Sea Urchin Development

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Contents

Introduction

Sea Urchin- 2 cell stage
Sea Urchin- activin B expression
Sea Urchin- early embryo cleavage pattern
Sea urchin ectoderm patterning model

The sea urchin embryo initially undergoes ten cycles of cell division forming a single epithelial layer enveloping a blastocoel, followed by gastrulation producing the three germ layers. This system has been used recently to study early molecular controls of patterning and axis formation.


Links: Category:Sea Urchin

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Some Recent Findings

  • Implication of HpEts in gene regulatory networks responsible for specification of sea urchin skeletogenic primary mesenchyme cells[1] "The large micromeres of the 32-cell stage of sea urchin embryos are autonomously specified and differentiate into primary mesenchyme cells (PMCs), giving rise to the skeletogenic cells. We previously demonstrated that HpEts, an ets-related transcription factor, plays an essential role in the specification of PMCs in sea urchin embryos."
  • Dynamics of Delta/Notch signaling on endomesoderm segregation in the sea urchin embryo.[2] "Endomesoderm is the common progenitor of endoderm and mesoderm early in the development of many animals. In the sea urchin embryo, the Delta/Notch pathway is necessary for the diversification of this tissue, as are two early transcription factors, Gcm and FoxA, which are expressed in mesoderm and endoderm, respectively. Here, we provide a detailed lineage analysis of the cleavages leading to endomesoderm segregation, and examine the expression patterns and the regulatory relationships of three known regulators of this cell fate dichotomy in the context of the lineages."
  • The expression and distribution of Wnt and Wnt receptor mRNAs during early sea urchin development. [3] "In this study, we identified all Wnt and Wnt receptor mRNAs that are present in unfertilized sea urchin eggs and early embryos and analyzed their distributions along the primary (AV) axis. Our findings indicate that the asymmetric distribution of a maternal Wnt or Wnt receptor mRNA is unlikely to be a primary determinant of the polarized stabilization of beta-catenin along the AV axis. This contrasts sharply with findings in other organisms and points to remarkable evolutionary flexibility in the molecular mechanisms that underlie this otherwise very highly conserved patterning process."

Early Development

Sea urchin SEM01.jpg

Sea urchin SEM02.jpg

Sea urchin SEM03.jpg

Endomesoderm Induction

Sea Urchin-endomesoderm induction.png

Sea Urchin-endomesoderm induction[4]

Figure illustrates gene regulatory networks required for the early developmental process of endomesoderm induction.


Ectoderm Development

Sea urchin ectoderm patterning model.jpg

Changes in identity of ectodermal territories following perturbations of Nodal or BMP signaling and novel model of ectoderm patterning[5]

Schemes describing the morphology of control embryos and perturbed embryos.

(A) control embryo. The thick ciliated epithelium of the ciliary band is restricted to a belt of cells at the interface between the ventral and dorsal ectoderm.

(B) Nodal morphant. Most of the ectoderm differentiates into an expanded large ciliary band. An animal pole domain is nevertheless present in these embryos as shown by the presence of the apical tuft and at the molecular level by the expression of apical domain marker genes. In these embryos, the ectoderm surrounding the blastopore differentiates into dorsal ectoderm.

(C) embryo overexpressing Nodal. Most of the ectoderm differentiates into ventral ectoderm. A ciliary band-like ectoderm forms at the animal pole and in the ectoderm surrounding the blastopore.

(D) BMP2/4 morphants. An ectopic ciliary band forms in the dorsal ectoderm in addition to the normal ciliary band.

(E) bmp2/4 overexpressing embryo. All the ectoderm has a dorsal identity. The animal pole domain is largely absent. The triradiated stars represent the spicule rudiments.

(F) Proposed model for regionalization of the ectoderm of the sea urchin embryo through restriction of the ciliary band fate by Nodal and BMP signaling. Maternal factors such as SoxB1 promote the early expression of ciliary band genes within the ectoderm. Nodal signaling on the ventral side promotes differentiation of the ventral ectoderm and stomodeum and represses the ciliary band fate probably through the activity of Goosecoid as well as of additional repressors. Nodal induces its antagonist Lefty, which diffuses away from the ventral ectoderm up to the presumptive ciliary band territory. Within the ventral ectoderm, Nodal induces expression of bmp2/4 and of its antagonist chordin. Chordin prevents BMP signaling within the ventral ectoderm and probably within the presumptive ciliary band region. At blastula stages, protein complexes containing BMP2/4 and Chordin can diffuse towards the dorsal side to specify dorsal fates. In the dorsal ectoderm, BMP signaling strongly repress the ciliary band fate partly by inducing the expression of the irxA repressor. A high level of MAP kinase activity resulting from FGFA signaling in the lateral ectoderm likely contributes to maintain a low level of Nodal and BMP signaling within the presumptive ciliary band region by phosphorylating Smad1/5/8 and Smad2/3 in the linker region, which inhibits their activity. The presence of Chordin and Lefty in the prospective ciliary band allows expression of ciliary band genes to be maintained in this region. The ectoderm surrounding the blastopore differentiates into dorsal ectoderm likely because it receives Wnt signals that antagonize GSK3 and promote BMP signaling.

(G) In the absence of Nodal signaling, both the ventral and the dorsal inducing signals are not produced, ciliary band genes are not repressed and unrestricted MAP kinase signaling promotes differentiation of the ventral and dorsal ectoderm into neural ectoderm and ciliary band. The genes or proteins that are inactive are represented in light grey.


Wnt patterning

Sea urchin Wnt patterning model.jpg

Sea urchin Wnt patterning model[6]

Historic Images

References

  1. Mamiko Yajima, Rieko Umeda, Takuya Fuchikami, Miho Kataoka, Naoaki Sakamoto, Takashi Yamamoto, Koji Akasaka Implication of HpEts in gene regulatory networks responsible for specification of sea urchin skeletogenic primary mesenchyme cells. Zool. Sci.: 2010, 27(8);638-46 PMID:20695779
  2. Jenifer C Croce, David R McClay Dynamics of Delta/Notch signaling on endomesoderm segregation in the sea urchin embryo. Development: 2010, 137(1);83-91 PMID:20023163
  3. Rachel E Stamateris, Kiran Rafiq, Charles A Ettensohn The expression and distribution of Wnt and Wnt receptor mRNAs during early sea urchin development. Gene Expr. Patterns: 2010, 10(1);60-4 PMID:19853669
  4. Aditya J Sethi, Robert C Angerer, Lynne M Angerer Gene regulatory network interactions in sea urchin endomesoderm induction. PLoS Biol.: 2009, 7(2);e1000029 PMID:19192949 | PLoS Biol.
  5. Alexandra Saudemont, Emmanuel Haillot, Flavien Mekpoh, Nathalie Bessodes, Magali Quirin, François Lapraz, Véronique Duboc, Eric Röttinger, Ryan Range, Arnaud Oisel, Lydia Besnardeau, Patrick Wincker, Thierry Lepage Ancestral regulatory circuits governing ectoderm patterning downstream of Nodal and BMP2/4 revealed by gene regulatory network analysis in an echinoderm. PLoS Genet.: 2010, 6(12);e1001259 PMID:21203442
  6. Ryan C Range, Robert C Angerer, Lynne M Angerer Integration of canonical and noncanonical wnt signaling pathways patterns the neuroectoderm along the anterior-posterior axis of sea urchin embryos. PLoS Biol.: 2013, 11(1);e1001467 PMID:23335859 | PLoS Biol.

Reviews

Tetsuya Kominami, Hiromi Takata Gastrulation in the sea urchin embryo: a model system for analyzing the morphogenesis of a monolayered epithelium. Dev. Growth Differ.: 2004, 46(4);309-26 PMID:15367199


Articles

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Animal Development: Axolotl | Bat | Cat | Chicken | Cow | Dog | Dolphin | Echidna | Fly | Frog | Grasshopper | Guinea Pig | Hamster | Kangaroo | Koala | Lizard | Medaka | Mouse | Pig | Platypus | Rabbit | Rat | Sea Squirt | Sea Urchin | Sheep | Worm | Zebrafish | Life Cycles | Development Timetable | K12
Historic Animals: 1897 Pig | 1900 Chicken | 1901 Lungfish | 1904 Sand Lizard | 1905 Rabbit | 19066 Deer | 1907 Tarsiers | 1908 Human | 1909 Northern Lapwing | 1909 South American and African Lungfish | 1910 Salamander | Embryology History | Historic Disclaimer

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Cite this page: Hill, M.A. (2014) Embryology Sea Urchin Development. Retrieved April 16, 2014, from http://embryology.med.unsw.edu.au/embryology/index.php?title=Sea_Urchin_Development

What Links Here?
Dr Mark Hill 2014, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G
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