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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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CAN neurons inhibit Wnt signaling in epidermal progenitors.(A) Pn.px stage animals showing syIs187 mCherry Wnt reporter activity. Scale bar is 20 µm. (B) Quantification of reporter data. Reporter activity was lower in P5.px–P7.px cells than in P3.px, P4.px, and P8.px cells, so data were collected using a higher brightness setting. p-Values were calculated using a two-tailed Fisher's exact test versus wild-type animals. (C and D) Location of egl-20/wnt- and cwn-1/wnt-expressing cells relative to epidermal cells in L3, Pn.px stage animals. Scale bar is 10 µm. (C) muIs49[Pegl-20::egl-20::gfp] transgenic animal. (D) dyEx10[Pcwn-1::DsRed2] transgenic animal. To simultaneously visualize neurons and muscle, images were taken in different focal planes, differentially colored either green or red, and merged. (E–H) Location of Wnt-producing cells relative to CAN neurons. Only one CAN cell body is visible. (G and H) Blow-up of (E) and (F), respectively. Scale bars are 50 µm (E and F) and 25 µm (G and H). Transgenic arrays were akEx906 (E and G) and akEx908 (F and H).
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pbio-1001465-g004: CAN neurons inhibit Wnt signaling in epidermal progenitors.(A) Pn.px stage animals showing syIs187 mCherry Wnt reporter activity. Scale bar is 20 µm. (B) Quantification of reporter data. Reporter activity was lower in P5.px–P7.px cells than in P3.px, P4.px, and P8.px cells, so data were collected using a higher brightness setting. p-Values were calculated using a two-tailed Fisher's exact test versus wild-type animals. (C and D) Location of egl-20/wnt- and cwn-1/wnt-expressing cells relative to epidermal cells in L3, Pn.px stage animals. Scale bar is 10 µm. (C) muIs49[Pegl-20::egl-20::gfp] transgenic animal. (D) dyEx10[Pcwn-1::DsRed2] transgenic animal. To simultaneously visualize neurons and muscle, images were taken in different focal planes, differentially colored either green or red, and merged. (E–H) Location of Wnt-producing cells relative to CAN neurons. Only one CAN cell body is visible. (G and H) Blow-up of (E) and (F), respectively. Scale bars are 50 µm (E and F) and 25 µm (G and H). Transgenic arrays were akEx906 (E and G) and akEx908 (F and H).

Mentions: Since our genetic and phenotypic analyses suggested the CANs inhibit Wnt activity, we directly examined whether CAN displacement might increase Wnt activity in epidermal progenitors [16]. An mCherry-based Wnt reporter has been described that specifically reflects Wnt signaling in epidermal progenitors beginning after their first division (Pn.px stage) and extending through their second division (Pn.pxx) (Figure 1D) [16]. In axin/pry-1 Wnt inhibitor mutants, both the frequency and intensity of reporter activity was increased in these cells (Figure S2A–S2C). Although vab-8(gm99) and vab-8(gm138) mutations did not increase Wnt reporter intensity as dramatically as an axin/pry-1 mutation, they did cause more animals to show reporter activity in P3.px, P4.px, P6.px, and P8.x progeny (Figure 4A and 4B). These data suggest that the CANs dampen Wnt signaling along much of the anterior–posterior axis, and that deregulation of this signaling might account for the epidermal patterning defects observed in vab-8 mutants.


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)

CAN neurons inhibit Wnt signaling in epidermal progenitors.(A) Pn.px stage animals showing syIs187 mCherry Wnt reporter activity. Scale bar is 20 µm. (B) Quantification of reporter data. Reporter activity was lower in P5.px–P7.px cells than in P3.px, P4.px, and P8.px cells, so data were collected using a higher brightness setting. p-Values were calculated using a two-tailed Fisher's exact test versus wild-type animals. (C and D) Location of egl-20/wnt- and cwn-1/wnt-expressing cells relative to epidermal cells in L3, Pn.px stage animals. Scale bar is 10 µm. (C) muIs49[Pegl-20::egl-20::gfp] transgenic animal. (D) dyEx10[Pcwn-1::DsRed2] transgenic animal. To simultaneously visualize neurons and muscle, images were taken in different focal planes, differentially colored either green or red, and merged. (E–H) Location of Wnt-producing cells relative to CAN neurons. Only one CAN cell body is visible. (G and H) Blow-up of (E) and (F), respectively. Scale bars are 50 µm (E and F) and 25 µm (G and H). Transgenic arrays were akEx906 (E and G) and akEx908 (F and H).
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3539944&req=5

pbio-1001465-g004: CAN neurons inhibit Wnt signaling in epidermal progenitors.(A) Pn.px stage animals showing syIs187 mCherry Wnt reporter activity. Scale bar is 20 µm. (B) Quantification of reporter data. Reporter activity was lower in P5.px–P7.px cells than in P3.px, P4.px, and P8.px cells, so data were collected using a higher brightness setting. p-Values were calculated using a two-tailed Fisher's exact test versus wild-type animals. (C and D) Location of egl-20/wnt- and cwn-1/wnt-expressing cells relative to epidermal cells in L3, Pn.px stage animals. Scale bar is 10 µm. (C) muIs49[Pegl-20::egl-20::gfp] transgenic animal. (D) dyEx10[Pcwn-1::DsRed2] transgenic animal. To simultaneously visualize neurons and muscle, images were taken in different focal planes, differentially colored either green or red, and merged. (E–H) Location of Wnt-producing cells relative to CAN neurons. Only one CAN cell body is visible. (G and H) Blow-up of (E) and (F), respectively. Scale bars are 50 µm (E and F) and 25 µm (G and H). Transgenic arrays were akEx906 (E and G) and akEx908 (F and H).
Mentions: Since our genetic and phenotypic analyses suggested the CANs inhibit Wnt activity, we directly examined whether CAN displacement might increase Wnt activity in epidermal progenitors [16]. An mCherry-based Wnt reporter has been described that specifically reflects Wnt signaling in epidermal progenitors beginning after their first division (Pn.px stage) and extending through their second division (Pn.pxx) (Figure 1D) [16]. In axin/pry-1 Wnt inhibitor mutants, both the frequency and intensity of reporter activity was increased in these cells (Figure S2A–S2C). Although vab-8(gm99) and vab-8(gm138) mutations did not increase Wnt reporter intensity as dramatically as an axin/pry-1 mutation, they did cause more animals to show reporter activity in P3.px, P4.px, P6.px, and P8.x progeny (Figure 4A and 4B). These data suggest that the CANs dampen Wnt signaling along much of the anterior–posterior axis, and that deregulation of this signaling might account for the epidermal patterning defects observed in vab-8 mutants.

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