scholarly journals A BMP pathway regulates cell fate allocation along the sea urchin animal-vegetal embryonic axis

Development ◽  
2000 ◽  
Vol 127 (5) ◽  
pp. 1105-1114 ◽  
Author(s):  
L.M. Angerer ◽  
D.W. Oleksyn ◽  
C.Y. Logan ◽  
D.R. McClay ◽  
L. Dale ◽  
...  
Keyword(s):  
Cell Fate ◽  
Sea Urchin ◽  
Animal Cell ◽  
Bmp Signaling ◽  
Epithelial Tissue ◽  
Cell Fates ◽  
Cell Stage ◽  
Bmp Pathway ◽  
The One ◽  
Dose Dependent

To examine whether a BMP signaling pathway functions in specification of cell fates in sea urchin embryos, we have cloned sea urchin BMP2/4, analyzed its expression in time and space in developing embryos and assayed the developmental consequences of changing its concentration through mRNA injection experiments. These studies show that BMP4 mRNAs accumulate transiently during blastula stages, beginning around the 200-cell stage, 14 hours postfertilization. Soon after the hatching blastula stage, BMP2/4 transcripts can be detected in presumptive ectoderm, where they are enriched on the oral side. Injection of BMP2/4 mRNA at the one-cell stage causes a dose-dependent suppression of commitment of cells to vegetal fates and ectoderm differentiates almost exclusively as a squamous epithelial tissue. In contrast, NOGGIN, an antagonist of BMP2/4, enhances differentiation of endoderm, a vegetal tissue, and promotes differentiation of cells characteristic of the ciliated band, which contains neurogenic ectoderm. These findings support a model in which the balance of BMP2/4 signals produced by animal cell progeny and opposing vegetalizing signals sent during cleavage stages regulate the position of the ectoderm/ endoderm boundary. In addition, BMP2/4 levels influence the decision within ectoderm between epidermal and nonepidermal differentiation.

Nuclear beta-catenin is required to specify vegetal cell fates in the sea urchin embryo

Development ◽  
1999 ◽  
Vol 126 (2) ◽  
pp. 345-357 ◽  
Author(s):  
C.Y. Logan ◽  
J.R. Miller ◽  
M.J. Ferkowicz ◽  
D.R. McClay
Keyword(s):  
Cell Fate ◽  
Sea Urchin ◽  
Beta Catenin ◽  
Cell Fate Specification ◽  
Cell Fates ◽  
Cell Stage ◽  
Animal Pole ◽  
Fate Specification ◽  
The Relationship ◽  
Vegetal Cell

Beta-catenin is thought to mediate cell fate specification events by localizing to the nucleus where it modulates gene expression. To ask whether beta-catenin is involved in cell fate specification during sea urchin embryogenesis, we analyzed the distribution of nuclear beta-catenin in both normal and experimentally manipulated embryos. In unperturbed embryos, beta-catenin accumulates in nuclei that include the precursors of the endoderm and mesoderm, suggesting that it plays a role in vegetal specification. Using pharmacological, embryological and molecular approaches, we determined the function of beta-catenin in vegetal development by examining the relationship between the pattern of nuclear beta-catenin and the formation of endodermal and mesodermal tissues. Treatment of embryos with LiCl, a known vegetalizing agent, caused both an enhancement in the levels of nuclear beta-catenin and an expansion in the pattern of nuclear beta-catenin that coincided with an increase in endoderm and mesoderm. Conversely, overexpression of a sea urchin cadherin blocked the accumulation of nuclear beta-catenin and consequently inhibited the formation of endodermal and mesodermal tissues including micromere-derived skeletogenic mesenchyme. In addition, nuclear beta-catenin-deficient micromeres failed to induce a secondary axis when transplanted to the animal pole of uninjected host embryos, indicating that nuclear beta-catenin also plays a role in the production of micromere-derived signals. To examine further the relationship between nuclear beta-catenin in vegetal nuclei and micromere signaling, we performed both transplantations and deletions of micromeres at the 16-cell stage and demonstrated that the accumulation of beta-catenin in vegetal nuclei does not require micromere-derived cues. Moreover, we demonstrate that cell autonomous signals appear to regulate the pattern of nuclear beta-catenin since dissociated blastomeres possessed nuclear beta-catenin in approximately the same proportion as that seen in intact embryos. Together, these data show that the accumulation of beta-catenin in nuclei of vegetal cells is regulated cell autonomously and that this localization is required for the establishment of all vegetal cell fates and the production of micromere-derived signals.

Altering cell fates in sea urchin embryos by overexpressing SpOtx, an orthodenticle-related protein

Development ◽  
1996 ◽  
Vol 122 (5) ◽  
pp. 1489-1498 ◽  
Author(s):  
C.A. Mao ◽  
A.H. Wikramanayake ◽  
L. Gan ◽  
C.K. Chuang ◽  
R.G. Summers ◽  
...  
Keyword(s):  
Cell Fate ◽  
Sea Urchin ◽  
Biological Effects ◽  
Gene Activation ◽  
Related Protein ◽  
Cell Fates ◽  
Cell Stage ◽  
Morphological Alterations ◽  
Transactivation Domains ◽  
Sea Urchin Embryo

While many general features of cell fate specification in the sea urchin embryo are understood, specific factors associated with these events remain unidentified. SpOtx, an orthodenticle-related protein, has been implicated as a transcriptional activator of the aboral ectoderm-specific Spec2a gene. Here, we present evidence that SpOtx has the potential to alter cell fates. SpOtx was found in the cytoplasm of early cleavage stage embryos and was translocated into nuclei between the 60- and 120-cell stage, coincident with Spec gene activation. Eggs injected with SpOtx mRNA developed into epithelial balls of aboral ectoderm suggesting that SpOtx redirected nonaboral ectoderm cells to an aboral ectoderm fate. At least three distinct domains on SpOtx, the homeobox and regions in the N-terminal and C-terminal halves of the protein, were required for the morphological alterations. These same N-terminal and C-terminal regions were shown to be transactivation domains in a yeast transactivation assay, indicating that the biological effects of overexpressing SpOtx were due to its action as a transcription factor. Our results suggest that SpOtx is involved in aboral ectoderm differentiation by activating aboral ectoderm-specific genes and that modulating its expression can lead to changes in cell fate.

Functional Distinctions for Smad1 and Smad5 during Hematopoiesis Revealed by the Zebrafish Model System.

Blood ◽  
2005 ◽  
Vol 106 (11) ◽  
pp. 3606-3606
Author(s):  
Lisa J. McReynolds ◽  
Mary Mullins ◽  
Todd Evans
Keyword(s):  
Blood Cell ◽  
Hemolytic Anemia ◽  
Expression Patterns ◽  
Bmp Signaling ◽  
Zebrafish Model ◽  
Cell Stage ◽  
Erythroid Progenitor ◽  
Caudal Region ◽  
The One ◽  
Intracellular Mediators

Abstract Smad1 and Smad5 proteins are intracellular mediators of BMP signaling, which has been implicated in regulating hemato-vascular development. Both Smad 1 and 5 are expressed widely in the developing hematopoietic mesoderm, and mutation of either mouse gene is embryonic lethal, limiting progress in defining their function in hematopoiesis. To compare the functions of these two closely related regulatory proteins, we used specific Smad5 mutants and Smad1 morpholinos in the zebrafish model. In the Smad5 mutant, piggytail (pgy), homozygous embryos are dorsalized and live until day 3–5, but have little to no blood and no circulation. Key hematopoietic regulatory genes are expressed in the pgy/pgy mutant fish, but the pattern of expression is altered in early embryos. Gata1, Gata2, Lmo2, draculin and Scl expression patterns are expanded at the five somite stage toward the more caudal region of the mutant embryos. In contrast, the expression pattern of the general mesoderm marker ‘no tail’ is not affected by loss of Smad5. The cells in the most caudal region of the mutant embryos express Gata1 precociously, indicating that they are specified along the erythroid lineage but fail to differentiate. However, Gata1 expression is lost by 48 hpf, as demonstrated in embryos carrying a gata1:gfp transgene on the pgy/pgy background. As in the pgy embryos, injection of a Smad1 morpholino at the one-cell stage leads to a dorzalized phenotype. However, in contrast to pgy embryos, Gata1 expression is maintained in the Smad1 morphants and Gata1 positive cells are found to circulate in the morphant embryos through at least 72 hpf. Our data support an essential role for Smad5 and not Smad1 in embryonic hematopoiesis. To analyze Smad5 function in the adult hematopoietic system, we established adult pgy fish that carry the gata1:gfp transgene, for analysis of blood cell profiles using flow cytometry. Blood cell populations were monitored under normal conditions and following phenylhydrazine induced hemolytic anemia in wildtype and pgy/+ fish. The pgy/+ adult fish are able to mount an erythropoietic response to hemolytic anemia. However, pgy/+ fish at two days post-treatment accumulate 30% of their erythroid progenitor population at the polychromatophilic stage, compared to 10% in wildtype. The pgy/+ fish are thus unable to reconstitute the erythrocyte population in the kidney at a rate comparable to wildtype fish. In summary, our data indicate that Smad5 has a role in the kinetics of embryonic stage erythropoiesis, distinct from the function of Smad1, and in adult erythropoiesis specifically at the transition from the proeyrthroblast to the polychromatophilic erythroblast stage.

Altered expression of spatially regulated embryonic genes in the progeny of separated sea urchin blastomeres

Development ◽  
1989 ◽  
Vol 106 (3) ◽  
pp. 567-579 ◽  
Author(s):  
D.L. Hurley ◽  
L.M. Angerer ◽  
R.C. Angerer
Keyword(s):  
Cell Fate ◽  
Sea Urchin ◽  
Sea Water ◽  
Negative Control ◽  
Normal Embryo ◽  
Cell Stage ◽  
Mrna Accumulation ◽  
Altered Expression ◽  
Intact Embryo ◽  
Dissociated Cells

We have examined the importance of the extracellular environment on the ability of separated cells of sea urchin embryos (Strongylocentrotus purpuratus) to carry out patterns of mRNA accumulation and decay characteristic of intact embryos. Embryos were dissociated into individual blastomeres at 16-cell stage and maintained in calcium-free sea water so that daughter cells continuously separated. Levels of eleven different mRNAs in these cells were compared to those in control embryos when the latter reached mesenchyme blastula stage, by which time cells in major regions of the intact embryo have assumed distinctive patterns of message accumulation. Abrogation of interactions among cells resulted in marked differences in accumulation and/or turnover of the individual mRNAs, which are expressed with diverse temporal and spatial patterns of prevalence in intact embryos. In general, separated cells are competent to execute initial events of mRNA accumulation and decay that occur uniformly in most or all blastomeres of the intact embryo and are likely to be regulated by maternal molecules. The ability of separated cells to accumulate mRNAs that appear slightly later in development depends upon the presumptive tissue in which a given mRNA is found in the normal embryo. Messages that normally accumulate in cells at the vegetal pole also accumulate in dissociated cells either at nearly normal levels or at increased levels. In one such case, that of actin CyIIa, which is normally restricted to mesenchyme cells, in situ hybridization demonstrates that the fraction of dissociated cells expressing this message is 4- to 5-fold higher than in the normal embryo. In contrast, separated cells accumulate significant levels of a message expressed uniformly in the early ectoderm but are unable to execute accumulation and decay of different messages that distinguish oral and aboral ectodermal regions. These data are consistent with the idea that interactions among cells in the intact embryo are important for both positive and negative control of expression of different genes that are early indicators of the specification of cell fate.

scholarly journals β-Catenin is essential for patterning the maternally specified animal-vegetal axis in the sea urchin embryo

1998 ◽  
Vol 95 (16) ◽  
pp. 9343-9348 ◽  
Author(s):  
Athula H. Wikramanayake ◽  
Ling Huang ◽  
William H. Klein
Keyword(s):  
Sea Urchin ◽  
Molecular Mechanisms ◽  
Early Embryo ◽  
Cell Fates ◽  
Cell Stage ◽  
Signal Transduction Cascade ◽  
Sea Urchin Embryos ◽  
Sea Urchin Embryo ◽  
Vegetal Pole ◽  
Vegetal Cell

In sea urchin embryos, the animal-vegetal axis is specified during oogenesis. After fertilization, this axis is patterned to produce five distinct territories by the 60-cell stage. Territorial specification is thought to occur by a signal transduction cascade that is initiated by the large micromeres located at the vegetal pole. The molecular mechanisms that mediate the specification events along the animal–vegetal axis in sea urchin embryos are largely unknown. Nuclear β-catenin is seen in vegetal cells of the early embryo, suggesting that this protein plays a role in specifying vegetal cell fates. Here, we test this hypothesis and show that β-catenin is necessary for vegetal plate specification and is also sufficient for endoderm formation. In addition, we show that β-catenin has pronounced effects on animal blastomeres and is critical for specification of aboral ectoderm and for ectoderm patterning, presumably via a noncell-autonomous mechanism. These results support a model in which a Wnt-like signal released by vegetal cells patterns the early embryo along the animal–vegetal axis. Our results also reveal similarities between the sea urchin animal–vegetal axis and the vertebrate dorsal–ventral axis, suggesting that these axes share a common evolutionary origin.

The allocation of early blastomeres to the ectoderm and endoderm is variable in the sea urchin embryo

Development ◽  
1997 ◽  
Vol 124 (11) ◽  
pp. 2213-2223 ◽  
Author(s):  
C.Y. Logan ◽  
D.R. McClay
Keyword(s):  
Sea Urchin ◽  
Low Frequency ◽  
Initial Step ◽  
Cell Types ◽  
Lytechinus Variegatus ◽  
Cell Fates ◽  
Cell Stage ◽  
Sea Urchin Embryo

During sea urchin development, a tier-to-tier progression of cell signaling events is thought to segregate the early blastomeres to five different cell lineages by the 60-cell stage (E. H. Davidson, 1989, Development 105, 421–445). For example, the sixth equatorial cleavage produces two tiers of sister cells called ‘veg1′ and ‘veg2,’ which were projected by early studies to be allocated to the ectoderm and endoderm, respectively. Recent in vitro studies have proposed that the segregation of veg1 and veg2 cells to distinct fates involves signaling between the veg1 and veg2 tiers (O. Khaner and F. Wilt, 1991, Development 112, 881–890). However, fate-mapping studies on 60-cell stage embryos have not been performed with modern lineage tracers, and cell interactions between veg1 and veg2 cells have not been shown in vivo. Therefore, as an initial step towards examining how archenteron precursors are specified, a clonal analysis of veg1 and veg2 cells was performed using the lipophilic dye, DiI(C16), in the sea urchin species, Lytechinus variegatus. Both veg1 and veg2 descendants form archenteron tissues, revealing that the ectoderm and endoderm are not segregated at the sixth cleavage. Also, this division does not demarcate cell type boundaries within the endoderm, because both veg1 and veg2 descendants make an overlapping range of endodermal cell types. The allocation of veg1 cells to ectoderm and endoderm during cleavage is variable, as revealed by both the failure of veg1 descendants labeled at the eighth equatorial division to segregate predictably to either tissue and the large differences in the numbers of veg1 descendants that contribute to the ectoderm. Furthermore, DiI-labeled mesomeres of 32-cell stage embryos also contribute to the endoderm at a low frequency. These results show that the prospective archenteron is produced by a larger population of cleavage-stage blastomeres than believed previously. The segregation of veg1 cells to the ectoderm and endoderm occurs relatively late during development and is unpredictable, indicating that later cell position is more important than the early cleavage pattern in determining ectodermal and archenteron cell fates.

scholarly journals The BMP signaling pathway is required together with the FGF pathway for notochord induction in the ascidian embryo

Development ◽  
2001 ◽  
Vol 128 (14) ◽  
pp. 2629-2638 ◽  
Author(s):  
Sébastien Darras ◽  
Hiroki Nishida
Keyword(s):  
Time Window ◽  
Bmp Signaling ◽  
Cell Stage ◽  
Morphogenetic Protein ◽  
Positive Target ◽  
Bmp Pathway ◽  
Notochord Cells ◽  
Bmp Antagonist ◽  
Ascidian Embryo

The 40 notochord cells of the ascidian tadpole invariably arise from two different lineages: the primary (A-line) and the secondary (B-line) lineages. It has been shown that the primary notochord cells are induced by presumptive endoderm blastomeres between the 24-cell and the 64-cell stage. Signaling through the fibroblast growth factor (FGF) pathway is required for this induction. We have investigated the role of the bone morphogenetic protein (BMP) pathway in ascidian notochord formation. HrBMPb (the ascidian BMP2/4 homologue) is expressed in the anterior endoderm at the 44-cell stage before the completion of notochord induction. The BMP antagonist Hrchordin is expressed in a complementary manner in all surrounding blastomeres and appears to be a positive target of the BMP pathway. Unexpectedly, chordin overexpression reduced formation of both primary and secondary notochord. Conversely, primary notochord precursors isolated prior to induction formed notochord in presence of BMP-4 protein. While bFGF protein had a similar activity, notochord precursors showed a different time window of competence to respond to BMP-4 and bFGF. Our data are consistent with bFGF acting from the 24-cell stage, while BMP-4 acts during the 44-cell stage. However, active FGF signaling was also required for induction by BMP-4. In the secondary lineage, notochord specification also required two inducing signals: an FGF signal from anterior and posterior endoderm from the 24-cell stage and a BMP signal from anterior endoderm during the 44-cell stage.

Tracing the origin of the placental trophoblast cells in mouse embryo development†

2019 ◽  
Vol 102 (3) ◽  
pp. 598-606
Author(s):  
Shanshan Guo ◽  
Xiuhong Cui ◽  
Xiangxiang Jiang ◽  
Shuguang Duo ◽  
Shiwen Li ◽  
...  
Keyword(s):  
Gene Expression ◽  
Cell Fate ◽  
Inner Cell Mass ◽  
Expression Patterns ◽  
Cell Mass ◽  
Cell Fates ◽  
Cell Stage ◽  
Mouse Fetus ◽  
Cell Fate Decisions ◽  
Distinct Cell

Abstract The placenta, which originates from the trophectoderm (TE), is the first organ to form during mammalian embryogenesis. Recent studies based on bioinformatics analysis have revealed that heterogeneous gene expression initiates cell-fate decisions and directs two distinct cell fates by modulating the balance of pluripotency and differentiation as early as the four-cell stage. However, direct developmental evidence to support this is still lacking. To address at which stage the cell fate of the TE and inner cell mass (ICM) is determined, in this study, we administered a microinjection of Cre mRNA into a single blastomere of the mTmG mouse at different cleavage stages before implantation to examine the distributions of the descendants of the single-labeled cell in the mouse fetus and the placenta at E12.5. We found that the descendants of the labeled cells at the two-cell stage contributed to both the placenta and the fetus. Notably, the derivatives of the labeled cells at the four-cell stage fell into three categories: (1) distributed in both embryonic and extraembryonic lineages, (2) distributed only in mouse placental trophoblast layers, or (3) distributed only in the lineage derived from the ICM. In addition, these results fell in line with single-cell studies focusing on gene expression patterns that characterize particular lineages within the blastocyst. In conclusion, this study shows that the four-cell blastomeres differ in their individual developmental properties insofar as they contribute to either or both the ICM and trophoblast fate.

HpEtsimplicated in primary mesenchyme cell differentiation of the sea urchin (Hemicentrotus pulcherrimus) embryo

Zygote ◽  
1999 ◽  
Vol 8 (S1) ◽  
pp. S33-S34 ◽  
Author(s):  
Daisuke Kurokawa ◽  
Takashi Kitajima ◽  
Keiko Mitsunaga-Nakatsubo ◽  
Shonan Amemiya ◽  
Hiraku Shimada ◽  
...  
Keyword(s):  
Cell Fate ◽  
Sea Urchin ◽  
Sea Urchins ◽  
Marker Genes ◽  
Asymmetric Distribution ◽  
Specific Marker ◽  
Cell Stage ◽  
Mesenchyme Cell ◽  
Maternal Determinants ◽  
And Function

In sea urchin embryogenesis it has been suggested that the initial territories are specified by a combination of the asymmetric distribution of cytoplasmic determinants and cell-cell interactions. At the 60-cell stage blastomeres clonally originated from founder cells divide the embryo into five distinct territories: small micromeres, large micromeres, vegetal plate, oral ectoderm and aboral ectoderm. The territories are identified by the expression of specific marker genes and their cell lineages (Davidson, 1989, 1991). The large micromeres are thought to play a role as an organiser and initiate a cascade of signal transduction toward overlying cells (Davidson, 1989). In this model the large micromeres induce the overlying veg2 tier, specifying the vegetal plate (Ransick & Davidson, 1993, 1995). The veg2 tier then induces the overlying cells, which include gut cells and cells of the prospective ectodermal territories (Wikramanayakeet al., 1995; Wikramanayake & Klein, 1997). Thus, the large micromeres, which are the prospective primary mesenchyme cells (PMCs), play a key role in cell fate specification and axis determination during sea urchin embryogenesis. Previous data suggested that the large micromeres are autonomously specified to become PMCs by maternally inherited determinants (Okazaki, 1975; Kitajima & Okazaki, 1980). An important question in sea urchins embryogenesis is the identity and function of the proposed maternal determinants.

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