goldstein, B., Takeshita, H., Mizumoto, K. and Sawa, H. (2006). Wnt signals
can function as positional cues in establishing cell polarity. Dev. Cell 10, 391-
Green, J. L., Inoue, T. and Sternberg, P. W. (2007). The C. elegans ROR receptor
tyrosine kinase, CAM-1, non-autonomously inhibits the Wnt pathway.
Development 134, 4053-4062.
Green, J. L., Inoue, T. and Sternberg, P. W. (2008). Opposing Wnt pathways
orient cell polarity during organogenesis. Cell 134, 646-656.
Harterink, M., Kim, D. H., Middelkoop, T. C., Doan, T. D., van Oudenaarden,
A. and Korswagen, H. C. (2011). Neuroblast migration along the
anteroposterior axis of C. elegans is controlled by opposing gradients of Wnts
and a secreted Frizzled-related protein. Development 138, 2915-2924.
Haspel, G., O’Donovan, M. J. and Hart, A. C. (2010). Motoneurons dedicated
to either forward or backward locomotion in the nematode Caenorhabditis
elegans. J. Neurosci. 30, 11151-11156.
Henriquez, J. P., Webb, A., Bence, M., Bildsoe, H., Sahores, M., Hughes, S.
M. and Salinas, P. C. (2008). Wnt signaling promotes AChR aggregation at the
neuromuscular synapse in collaboration with agrin. Proc. Natl. Acad. Sci. USA
Herman, M. A., Vassilieva, L. L., Horvitz, H. R., Shaw, J. E. and Herman, R. K.
(1995). The C. elegans gene lin-44, which controls the polarity of certain
asymmetric cell divisions, encodes a Wnt protein and acts cell nonautonomously.
Cell 83, 101-110.
Hestrin, S. and Galarreta, M. (2005). Electrical synapses define networks of
neocortical GABAergic neurons. Trends Neurosci. 28, 304-309.
Hilliard, M. A. and Bargmann, C. I. (2006). Wnt signals and frizzled activity
orient anterior-posterior axon outgrowth in C. elegans. Dev. Cell 10, 379-390.
Inaki, M., Yoshikawa, S., Thomas, J. B., Aburatani, H. and Nose, A. (2007).
Wnt4 is a local repulsive cue that determines synaptic target specificity. Curr.
Biol. 17, 1574-1579.
Inoue, T., Oz, H. S., Wiland, D., Gharib, S., Deshpande, R., Hill, R. J., Katz, W.
S. and Sternberg, P. W. (2004). C. elegans LIN-18 is a Ryk ortholog and
functions in parallel to LIN-17/Frizzled in Wnt signaling. Cell 118, 795-806.
Jing, L., Lefebvre, J. L., Gordon, L. R. and Granato, M. (2009). Wnt signals
organize synaptic prepattern and axon guidance through the zebrafish
unplugged/MuSK receptor. Neuron 61, 721-733.
Klassen, M. P. and Shen, K. (2007). Wnt signaling positions neuromuscular
connectivity by inhibiting synapse formation in C. elegans. Cell 130, 704-716.
Korswagen, H. C., Herman, M. A. and Clevers, H. C. (2000). Distinct beta-
catenins mediate adhesion and signalling functions in C. elegans. Nature 406,
Korswagen, H. C., Coudreuse, D. Y., Betist, M. C., van de Water, S., Zivkovic,
D. and Clevers, H. C. (2002). The Axin-like protein PRY-1 is a negative
regulator of a canonical Wnt pathway in C. elegans. Genes Dev. 16, 1291-1302.
Li, W. C., Roberts, A. and Soffe, S. R. (2009). Locomotor rhythm maintenance:
electrical coupling among premotor excitatory interneurons in the brainstem and
spinal cord of young Xenopus tadpoles. J. Physiol. 587, 1677-1693.
Liu, Y., Shi, J., Lu, C. C., Wang, Z. B., Lyuksyutova, A. I., Song, X. J. and Zou,
Y. (2005). Ryk-mediated Wnt repulsion regulates posterior-directed growth of
corticospinal tract. Nat. Neurosci. 8, 1151-1159.
Lyuksyutova, A. I., Lu, C. C., Milanesio, N., King, L. A., Guo, N., Wang, Y.,
Nathans, J., Tessier-Lavigne, M. and Zou, Y. (2003). Anterior-posterior
guidance of commissural axons by Wnt-frizzled signaling. Science 302, 1984-
Maloof, J. N. and Kenyon, C. (1998). The Hox gene lin-39 is required during C.
elegans vulval induction to select the outcome of Ras signaling. Development
Maro, G. S., Klassen, M. P. and Shen, K. (2009). A beta-catenin-dependent Wnt
pathway mediates anteroposterior axon guidance in C. elegans motor neurons.
PLoS ONE 4, e4690.
McColl, G., Killilea, D. W., Hubbard, A. E., Vantipalli, M. C., Melov, S. and
Lithgow, G. J. (2008). Pharmacogenetic analysis of lithium-induced delayed
aging in Caenorhabditis elegans. J. Biol. Chem. 283, 350-357.
Miech, C., Pauer, H. U., He, X. and Schwarz, T. L. (2008). Presynaptic local
signaling by a canonical wingless pathway regulates development of the
Drosophila neuromuscular junction. J. Neurosci. 28, 10875-10884.
Miller, D. and Niemeyer, C. (1995). Expression of the unc-4 homeoprotein in
Caenorhabditis elegans motor neurons specifies presynaptic input. Development
Miller, D., Shen, M., Shamu, C., Burglin, T., Ruvkun, G., Dubois, M., Ghee, M.
and Wilson, L. (1992). C. elegans unc-4 gene encodes a homeodomain protein
that determines the pattern of synaptic input to specific motor neurons. Nature
Packard, M., Koo, E. S., Gorczyca, M., Sharpe, J., Cumberledge, S. and
Budnik, V. (2002). The Drosophila Wnt, wingless, provides an essential signal
for pre- and postsynaptic differentiation. Cell 111, 319-330.
Pan, C. L., Howell, J. E., Clark, S. G., Hilliard, M., Cordes, S., Bargmann, C. I.
and Garriga, G. (2006). Multiple Wnts and frizzled receptors regulate anteriorly
directed cell and growth cone migrations in Caenorhabditis elegans. Dev. Cell
Pecho-Vrieseling, E., Sigrist, M., Yoshida, Y., Jessell, T. M. and Arber, S.
(2009). Specificity of sensory-motor connections encoded by Sema3e-Plxnd1
recognition. Nature 459, 842-846.
Pflugrad, A., Meir, J. Y., Barnes, T. M. and Miller, D. M., 3rd (1997). The
Groucho-like transcription factor UNC-37 functions with the neural specificity
gene unc-4 to govern motor neuron identity in C. elegans. Development 124,
Purro, S. A., Ciani, L., Hoyos-Flight, M., Stamatakou, E., Siomou, E. and
Salinas, P. C. (2008). Wnt regulates axon behavior through changes in
microtubule growth directionality: a new role for adenomatous polyposis coli. J.
Neurosci. 28, 8644-8654.
Wnt pathways control synaptic choice
Raj, A., van den Bogaard, P., Rifkin, S. A., van Oudenaarden, A. and Tyagi, S.
(2008). Imaging individual mRNA molecules using multiple singly labeled probes.
Nat. Methods 5, 877-879.
Rash, J. E., Staines, W. A., Yasumura, T., Patel, D., Furman, C. S., Stelmack, G.
L. and Nagy, J. I. (2000). Immunogold evidence that neuronal gap junctions in
adult rat brain and spinal cord contain connexin-36 but not connexin-32 or
connexin-43. Proc. Natl. Acad. Sci. USA 97, 7573-7578.
Sahores, M., Gibb, A. and Salinas, P. C. (2010). Frizzled-5, a receptor for the
synaptic organizer Wnt7a, regulates activity-mediated synaptogenesis.
Development 137, 2215-2225.
Sanes, J. R. and Yamagata, M. (2009). Many paths to synaptic specificity. Annu.
Rev. Cell Dev. Biol. 25, 161-195.
Sawa, H., Lobel, L. and Horvitz, H. R. (1996). The Caenorhabditis elegans gene
lin-17, which is required for certain asymmetric cell divisions, encodes a putative
seven-transmembrane protein similar to the Drosophila frizzled protein. Genes
Dev. 10, 2189-2197.
Shen, K. and Scheiffele, P. (2010). Genetics and cell biology of building specific
synaptic connectivity. Ann. Rev. Neurosci. 33, 473-507.
Shirasaki, R. and Pfaff, S. L. (2002). Transcriptional codes and the control of
neuronal identity. Ann. Rev. Neurosci. 25, 251-281.
Song, S., Zhang, B., Sun, H., Li, X., Xiang, Y., Liu, Z., Huang, X. and Ding, M.
(2010). A Wnt-Frz/Ror-Dsh pathway regulates neurite outgrowth in
Caenorhabditis elegans. PLoS Genet. 6, e1001056.
Starich, T. A., Xu, J., Skerrett, I. M., Nicholson, B. J. and Shaw, J. E. (2009).
Interactions between innexins UNC-7 and UNC-9 mediate electrical synapse
specificity in the Caenorhabditis elegans locomotory nervous system. Neural
Dev. 4, 16.
Tanizawa, Y., Kuhara, A., Inada, H., Kodama, E., Mizuno, T. and Mori, I.
(2006). Inositol monophosphatase regulates localization of synaptic components
and behavior in the mature nervous system of C. elegans. Genes Dev. 20, 3296-
Thaler, J., Harrison, K., Sharma, K., Lettieri, K., Kehrl, J. and Pfaff, S. L.
(1999). Active suppression of interneuron programs within developing motor
neurons revealed by analysis of homeodomain factor HB9. Neuron 23, 675-
Thorne, C. A., Hanson, A. J., Schneider, J., Tahinci, E., Orton, D., Cselenyi, C.
S., Jernigan, K. K., Meyers, K. C., Hang, B. I., Waterson, A. G. et al. (2010).
Small-molecule inhibition of Wnt signaling through activation of casein kinase
1alpha. Nat. Chem. Biol. 6, 829-836.
Thorpe, C. J., Schlesinger, A., Carter, J. C. and Bowerman, B. (1997). Wnt
signaling polarizes an early C. elegans blastomere to distinguish endoderm from
mesoderm. Cell 90, 695-705.
Van Der Giessen, R. S., Koekkoek, S. K., van Dorp, S., De Gruijl, J. R.,
Cupido, A., Khosrovani, S., Dortland, B., Wellershaus, K., Degen, J.,
Deuchars, J. et al. (2008). Role of olivary electrical coupling in cerebellar motor
learning. Neuron 58, 599-612.
Vashlishan, A. B., Madison, J. M., Dybbs, M., Bai, J., Sieburth, D., Ch’ng, Q.,
Tavazoie, M. and Kaplan, J. M. (2008). An RNAi screen identifies genes that
regulate GABA synapses. Neuron 58, 346-361.
Von Stetina, S., Watson, J., Fox, R., Olszewski, K., Spencer, W., Roy, P. and
Miller, D. (2007a). Cell-specific microarray profiling experiments reveal a
comprehensive picture of gene expression in the C. elegans nervous system.
Genome Biol. 8, R135.
Von Stetina, S. E., Fox, R. M., Watkins, K. L., Starich, T. A., Shaw, J. E. and
Miller, D. M., 3rd (2007b). UNC-4 represses CEH-12/HB9 to specify synaptic
inputs to VA motor neurons in C. elegans. Genes Dev. 21, 332-346.
Westerfield, M. and Frank, E. (1982). Specificity of electrical coupling among
neurons innervating forelimb muscles of the adult bullfrog. J. Neurophysiol. 48,
White, J., Southgate, E. and Thomson, J. (1992). Mutations in the
Caenorhabditis elegans unc-4 gene alter the synaptic input to ventral cord
motor neurons. Nature 355, 838-841.
White, J. G., Southgate, E., Thomson, J. N. and Brenner, S. (1986). The
structure of the nervous system of the nematode Caenorhabditis elegans. Philos.
Trans. R. Soc. Lond. B 314, 1-340.
Winnier, A. R., Meir, J. Y., Ross, J. M., Tavernarakis, N., Driscoll, M., Ishihara,
T., Katsura, I. and Miller, D. M., 3rd (1999). UNC-4/UNC-37-dependent
repression of motor neuron-specific genes controls synaptic choice in
Caenorhabditis elegans. Genes Dev. 13, 2774-2786.
Zinovyeva, A. Y. and Forrester, W. C. (2005). The C. elegans Frizzled CFZ-2 is
required for cell migration and interacts with multiple Wnt signaling pathways.
Dev. Biol. 285, 447-461.
Zinovyeva, A. Y., Yamamoto, Y., Sawa, H. and Forrester, W. C. (2008).
Complex network of Wnt signaling regulates neuronal migrations during
Caenorhabditis elegans development. Genetics 179, 1357-1371.