Cortical rotation of the Xenopus egg: consequences for the anteroposterior pattern of embryonic dorsal development

Development ◽  
1989 ◽  
Vol 107 (Supplement) ◽  
pp. 37-51 ◽  
Author(s):  
J. Gerhart ◽  
M. Danilchik ◽  
T. Doniach ◽  
S. Roberts ◽  
B. Rowning ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Organizer Region ◽  
Bilateral Symmetry ◽  
Cylindrical Symmetry ◽  
Gastrula Stage ◽  
Blastula Stage ◽  
Proximate Cause ◽  
Spemann Organizer ◽  
Anterior Dorsal ◽  
Xenopus Egg

We first review cortical–cytoplasmic rotation, a microtubule-mediated process by which the Xenopus egg, like other amphibian eggs, transforms its polarized cylindrical symmetry into bilateral symmetry within the first cell cycle after fertilization. This transformation, the earliest of many steps leading to dorsal development, involves the displacement of the egg's cortex relative to its cytoplasmic core by 30° in an animal–vegetal direction. As rotation is progressively reduced by microtubuledepolymerizing agents, embryos develop with body axes progressively deleted for dorsal structures at the anterior end. With no rotation, ventralized embryos are formed. In an effort to comprehend this progressive effect on embryonic organization, we go on to review subsequent developmental processes depending on rotation, and we propose, with evidence, that reduced rotation leads to a reduced number of vegetal dorsalizing cells, which induce during the blastula stage a Spemann organizer region of smaller than normal size. The reduced organizer then promotes a reduced amount of cell rearrangement (morphogenesis) at gastrulation. Reduced morphogenesis seems the proximate cause of the incompleteness of axial pattern, as shown further by the fact that embryos that are normal until the gastrula stage, if exposed to inhibitors of morphogenesis, develop body axes that are progressively less complete in their anterior dorsal organization the earlier their gastrulation had been blocked. We discuss why axial pattern might depend systematically on morphogenesis.

The anterior extent of dorsal development of the Xenopus embryonic axis depends on the quantity of organizer in the late blastula

Development ◽  
1990 ◽  
Vol 109 (2) ◽  
pp. 363-372 ◽  
Author(s):  
R.M. Stewart ◽  
J.C. Gerhart
Keyword(s):  
Xenopus Laevis ◽  
Cell Population ◽  
Marginal Zone ◽  
Organizer Region ◽  
Blastula Stage ◽  
Dorsal Midline ◽  
Anterior Dorsal ◽  
Lateral Width ◽  
Anterior Extent ◽  
Anterior Posterior

In amphibian gastrulae, the cell population of the organizer region of the marginal zone (MZ) establishes morphogenesis and patterning within itself and within surrounding regions of the MZ, presumptive neurectoderm, and archenteron roof. We have tested the effects on pattern of reducing the amount of organizer region by recombining halves of Xenopus laevis late blastulae cut at different angles from the bilateral plane. When regions within 30 degrees of the dorsal midline are excluded from recombinants, ventralized embryos develop lacking the entire anterior-posterior sequence of dorsal structures, suggesting that the organizer is only 60 degrees wide (centered on the dorsal midline) at the late blastula stage. As more and more dorsal MZ (organizer) is included in the recombinant, progressively more anterior dorsal structures are formed. In all cases, when any dorsal structures are missing they are deleted serially from the anterior end. Thus, we suggest that the amount (lateral width) of the organizer in the MZ determines the anterior extent of dorsal development.

scholarly journals Multiple mechanisms determine ER network morphology during the cell cycle in Xenopus egg extracts

2013 ◽  
Vol 203 (5) ◽  
pp. 801-814 ◽  
Author(s):  
Songyu Wang ◽  
Fabian B. Romano ◽  
Christine M. Field ◽  
Tim J. Mitchison ◽  
Tom A. Rapoport
Keyword(s):  
Cell Cycle ◽  
Adaptor Protein ◽  
Sensitive Factor ◽  
Protein Receptors ◽  
Egg Extracts ◽  
Organizing Center ◽  
Xenopus Egg ◽  
Guanosine Triphosphatase ◽  
Xenopus Egg Extracts ◽  
Network Morphology

In metazoans the endoplasmic reticulum (ER) changes during the cell cycle, with the nuclear envelope (NE) disassembling and reassembling during mitosis and the peripheral ER undergoing extensive remodeling. Here we address how ER morphology is generated during the cell cycle using crude and fractionated Xenopus laevis egg extracts. We show that in interphase the ER is concentrated at the microtubule (MT)-organizing center by dynein and is spread by outward extension of ER tubules through their association with plus ends of growing MTs. Fusion of membranes into an ER network is dependent on the guanosine triphosphatase atlastin (ATL). NE assembly requires fusion by both ATL and ER-soluble N-ethyl-maleimide–sensitive factor adaptor protein receptors. In mitotic extracts, the ER converts into a network of sheets connected by ER tubules and loses most of its interactions with MTs. Together, these results indicate that fusion of ER membranes by ATL and interaction of ER with growing MT ends and dynein cooperate to generate distinct ER morphologies during the cell cycle.

Expression of a novel FGF in the Xenopus embryo. A new candidate inducing factor for mesoderm formation and anteroposterior specification

Development ◽  
1992 ◽  
Vol 114 (3) ◽  
pp. 711-720 ◽  
Author(s):  
H.V. Isaacs ◽  
D. Tannahill ◽  
J.M. Slack
Keyword(s):  
Specific Activity ◽  
Biological Properties ◽  
The Body ◽  
Mesoderm Induction ◽  
Gastrula Stage ◽  
Blastula Stage ◽  
Mesoderm Formation ◽  
Low Levels

We have cloned and sequenced a new member of the fibroblast growth factor family from Xenopus laevis embryo cDNA. It is most closely related to both mammalian kFGF (FGF-4) and FGF-6 but as it is not clear whether it is a true homologue of either of these genes we provisionally refer to it as XeFGF (Xenopus embryonic FGF). Two sequences were obtained, differing by 11% in derived amino acid sequence, which probably represent pseudotetraploid variants. Both the sequence and the behaviour of in vitro translated protein indicates that, unlike bFGF (FGF-2), XeFGF is a secreted molecule. Recombinant XeFGF protein has mesoderm-inducing activity with a specific activity similar to bFGF. XeFGF mRNA is expressed maternally and zygotically with a peak during the gastrula stage. Both probe protection and in situ hybridization showed that the zygotic expression is concentrated in the posterior of the body axis and later in the tailbud. Later domains of expression were found near the midbrain/hindbrain boundary and at low levels in the myotomes. Because of its biological properties and expression pattern, XeFGF is a good candidate for an inducing factor with possible roles both in mesoderm induction at the blastula stage and in the formation of the anteroposterior axis at the gastrula stage.

A functional test for maternally inherited cadherin in Xenopus shows its importance in cell adhesion at the blastula stage

Development ◽  
1994 ◽  
Vol 120 (1) ◽  
pp. 49-57 ◽  
Author(s):  
J. Heasman ◽  
D. Ginsberg ◽  
B. Geiger ◽  
K. Goldstone ◽  
T. Pratt ◽  
...  
Keyword(s):  
Cell Adhesion ◽  
Protein Level ◽  
Mrna Level ◽  
Functional Test ◽  
Gastrula Stage ◽  
Blastula Stage ◽  
Xenopus Development ◽  
Dose Dependent ◽  
Embryonic Ectoderm ◽  
E Cadherin

We report here on the consequences of reducing the expression of EP-cadherin at the earliest stages of Xenopus development. Injection of oligodeoxynucleotides antisense to maternal EP-cadherin mRNA into full-grown oocytes reduced the mRNA level in oocytes, and the protein level in blastulae. Adhesion between blastomeres was significantly reduced, as seen in whole embryos, and in assays of the ability of blastomeres to reaggregate in culture. This effect was especially conspicuous in the inner cells of the blastula and included the disruption of the blastocoel. The severity of the EP-cadherin mRNA depletion and of the disaggregation phenotype was dose dependent. This phenotype was rescued by the injection into EP-cadherin mRNA-depleted oocytes of the mRNA coding for a related cadherin, E-cadherin, that is normally expressed at the gastrula stage in the embryonic ectoderm.

Muscle gene activation in Xenopus requires intercellular communication during gastrula as well as blastula stages

Development ◽  
1992 ◽  
Vol 116 (Supplement) ◽  
pp. 137-142 ◽  
Author(s):  
J. B. Gurdon ◽  
K. Kao ◽  
K. Kato ◽  
N. D. Hopwood
Keyword(s):  
Protein Synthesis ◽  
Developmental Stage ◽  
Cell Transplantation ◽  
Intercellular Communication ◽  
Gene Activation ◽  
Gastrula Stage ◽  
Blastula Stage ◽  
Morphological Marker ◽  
Muscle Gene ◽  
Early Gastrula

In Xenopus an early morphological marker of mesodermal induction is the elongation of the mesoderm at the early gastrula stage (Symes and Smith, 1987). We show here that the elongation of equatorial (marginal) tissue is dependent on protein synthesis in a mid blastula, but has become independent of it by the late blastula stage. In animal caps induced to become mesoderm, the time when protein synthesis is required for subsequent elongation immediately follows the time of induction, and is not related to developmental stage. For elongation, intercellular communication during the blastula stage is of primary importance. Current experiments involving cell transplantation indicate a need for further celhcell interactions during gastrulation, and therefore after the vegetal-animal induction during blastula stages. These secondary cell interactions are believed to take place among cells that have already received a vegetal induction, and may facilitate some of the later intracellular events known to accompany muscle gene activation.

Efficient reactivation of Xenopus erythrocyte nuclei in Xenopus egg extracts

1995 ◽  
Vol 108 (6) ◽  
pp. 2187-2196 ◽  
Author(s):  
L.J. Wangh ◽  
D. DeGrace ◽  
J.A. Sanchez ◽  
A. Gold ◽  
Y. Yeghiazarians ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Somatic Cell ◽  
Nuclear Transplantation ◽  
Optimal Time ◽  
Genome Replication ◽  
Cell Nuclei ◽  
Egg Extracts ◽  
Xenopus Egg ◽  
Xenopus Egg Extracts

Rapid genome replication is one of the hallmarks of the frog embryonic cell cycle. We report here that complete reactivation of quiescent somatic cell nuclei in Xenopus egg extracts depends on prior restructuring of the nuclear substrate and prior preparation of cytoplasmic extract with the highest capacity to initiate and sustain DNA synthesis. Nuclei from mature erythrocytes swell, replicate their DNA efficiently, and enter mitosis in frozen/thawed extracts prepared from activated Xenopus eggs, provided the nuclei are first treated with trypsin, heparin, and an extract prepared from unactivated, meiotically arrested, eggs. Optimal replicating extracts are prepared from large batches of unfertilized eggs that are synchronously activated into the cell cycle for 28 minutes (at 20 degrees C). Because the Xenopus cell cycle progresses so rapidly, extracts prepared just a few minutes before or after this time have substantially lower DNA synthetic capacities. At the optimal time and temperature, eggs have just reached the G1/S boundary of the first cell cycle. This fact was revealed by injecting and replicating an SV40 plasmid in intact unfertilized eggs as described previously. We estimate that under optimal conditions approximately 6.14 × 10(9) base pairs of DNA/per nucleus are synthesized in 30–40 minutes, a rate that rivals that observed in the zygotic nucleus. The findings reported here are one step in our long term effort to develop a new in vitro/in vivo approach to nuclear transplantation. Nuclear transplantation in amphibian embryos has been used to establish that the genomes of many types of differentiated somatic cells are pluripotent. But very few such nuclei have ever developed into advanced tadpoles or adult frogs, probably because somatic nuclei injected directly into activated eggs fail to reactivate quickly enough to avoid being damaged during first mitosis. We have already shown that unfertilized eggs can be injected prior to activation of the first cell cycle. Future experiments will reveal whether in vitro reactivated somatic cell nuclei transplanted into such eggs reliably reach advanced stages of development.

The increase in intracellular pH associated with Xenopus egg activation is a Ca(2+)-dependent wave

1992 ◽  
Vol 101 (1) ◽  
pp. 55-67 ◽  
Author(s):  
N. Grandin ◽  
M. Charbonneau
Keyword(s):  
Cell Cycle ◽  
Intracellular Ph ◽  
Egg Activation ◽  
Free Calcium ◽  
Slowing Down ◽  
M Phase ◽  
Xenopus Egg ◽  
General Slowing ◽  
The Impact ◽  
Kinetics Of

In Xenopus eggs, the transient increase in intracellular free calcium ([Ca2+]i), or Ca2+ transient, which occurs 1–3 min after egg activation, is likely to be partly responsible for the release of the cell cycle blockade. In the present study, we have used microinjection of BAPTA or EGTA, two potent chelators of Ca2+, to buffer [Ca2+]i at various steps during Xenopus egg activation and evaluate the impact on some of the associated events. Microinjection of either one of the Ca2+ chelators into unactivated eggs prevented egg activation without, however, lowering [Ca2+]i, suggesting that only physiological [Ca2+]i changes, but not [Ca2+]i levels, were affected by the Ca2+ buffer. When BAPTA was microinjected around the time of occurrence of the Ca2+ transient, the egg activation-associated increase in intracellular pH (pHi) was clearly delayed. That delay was not due to a general slowing down of the cell cycle, since under the same conditions of microinjection of BAPTA the kinetics of MPF (a universal M-phase promoting factor) inactivation were unaffected. These results represent the first indication that the Ca2+ transient participates in determining the time of initiation of the pHi increase during Xenopus egg activation. The present results also demonstrate that the egg activation-associated pHi changes (a slight, transient decrease in pHi followed by a permanent increase in pHi) proceed as a wave propagating from the site of triggering of egg activation. Experiments of local microinjection of BAPTA support the view that the pH wave is a consequence of the Ca2+ wave, which it follows closely.

Requirement of Sox2-mediated signaling for differentiation of early Xenopus neuroectoderm

Development ◽  
2000 ◽  
Vol 127 (4) ◽  
pp. 791-800 ◽  
Author(s):  
M. Kishi ◽  
K. Mizuseki ◽  
N. Sasai ◽  
H. Yamazaki ◽  
K. Shiota ◽  
...  
Keyword(s):  
Transcription Factors ◽  
Glucocorticoid Receptor ◽  
Ligand Binding ◽  
Cell Fate ◽  
Neural Differentiation ◽  
Dominant Negative ◽  
Gastrula Stage ◽  
Blastula Stage ◽  
Sensory Epithelia ◽  
Neural Tissues

From early stages of development, Sox2-class transcription factors (Sox1, Sox2 and Sox3) are expressed in neural tissues and sensory epithelia. In this report, we show that Sox2 function is required for neural differentiation of early Xenopus ectoderm. Microinjection of dominant-negative forms of Sox2 (dnSox2) mRNA inhibits neural differentiation of animal caps caused by attenuation of BMP signals. Expression of dnSox2 in developing embryos suppresses expression of N-CAM and regional neural markers. We have analyzed temporal requirement of Sox2-mediated signaling by using an inducible dnSox2 construct fused to the ligand-binding domain of the glucocorticoid receptor. Attenuation of Sox2 function both from the late blastula stage and from the late gastrula stage onwards causes an inhibition of neural differentiation in animal caps and in whole embryos. Additionally, dnSox2-injected cells that fail to differentiate into neural tissues are not able to adopt epidermal cell fate. These data suggest that Sox2-class genes are essential for early neuroectoderm cells to consolidate their neural identity during secondary steps of neural differentiation.

Expression of the LIM class homeobox gene Xlim-1 in pronephros and CNS cell lineages of Xenopus embryos is affected by retinoic acid and exogastrulation

Development ◽  
1994 ◽  
Vol 120 (6) ◽  
pp. 1525-1536 ◽  
Author(s):  
M. Taira ◽  
H. Otani ◽  
M. Jamrich ◽  
I.B. Dawid
Keyword(s):  
Retinoic Acid ◽  
Organizer Region ◽  
Homeobox Gene ◽  
Second Phase ◽  
Cell Specification ◽  
Spemann Organizer ◽  
Xenopus Embryos ◽  
Prechordal Mesoderm ◽  
The Central Nervous System ◽  
Lateral Mesoderm

The LIM class homeobox gene Xlim-1 is expressed in Xenopus embryos in the lineages leading to (i) the notochord, (ii) the pronephros, and (iii) certain cells of the central nervous system (CNS). In its first expression phase, Xlim-1 mRNA arises in the Spemann organizer region, accumulates in prechordal mesoderm and notochord during gastrulation, and decays in these tissues during neurula stages except that it persists in the posterior tip of the notochord. In the second phase, expression in lateral mesoderm begins at late gastrula, and converges to the pronephros at tailbud stages. Expression in a central location of the neural plate also initiates at late gastrula, expands anteriorly and posteriorly, and becomes established in the lateral regions of the spinal cord and hindbrain at tailbud stages. Thus Xlim-1 expression precedes morphogenesis, suggesting that it may be involved in cell specification in these lineages. Enhancement of Xlim-1 expression by retinoic acid (RA) was first detectable in the dorsal mesoderm at initial gastrula. During gastrulation and early neurulation, RA strongly enhanced Xlim-1 expression in all three lineages and also expanded its expressing domains; this overexpression correlated well with RA phenotypes such as enlarged pronephros and hindbrain-like structure. Exogastrulation reduced Xlim-1 expression in the lateral mesoderm and ectoderm but not in the notochord, suggesting that the second phase of Xlim-1 expression requires mesoderm/ectoderm interactions. RA treatment of exogastrulae did not revert this reduction.

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