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Neurons refine the Caenorhabditis elegans body plan by directing axial patterning by Wnts.

Modzelewska K, Lauritzen A, Hasenoeder S, Brown L, Georgiou J, Moghal N - PLoS Biol. (2013)

Bottom Line: Surprisingly, despite high levels of Ror expression in many other cells, these cells cannot substitute for the CAN axons in patterning the epidermis, nor can cells expressing a secreted Wnt inhibitor, SFRP-1.Thus, unmyelinated axon tracts are critical for patterning the C. elegans body.Our findings suggest that the evolution of neurons not only improved metazoans by increasing behavioral complexity, but also by expanding the diversity of developmental patterns generated by growth factors such as Wnts.

View Article: PubMed Central - PubMed

Affiliation: Department of Oncological Sciences, Huntsman Cancer Institute, University of Utah, Salt Lake City, Utah, USA.

ABSTRACT
Metazoans display remarkable conservation of gene families, including growth factors, yet somehow these genes are used in different ways to generate tremendous morphological diversity. While variations in the magnitude and spatio-temporal aspects of signaling by a growth factor can generate different body patterns, how these signaling variations are organized and coordinated during development is unclear. Basic body plans are organized by the end of gastrulation and are refined as limbs, organs, and nervous systems co-develop. Despite their proximity to developing tissues, neurons are primarily thought to act after development, on behavior. Here, we show that in Caenorhabditis elegans, the axonal projections of neurons regulate tissue progenitor responses to Wnts so that certain organs develop with the correct morphology at the right axial positions. We find that foreshortening of the posteriorly directed axons of the two canal-associated neurons (CANs) disrupts mid-body vulval morphology, and produces ectopic vulval tissue in the posterior epidermis, in a Wnt-dependent manner. We also provide evidence that suggests that the posterior CAN axons modulate the location and strength of Wnt signaling along the anterior-posterior axis by employing a Ror family Wnt receptor to bind posteriorly derived Wnts, and hence, refine their distributions. Surprisingly, despite high levels of Ror expression in many other cells, these cells cannot substitute for the CAN axons in patterning the epidermis, nor can cells expressing a secreted Wnt inhibitor, SFRP-1. Thus, unmyelinated axon tracts are critical for patterning the C. elegans body. Our findings suggest that the evolution of neurons not only improved metazoans by increasing behavioral complexity, but also by expanding the diversity of developmental patterns generated by growth factors such as Wnts.

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Ror/CAM-1 has negative and positive effects on vulval fate signaling.(A) Ror/CAM-1 is broadly expressed. L2 stage animal with the cwIs6 transgenic array, which expresses a rescuing Ror/CAM-1 translational fusion to GFP from the cam-1 promoter. Red arrows indicate axons of non-CAN neurons. Scale bar is 10 µm. (B) Ror/CAM-1 inhibits Wnt signaling in epidermal progenitors. Quantification of syIs187 Wnt reporter transgene activity in Pn.px stage ror/cam-1 mutants. Pn.px signals were scored as in Figure 4B. (C) Schematic description of ror/cam-1 mutations and the cam-1 transgenic mutant (ΔIntra) used in this study. Numbers indicate amino acid positions. Fz, Frizzled, Wnt-binding extracellular domain; TM, transmembrane domain. (D) Ror/CAM-1 inhibits P3.p from becoming a vulval progenitor in larvae, and helps restrict the Wnt-dependent P12 fate to only the P12 blast cell in embryos. Pegl-20::egl-20 is an integrated transgenic array that introduces extra functional copies of egl-20/wnt fused to gfp into the genome (see Figures S4 and S7). (E) Ror/CAM-1 is required for foreshortening of the posterior CAN axon to promote a vulval fate in the posterior P8.p progenitor. Model depicting negative and positive roles of Ror/CAM-1 on Wnt signaling in epidermal progenitors. p-Values were calculated using a two-tailed Fisher's exact test versus wild-type animals (B and D) or as otherwise indicated (E).
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pbio-1001465-g006: Ror/CAM-1 has negative and positive effects on vulval fate signaling.(A) Ror/CAM-1 is broadly expressed. L2 stage animal with the cwIs6 transgenic array, which expresses a rescuing Ror/CAM-1 translational fusion to GFP from the cam-1 promoter. Red arrows indicate axons of non-CAN neurons. Scale bar is 10 µm. (B) Ror/CAM-1 inhibits Wnt signaling in epidermal progenitors. Quantification of syIs187 Wnt reporter transgene activity in Pn.px stage ror/cam-1 mutants. Pn.px signals were scored as in Figure 4B. (C) Schematic description of ror/cam-1 mutations and the cam-1 transgenic mutant (ΔIntra) used in this study. Numbers indicate amino acid positions. Fz, Frizzled, Wnt-binding extracellular domain; TM, transmembrane domain. (D) Ror/CAM-1 inhibits P3.p from becoming a vulval progenitor in larvae, and helps restrict the Wnt-dependent P12 fate to only the P12 blast cell in embryos. Pegl-20::egl-20 is an integrated transgenic array that introduces extra functional copies of egl-20/wnt fused to gfp into the genome (see Figures S4 and S7). (E) Ror/CAM-1 is required for foreshortening of the posterior CAN axon to promote a vulval fate in the posterior P8.p progenitor. Model depicting negative and positive roles of Ror/CAM-1 on Wnt signaling in epidermal progenitors. p-Values were calculated using a two-tailed Fisher's exact test versus wild-type animals (B and D) or as otherwise indicated (E).

Mentions: The C. elegans genome encodes one diffusible Wnt antagonist, SFRP-1 [38]. However, SFRP-1 does not mediate the effects of the CANs on epidermal development: its expression is largely restricted to anterior body wall muscle [38], and unlike CAN-displacing vab-8 mutations, mutation of sfrp-1 did not suppress the underinduced phenotype of egfr/let-23(lf) mutants (Table 1), and did not cause a P-Rvl phenotype or ectopic vulval fates at P8.p (n = 166). However, the only other known extracellularly acting Wnt inhibitor in C. elegans, the transmembrane Wnt-binding Ror/CAM-1 tyrosine kinase, could mediate the effects of the CAN axons on Wnt signaling. Ror/CAM-1 is widely expressed in muscle, the vulval progenitors, and many neurons, including the CANs (Figure 6A) [7],[37],[44]–[46]. While in certain contexts, such as EGL-20/Wnt-mediated polarization of P7.p, it transduces Wnt signals [16], in other contexts such as inhibition of HSN migration, P3.p vulval progenitor cell specification, and the induction of vulval fates, it appears to antagonize Wnt signaling [7],[47]. Based on its ability to physically bind Wnts such as EGL-20 and CWN-1 (potential targets of vab-8 mutations), and to interfere with vulval fate signaling in the P6.p epidermal progenitor when overexpressed in non-epidermal cells, it has been proposed that Ror/CAM-1 inhibits Wnt signaling by sequestering Wnts away from Wnt-responding cells [7]. While this model is plausible, how such a broadly expressed antagonist might refine Wnt gradients to allow specific migratory and tissue patterns is unclear.


Neurons refine the Caenorhabditis elegans body plan by directing axial patterning by Wnts.

Modzelewska K, Lauritzen A, Hasenoeder S, Brown L, Georgiou J, Moghal N - PLoS Biol. (2013)

Ror/CAM-1 has negative and positive effects on vulval fate signaling.(A) Ror/CAM-1 is broadly expressed. L2 stage animal with the cwIs6 transgenic array, which expresses a rescuing Ror/CAM-1 translational fusion to GFP from the cam-1 promoter. Red arrows indicate axons of non-CAN neurons. Scale bar is 10 µm. (B) Ror/CAM-1 inhibits Wnt signaling in epidermal progenitors. Quantification of syIs187 Wnt reporter transgene activity in Pn.px stage ror/cam-1 mutants. Pn.px signals were scored as in Figure 4B. (C) Schematic description of ror/cam-1 mutations and the cam-1 transgenic mutant (ΔIntra) used in this study. Numbers indicate amino acid positions. Fz, Frizzled, Wnt-binding extracellular domain; TM, transmembrane domain. (D) Ror/CAM-1 inhibits P3.p from becoming a vulval progenitor in larvae, and helps restrict the Wnt-dependent P12 fate to only the P12 blast cell in embryos. Pegl-20::egl-20 is an integrated transgenic array that introduces extra functional copies of egl-20/wnt fused to gfp into the genome (see Figures S4 and S7). (E) Ror/CAM-1 is required for foreshortening of the posterior CAN axon to promote a vulval fate in the posterior P8.p progenitor. Model depicting negative and positive roles of Ror/CAM-1 on Wnt signaling in epidermal progenitors. p-Values were calculated using a two-tailed Fisher's exact test versus wild-type animals (B and D) or as otherwise indicated (E).
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC3539944&req=5

pbio-1001465-g006: Ror/CAM-1 has negative and positive effects on vulval fate signaling.(A) Ror/CAM-1 is broadly expressed. L2 stage animal with the cwIs6 transgenic array, which expresses a rescuing Ror/CAM-1 translational fusion to GFP from the cam-1 promoter. Red arrows indicate axons of non-CAN neurons. Scale bar is 10 µm. (B) Ror/CAM-1 inhibits Wnt signaling in epidermal progenitors. Quantification of syIs187 Wnt reporter transgene activity in Pn.px stage ror/cam-1 mutants. Pn.px signals were scored as in Figure 4B. (C) Schematic description of ror/cam-1 mutations and the cam-1 transgenic mutant (ΔIntra) used in this study. Numbers indicate amino acid positions. Fz, Frizzled, Wnt-binding extracellular domain; TM, transmembrane domain. (D) Ror/CAM-1 inhibits P3.p from becoming a vulval progenitor in larvae, and helps restrict the Wnt-dependent P12 fate to only the P12 blast cell in embryos. Pegl-20::egl-20 is an integrated transgenic array that introduces extra functional copies of egl-20/wnt fused to gfp into the genome (see Figures S4 and S7). (E) Ror/CAM-1 is required for foreshortening of the posterior CAN axon to promote a vulval fate in the posterior P8.p progenitor. Model depicting negative and positive roles of Ror/CAM-1 on Wnt signaling in epidermal progenitors. p-Values were calculated using a two-tailed Fisher's exact test versus wild-type animals (B and D) or as otherwise indicated (E).
Mentions: The C. elegans genome encodes one diffusible Wnt antagonist, SFRP-1 [38]. However, SFRP-1 does not mediate the effects of the CANs on epidermal development: its expression is largely restricted to anterior body wall muscle [38], and unlike CAN-displacing vab-8 mutations, mutation of sfrp-1 did not suppress the underinduced phenotype of egfr/let-23(lf) mutants (Table 1), and did not cause a P-Rvl phenotype or ectopic vulval fates at P8.p (n = 166). However, the only other known extracellularly acting Wnt inhibitor in C. elegans, the transmembrane Wnt-binding Ror/CAM-1 tyrosine kinase, could mediate the effects of the CAN axons on Wnt signaling. Ror/CAM-1 is widely expressed in muscle, the vulval progenitors, and many neurons, including the CANs (Figure 6A) [7],[37],[44]–[46]. While in certain contexts, such as EGL-20/Wnt-mediated polarization of P7.p, it transduces Wnt signals [16], in other contexts such as inhibition of HSN migration, P3.p vulval progenitor cell specification, and the induction of vulval fates, it appears to antagonize Wnt signaling [7],[47]. Based on its ability to physically bind Wnts such as EGL-20 and CWN-1 (potential targets of vab-8 mutations), and to interfere with vulval fate signaling in the P6.p epidermal progenitor when overexpressed in non-epidermal cells, it has been proposed that Ror/CAM-1 inhibits Wnt signaling by sequestering Wnts away from Wnt-responding cells [7]. While this model is plausible, how such a broadly expressed antagonist might refine Wnt gradients to allow specific migratory and tissue patterns is unclear.

Bottom Line: Surprisingly, despite high levels of Ror expression in many other cells, these cells cannot substitute for the CAN axons in patterning the epidermis, nor can cells expressing a secreted Wnt inhibitor, SFRP-1.Thus, unmyelinated axon tracts are critical for patterning the C. elegans body.Our findings suggest that the evolution of neurons not only improved metazoans by increasing behavioral complexity, but also by expanding the diversity of developmental patterns generated by growth factors such as Wnts.

View Article: PubMed Central - PubMed

Affiliation: Department of Oncological Sciences, Huntsman Cancer Institute, University of Utah, Salt Lake City, Utah, USA.

ABSTRACT
Metazoans display remarkable conservation of gene families, including growth factors, yet somehow these genes are used in different ways to generate tremendous morphological diversity. While variations in the magnitude and spatio-temporal aspects of signaling by a growth factor can generate different body patterns, how these signaling variations are organized and coordinated during development is unclear. Basic body plans are organized by the end of gastrulation and are refined as limbs, organs, and nervous systems co-develop. Despite their proximity to developing tissues, neurons are primarily thought to act after development, on behavior. Here, we show that in Caenorhabditis elegans, the axonal projections of neurons regulate tissue progenitor responses to Wnts so that certain organs develop with the correct morphology at the right axial positions. We find that foreshortening of the posteriorly directed axons of the two canal-associated neurons (CANs) disrupts mid-body vulval morphology, and produces ectopic vulval tissue in the posterior epidermis, in a Wnt-dependent manner. We also provide evidence that suggests that the posterior CAN axons modulate the location and strength of Wnt signaling along the anterior-posterior axis by employing a Ror family Wnt receptor to bind posteriorly derived Wnts, and hence, refine their distributions. Surprisingly, despite high levels of Ror expression in many other cells, these cells cannot substitute for the CAN axons in patterning the epidermis, nor can cells expressing a secreted Wnt inhibitor, SFRP-1. Thus, unmyelinated axon tracts are critical for patterning the C. elegans body. Our findings suggest that the evolution of neurons not only improved metazoans by increasing behavioral complexity, but also by expanding the diversity of developmental patterns generated by growth factors such as Wnts.

Show MeSH
Related in: MedlinePlus