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Abstract
BACKGROUND: In many bilaterians, asymmetric activation of canonical Wnt (cWnt) signaling at the posterior pole is critical for anterior-posterior (AP) body axis formation. In 16-cell stage sea urchins, nuclearization of β-catenin in micromeres activates a gene regulatory network that defines body axes and induces endomesoderm. Transplanting micromeres to the animal pole of a host embryo induces ectopic endomesoderm in the mesomeres (ectoderm precursors) whereas inhibiting cWnt signaling blocks their endomesoderm-inducing activity and the micromeres become ectoderm-like. We have tested whether ectopic activation of cWnt signaling in mesomeres is sufficient to impart the cells with organizer-like abilities, allowing them to pattern normal embryonic body axes when recombined with a field of mesomeres.
RESULTS: Fertilized eggs were microinjected with constitutively active Xenopus β-catenin (actβ-cat) mRNA and allowed to develop until the 16-cell stage. Two mesomeres from injected embryos were then recombined with isolated animal halves (AH) from uninjected 16-cell stage embryos. Control chimeras produced animalized phenotypes (hollow balls of ectoderm) and rarely formed skeletogenic mesoderm (SM)-derived spicules, endoderm or pigment cells, a type of non-skeletogenic mesoderm (NSM). In contrast, over half of the 0.5 pg/pL actβ-cat mesomere/AH chimeras formed a partial or complete gut (exhibiting AP polarity), contained mesenchyme-like cells similar to SM, and produced pigment cells. At three days, chimeras formed plutei with normal embryonic body axes. When fates of the actβ-cat mRNA-injected mesomeres were tracked, we found that injected mesomeres formed mesenchyme-like and pigment cells, but endoderm was induced. Higher concentrations of actβ-cat mRNA were less likely to induce endoderm or pigment cells, but had similar mesenchyme-like cell production to 0.5 pg/pL actβ-cat mesomere/AH chimeras.
CONCLUSIONS: Our results show that nuclear β-catenin is sufficient to endow naïve cells with the ability to act as an organizing center and that β-catenin has both cell-autonomous and non-autonomous effects on cell fate specification in a concentration-dependent manner. These results are consistent with the hypothesis that a shift in the site of early cWnt signaling in cleaving embryos could have modified polarity of the main body axes during metazoan evolution.
Figure 1. Summary of the controls used in experiments. (A-D) Controls, bright field images. (C’, D’) Controls, fluorescent images. (A) Uninjected embryo at 27 hours post fertilization (hpf). (B) The uninjected animal half (AH) forms a hollow ciliated ball of ectoderm lacking endomesoderm and patterning along the oral-aboral axis (dauerblastula), 24 hpf. (C, C’) A chimera was made at the 16-cell stage in which micromeres removed from an embryo injected with rhodamine-dextran (RDX) were recombined with the uninjected AH. This produces a nearly normal prism stage embryo, although few pigment cells were present in many individuals. The RDX-labeled micromeres contributed to mesenchyme-like cells and occasionally to pigment cells (not shown). (D, D’) When RDX-labeled mesomeres from a 16-cell embryo were recombined with an AH, the chimera formed a dauerblastula and most of the labeled cells remained in the ectoderm. Note the expanded apical plate at the animal pole (B and D, D’). This is a typical feature of the dauerblastula. Orientations of the embryos are as follows: (A) Lateral view, oral side up. (B, C, C’, D, D’) All other images are frontal views with the animal pole oriented towards the top. Scale bars = 100 μm.
Figure 2. Summary of cell transplantation experiments and results at 23 to 27 hours post fertilization. (A) A mesomere pair from a 16-cell embryo injected with actβ-cat mRNA (shaded embryo) was recombined with the eight mesomeres of an uninjected animal half (AH). (B-G) Bright field images of chimeras in which a labeled mesomere pair injected with 0.5 pg/pL actβ-cat mRNA was recombined with an uninjected AH. (B’-G’) Corresponding fluorescent images. Labeled/injected mesomeres formed mesenchyme-like cells and pigment cells. Absence of label in the gut (gut indicated with arrowheads in B’, C’, D’) suggests that this tissue is induced in mesomeres from the uninjected AH. Some embryos were similar to uninjected controls (B, B’, C, C’, F, F’, G, G’), forming a complete gut, mesenchyme-like cells (indicated with arrows in B’) that produced spicules, and pigment cells (development in the injected cells and transplants is delayed compared to that in uninjected embryos). Others (D, D’) only formed a partial gut or lacked a gut (E, E’). (F, F’-G, G’) In some, the labeled cells were observed at the tip of the archenteron (arrowheads in F’ and G’). In this Figure, labeled mesenchymal cells are also clearly evident in the blastocoel. These are likely skeletogenic mesoderm and/or non-skeletogenic mesoderm cells such as pigment cells, but it is interesting that, unlike other chimeras, many of the labeled cells in these individuals remain concentrated at the tip of the archenteron. Orientation: (B, B’) vegetal view, (C-E, C’-E’) lateral views. (F-G, F’-G’) Frontal views with the animal pole at the top of the photograph.
Figure 3. Results of cell transplantation experiments at 3 days post fertilization. (A) Uninjected control. (B) Animal half (AH) control. (C) Bright field image of a 3-day chimera formed from a labeled mesomere pair injected with 0.5 pg/pL actβ-cat mRNA recombined with an uninjected AH. Note that features such the spicules, a tripartite gut, and pigment cells are all present. Larvae appear to be normal. (C’) Fluorescent image shows that the actβ-cat mRNA-injected mesomeres gave rise to mesenchyme-like cells and pigment cells (arrows in C, C’, D, and D’ indicate pigment cells). (D, D’) Different focal plane in the same embryo, showing that cells in the gut are not derived from the actβ-cat mRNA-injected mesomeres. Arrowheads in C, C’, D, and D’ indicate the induced, unlabeled gut.
Figure 4. Chimeras generated using higher levels of actβ-cat (1.0 pg/pL). (A) Some embryos appeared to be nearly normal, forming spicules, a gut, and pigment cells. (B) In other cases, the gut was absent, but many pigment cells and some skeletal elements (arrowhead) are present, or (C) few pigment cells formed. All images are lateral views.
Amemiya,
Complete regulation of development throughout metamorphosis of sea urchin embryos devoid of macromeres.
1996, Pubmed,
Echinobase
Amemiya,
Complete regulation of development throughout metamorphosis of sea urchin embryos devoid of macromeres.
1996,
Pubmed
,
Echinobase
Angerer,
The evolution of nervous system patterning: insights from sea urchin development.
2011,
Pubmed
,
Echinobase
Bince,
Functional analysis of Wnt signaling in the early sea urchin embryo using mRNA microinjection.
2008,
Pubmed
,
Echinobase
Bisgrove,
Development of Serotonergic Neurons in Embryos of the Sea Urchin, Strongylocentrotus purpuratus: (serotonergic/neural development/embryo/echinoid).
1986,
Pubmed
,
Echinobase
Cameron,
Lineage and fate of each blastomere of the eight-cell sea urchin embryo.
1987,
Pubmed
,
Echinobase
Christian,
Interactions between Xwnt-8 and Spemann organizer signaling pathways generate dorsoventral pattern in the embryonic mesoderm of Xenopus.
1993,
Pubmed
Croce,
Wnt6 activates endoderm in the sea urchin gene regulatory network.
2011,
Pubmed
,
Echinobase
Croce,
The canonical Wnt pathway in embryonic axis polarity.
2006,
Pubmed
,
Echinobase
Darras,
β-catenin specifies the endomesoderm and defines the posterior organizer of the hemichordate Saccoglossus kowalevskii.
2011,
Pubmed
,
Echinobase
Davidson,
A provisional regulatory gene network for specification of endomesoderm in the sea urchin embryo.
2002,
Pubmed
,
Echinobase
Duboc,
Nodal and BMP2/4 signaling organizes the oral-aboral axis of the sea urchin embryo.
2004,
Pubmed
,
Echinobase
Emily-Fenouil,
GSK3beta/shaggy mediates patterning along the animal-vegetal axis of the sea urchin embryo.
1998,
Pubmed
,
Echinobase
Ettensohn,
Cell lineage conversion in the sea urchin embryo.
1988,
Pubmed
,
Echinobase
Gurley,
Beta-catenin defines head versus tail identity during planarian regeneration and homeostasis.
2008,
Pubmed
Henry,
Beta-catenin is required for the establishment of vegetal embryonic fates in the nemertean, Cerebratulus lacteus.
2008,
Pubmed
Henry,
β-catenin and early development in the gastropod, Crepidula fornicata.
2010,
Pubmed
Hikasa,
Wnt signaling in vertebrate axis specification.
2013,
Pubmed
Hörstadius,
[Not Available].
1936,
Pubmed
Hörstadius,
[Not Available].
1936,
Pubmed
Huang,
Involvement of Tcf/Lef in establishing cell types along the animal-vegetal axis of sea urchins.
2000,
Pubmed
,
Echinobase
Hudson,
β-Catenin-driven binary fate specification segregates germ layers in ascidian embryos.
2013,
Pubmed
Iglesias,
Silencing of Smed-betacatenin1 generates radial-like hypercephalized planarians.
2008,
Pubmed
Imai,
(beta)-catenin mediates the specification of endoderm cells in ascidian embryos.
2000,
Pubmed
Juliano,
An evolutionary transition of Vasa regulation in echinoderms.
2009,
Pubmed
,
Echinobase
Kawai,
Nuclear accumulation of beta-catenin and transcription of downstream genes are regulated by zygotic Wnt5alpha and maternal Dsh in ascidian embryos.
2007,
Pubmed
Klein,
A molecular mechanism for the effect of lithium on development.
1996,
Pubmed
Kumburegama,
Strabismus-mediated primary archenteron invagination is uncoupled from Wnt/β-catenin-dependent endoderm cell fate specification in Nematostella vectensis (Anthozoa, Cnidaria): Implications for the evolution of gastrulation.
2011,
Pubmed
Lee,
Asymmetric developmental potential along the animal-vegetal axis in the anthozoan cnidarian, Nematostella vectensis, is mediated by Dishevelled.
2007,
Pubmed
Leonard,
Analysis of dishevelled localization and function in the early sea urchin embryo.
2007,
Pubmed
,
Echinobase
Lhomond,
Frizzled1/2/7 signaling directs β-catenin nuclearisation and initiates endoderm specification in macromeres during sea urchin embryogenesis.
2012,
Pubmed
,
Echinobase
Livingston,
Range and stability of cell fate determination in isolated sea urchin blastomeres.
1990,
Pubmed
,
Echinobase
Livingston,
Lithium evokes expression of vegetal-specific molecules in the animal blastomeres of sea urchin embryos.
1989,
Pubmed
,
Echinobase
Logan,
Nuclear beta-catenin is required to specify vegetal cell fates in the sea urchin embryo.
1999,
Pubmed
,
Echinobase
Martindale,
A developmental perspective: changes in the position of the blastopore during bilaterian evolution.
2009,
Pubmed
Martindale,
The evolution of metazoan axial properties.
2005,
Pubmed
Martín-Durán,
Germ layer specification and axial patterning in the embryonic development of the freshwater planarian Schmidtea polychroa.
2010,
Pubmed
McClay,
A micromere induction signal is activated by beta-catenin and acts through notch to initiate specification of secondary mesenchyme cells in the sea urchin embryo.
2000,
Pubmed
,
Echinobase
McClay,
Embryo dissociation, cell isolation, and cell reassociation.
1986,
Pubmed
,
Echinobase
Minokawa,
Timing of the potential of micromere-descendants in echinoid embryos to induce endoderm differentiation of mesomere-descendants.
1999,
Pubmed
,
Echinobase
Mohamed,
Beta-catenin signaling marks the prospective site of primitive streak formation in the mouse embryo.
2004,
Pubmed
Nakajima,
Development of the Nervous System of Sea Urchin Embryos: Formation of Ciliary Bands and the Appearance of Two Types of Ectoneural Cells in the Pluteus: (ectoneural cell/sea urchin pluteus/ciliary band/axoneme).
1986,
Pubmed
,
Echinobase
Oliveri,
A regulatory gene network that directs micromere specification in the sea urchin embryo.
2002,
Pubmed
,
Echinobase
Oliveri,
Activation of pmar1 controls specification of micromeres in the sea urchin embryo.
2003,
Pubmed
,
Echinobase
Petersen,
Wnt signaling and the polarity of the primary body axis.
2009,
Pubmed
Petersen,
Smed-betacatenin-1 is required for anteroposterior blastema polarity in planarian regeneration.
2008,
Pubmed
Range,
Integration of canonical and noncanonical Wnt signaling pathways patterns the neuroectoderm along the anterior-posterior axis of sea urchin embryos.
2013,
Pubmed
,
Echinobase
Ransick,
Micromeres are required for normal vegetal plate specification in sea urchin embryos.
1995,
Pubmed
,
Echinobase
Ransick,
A complete second gut induced by transplanted micromeres in the sea urchin embryo.
1993,
Pubmed
,
Echinobase
Revilla-i-Domingo,
A missing link in the sea urchin embryo gene regulatory network: hesC and the double-negative specification of micromeres.
2007,
Pubmed
,
Echinobase
Röttinger,
Nemo-like kinase (NLK) acts downstream of Notch/Delta signalling to downregulate TCF during mesoderm induction in the sea urchin embryo.
2006,
Pubmed
,
Echinobase
Ruffins,
A fate map of the vegetal plate of the sea urchin (Lytechinus variegatus) mesenchyme blastula.
1996,
Pubmed
,
Echinobase
Sethi,
Sequential signaling crosstalk regulates endomesoderm segregation in sea urchin embryos.
2012,
Pubmed
,
Echinobase
Sweet,
LvDelta is a mesoderm-inducing signal in the sea urchin embryo and can endow blastomeres with organizer-like properties.
2002,
Pubmed
,
Echinobase
Thorpe,
Wnt signaling polarizes an early C. elegans blastomere to distinguish endoderm from mesoderm.
1997,
Pubmed
Vonica,
TCF is the nuclear effector of the beta-catenin signal that patterns the sea urchin animal-vegetal axis.
2000,
Pubmed
,
Echinobase
V Ubisch,
[Not Available].
1929,
Pubmed
Wei,
Axial patterning interactions in the sea urchin embryo: suppression of nodal by Wnt1 signaling.
2012,
Pubmed
,
Echinobase
Wei,
The sea urchin animal pole domain is a Six3-dependent neurogenic patterning center.
2009,
Pubmed
,
Echinobase
Weitzel,
Differential stability of beta-catenin along the animal-vegetal axis of the sea urchin embryo mediated by dishevelled.
2004,
Pubmed
,
Echinobase
Wessel,
How to grow a gut: ontogeny of the endoderm in the sea urchin embryo.
1999,
Pubmed
,
Echinobase
Wikramanayake,
beta-Catenin is essential for patterning the maternally specified animal-vegetal axis in the sea urchin embryo.
1998,
Pubmed
,
Echinobase
Wikramanayake,
Autonomous and non-autonomous differentiation of ectoderm in different sea urchin species.
1995,
Pubmed
,
Echinobase
Wikramanayake,
Multiple signaling events specify ectoderm and pattern the oral-aboral axis in the sea urchin embryo.
1997,
Pubmed
,
Echinobase
Wikramanayake,
An ancient role for nuclear beta-catenin in the evolution of axial polarity and germ layer segregation.
2003,
Pubmed
Yaguchi,
A Wnt-FoxQ2-nodal pathway links primary and secondary axis specification in sea urchin embryos.
2008,
Pubmed
,
Echinobase
Yaguchi,
Specification of ectoderm restricts the size of the animal plate and patterns neurogenesis in sea urchin embryos.
2006,
Pubmed
,
Echinobase
Yajima,
Small micromeres contribute to the germline in the sea urchin.
2011,
Pubmed
,
Echinobase
Yost,
The axis-inducing activity, stability, and subcellular distribution of beta-catenin is regulated in Xenopus embryos by glycogen synthase kinase 3.
1996,
Pubmed
