Skip to main page content
Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2016 Jun 21;6:28071.
doi: 10.1038/srep28071.

Evolution of the EGFR Pathway in Metazoa and Its Diversification in the Planarian Schmidtea Mediterranea

Affiliations
Free PMC article

Evolution of the EGFR Pathway in Metazoa and Its Diversification in the Planarian Schmidtea Mediterranea

Sara Barberán et al. Sci Rep. .
Free PMC article

Abstract

The EGFR pathway is an essential signaling system in animals, whose core components are the epidermal growth factors (EGF ligands) and their trans-membrane tyrosine kinase receptors (EGFRs). Despite extensive knowledge in classical model organisms, little is known of the composition and function of the EGFR pathway in most animal lineages. Here, we have performed an extensive search for the presence of EGFRs and EGF ligands in representative species of most major animal clades, with special focus on the planarian Schmidtea mediterranea. With the exception of placozoans and cnidarians, we found that the EGFR pathway is potentially present in all other analyzed animal groups, and has experienced frequent independent expansions. We further characterized the expression domains of the EGFR/EGF identified in S. mediterranea, revealing a wide variety of patterns and localization in almost all planarian tissues. Finally, functional experiments suggest an interaction between one of the previously described receptors, Smed-egfr-5, and the newly found ligand Smed-egf-6. Our findings provide the most comprehensive overview to date of the EGFR pathway, and indicate that the last common metazoan ancestor had an initial complement of one EGFR and one putative EGF ligand, which was often expanded or lost during animal evolution.

Figures

Figure 1
Figure 1. Maximum likelihood (ML) phylogenetic tree of representative EGFRs as obtained by RAxML.
The tree was rooted with the EGFR-related tyrosine kinases SHARK and ZAP-70. The model of protein evolution used was LG + G + I. Nodal support was obtained by RAxML 1000 replicates (bootstrap value [BV]) and Bayesian posterior probabilities (PP). Both values are shown for key branches. A blue dot at the node indicates BV > 95% and PP > 0.95. Fast evolving sequences, such as those of the planarian S. mediterranea, were not included in this analysis (for the entire dataset, see Additional file 1: Figure S1). The archetypical domain architecture of an EGFR is shown on the left.
Figure 2
Figure 2. Maximum likelihood (ML) phylogenetic tree of flatworm EGFRs as obtained by RAxML.
(A) The tree was rooted with the EGFRs of representative spiralian taxa. The model of protein evolution used was LG + G + I. Nodal support was obtained by RAxML 550 replicates (bootstrap value [BV]) and Bayesian posterior probabilities (PP). Both values are shown in key branches. A blue dot in the node indicates BV > 95% and PP > 0.95. Planarian sequences are highlighted in red. (B) Schematic representation of the domain architecture of each S. mediterranea EGFR, drawn to scale.
Figure 3
Figure 3. Expression patterns of planarian EGFRs.
(A) Whole-mount in situ hybridizations of all planarian EGFRs on intact adult specimens of S. mediterranea, grouped according to their phylogenetic relationship. See main text for details of the expression patterns. (B) Schematic summary of the expression patterns of planarian EGFRs and the phenotype observed after their silencing by dsRNA injection, a dash indicates no phenotype was observed (see references for further details). In (A), anterior is to the left. ph: pharynx. Scale bars: 500 μm in all panels.
Figure 4
Figure 4. Maximum likelihood (ML) phylogenetic tree of the putative EGF ligands as obtained by RAxML.
(A) Unrooted tree of the EGF-type of EGF ligands, using the Whelan and Goldman (WAG) + G model of protein evolution. Nodal support was obtained by RAxML 500 replicates (bootstrap value [BV]) and Bayesian posterior probabilities (PP). (B) Unrooted tree of the NRG-type of EGF ligands, using the LG + G model of protein evolution. Nodal support was obtained by RAxML 1000 replicates (BV) and Bayesian posterior probabilities (PP). Fast evolving sequences, such as those of the planarian S. mediterranea, were not included in these analyses (for the entire dataset, see Additional files 4, 5: Figure S4, S5). The archetypal domain architectures of the EGF-type and NRG-type of ligands are shown on the left.
Figure 5
Figure 5. Maximum likelihood (ML) phylogenetic tree of the putative flatworm EGF ligands as obtained by RAxML.
(A) Unrooted tree of the EGF-type of EGF ligands, using the Whelan and Goldman (WAG) + G model of protein evolution. Nodal support was obtained by RAxML 900 replicates (bootstrap value [BV]) and Bayesian posterior probabilities (PP). (B) Unrooted tree of the NRG-type of EGF ligands, using the LG + G model of protein evolution. Nodal support was obtained by RAxML 450 replicates (BV) and Bayesian posterior probabilities (PP). The domain architectures of each subgroup of planarian EGF ligands are shown on the right. Planarian sequences are highlighted in red.
Figure 6
Figure 6. Planarian epidermal growth factors ligands.
(A) Whole-mount in situ hybridizations of all putative planarian EGF ligands on intact adult specimens of S. mediterranea, grouped according to their subtype and phylogenetic relationships. See main text for details of the expression patterns. In egf-4, the yellow arrowheads indicate the central nervous system. In egf-6, the yellow arrowheads indicate expression in the body margin, and the inset (region delimited by the yellow rectangle) is a magnification of the expression in the dorsal anterior midline. Faint signal in the pharynx and central body region in egf-6 is background staining. In egf-7, the inset is a magnification showing the expression in the brain. (B) Schematic summary of the expression patterns of the planarian putative EGF ligands and the phenotype observed after their silencing by dsRNA injection (see references and main text for further details). In (A), anterior is to the left. ph: pharynx. Scale bars: 500 μm in all panels.
Figure 7
Figure 7. Role of Smed-egf-6 during adult planarian regeneration and homeostasis.
Regenerating (A) and intact (B) animals were injected on three consecutive days, and fixed two weeks after the last injection. Treated animals form edemas (yellow arrowheads) during both regeneration (A) and homeostasis (B). Whole-mount in situ hybridization of the protonephridial marker Smed-CAVII-1 in Smed-egf-6(RNAi) animals demonstrates a decrease in the number of protonephridial tubules compared to control animals. Numbers in each panel refer to the frequency of the phenotype. In all panels, anterior is to the top. Scale bars: 500 μm in all panels.
Figure 8
Figure 8. Summary scenario for the evolution of the EGFR signaling pathway in Metazoa.
On the right, distribution of the identified EGFRs (yellow rectangles) and putative EGF ligands (EGF-type, green dots; NRG-type, purple dots) in the analyzed animal lineages is shown. A triplicate symbol indicates that this particular type of protein (EGFR, EGF-type and NRG-type of ligands) appears expanded in this lineage. Our findings indicate that the last common metazoan ancestor had one EGFR and one putative EGF-type ligand. The NRG-type of EGF ligand is Bilateria-specific. The ancestral bilaterian set of one EGFR, one EGF-type and one NRG-type of ligands seems to be retained in the last common ancestors of both Deuterostomia and Protostomia. Subsequently, particular bilaterian lineages have experienced expansions of one or more of these basic EGFR signaling components. Additionally, vertebrates, the limpet L. gigantea and the planarian S. mediterranea have an EGFR with an inactive tyrosine kinase domain, which suggests the independent evolution of alternative regulatory mechanisms of this signaling pathway. Tree topology based on.

Similar articles

See all similar articles

Cited by 4 articles

References

    1. Schlessinger J. Receptor tyrosine kinases: legacy of the first two decades. Cold Spring Harb Perspect Biol 6, doi: 10.1101/cshperspect.a008912 (2014). - DOI - PMC - PubMed
    1. Pires-daSilva A. & Sommer R. J. The evolution of signalling pathways in animal development. Nat Rev Genet 4, 39–49, doi: 10.1038/nrg977 (2003). - DOI - PubMed
    1. Sibilia M. et al. The epidermal growth factor receptor: from development to tumorigenesis. Differentiation 75, 770–787, doi: 10.1111/j.1432-0436.2007.00238.x (2007). - DOI - PubMed
    1. Schweitzer R. & Shilo B. Z. A thousand and one roles for the Drosophila EGF receptor. Trends Genet 13, 191–196 (1997). - PubMed
    1. Chang C. & Sternberg P. W. C. elegans vulval development as a model system to study the cancer biology of EGFR signaling. Cancer Metastasis Rev 18, 203–213 (1999). - PubMed

Publication types

MeSH terms

Feedback