The Xenopus homologue of Bicaudal-C is a localized maternal mRNA that can induce endoderm formation

Development ◽  
2000 ◽  
Vol 127 (10) ◽  
pp. 2053-2062 ◽  
Author(s):  
O. Wessely ◽  
E.M. De Robertis
Keyword(s):  
Rna Binding ◽  
Ectopic Expression ◽  
Dorsal Side ◽  
Mesoderm Induction ◽  
Midblastula Transition ◽  
Dorsoventral Axis ◽  
Maternal Mrna ◽  
Zygotic Transcription ◽  
Maternal Mrnas ◽  
Synthetic Mrna

In Xenopus, zygotic transcription starts 6 hours after fertilization at the midblastula transition and therefore the first steps in embryonic development are regulated by maternally inherited proteins and mRNAs. While animal-vegetal polarity is already present in the oocyte, the dorsoventral axis is only established upon fertilization by the entry of the sperm and the subsequent rotation of the egg cortex. In a screen for maternal mRNAs whose stability is regulated by this cortical rotation, we isolated the Xenopus homologue of the Drosophila gene Bicaudal-C (xBic-C). It encodes a putative RNA-binding molecule expressed maternally and localized predominantly to the vegetal half of the egg. Upon fertilization and cortical rotation, xBic-C mRNA is displaced together with the heavy yolk towards the future dorsal side of the embryo. In UV-ventralized embryos, xBic-C is polyadenylated less than in untreated embryos that undergo cortical rotation. Overexpression of xBic-C by injection of synthetic mRNA in whole embryos or in ectodermal explants leads to ectopic endoderm formation. This endoderm-inducing activity is dependent on the presence of the RNA-binding domain of the protein. In contrast to the two other known maternally encoded endoderm inducers, Vg1 and VegT, xBic-C ectopic expression leads specifically to endoderm formation in the absence of mesoderm induction.

scholarly journals Sequential regulation of maternal mRNAs through a conserved cis-acting element in their 3’UTRs

2018 ◽  
Author(s):  
Pooja Flora ◽  
Siu Wah Wong-Deyrup ◽  
Elliot Todd Martin ◽  
Ryan J Palumbo ◽  
Mohamad Nasrallah ◽  
...  
Keyword(s):  
Rna Binding ◽  
Rna Binding Proteins ◽  
Polar Granule ◽  
Regulatory Sequence ◽  
Cis Acting ◽  
Maternal Mrna ◽  
Hand Off ◽  
Maternal Mrnas ◽  
Translational Regulators ◽  
Regulatory Landscape

AbstractMaternal mRNAs are synthesized during oogenesis to initiate the development of future generations. Some maternal mRNAs are determinants of somatic or germline fate and must be translationally repressed until embryogenesis. However, the translational repressors themselves are also temporally regulated. We use polar granule component (pgc), a Drosophila maternal mRNA, as a model system to ask how maternal mRNAs are repressed while the regulatory landscape is continually shifting. pgc, a potent transcriptional silencer and germline determinant, is translationally regulated throughout oogenesis. We find that the 3’UTR of pgc mRNA contains a conserved ten-nucleotide sequence that is bound by different conserved RNA binding proteins (RBPs) at different stages of oogenesis to continuously repress translation except for a brief expression in the stem cell daughter. Pumilio (Pum) binds to this sequence in undifferentiated and early differentiating oocytes and recruits other temporally restricted translational regulators to block pgc translation. After differentiation, Pum levels diminish and Bruno (Bru) levels increase, allowing Bru to bind the same 3’UTR sequence and take over translational repression of pgc mRNA. We have identified a class of maternal mRNAs regulated during oogenesis by both Pum and Bru, including Zelda, activator of the zygotic genome, which contain this core 10-nt regulatory sequence. Our data suggests that this hand off mechanism is more generally utilized to inhibit translation of maternal mRNAs during oogenesis.

Localized synthesis of the Vg1 protein during early Xenopus development

Development ◽  
1989 ◽  
Vol 106 (4) ◽  
pp. 775-785 ◽  
Author(s):  
D. Tannahill ◽  
D.A. Melton
Keyword(s):  
Growth Factors ◽  
Growth Factor ◽  
Small Proportion ◽  
Stage Iv ◽  
Early Embryo ◽  
Mesoderm Induction ◽  
Gastrula Stage ◽  
Small Peptide ◽  
Amphibian Embryo ◽  
Maternal Mrna

The Xenopus Vg1 gene encodes a maternal mRNA that is localized to the vegetal hemisphere of both oocytes and embryos and encodes a protein related to the TGF-beta family of small secreted growth factors. We have raised antibodies to recombinant Vg1 protein and used them to show that Vg1 protein is first detected in stage IV oocytes and reaches maximal levels in stage VI oocytes and eggs. During embryogenesis, Vg1 protein is synthesized until the gastrula stage. The embryonically synthesized Vg1 protein is present only in vegetal cells of an early blastula. We find that Vg1 protein is glycosylated and associated with membranes in the early embryo. Our results also suggest that a small proportion of the full-length Vg1 protein is cleaved to give a small peptide of M(r) = approximately 17 × 10(3). These results support the proposal that the Vg1 protein is an endogenous growth-factor-like molecule involved in mesoderm induction within the amphibian embryo.

Misexpression of chick Vg1 in the marginal zone induces primitive streak formation

Development ◽  
1997 ◽  
Vol 124 (24) ◽  
pp. 5127-5138 ◽  
Author(s):  
S.B. Shah ◽  
I. Skromne ◽  
C.R. Hume ◽  
D.S. Kessler ◽  
K.J. Lee ◽  
...  
Keyword(s):  
Marginal Zone ◽  
Ectopic Expression ◽  
Primitive Streak ◽  
Axis Formation ◽  
Mesoderm Induction ◽  
Cell Fates ◽  
Signalling Molecules ◽  
Posterior Area ◽  
Area Pellucida

In the chick embryo, the primitive streak is the first axial structure to develop. The initiation of primitive streak formation in the posterior area pellucida is influenced by the adjacent posterior marginal zone (PMZ). We show here that chick Vg1 (cVg1), a member of the TGFbeta family of signalling molecules whose homolog in Xenopus is implicated in mesoderm induction, is expressed in the PMZ of prestreak embryos. Ectopic expression of cVg1 protein in the marginal zone chick blastoderms directs the formation of a secondary primitive streak, which subsequently develops into an ectopic embryo. We have used cell marking techniques to show that cells that contribute to the ectopic primitive streak change fate, acquiring two distinct properties of primitive streak cells, defined by gene expression and cell movements. Furthermore, naive epiblast explants exposed to cVg1 protein in vitro acquire axial mesodermal properties. Together, these results show that cVg1 can mediate ectopic axis formation in the chick by inducing new cell fates and they permit the analysis of distinct events that occur during primitive streak formation.

scholarly journals Specificity of RNA Binding by CPEB: Requirement for RNA Recognition Motifs and a Novel Zinc Finger

1998 ◽  
Vol 18 (2) ◽  
pp. 685-693 ◽  
Author(s):  
Laura E. Hake ◽  
Raul Mendez ◽  
Joel D. Richter
Keyword(s):  
Zinc Finger ◽  
Rna Binding ◽  
Rna Recognition ◽  
Cytoplasmic Polyadenylation ◽  
Functional Motif ◽  
Rna Recognition Motifs ◽  
Amino Terminal ◽  
Terminal Amino ◽  
Maternal Mrnas ◽  
Recognition Motifs

ABSTRACT CPEB is an RNA binding protein that interacts with the maturation-type cytoplasmic polyadenylation element (CPE) (consensus UUUUUAU) to promote polyadenylation and translational activation of maternal mRNAs in Xenopus laevis. CPEB, which is conserved from mammals to invertebrates, is composed of three regions: an amino-terminal portion with no obvious functional motif, two RNA recognition motifs (RRMs), and a cysteine-histidine region that is reminiscent of a zinc finger. In this study, we investigated the physical properties of CPEB required for RNA binding. CPEB can interact with RNA as a monomer, and phosphorylation, which modifies the protein during oocyte maturation, has little effect on RNA binding. Deletion mutations of CPEB have been overexpressed inEscherichia coli and used in a series of RNA gel shift experiments. Although a full-length and a truncated CPEB that lacks 139 amino-terminal amino acids bind CPE-containing RNA avidly, proteins that have had either RRM deleted bind RNA much less efficiently. CPEB that has had the cysteine-histidine region deleted has no detectable capacity to bind RNA. Single alanine substitutions of specific cysteine or histidine residues within this region also abolish RNA binding, pointing to the importance of this highly conserved domain of the protein. Chelation of metal ions by 1,10-phenanthroline inhibits the ability of CPEB to bind RNA; however, RNA binding is restored if the reaction is supplemented with zinc. CPEB also binds other metals such as cobalt and cadmium, but these destroy RNA binding. These data indicate that the RRMs and a zinc finger region of CPEB are essential for RNA binding.

Endogenous patterns of TGFbeta superfamily signaling during early Xenopus development

Development ◽  
2000 ◽  
Vol 127 (13) ◽  
pp. 2917-2931 ◽  
Author(s):  
S. Faure ◽  
M.A. Lee ◽  
T. Keller ◽  
P. ten Dijke ◽  
M. Whitman
Keyword(s):  
Transforming Growth Factor Beta ◽  
Transforming Growth Factor ◽  
Ectopic Expression ◽  
Xenopus Embryo ◽  
Bmp Signaling ◽  
Type I ◽  
Embryonic Cells ◽  
Xenopus Development ◽  
Zygotic Transcription ◽  
Carboxy Terminal

Transforming growth factor beta (TGFbeta) superfamily signaling has been implicated in patterning of the early Xenopus embryo. Upon ligand stimulation, TGFbeta receptors phosphorylate Smad proteins at carboxy-terminal SS(V/M)S consensus motifs. Smads 1/5/8, activated by bone morphogenetic protein (BMP) signaling, induce ventral mesoderm whereas Smad2, activated by activin-like ligands, induces dorsal mesoderm. Although ectopic expression studies are consistent with roles for TGFbeta signals in early Xenopus embryogenesis, when and where BMP and activin-like signaling pathways are active endogenously has not been directly examined. In this study, we investigate the temporal and spatial activation of TGFbeta superfamily signaling in early Xenopus development by using antibodies specific for the type I receptor-phosphorylated forms of Smad1/5/8 and Smad2. We find that Smad1/5/8 and two distinct isoforms of Smad2, full-length Smad2 and Smad2(delta)exon3, are phosphorylated in early embryos. Both Smad1/5/8 and Smad2/Smad2(delta)exon3 are activated after, but not before, the mid-blastula transition (MBT). Endogenous activation of Smad2/Smad2(delta)exon3 requires zygotic transcription, while Smad1/5/8 activation at MBT appears to involve transcription-independent regulation. We also find that the competence of embryonic cells to respond to TGF(delta) superfamily ligands is temporally regulated and may be a determinant of early patterning. Levels of phospho-Smad1/5/8 and of phospho-Smad2/Smad2(delta)exon3 are asymmetrically distributed across both the animal-vegetal and dorsoventral axes. The timing of the development of these asymmetries differs for phospho-Smad1/5/8 and for phospho-Smad2/Smad2(delta)exon3, and the spatial distribution of phosphorylation of each Smad changes dramatically as gastrulation begins. We discuss the implications of our results for endogenous functions of BMP and activin-like signals as candidate morphogens regulating primary germ layer formation and dorsoventral patterning of the early Xenopus embryo.

FGF signalling in the early specification of mesoderm in Xenopus

Development ◽  
1993 ◽  
Vol 118 (2) ◽  
pp. 477-487 ◽  
Author(s):  
E. Amaya ◽  
P.A. Stein ◽  
T.J. Musci ◽  
M.W. Kirschner
Keyword(s):  
Dorsal Side ◽  
Dominant Negative ◽  
Early Gene ◽  
Immediate Early ◽  
Mesoderm Induction ◽  
Fgf Receptor ◽  
Muscle Formation ◽  
Fgf Signalling ◽  
Lateral Mesoderm

We have examined the role of FGF signalling in the development of muscle and notochord and in the expression of early mesodermal markers in Xenopus embryos. Disruption of the FGF signalling pathway by expression of a dominant negative construct of the FGF receptor (XFD) generally results in gastrulation defects that are later evident in the formation of the trunk and tail, though head structures are formed nearly normally. These defects are reflected in the loss of notochord and muscle. Even in embryos that show mild defects and gastrulate properly, muscle formation is impaired, suggesting that morphogenesis and tissue differentiation each depend on FGF. The XFD protein inhibits the expression of the immediate early gene brachyury throughout the marginal zone, including the dorsal side; it does not, however, inhibit the dorsal lip marker goosecoid, which is expressed in the first involuting mesoderm at the dorsal side that will underlie the head. The XFD protein also inhibits Xpo expression, an immediate early marker of ventral and lateral mesoderm. These results suggest that FGF is involved in the earliest events of most mesoderm induction that occur before gastrulation and that the early dorsal mesoderm is already composed of two cell populations that differ in their requirements for FGF.

Maternal beta-catenin establishes a ‘dorsal signal’ in early Xenopus embryos

Development ◽  
1996 ◽  
Vol 122 (10) ◽  
pp. 2987-2996 ◽  
Author(s):  
C. Wylie ◽  
M. Kofron ◽  
C. Payne ◽  
R. Anderson ◽  
M. Hosobuchi ◽  
...  
Keyword(s):  
Glycogen Synthase ◽  
Axis Formation ◽  
Beta Catenin ◽  
Cell Stage ◽  
Midblastula Transition ◽  
Xenopus Embryos ◽  
Ability To Act ◽  
Zygotic Transcription ◽  
Spatial Terms ◽  
Marginal Zones

In previous work, we demonstrated that maternally encoded beta-catenin, the vertebrate homolog of armadillo, is required for formation of dorsal axial structures in early Xenopus embryos (Heasman, J., Crawford, A., Goldstone, K., Garner-Hamrick, P., Gumbiner, B., Kintner, C., Yoshida-Noro, C. and Wylie, C. (1994). Cell 79, 791–803). Here we investigated, firstly, the role(s) of beta-catenin in spatial terms, in different regions of the embryo, by injecting beta-catenin mRNA into individual blastomeres of beta-catenin-depleted embryos at the 32 cell stage. The results indicate that beta-catenin can rescue the dorsal axial structures in a non-cell-autonomous way and without changing the fates of the injected cells. This suggests that cells overexpressing beta-catenin send a ‘dorsal signal’ to other cells. This was confirmed by showing that beta-catenin overexpressing animal caps did not cause wild-type caps to form mesoderm, but did cause isolated beta-catenin-deficient marginal zones to form dorsal mesoderm. Furthermore beta-catenin-deficient vegetal masses treated with overexpressing caps regained their ability to act as Nieuwkoop Centers. Secondly, we studied the temporal activity of beta-catenin. We showed that zygotic transcription of beta-catenin starts after the midblastula transition (MBT), but does not rescue dorsal axial structures. We further demonstrated that the vegetal mass does not release a dorsal signal until after the onset of transcription, at the midblastula stage, suggesting that maternal beta-catenin protein is required at or before this time. Thirdly we investigated where, in relationship to other gene products known to be active in axis formation, beta-catenin is placed. We find that BVg1, bFGF, tBR (the truncated form of BMP2/4R), siamois and noggin activities are all downstream of beta-catenin, as shown by the fact that injection of their mRNAs rescues the effect of depleting maternally encoded beta-catenin. Interference with the action of glycogen synthase kinase (GSK), a vertebrate homolog of the Drosophila gene product, zeste white 3 kinase, does not rescue the effect, suggesting that it is upstream.

XIPOU 2, a noggin-inducible gene, has direct neuralizing activity

Development ◽  
1995 ◽  
Vol 121 (3) ◽  
pp. 721-730 ◽  
Author(s):  
S.E. Witta ◽  
V.R. Agarwal ◽  
S.M. Sato
Keyword(s):  
Cell Fate ◽  
Neural Induction ◽  
Mesoderm Induction ◽  
Class Iii ◽  
Cell Stage ◽  
Neuronal Phenotype ◽  
Pou Domain ◽  
Spemann's Organizer ◽  
Stage Embryo ◽  
Synthetic Mrna

XIPOU 2, a member of the class III POU domain family, is expressed initially in Spemann's organizer, and later, in discrete regions of the developing nervous system in Xenopus laevis. XIPOU 2 may act downstream from initial neural induction events, since it is activated by the neural inducer, noggin. To determine if XIPOU 2 participates in the early events of neurogenesis, synthetic mRNA was microinjected into specific blastomeres of the 32-cell stage embryo. Misexpression of XIPOU 2 in the epidermis causes a direct switch in cell fate from an epidermal to a neuronal phenotype. In the absence of mesoderm induction, XIPOU 2 has the ability to induce a neuronal phenotype in uncommitted ectoderm. These data demonstrate the potential of XIPOU 2 to act as a master regulator of neurogenesis.

Sequential activation of the EGF receptor pathway during Drosophila oogenesis establishes the dorsoventral axis

Development ◽  
1998 ◽  
Vol 125 (2) ◽  
pp. 191-200 ◽  
Author(s):  
A. Sapir ◽  
R. Schweitzer ◽  
B.Z. Shilo
Keyword(s):  
Target Genes ◽  
Egf Receptor ◽  
Ectopic Expression ◽  
Follicle Cell ◽  
Follicle Cells ◽  
Cell Fates ◽  
Dorsoventral Axis ◽  
Spatial Coordinates ◽  
Sequential Activation

Previous work has demonstrated a role for the Drosophila EGF receptor (Torpedo/DER) and its ligand, Gurken, in the determination of anterioposterior and dorsoventral axes of the follicle cells and oocyte. The roles of DER in establishing the polarity of the follicle cells were examined further, by following the expression of DER-target genes. One class of genes (e.g. kekon) is induced by the DER pathway at all stages. Broad expression of kekon at the stage in which the follicle cells migrate posteriorly over the oocyte, demonstrates the capacity of the pathway to pattern all follicle cells except the ventral-most rows. This may provide the spatial coordinates for the ventral-most follicle cell fates. A second group of target genes (e.g. rhomboid (rho)) is induced only at later stages of oogenesis, and may require additional inputs by signals emanating from the anterior, stretch follicle cells. The function of Rho was analyzed by ectopic expression in the stretch follicle cells, and shown to induce a non-autonomous dorsalizing activity that is independent of Gurken. Rho thus appears to be involved in processing a DER ligand in the follicle cells, to pattern the egg chamber and allow persistent activation of the DER pathway during formation of the dorsal appendages.

Regulation of dorsal-ventral patterning: the ventralizing effects of the novel Xenopus homeobox gene Vox

Development ◽  
1996 ◽  
Vol 122 (6) ◽  
pp. 1711-1721 ◽  
Author(s):  
J.E. Schmidt ◽  
G. von Dassow ◽  
D. Kimelman
Keyword(s):  
Dynamic Process ◽  
Regulatory Network ◽  
Ectopic Expression ◽  
Homeobox Gene ◽  
Normal Function ◽  
Dorsal Side ◽  
Neural Plate ◽  
The Novel ◽  
Cell Fates ◽  
Early Developmental

The formation of the dorsal-ventral axis in Xenopus laevis is elicited by a signaling cascade on the dorsal side of the embryo initiated by cortical rotation. These early developmental events impart an initial axial polarity to the embryo. By the time gastrulation occurs, the embryo has established opposing dorsal and ventral regulatory regions. Through a dynamic process, the embryo acquires a definitive pattern that reflects the distribution of future cell fates. Here we present a novel homeobox gene, Vox, whose expression reflects this dynamic process. Vox is first expressed throughout the embryo and subsequently eliminated from the notochord and neural plate. Ectopic expression of Vox demonstrates that the normal function of this gene may be to suppress dorsal genes such as Xnot and chordin, and induce ventral and paraxial genes such as Bmp-4 and MyoD. Ectopic expression of BMP-4 ventralizes embryos and positively regulates the expression of Vox, suggesting that these genes are components of a reciprocal regulatory network.

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