LvDelta is a mesoderm-inducing signal in the sea urchin embryo and can endow blastomeres with organizer-like properties

Development ◽  
2002 ◽  
Vol 129 (8) ◽  
pp. 1945-1955 ◽  
Author(s):  
Hyla C. Sweet ◽  
Michael Gehring ◽  
Charles A. Ettensohn
Keyword(s):  
Sea Urchin ◽  
Critical Role ◽  
Cell Types ◽  
Notch Signaling Pathway ◽  
Notch Receptor ◽  
Pigment Cells ◽  
Mesodermal Cell ◽  
Sea Urchin Embryo ◽  
Organizing Center ◽  
Necessary And Sufficient

Signals from micromere descendants play a critical role in patterning the early sea urchin embryo. Previous work demonstrated a link between the induction of mesoderm by micromere descendants and the Notch signaling pathway. In this study, we demonstrate that these micromere descendants express LvDelta, a ligand for the Notch receptor. LvDelta is expressed by micromere descendants during the blastula stage, a time when signaling has been shown to occur. By a combination of embryo microsurgery, mRNA injection and antisense morpholino experiments, we show that expression of LvDelta by micromere descendants is both necessary and sufficient for the development of two mesodermal cell types, pigment cells and blastocoelar cells. We also demonstrate that LvDelta is expressed by macromere descendants during mesenchyme blastula and early gastrula stages. Macromere-derived LvDelta is necessary for blastocoelar cell and muscle cell development. Finally, we find that expression of LvDelta is sufficient to endow blastomeres with the ability to function as a vegetal organizing center and to coordinate the development of a complete pluteus larva.

The role of micromere signaling in Notch activation and mesoderm specification during sea urchin embryogenesis

Development ◽  
1999 ◽  
Vol 126 (23) ◽  
pp. 5255-5265 ◽  
Author(s):  
H.C. Sweet ◽  
P.G. Hodor ◽  
C.A. Ettensohn
Keyword(s):  
Notch Signaling ◽  
Sea Urchin ◽  
Muscle Cells ◽  
Cell Types ◽  
Notch Signaling Pathway ◽  
Notch Receptor ◽  
Pigment Cells ◽  
Animal Cells ◽  
Mesodermal Cell ◽  
Mesoderm Development

In the sea urchin embryo, the micromeres act as a vegetal signaling center. These cells have been shown to induce endoderm; however, their role in mesoderm development has been less clear. We demonstrate that the micromeres play an important role in the induction of secondary mesenchyme cells (SMCs), possibly by activating the Notch signaling pathway. After removing the micromeres, we observed a significant delay in the formation of all mesodermal cell types examined. In addition, there was a marked reduction in the numbers of pigment cells, blastocoelar cells and cells expressing the SMC1 antigen, a marker for prospective SMCs. The development of skeletogenic cells and muscle cells, however, was not severely affected. Transplantation of micromeres to animal cells resulted in the induction of SMC1-positive cells, pigment cells, blastocoelar cells and muscle cells. The numbers of these cell types were less than those found in sham transplantation control embryos, suggesting that animal cells are less responsive to the micromere-derived signal than vegetal cells. Previous studies have demonstrated a role for Notch signaling in the development of SMCs. We show that the micromere-derived signal is necessary for the downregulation of the Notch protein, which is correlated with its activation, in prospective SMCs. We propose that the micromeres induce adjacent cells to form SMCs, possibly by presenting a ligand for the Notch receptor.

LvNotch signaling mediates secondary mesenchyme specification in the sea urchin embryo

Development ◽  
1999 ◽  
Vol 126 (8) ◽  
pp. 1703-1713 ◽  
Author(s):  
D.R. Sherwood ◽  
D.R. McClay
Keyword(s):  
Sea Urchin ◽  
Cell Types ◽  
Notch Signaling Pathway ◽  
Notch Receptor ◽  
Dominant Negative ◽  
Sea Urchin Embryo ◽  
Numerous Cell ◽  
Vertebrate Embryos ◽  
Mesenchyme Cells ◽  
Molecular Bases

Cell-cell interactions are thought to regulate the differential specification of secondary mesenchyme cells (SMCs) and endoderm in the sea urchin embryo. The molecular bases of these interactions, however, are unknown. We have previously shown that the sea urchin homologue of the LIN-12/Notch receptor, LvNotch, displays dynamic patterns of expression within both the presumptive SMCs and endoderm during the blastula stage, the time at which these two cell types are thought to be differentially specified (Sherwood, D. R. and McClay, D. R. (1997) Development 124, 3363–3374). The LIN-12/Notch signaling pathway has been shown to mediate the segregation of numerous cell types in both invertebrate and vertebrate embryos. To directly examine whether LvNotch signaling has a role in the differential specification of SMCs and endoderm, we have overexpressed activated and dominant negative forms of LvNotch during early sea urchin development. We show that activation of LvNotch signaling increases SMC specification, while loss or reduction of LvNotch signaling eliminates or significantly decreases SMC specification. Furthermore, results from a mosaic analysis of LvNotch function as well as endogenous LvNotch expression strongly suggest that LvNotch signaling acts autonomously within the presumptive SMCs to mediate SMC specification. Finally, we demonstrate that the expansion of SMCs seen with activation of LvNotch signaling comes at the expense of presumptive endoderm cells, while loss of SMC specification results in the endoderm expanding into territory where SMCs usually arise. Taken together, these results offer compelling evidence that LvNotch signaling directly specifies the SMC fate, and that this signaling is critical for the differential specification of SMCs and endoderm in the sea urchin embryo.

Pattern formation during gastrulation in the sea urchin embryo

Development ◽  
1992 ◽  
Vol 116 (Supplement) ◽  
pp. 33-41 ◽  
Author(s):  
David R. McClay ◽  
Norris A. Armstrong ◽  
Jeff Hardin
Keyword(s):  
Sea Urchin ◽  
Spatial Information ◽  
Cell Types ◽  
Cell Interactions ◽  
Pigment Cells ◽  
Original Position ◽  
Embryonic Cells ◽  
Sea Urchin Embryo ◽  
Mesenchyme Cells ◽  
Primary Mesenchyme Cells

The sea urchin embryo follows a relatively simple cell behavioral sequence in its gastrulation movements. To form the mesoderm, primary mesenchyme cells ingress from the vegetal plate and then migrate along the basal lamina lining the blastocoel. The presumptive secondary mesenchyme and endoderm then invaginate from the vegetal pole of the embryo. The archenteron elongates and extends across the blastocoel until the tip of the archenteron touches and attaches to the opposite side of the blastocoel. Secondary mesenchyme cells, originally at the tip of the archenteron, differentiate to form a variety of structures including coelomic pouches, esophageai muscles, pigment cells and other cell types. After migration of the secondary mesenchyme cells from their original position at the tip of the archenteron, the endoderm fuses with an invagination of the ventral ectoderm (the stomodaem), to form the mouth and complete the process of gastrulation. A larval skeleton is made by primary mesenchyme cells during the time of archenteron and mouth formation. A number of experiments have established that these morphogenetic movements involve a number of cell autonomous behaviors plus a series of cell interactions that provide spatial, temporal and scalar information to cells of the mesoderm and endoderm. The cell autonomous behaviors can be demonstrated by the ability of micromeres or endoderm to perform their morphogenetic functions if either is isolated and grown in culture. The requirement for cell interactions has been demonstrated by manipulative experiments where it has been shown that axial information, temporal information, spatial information and scalar information is obtained by mesoderm and endoderm from other embryonic cells. This information governs the cell autonomous behavior and places the cells in the correct embryonic context.

Mesodermal cell interactions in the sea urchin embryo: properties of skeletogenic secondary mesenchyme cells

Development ◽  
1993 ◽  
Vol 117 (4) ◽  
pp. 1275-1285 ◽  
Author(s):  
C.A. Ettensohn ◽  
S.W. Ruffins
Keyword(s):  
Sea Urchin ◽  
Pigment Cell ◽  
Cell Labeling ◽  
Pigment Cells ◽  
Cell Phenotype ◽  
Specific Cell ◽  
Mesodermal Cell ◽  
Developmental Potential ◽  
Sea Urchin Embryo ◽  
Mesenchyme Cells

An interaction between the two principal populations of mesodermal cells in the sea urchin embryo, primary and secondary mesenchyme cells (PMCs and SMCs, respectively), regulates SMC fates and the process of skeletogenesis. In the undisturbed embryo, skeletal elements are produced exclusively by PMCs. Certain SMCs also have the ability to express a skeletogenic phenotype; however, signals transmitted by the PMCs direct these cells into alternative developmental pathways. In this study, a combination of fluorescent cell-labeling methods, embryo microsurgery and cell-specific molecular markers have been used to study the lineage, numbers, normal fate(s) and developmental potential of the skeletogenic SMCs. Previous fate-mapping studies have shown that SMCs are derived from the veg2 layer of blastomeres of the 64-cell-stage embryo and from the small micromeres. By specifically labeling the small micromeres with 5-bromodeoxyuridine, we demonstrate that descendants of these cells do not participate in skeletogenesis in PMC-depleted larvae, even though they are the closest lineal relatives of PMCs. Skeletogenic SMCs are therefore derived exclusively from the veg2 blastomeres. Because the SMCs are a heterogeneous population of cells, we have sought to gain information concerning the normal fate(s) of skeletogenic SMCs by determining whether specific cell types are reduced or absent in PMC(−) larvae. Of the four known SMC derivatives: pigment cells, blastocoelar (basal) cells, muscle cells and coelomic pouch cells, only pigment cells show a major reduction (> 50%) in number following SMC skeletogenesis. We therefore propose that the PMC-derived signal regulates a developmental switch, directing SMCs to adopt a pigment cell phenotype instead of a default (skeletogenic) fate. Ablation of SMCs at the late gastrula stage does not result in the recruitment of any additional skeletogenic cells, demonstrating that, by this stage, the number of SMCs with skeletogenic potential is restricted to 60–70 cells. Previous studies showed that during their switch to a skeletogenic fate, SMCs alter their migratory behavior and cell surface properties. In this study, we demonstrate that during conversion, SMCs become insensitive to the PMC-derived signal, while at the same time they acquire PMC-specific signaling properties.

Cell interactions and mesodermal cell fates in the sea urchin embryo

Development ◽  
1992 ◽  
Vol 116 (Supplement) ◽  
pp. 43-51 ◽  
Author(s):  
Charles A. Ettensohn
Keyword(s):  
Sea Urchin ◽  
Cell Interactions ◽  
Cell Labeling ◽  
Cell Fates ◽  
Mesodermal Cell ◽  
Sea Urchin Embryo ◽  
Present Information ◽  
Cell Type Specific ◽  
Mesenchyme Cells

Cell interactions during gastrulation play a key role in the determination of mesodermal cell fates in the sea urchin embryo. An interaction between primary and secondary mesenchyme cells (PMCs and SMCs, respectively), the two principal populations of mesodermal cells, regulates the expression of SMC fates. PMCs are committed early in cleavage to express a skeletogenic phenotype. During gastrulation, they transmit a signal that suppresses the skeletogenic potential of a subpopulation of SMCs and directs these cells into an alternative developmental pathway. This review summarizes present information concerning the cellular basis of the PMC-SMC interaction, as analyzed by cell transplantation and ablation experiments, fluorescent cell labeling methods and the use of cell type-specific molecular markers. The nature and stability of SMC fate switching, the timing of the PMC-SMC interaction and its quantitative characteristics, and the lineage, numbers and normal fate of the population of skeletogenic SMCs are discussed. Evidence is presented indicating that PMCs and SMCs come into direct filopodial contact during the late gastrula stage, when the signal is transmitted. Finally, evolutionary questions raised by these studies are briefly addressed.

Identification and localization of a sea urchin Notch homologue: insights into vegetal plate regionalization and Notch receptor regulation

Development ◽  
1997 ◽  
Vol 124 (17) ◽  
pp. 3363-3374 ◽  
Author(s):  
D.R. Sherwood ◽  
D.R. McClay
Keyword(s):  
Sea Urchin ◽  
Basolateral Membrane ◽  
Notch Pathway ◽  
Cell Types ◽  
Dorsal Side ◽  
Notch Receptor ◽  
Molecular Organization ◽  
Intercellular Signaling ◽  
Vegetal Pole ◽  
Numerous Cell

The specifications of cell types and germ-layers that arise from the vegetal plate of the sea urchin embryo are thought to be regulated by cell-cell interactions, the molecular basis of which are unknown. The Notch intercellular signaling pathway mediates the specification of numerous cell fates in both invertebrate and vertebrate development. To gain insights into mechanisms underlying the diversification of vegetal plate cell types, we have identified and made antibodies to a sea urchin homolog of Notch (LvNotch). We show that in the early blastula embryo, LvNotch is absent from the vegetal pole and concentrated in basolateral membranes of cells in the animal half of the embryo. However, in the mesenchyme blastula embryo LvNotch shifts strikingly in subcellular localization into a ring of cells which surround the central vegetal plate. This ring of LvNotch delineates a boundary between the presumptive secondary mesoderm and presumptive endoderm, and has an asymmetric bias towards the dorsal side of the vegetal plate. Experimental perturbations and quantitative analysis of LvNotch expression demonstrate that the mesenchyme blastula vegetal plate contains both animal/vegetal and dorsoventral molecular organization even before this territory invaginates to form the archenteron. Furthermore, these experiments suggest roles for the Notch pathway in secondary mesoderm and endoderm lineage segregation, and in the establishment of dorsoventral polarity in the endoderm. Finally, the specific and differential subcellular expression of LvNotch in apical and basolateral membrane domains provides compelling evidence that changes in membrane domain localization of LvNotch are an important aspect of Notch receptor function.

The micro1 gene is necessary and sufficient for micromere differentiation and mid/hindgut-inducing activity in the sea urchin embryo

2005 ◽  
Vol 215 (9) ◽  
pp. 450-459 ◽  
Author(s):  
Atsuko Yamazaki ◽  
Rika Kawabata ◽  
Kosuke Shiomi ◽  
Shonan Amemiya ◽  
Masaya Sawaguchi ◽  
...  
Keyword(s):  
Sea Urchin ◽  
Sea Urchin Embryo ◽  
Necessary And Sufficient

scholarly journals Ciliary photoreceptors in sea urchin larvae indicate pan-deuterostome cell type conservation

2019 ◽  
Author(s):  
Jonathan E. Valencia ◽  
Roberto Feuda ◽  
Dan O. Mellott ◽  
Robert D. Burke ◽  
Isabelle S. Peter
Keyword(s):  
Transcription Factor ◽  
Transcription Factors ◽  
Sea Urchin ◽  
Cell Types ◽  
Pigment Cells ◽  
Current Evidence ◽  
Regulatory State ◽  
Developmental Context ◽  
Immotile Cilia ◽  
Retinal Determination

ABSTRACTOne of the signatures of evolutionarily related cell types is the expression of similar combinations of transcription factors in distantly related animals. Here we present evidence that sea urchin larvae possess bilateral clusters of ciliary photoreceptors that are positioned in the oral/anterior apical neurogenic domain and associated with pigment cells. The expression of synaptotagmin indicates that the photoreceptors are neurons. Immunostaining shows that the sea urchin photoreceptors express an RGR/GO-opsin, opsin3.2, which co-localizes with tubulin on immotile cilia on the cell surface. Furthermore, orthologs of several transcription factors expressed in vertebrate photoreceptors are expressed in sea urchin ciliary photoreceptors, including Otx, Six3, Tbx2/3, and Rx, a transcription factor typically associated with ciliary photoreceptors. Analysis of gene expression during sea urchin development indicates that the photoreceptors derive from the anterior apical neurogenic domain. Thus, based on location, developmental origin, and transcription factor expression, sea urchin ciliary photoreceptors are likely homologous to vertebrate rods and cones. However, we found that genes typically involved in eye development in many animals, including pax6, six1/2, eya, and dac, are not expressed in sea urchin ciliary photoreceptors. Instead, all four genes are co-expressed in the hydropore canal, indicating that these genes operate as a module in an unrelated developmental context. Thus, based on current evidence, we conclude that at least within deuterostomes, ciliary photoreceptors share a common evolutionary origin and express a shared regulatory state that includes Rx, Otx, and Six3, but not transcription factors that are commonly associated with the retinal determination circuit.

scholarly journals Macromere cell fates during sea urchin development

Development ◽  
1991 ◽  
Vol 113 (4) ◽  
pp. 1085-1091 ◽  
Author(s):  
R.A. Cameron ◽  
S.E. Fraser ◽  
R.J. Britten ◽  
E.H. Davidson
Keyword(s):  
Sea Urchin ◽  
Pigment Cell ◽  
Cell Lineage ◽  
Cell Types ◽  
Cellular Migration ◽  
The Other ◽  
Pigment Cells ◽  
Basal Cells ◽  
Cell Fates ◽  
Gut Pigment

This paper examines the cell lineage relationships and cell fates in embryos of the sea urchin Strongylocentrotus purpuratus leading to the various cell types derived from the definitive vegetal plate territory or the veg2 tier of cells. These cell types are gut, pigment cells, basal cells and coelomic pouches. They are cell types that constitute embryonic structures through cellular migration or rearrangement unlike the relatively non-motile ectoderm cell types. For this analysis, we use previous knowledge of lineage to assign macromeres to one of four types: VOM, the oral macromere; VAM, the aboral macromere, right and left VLM, the lateral macromeres. Each of the four macromeres contributes progeny to all of the cell types that descend from the definitive vegetal plate. Thus in the gut each macromere contributes to the esophagus, stomach and intestine, and the stripe of labeled cells descendant from a macromere reflects the re-arrangement of cells that occurs during archenteron elongation. Pigment cell contributions exhibit no consistent pattern among the four macromeres, and are haphazardly distributed throughout the ectoderm. Gut and pigment cell contributions are thus radially symmetrical. In contrast, the VOM blastomere contributes to both of the coelomic pouches while the other three macromeres contribute to only one or the other pouch. The total of the macromere contribution amounts to 60% of the cells constituting the coelomic pouches.

scholarly journals Specification of cell fate in the sea urchin embryo: summary and some proposed mechanisms

Development ◽  
1998 ◽  
Vol 125 (17) ◽  
pp. 3269-3290 ◽  
Author(s):  
E.H. Davidson ◽  
R.A. Cameron ◽  
A. Ransick
Keyword(s):  
Cell Fate ◽  
Sea Urchin ◽  
Cell Types ◽  
Expression Of Genes ◽  
Sea Urchin Embryo ◽  
Indirect Development ◽  
Genes Encoding ◽  
Stage Embryo ◽  
Gene Regulatory ◽  
Signaling Interactions

An early set of blastomere specifications occurs during cleavage in the sea urchin embryo, the result of both conditional and autonomous processes, as proposed in the model for this embryo set forth in 1989. Recent experimental results have greatly illuminated the mechanisms of specification in some early embryonic territories, though others remain obscure. We review the progressive process of specification within given lineage elements, and with reference to the early axial organization of the embryo. Evidence for the conditional specification of the veg2 lineage subelement of the endoderm and other potential interblastomere signaling interactions in the cleavage-stage embryo are summarized. Definitive boundaries between mesoderm and endoderm territories of the vegetal plate, and between endoderm and overlying ectoderm, are not established until later in development. These processes have been clarified by numerous observations on spatial expression of various genes, and by elegant lineage labeling studies. The early specification events depend on regional mobilization of maternal regulatory factors resulting at once in the zygotic expression of genes encoding transcription factors, as well as downstream genes encoding proteins characteristic of the cell types that will much later arise from the progeny of the specified blastomeres. This embryo displays a maximal form of indirect development. The gene regulatory network underlying the embryonic development reflects the relative simplicity of the completed larva and of the processes required for its formation. The requirements for postembryonic adult body plan formation in the larval rudiment include engagement of a new level of genetic regulatory apparatus, exemplified by the Hox gene complex.

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