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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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The CANs use the extracellular Wnt-binding domain of Ror/CAM-1 to direct epidermal patterning.(A and B) Distributions of positions of CAN cell bodies and furthest posterior CAN axon termini in ror/cam-1 mutants and in cam-1 mutants expressing wild-type or intracellular-domain-deleted CAM-1(ΔIntra) only in the CANs. In non-ror/cam-1 rescue experiments, CANs were visualized with the kyIs4[Pceh-23::gfp] transgene. In ror/cam-1 rescue experiments, CANs were visualized by expression of GFP-tagged Ror/CAM-1 in the CANs. In ror/cam-1 rescue experiments, strains also harbored an egf/lin-3(lf) mutation. x-Axis indicates Pn.p or Pn.px positions. H, head/pharyngeal region. p-Values were calculated using a two-tailed Mann-Whitney U test. (C) Ror/CAM-1 inhibits vulval fate signaling in central vulval progenitors. (D) Transgenic CAN-specific expression of Ror/CAM-1::GFP restores inhibition of vulval development in ror/cam-1 mutants. (E) Transgenic CAN-specific expression of a Ror/CAM-1::GFP mutant lacking the intracellular domain (ΔIntra, see Figure 6C) also restores inhibition of vulval development in ror/cam-1 mutants. In (D) and (E), scale bar is 20 µm. (F) Under physiologic conditions, the majority of Ror/CAM-1 inhibition of vulval fate signaling is mediated by the CANs. If the CAN cell bodies are anteriorly displaced and the posterior axons are severely foreshortened, loss of Ror/CAM-1 activity from all cells does not further increase P3.p progenitor frequency or the amount of vulval development in sensitized backgrounds. Drawings depict the cellular distribution of Ror/CAM-1 as described in Figure 6E. M, muscle cells; N, neurons; P, vulval progenitors. In (C–E), vulval fates: number of vulval progenitor cells adopting vulval fates. Wild-type is 3.00. p-Values were calculated using a two-tailed Student's t test. The PCAN::cam-1::gfp and PCAN::ΔIntra::gfp rescuing transgenic arrays are dyEx44 and dyEx45, respectively.
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pbio-1001465-g007: The CANs use the extracellular Wnt-binding domain of Ror/CAM-1 to direct epidermal patterning.(A and B) Distributions of positions of CAN cell bodies and furthest posterior CAN axon termini in ror/cam-1 mutants and in cam-1 mutants expressing wild-type or intracellular-domain-deleted CAM-1(ΔIntra) only in the CANs. In non-ror/cam-1 rescue experiments, CANs were visualized with the kyIs4[Pceh-23::gfp] transgene. In ror/cam-1 rescue experiments, CANs were visualized by expression of GFP-tagged Ror/CAM-1 in the CANs. In ror/cam-1 rescue experiments, strains also harbored an egf/lin-3(lf) mutation. x-Axis indicates Pn.p or Pn.px positions. H, head/pharyngeal region. p-Values were calculated using a two-tailed Mann-Whitney U test. (C) Ror/CAM-1 inhibits vulval fate signaling in central vulval progenitors. (D) Transgenic CAN-specific expression of Ror/CAM-1::GFP restores inhibition of vulval development in ror/cam-1 mutants. (E) Transgenic CAN-specific expression of a Ror/CAM-1::GFP mutant lacking the intracellular domain (ΔIntra, see Figure 6C) also restores inhibition of vulval development in ror/cam-1 mutants. In (D) and (E), scale bar is 20 µm. (F) Under physiologic conditions, the majority of Ror/CAM-1 inhibition of vulval fate signaling is mediated by the CANs. If the CAN cell bodies are anteriorly displaced and the posterior axons are severely foreshortened, loss of Ror/CAM-1 activity from all cells does not further increase P3.p progenitor frequency or the amount of vulval development in sensitized backgrounds. Drawings depict the cellular distribution of Ror/CAM-1 as described in Figure 6E. M, muscle cells; N, neurons; P, vulval progenitors. In (C–E), vulval fates: number of vulval progenitor cells adopting vulval fates. Wild-type is 3.00. p-Values were calculated using a two-tailed Student's t test. The PCAN::cam-1::gfp and PCAN::ΔIntra::gfp rescuing transgenic arrays are dyEx44 and dyEx45, respectively.

Mentions: Since Ror/CAM-1 has been reported to affect CAN cell body positioning and axon outgrowth [35], we evaluated whether cam-1 mutations might increase posteriorly derived Wnt signaling by affecting the location of the CANs and their axon termini. As has been previously reported, we found that ror/cam-1 mutations caused anterior displacement of the CAN cell bodies that was as severe as that caused by ceh-10 mutation [35] (Figures 5A and 7A). However, since ceh-10 mutants do not have as strong Wnt phenotypes as ror/cam-1 mutants, the CAN cell body displacement in cam-1 mutants cannot explain their increased Wnt signaling. Also, in ror/cam-1 mutants, outgrowth of the posterior CAN axon was only mildly affected, with the median end point being even more posterior than in vab-8(ev411) and ceh-10(lf) mutants that have no or weaker Wnt phenotypes (Figures 5B and 7B). Thus, Ror/CAM-1 does not inhibit Wnt signaling by regulating posterior CAN axon outgrowth, but could mediate an inhibitory effect of the extended axons.


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)

The CANs use the extracellular Wnt-binding domain of Ror/CAM-1 to direct epidermal patterning.(A and B) Distributions of positions of CAN cell bodies and furthest posterior CAN axon termini in ror/cam-1 mutants and in cam-1 mutants expressing wild-type or intracellular-domain-deleted CAM-1(ΔIntra) only in the CANs. In non-ror/cam-1 rescue experiments, CANs were visualized with the kyIs4[Pceh-23::gfp] transgene. In ror/cam-1 rescue experiments, CANs were visualized by expression of GFP-tagged Ror/CAM-1 in the CANs. In ror/cam-1 rescue experiments, strains also harbored an egf/lin-3(lf) mutation. x-Axis indicates Pn.p or Pn.px positions. H, head/pharyngeal region. p-Values were calculated using a two-tailed Mann-Whitney U test. (C) Ror/CAM-1 inhibits vulval fate signaling in central vulval progenitors. (D) Transgenic CAN-specific expression of Ror/CAM-1::GFP restores inhibition of vulval development in ror/cam-1 mutants. (E) Transgenic CAN-specific expression of a Ror/CAM-1::GFP mutant lacking the intracellular domain (ΔIntra, see Figure 6C) also restores inhibition of vulval development in ror/cam-1 mutants. In (D) and (E), scale bar is 20 µm. (F) Under physiologic conditions, the majority of Ror/CAM-1 inhibition of vulval fate signaling is mediated by the CANs. If the CAN cell bodies are anteriorly displaced and the posterior axons are severely foreshortened, loss of Ror/CAM-1 activity from all cells does not further increase P3.p progenitor frequency or the amount of vulval development in sensitized backgrounds. Drawings depict the cellular distribution of Ror/CAM-1 as described in Figure 6E. M, muscle cells; N, neurons; P, vulval progenitors. In (C–E), vulval fates: number of vulval progenitor cells adopting vulval fates. Wild-type is 3.00. p-Values were calculated using a two-tailed Student's t test. The PCAN::cam-1::gfp and PCAN::ΔIntra::gfp rescuing transgenic arrays are dyEx44 and dyEx45, respectively.
© Copyright Policy
Related In: Results  -  Collection

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

pbio-1001465-g007: The CANs use the extracellular Wnt-binding domain of Ror/CAM-1 to direct epidermal patterning.(A and B) Distributions of positions of CAN cell bodies and furthest posterior CAN axon termini in ror/cam-1 mutants and in cam-1 mutants expressing wild-type or intracellular-domain-deleted CAM-1(ΔIntra) only in the CANs. In non-ror/cam-1 rescue experiments, CANs were visualized with the kyIs4[Pceh-23::gfp] transgene. In ror/cam-1 rescue experiments, CANs were visualized by expression of GFP-tagged Ror/CAM-1 in the CANs. In ror/cam-1 rescue experiments, strains also harbored an egf/lin-3(lf) mutation. x-Axis indicates Pn.p or Pn.px positions. H, head/pharyngeal region. p-Values were calculated using a two-tailed Mann-Whitney U test. (C) Ror/CAM-1 inhibits vulval fate signaling in central vulval progenitors. (D) Transgenic CAN-specific expression of Ror/CAM-1::GFP restores inhibition of vulval development in ror/cam-1 mutants. (E) Transgenic CAN-specific expression of a Ror/CAM-1::GFP mutant lacking the intracellular domain (ΔIntra, see Figure 6C) also restores inhibition of vulval development in ror/cam-1 mutants. In (D) and (E), scale bar is 20 µm. (F) Under physiologic conditions, the majority of Ror/CAM-1 inhibition of vulval fate signaling is mediated by the CANs. If the CAN cell bodies are anteriorly displaced and the posterior axons are severely foreshortened, loss of Ror/CAM-1 activity from all cells does not further increase P3.p progenitor frequency or the amount of vulval development in sensitized backgrounds. Drawings depict the cellular distribution of Ror/CAM-1 as described in Figure 6E. M, muscle cells; N, neurons; P, vulval progenitors. In (C–E), vulval fates: number of vulval progenitor cells adopting vulval fates. Wild-type is 3.00. p-Values were calculated using a two-tailed Student's t test. The PCAN::cam-1::gfp and PCAN::ΔIntra::gfp rescuing transgenic arrays are dyEx44 and dyEx45, respectively.
Mentions: Since Ror/CAM-1 has been reported to affect CAN cell body positioning and axon outgrowth [35], we evaluated whether cam-1 mutations might increase posteriorly derived Wnt signaling by affecting the location of the CANs and their axon termini. As has been previously reported, we found that ror/cam-1 mutations caused anterior displacement of the CAN cell bodies that was as severe as that caused by ceh-10 mutation [35] (Figures 5A and 7A). However, since ceh-10 mutants do not have as strong Wnt phenotypes as ror/cam-1 mutants, the CAN cell body displacement in cam-1 mutants cannot explain their increased Wnt signaling. Also, in ror/cam-1 mutants, outgrowth of the posterior CAN axon was only mildly affected, with the median end point being even more posterior than in vab-8(ev411) and ceh-10(lf) mutants that have no or weaker Wnt phenotypes (Figures 5B and 7B). Thus, Ror/CAM-1 does not inhibit Wnt signaling by regulating posterior CAN axon outgrowth, but could mediate an inhibitory effect of the extended axons.

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