The nature of developmental restrictions in Xenopus laevis embryos

Development ◽  
1986 ◽  
Vol 97 (Supplement) ◽  
pp. 65-73
Author(s):  
Janet Heasman ◽  
Alison Snape ◽  
J. C. Smith ◽  
C. C. Wylie
Keyword(s):  
Xenopus Laevis ◽  
Single Cells ◽  
Cell Interaction ◽  
Blastula Stage ◽  
Vegetal Pole ◽  
Transplantation Technique ◽  
Pole Cells ◽  
Early Gastrula ◽  
Xenopus Laevis Embryos

Fate maps of the late blastula stage of the Xenopus laevis embryo indicate that the cells of the vegetal pole area are destined to become part of the endoderm germ layer (Keller, 1975; Heasman, Wylie, Hausen & Smith, 1984). By labelling single cells from this region and transplanting them into the blastocoel cavity of host embryos, we have shown that the determinative process that restricts blastomeres to this their normal fate occurs between the early blastula and early gastrula stages (Heasman et al. 1984). To progress towards an understanding of this process, we need to establish some fundamental points. In particular, the following issues are discussed here. (1) Is cell interaction required for determination to proceed? (2) What is the cellular nature of determination? We have used the labelling and transplantation technique described previously (Heasman, Snape, Smith & Wylie, 1985; Heasman, Snape, Smith, Holwill & Wylie, 1985) to study these questions in relation to the mechanism of determination of vegetal pole cells in Xenopus laevis.

scholarly journals Postfertilization deadenylation of mRNAs in Xenopus laevis embryos is sufficient to cause their degradation at the blastula stage.

1997 ◽  
Vol 17 (1) ◽  
pp. 209-218 ◽  
Author(s):  
Y Audic ◽  
F Omilli ◽  
H B Osborne
Keyword(s):  
Xenopus Laevis ◽  
Untranslated Region ◽  
Sequence Information ◽  
Blastula Stage ◽  
Cytoplasmic Polyadenylation ◽  
Cis Acting ◽  
Stage Of Development ◽  
Chimeric Rnas ◽  
Xenopus Laevis Embryos

Although the maternal Xenopus laevis Eg mRNAs are deadenylated after fertilization, they are not immediately degraded and they persist in the embryos as poly(A)- transcripts. The degradation of these RNAs is not detected until the blastula stage of development (6 to 7 h postfertilization). To understand the basis for this delay between deadenylation and degradation, it is necessary to identify the cis-acting element(s) required to trigger degradation in blastula stage embryos. To this end, several chimeric RNAs containing different portions of the 3' untranslated region of Eg2 mRNA were injected into two-cell X. laevis embryos. We observed that only the RNAs that contained the cis-acting elements that confer rapid deadenylation were subsequently degraded at the blastula stage. This suggested that deadenylation may be sufficient to trigger degradation. By injecting chimeric RNAs devoid of Eg sequence information, we further showed that only deadenylated RNAs were degraded in X. laevis embryos. Last, introduction of a functional cytoplasmic polyadenylation element into a poly(A)- RNA, thereby causing its polyadenylation after injection into embryos, protected the RNA from degradation. Hence, in X. laevis embryos, the postfertilization deadenylation of maternal Eg mRNAs is sufficient to cause the degradation of an mRNA, which, however, only becomes apparent at the blastula stage. Possible causes for this delay between deadenylation and degradation are discussed in the light of these results.

scholarly journals Gastrulation movements provide an early marker of mesoderm induction in Xenopus laevis

Development ◽  
1987 ◽  
Vol 101 (2) ◽  
pp. 339-349 ◽  
Author(s):  
K. Symes ◽  
J.C. Smith
Keyword(s):  
Cell Division ◽  
Xenopus Laevis ◽  
Early Response ◽  
Model System ◽  
Mesoderm Induction ◽  
Animal Pole ◽  
Inductive Interaction ◽  
Vegetal Pole ◽  
Pole Cells ◽  
General Appearance

The first inductive interaction in amphibian development is mesoderm induction, in which an equatorial mesodermal rudiment is induced from the animal hemisphere under the influence of a signal from vegetal pole blastomeres. We have recently discovered that the Xenopus XTC cell line secretes a factor which has the properties we would expect of a mesoderm-inducing factor. In this paper, we show that an early response to this factor by isolated Xenopus animal pole regions is a change in shape, involving elongation and constriction. We show by several criteria, including general appearance, timing, rate of elongation and the nonrequirement for cell division that these movements resemble the events of gastrulation. We also demonstrate that the movements provide an early, simple and reliable indicator of mesoderm induction and are of use in providing a ‘model system’ for the study of mesoderm induction and gastrulation. For example, we show that the timing of gastrulation movements does not depend upon the time of receipt of a mesoderm-induction signal, but on an intrinsic gastrulation ‘clock’ which is present even in those animal pole cells that would not nomally require it.

An autoradiographic analysis of nucleic acid synthesis in the presumptive primordial germ cells of Xenopus laevis

Development ◽  
1977 ◽  
Vol 37 (1) ◽  
pp. 13-31
Author(s):  
Marie Dziadek ◽  
K. E. Dixon
Keyword(s):  
Xenopus Laevis ◽  
Germ Cells ◽  
Rna Synthesis ◽  
Primordial Germ Cells ◽  
Acid Synthesis ◽  
Tail Bud ◽  
Blastula Stage ◽  
Autoradiographic Analysis ◽  
The One ◽  
Xenopus Laevis Embryos

Microinjection of [3H]thymidine into Xenopus laevis embryos between late blastula (stage 10) and early tadpole (stage 44) showed that the presumptive primordial germ cells synthesise DNA between stages 10–33. The percentage of labelled cells was highest between stages 10 and 16, declined sharply between stages 22 and 26 and rose again between stages 26 and 33. The fluctuations in the labelling patterns together with increase in the number of presumptive primordial germ cells and direct observation of germ cells in mitosis suggested that the germ cells divide three times between stages 10 and 44. The first divisions probably take place during gastrulation (stages 10–12), the second relatively synchronously at about stages 22–24 and the third series again relatively synchronously about stages 37–39. This period of proliferative activity is distinguishable on the one hand from the cleavage divisions in which the number of germ cells does not increase and on the other hand from the next proliferative phase by a period of mitotic inactivity. Microinjection of [3H]uridine showed that the presumptive primordial germ cells synthesize RNA only in mid-gastrula to early tail-bud-stage embryos. There is no obvious simple causal relationship between RNA synthesis and the movement of the germ plasm to the nucleus, or with division of the germ cells or with their migration out of the endoderm.

Vegetal pole cells and commitment to form endoderm in Xenopus laevis

1987 ◽  
Vol 119 (2) ◽  
pp. 496-502 ◽  
Author(s):  
C.C. Wylie ◽  
Alison Snape ◽  
J. Heasman ◽  
J.C. Smith
Keyword(s):  
Xenopus Laevis ◽  
Vegetal Pole ◽  
Pole Cells

On the determination of the dorso-ventral polarity in Xenopus laevis embryos

Development ◽  
1975 ◽  
Vol 33 (4) ◽  
pp. 879-895
Author(s):  
Ulf Landström ◽  
Søren Løvtrup
Keyword(s):  
Oxygen Consumption ◽  
Xenopus Laevis ◽  
Oxygen Supply ◽  
Substantial Reduction ◽  
Total Consumption ◽  
Time Treatment ◽  
Oxygen Effects ◽  
Significant Difference ◽  
Xenopus Laevis Embryos

1. When embryos, or dorsal or ventral half-embryos, of Xenopus laevis are subjected to unilateral restriction of oxygen supply, the posterior end will always appear at the aerobic side, while the development of the anterior end, oriented towards the anaerobic side, will be partly suppressed. The shorter the time treatment lasts, the more normal the development will be. 2. When the restriction of oxygen effects an inversion of the dorso-ventral polarity, development is retarded, otherwise not. 3. Measurements of oxygen consumption show a substantial reduction in the experimental embryos, as compared with normal ones. The change in oxygen consumption in inverted embryos is delayed relative to non-inverted ones, but there is no significant difference in the total consumption of oxygen. 4. Our results support the idea that the dorso-ventral polarity is associated with a gradient in oxygen consumption, and various kinds of evidence suggest that oxygen consumption is, in part, required for the formation of Ruffini's flask-cells, responsible for the initiation of invagination. 5. It is suggested that the basic mechanisms involved in the determination of the normal, and the inverted, dorso-ventral polarity are fundamentally different, the latter being in fact an induction of a new polarity.

scholarly journals Fate map for the 32-cell stage of Xenopus laevis

Development ◽  
1987 ◽  
Vol 99 (4) ◽  
pp. 527-551 ◽  
Author(s):  
L. Dale ◽  
J.M. Slack
Keyword(s):  
Xenopus Laevis ◽  
Short Range ◽  
Three Dimensional ◽  
Spatial Localization ◽  
Spatial Location ◽  
Fate Map ◽  
Cell Stage ◽  
Range Cell ◽  
Early Gastrula ◽  
Xenopus Laevis Embryos

A complete fate map has been produced for the 32-cell stage of Xenopus laevis. Embryos with a regular cleavage pattern were selected and individual blastomeres were injected with the lineage label fluorescein-dextran-amine (FDA). The spatial location of the clones was deduced from three-dimensional (3D) reconstructions of later stages and the volume of each tissue colonized by labelled cells in each tissue was measured. The results from 107 cases were pooled to give a fate map which shows the fate of each blastomere in terms of tissue types, the composition of each tissue by blastomere, the location of each prospective region on the embryo and the fate of each blastomere in terms of spatial localization. Morphogenetic movements up to stage 10 (early gastrula) were assessed by carrying out a number of orthotopic grafts at blastula and gastrula stages using donor embryos uniformly labelled with FDA. Although there is a regular topographic projection from the 32-cell stage this varies a little between individuals because of variability of positions of cleavage planes and because of short-range cell mixing during gastrulation. The cell mixing means that the topographic projection fails for anteroposterior segments of the dorsal axial structures and it is not possible to include short segments of notochord or neural tube or individual somites on the pregastrulation fate map.

Determination of the zebrafish forebrain: induction and patterning

Development ◽  
1998 ◽  
Vol 125 (22) ◽  
pp. 4403-4416 ◽  
Author(s):  
Y. Grinblat ◽  
J. Gamse ◽  
M. Patel ◽  
H. Sive
Keyword(s):  
Danio Rerio ◽  
Zinc Finger Protein ◽  
Blastula Stage ◽  
Finger Protein ◽  
Forkhead Domain ◽  
Prechordal Plate ◽  
Organizing Center ◽  
Early Gastrula

We report an analysis of forebrain determination and patterning in the zebrafish Danio rerio. In order to study these events, we isolated zebrafish homologs of two neural markers, odd-paired-like (opl), which encodes a zinc finger protein, and fkh5, which encodes a forkhead domain protein. At mid-gastrula, expression of these genes defines a very early pattern in the presumptive neurectoderm, with opl later expressed in the telencephalon, and fkh5 in the diencephalon and more posterior neurectoderm. Using in vitro explant assays, we show that forebrain induction has occurred even earlier, by the onset of gastrulation (shield stage). Signaling from the early gastrula shield, previously shown to be an organizing center, is sufficient for activation of opl expression in vitro. In order to determine whether the organizer is required for opl regulation, we removed from late blastula stage embryos either the presumptive prechordal plate, marked by goosecoid (gsc) expression, or the entire organizer, marked by chordin (chd) expression. opl was correctly expressed after removal of the presumptive prechordal plate and consistently, opl was correctly expressed in one-eyed pinhead (oep) mutant embryos, where the prechordal plate fails to form. However, after removal of the entire organizer, no opl expression was observed, indicating that this region is crucial for forebrain induction. We further show that continued organizer function is required for forebrain induction, since beads of BMP4, which promotes ventral fates, also prevented opl expression when implanted during gastrulation. Our data show that forebrain specification begins early during gastrulation, and that a wide area of dorsal mesendoderm is required for its patterning.

scholarly journals Transcriptional Repression by XPc1, a New Polycomb Homolog in Xenopus laevis Embryos, Is Independent of Histone Deacetylase

1999 ◽  
Vol 19 (6) ◽  
pp. 3958-3968 ◽  
Author(s):  
John Strouboulis ◽  
Sashko Damjanovski ◽  
Danielle Vermaak ◽  
Funda Meric ◽  
Alan P. Wolffe
Keyword(s):  
Xenopus Laevis ◽  
Transcriptional Repression ◽  
Molecular Basis ◽  
Target Genes ◽  
Trichostatin A ◽  
Histone Deacetylation ◽  
Polycomb Group ◽  
Blastula Stage ◽  
Xenopus Laevis Embryos

ABSTRACT The Polycomb group (Pc-G) genes encode proteins that assemble into complexes implicated in the epigenetic maintenance of heritable patterns of expression of developmental genes, a function largely conserved from Drosophila to mammals and plants. The Pc-G is thought to act at the chromatin level to silence expression of target genes; however, little is known about the molecular basis of this repression. In keeping with the evidence that Pc-G homologs in higher vertebrates exist in related pairs, we report here the isolation of XPc1, a second Polycomb homolog in Xenopus laevis. We show that XPc1 message is maternally deposited in a translationally masked form in Xenopus oocytes, with XPc1 protein first appearing in embryonic nuclei shortly after the blastula stage. XPc1 acts as a transcriptional repressor in vivo when tethered to a promoter in Xenopus embryos. We find that XPc1-mediated repression can be only partially alleviated by an increase in transcription factor dosage and that inhibition of deacetylase activity by trichostatin A treatment has no effect on XPc1 repression, suggesting that histone deacetylation does not form the basis for Pc-G-mediated repression in our assay.

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