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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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Posterior CAN axons regulate axial positioning of vulval fates and P3.p vulval progenitor frequency.Distributions of positions of CAN cell bodies (A) and furthest posterior CAN axon termini (B) in different mutants. CAN neurons were visualized in L3, Pn.px stage (A and B) or L4 stage (E) animals with the kyIs4[Pceh-23::gfp] transgene. x-Axis indicates Pn.p or Pn.px positions. p-Value was calculated using a two-tailed Mann-Whitney U test. (C) Position of CAN cell bodies and posterior axon termini relative to egl-20/wnt-expressing cells in L2 stage vab-8 mutants. CANs and egl-20/wnt-expressing cells were marked with the akEx906 transgenic array. The bright green signal in the head/pharynx is from the coinjected Pmyo-2::cfp injection marker. Scale bar is 25 µm. (D) Frequency with which P8.p adopts a vulval fate in the total ceh-10 mutant population. (E) Correlation between the position of the furthest posterior CAN axon terminus and induction of ectopic vulval fates at P8.p in ceh-10(lf) mutants. For this study, an emphasis was placed on picking smaller animals to ensure that sufficient numbers of animals with short posterior CAN axons were obtained for statistical analysis. Thus, the combined frequency of ectopic vulval fates in this study is not an estimate of the actual frequency in the total population as conducted in (D). Top panels show animal 52, with normal epidermal development and normal position of furthest posterior CAN axon terminus. Bottom panels show animal 79, with an R-Pvl phenotype at P7.p and ectopic vulval fate at P8.p, and severely foreshortened furthest posterior CAN axon terminus. Scale bars are 10 µm. (F) Correlation between position of furthest posterior CAN axon terminus and frequency with which P3.p becomes a vulval progenitor in ceh-10(lf) mutants. In (D–F), p-Values were calculated using a two-tailed Fisher's exact test versus wild-type animals (D) or as otherwise indicated (E and F). H, head/pharyngeal region.
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pbio-1001465-g005: Posterior CAN axons regulate axial positioning of vulval fates and P3.p vulval progenitor frequency.Distributions of positions of CAN cell bodies (A) and furthest posterior CAN axon termini (B) in different mutants. CAN neurons were visualized in L3, Pn.px stage (A and B) or L4 stage (E) animals with the kyIs4[Pceh-23::gfp] transgene. x-Axis indicates Pn.p or Pn.px positions. p-Value was calculated using a two-tailed Mann-Whitney U test. (C) Position of CAN cell bodies and posterior axon termini relative to egl-20/wnt-expressing cells in L2 stage vab-8 mutants. CANs and egl-20/wnt-expressing cells were marked with the akEx906 transgenic array. The bright green signal in the head/pharynx is from the coinjected Pmyo-2::cfp injection marker. Scale bar is 25 µm. (D) Frequency with which P8.p adopts a vulval fate in the total ceh-10 mutant population. (E) Correlation between the position of the furthest posterior CAN axon terminus and induction of ectopic vulval fates at P8.p in ceh-10(lf) mutants. For this study, an emphasis was placed on picking smaller animals to ensure that sufficient numbers of animals with short posterior CAN axons were obtained for statistical analysis. Thus, the combined frequency of ectopic vulval fates in this study is not an estimate of the actual frequency in the total population as conducted in (D). Top panels show animal 52, with normal epidermal development and normal position of furthest posterior CAN axon terminus. Bottom panels show animal 79, with an R-Pvl phenotype at P7.p and ectopic vulval fate at P8.p, and severely foreshortened furthest posterior CAN axon terminus. Scale bars are 10 µm. (F) Correlation between position of furthest posterior CAN axon terminus and frequency with which P3.p becomes a vulval progenitor in ceh-10(lf) mutants. In (D–F), p-Values were calculated using a two-tailed Fisher's exact test versus wild-type animals (D) or as otherwise indicated (E and F). H, head/pharyngeal region.

Mentions: While in wild-type animals the median CAN cell body position along the anterior–posterior axis was near the P5.px progeny, and most posterior CAN axons terminated near P11.p and the EGL-20/Wnt-producing rectal cells (Figures 4E, 4G, 5A, and 5B), in vab-8(gm138) mutants, both the CAN cell bodies and posterior axon termini were severely displaced anteriorly (Figure 5A–5C). Given the normal proximity of the posterior CAN axon terminus to the EGL-20/Wnt-producing cells, the axons may secrete a short-range signal that inhibits EGL-20 production. However, severe mutation of vab-8 did not increase egl-20/wnt RNA levels (Figure S7), and the vab-8(ev411) mutation, which mildly shifted the posterior CAN axon terminus away from the EGL-20/Wnt-producing cells (Figure 5B and 5C), did not cause epidermal phenotypes (Figure 2A and 2B; Table 1).


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)

Posterior CAN axons regulate axial positioning of vulval fates and P3.p vulval progenitor frequency.Distributions of positions of CAN cell bodies (A) and furthest posterior CAN axon termini (B) in different mutants. CAN neurons were visualized in L3, Pn.px stage (A and B) or L4 stage (E) animals with the kyIs4[Pceh-23::gfp] transgene. x-Axis indicates Pn.p or Pn.px positions. p-Value was calculated using a two-tailed Mann-Whitney U test. (C) Position of CAN cell bodies and posterior axon termini relative to egl-20/wnt-expressing cells in L2 stage vab-8 mutants. CANs and egl-20/wnt-expressing cells were marked with the akEx906 transgenic array. The bright green signal in the head/pharynx is from the coinjected Pmyo-2::cfp injection marker. Scale bar is 25 µm. (D) Frequency with which P8.p adopts a vulval fate in the total ceh-10 mutant population. (E) Correlation between the position of the furthest posterior CAN axon terminus and induction of ectopic vulval fates at P8.p in ceh-10(lf) mutants. For this study, an emphasis was placed on picking smaller animals to ensure that sufficient numbers of animals with short posterior CAN axons were obtained for statistical analysis. Thus, the combined frequency of ectopic vulval fates in this study is not an estimate of the actual frequency in the total population as conducted in (D). Top panels show animal 52, with normal epidermal development and normal position of furthest posterior CAN axon terminus. Bottom panels show animal 79, with an R-Pvl phenotype at P7.p and ectopic vulval fate at P8.p, and severely foreshortened furthest posterior CAN axon terminus. Scale bars are 10 µm. (F) Correlation between position of furthest posterior CAN axon terminus and frequency with which P3.p becomes a vulval progenitor in ceh-10(lf) mutants. In (D–F), p-Values were calculated using a two-tailed Fisher's exact test versus wild-type animals (D) or as otherwise indicated (E and F). H, head/pharyngeal region.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3539944&req=5

pbio-1001465-g005: Posterior CAN axons regulate axial positioning of vulval fates and P3.p vulval progenitor frequency.Distributions of positions of CAN cell bodies (A) and furthest posterior CAN axon termini (B) in different mutants. CAN neurons were visualized in L3, Pn.px stage (A and B) or L4 stage (E) animals with the kyIs4[Pceh-23::gfp] transgene. x-Axis indicates Pn.p or Pn.px positions. p-Value was calculated using a two-tailed Mann-Whitney U test. (C) Position of CAN cell bodies and posterior axon termini relative to egl-20/wnt-expressing cells in L2 stage vab-8 mutants. CANs and egl-20/wnt-expressing cells were marked with the akEx906 transgenic array. The bright green signal in the head/pharynx is from the coinjected Pmyo-2::cfp injection marker. Scale bar is 25 µm. (D) Frequency with which P8.p adopts a vulval fate in the total ceh-10 mutant population. (E) Correlation between the position of the furthest posterior CAN axon terminus and induction of ectopic vulval fates at P8.p in ceh-10(lf) mutants. For this study, an emphasis was placed on picking smaller animals to ensure that sufficient numbers of animals with short posterior CAN axons were obtained for statistical analysis. Thus, the combined frequency of ectopic vulval fates in this study is not an estimate of the actual frequency in the total population as conducted in (D). Top panels show animal 52, with normal epidermal development and normal position of furthest posterior CAN axon terminus. Bottom panels show animal 79, with an R-Pvl phenotype at P7.p and ectopic vulval fate at P8.p, and severely foreshortened furthest posterior CAN axon terminus. Scale bars are 10 µm. (F) Correlation between position of furthest posterior CAN axon terminus and frequency with which P3.p becomes a vulval progenitor in ceh-10(lf) mutants. In (D–F), p-Values were calculated using a two-tailed Fisher's exact test versus wild-type animals (D) or as otherwise indicated (E and F). H, head/pharyngeal region.
Mentions: While in wild-type animals the median CAN cell body position along the anterior–posterior axis was near the P5.px progeny, and most posterior CAN axons terminated near P11.p and the EGL-20/Wnt-producing rectal cells (Figures 4E, 4G, 5A, and 5B), in vab-8(gm138) mutants, both the CAN cell bodies and posterior axon termini were severely displaced anteriorly (Figure 5A–5C). Given the normal proximity of the posterior CAN axon terminus to the EGL-20/Wnt-producing cells, the axons may secrete a short-range signal that inhibits EGL-20 production. However, severe mutation of vab-8 did not increase egl-20/wnt RNA levels (Figure S7), and the vab-8(ev411) mutation, which mildly shifted the posterior CAN axon terminus away from the EGL-20/Wnt-producing cells (Figure 5B and 5C), did not cause epidermal phenotypes (Figure 2A and 2B; Table 1).

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