Microtubule disruption reveals that Spemann's organizer is subdivided into two domains by the vegetal alignment zone

Development ◽  
1997 ◽  
Vol 124 (4) ◽  
pp. 895-906 ◽  
Author(s):  
M.C. Lane ◽  
R. Keller
Keyword(s):  
Marginal Zone ◽  
Axis Formation ◽  
Convergent Extension ◽  
Microtubule Depolymerization ◽  
Microtubule Disruption ◽  
Spemann's Organizer ◽  
And Function ◽  
Cell Intercalation ◽  
Somitic Mesoderm ◽  
Anterior Posterior

Mediolateral cell intercalation is proposed to drive morphogenesis of the primary embryonic axis in Xenopus. Mediolateral intercalation begins in a group of cells called the vegetal alignment zone, a subpopulation of cells in Spemann's organizer, and spreads through much of the marginal zone. To understand the functions of the vegetal alignment zone during gastrulation and axis formation, we have inhibited its formation by disrupting microtubules with nocodazole in early gastrula embryos. In such embryos, mediolateral intercalation, involution and convergent extension of the marginal zone do not occur. Although cell motility continues, and the anterior notochordal and somitic mesoderm differentiate in the pre-involution marginal zone, posterior notochordal and somitic mesoderm do not differentiate. In contrast, microtubule depolymerization in midgastrula embryos, after the vegetal alignment zone has formed, does not inhibit mediolateral cell intercalation, involution and convergent extension, or differentiation of posterior notochord and somites. We conclude that microtubules are required only for orienting and polarizing at stage 101/2 the first cells that undergo mediolateral intercalation and form the vegetal alignment zone, and not for subsequent morphogenesis. These results demonstrate that microtubules are required to form the vegetal alignment zone, and that both microtubules and the vegetal alignment zone play critical roles in the inductive and morphogenetic activities of Spemann's organizer. In addition, our results suggest that Spemann's organizer contains multiple organizers, which act in succession and change their location and function during gastrulation to generate the anterior/posterior axis in Xenopus.

Cell rearrangement during gastrulation of Xenopus: direct observation of cultured explants

Development ◽  
1991 ◽  
Vol 112 (1) ◽  
pp. 289-300 ◽  
Author(s):  
P. Wilson ◽  
R. Keller
Keyword(s):  
High Resolution ◽  
Organizer Region ◽  
Time Lapse ◽  
Second Phase ◽  
Convergent Extension ◽  
Dorsal Axis ◽  
Cell Intercalation ◽  
Somitic Mesoderm ◽  
High Resolution Microscopy ◽  
Anterior Posterior

We have analyzed cell behavior in the organizer region of the Xenopus laevis gastrula by making high resolution time-lapse recordings of cultured explants. The dorsal marginal zone, comprising among other tissues prospective notochord and somitic mesoderm, was cut from early gastrulae and cultured in a way that permits high resolution microscopy of the deep mesodermal cells, whose organized intercalation produces the dramatic movements of convergent extension. At first, the explants extend without much convergence. This initial expansion results from rapid radial intercalation, or exchange of cells between layers. During the second half of gastrulation, the explants begin to converge strongly toward the midline while continuing to extend vigorously. This second phase of extension is driven by mediolateral cell intercalation, the rearrangement of cells within each layer to lengthen and narrow the array. Toward the end of gastrulation, fissures separate the central notochord from the somitic mesoderm on each side, and cells in both tissues elongate mediolaterally as they intercalate. A detailed analysis of the spatial and temporal pattern of these behaviors shows that both radial and mediolateral intercalation begin first in anterior tissue, demonstrating that the anterior-posterior timing gradient so evident in the mesoderm of the neurula is already forming in the gastrula. Finally, time-lapse recordings of intact embryos reveal that radial intercalation takes places primarily before involution, while mediolateral intercalation begins as the mesoderm goes around the lip. We discuss the significance of these findings to our understanding of both the mechanics of gastrulation and the patterning of the dorsal axis.

Xenopus axis formation: induction of goosecoid by injected Xwnt-8 and activin mRNAs

Development ◽  
1993 ◽  
Vol 118 (2) ◽  
pp. 499-507 ◽  
Author(s):  
H. Steinbeisser ◽  
E.M. De Robertis ◽  
M. Ku ◽  
D.S. Kessler ◽  
D.A. Melton
Keyword(s):  
Uv Irradiation ◽  
High Frequency ◽  
Marginal Zone ◽  
Homeobox Gene ◽  
Dorsal Side ◽  
Axis Formation ◽  
Gene Products ◽  
Turn On ◽  
Xenopus Embryos ◽  
Spemann's Organizer

In this study, we compare the effects of three mRNAs-goosecoid, activin and Xwnt-8- that are able to induce partial or complete secondary axes when injected into Xenopus embryos. Xwnt-8 injection produces complete secondary axes including head structures whereas activin and goosecoid injection produce partial secondary axes at high frequency that lack head structures anterior to the auditory vesicle and often lack notochord. Xwnt-8 can activate goosecoid only in the deep marginal zone, i.e., in the region in which this organizer-specific homeobox gene is normally expressed on the dorsal side. Activin B mRNA, however, can turn on goosecoid in all regions of the embryo. We also tested the capacity of these gene products to restore axis formation in embryos in which the cortical rotation was blocked by UV irradiation. Whereas Xwnt-8 gives complete rescue of anterior structures, both goosecoid and activin give partial rescue. Rescued axes including hindbrain structures up to level of the auditory vesicle can be obtained at high frequency even in the absence of notochord structures. The possible functions of Wnt-like and activin-like signals and of the goosecoid homeobox gene, and their order of action in the formation of Spemann's organizer are discussed.

Cell rearrangement and segmentation in Xenopus: direct observation of cultured explants

Development ◽  
1989 ◽  
Vol 105 (1) ◽  
pp. 155-166 ◽  
Author(s):  
P.A. Wilson ◽  
G. Oster ◽  
R. Keller
Keyword(s):  
Explant Culture ◽  
Dorsal Side ◽  
Convergent Extension ◽  
Cell Behaviour ◽  
Cell Rearrangement ◽  
Radial Cell ◽  
Cell Intercalation ◽  
First Time ◽  
The Relationship ◽  
Somitic Mesoderm

We make use of a novel system of explant culture and high resolution video-film recording to analyse for the first time the cell behaviour underlying convergent extension and segmentation in the somitic mesoderm of Xenopus. We find that a sequence of activities sweeps through the somitic mesoderm from anterior to posterior during gastrulation and neurulation, beginning with radial cell intercalation or thinning, continuing with mediolateral intercalation and cell elongation, and culminating in segmentation and somite rotation. Radial intercalation at the posterior tip lengthens the tissue, while mediolateral intercalation farther anterior converges it toward the midline. This extension of the somitic mesoderm helps to elongate the dorsal side of intact neurulae. By separating tissues, we demonstrate that cell rearrangement is independent of the notochord, but radial intercalation - and thus the bulk of extension - requires the presence of an epithelium, either endodermal or ectodermal. Segmentation, on the other hand, can proceed in somitic mesoderm isolated at the end of gastrulation. Finally, we discuss the relationship between cell rearrangement and segmentation.

Caudalization by the amphibian organizer: brachyury, convergent extension and retinoic acid

Development ◽  
1994 ◽  
Vol 120 (11) ◽  
pp. 3051-3062 ◽  
Author(s):  
T. Yamada
Keyword(s):  
Cell Motility ◽  
Neural Development ◽  
Marginal Zone ◽  
Floor Plate ◽  
Convergent Extension ◽  
Neural Tissues ◽  
Dorsal Mesoderm ◽  
The One ◽  
Cell Intercalation ◽  
Morphogenetic Effects

Caudalization, which is proposed to be one of two functions of the amphibian organizer, initiates posterior pathways of neural development in the dorsalized ectoderm. In the absence of caudalization, dorsalized ectoderm only expresses the most anterior (archencephalic) differentiation. In the presence of caudalization, dorsalized ectorderm develops various levels of posterior neural tissues, depending on the extent of caudalization. A series of induction experiments have shown that caudalization is mediated by convergent extension: cell motility that is based on directed cell intercalation, and is essential for the morphogenesis of posterior axial tissues. During amphibian development, convergent extension is first expressed all-over the mesoderm and, after mesoderm involution, it becomes localized to the posterior mid-dorsal mesoderm, which produces notochord. This expression pattern of specific down regulation of convergent extension is also followed by the expression of the brachyury homolog. Furthermore, mouse brachyury has been implicated in the regulation of tissue elongation on the one hand, and in the control of posterior differentiation on the other. These observations suggest that protein encoded by the brachyury homolog controls the expression of convergent extension in the mesoderm. The idea is fully corroborated by a genetic study of mouse brachyury, which demonstrates that the gene product produces elongation of the posterior embryonic axis. However, there exists evidence for the induction of posterior dorsal mesodermal tissues, if brachyury homolog protein is expressed in the ectoderm. In both cases the brachyury homolog contributes to caudalization. A number of other genes appear to be involved in caudalization. The most important of these is pintavallis, which contains a fork-head DNA binding domain. It is first expressed in the marginal zone. After mesoderm involution, it is present not only in the presumptive notochord, but also in the floor plate. This is in contrast to the brachyury homolog, whose expression is restricted to mesoderm. The morphogenetic effects of exogenous RA on anteroposterior specification during amphibian embryogenesis are reviewed. The agent inhibits archencephalic differentiation and enhances differentiation of deuterencephalic and trunk levels. Thus the effect of exogenous RA on morphogenesis of CNS is very similar to that of caudalization, which is proposed to occur through the normal action of the organizer. According to a detailed analysis of the effect of lithium on morphogenesis induced by the Cynops organizer, lithium has a caudalizing effect closely comparable with that of RA. Furthermore, lithium induces convergent extension in the prechordal plate, which normally does not show cell motility.(ABSTRACT TRUNCATED AT 400 WORDS)

scholarly journals Dynamic determinations: patterning the cell behaviours that close the amphibian blastopore

2008 ◽  
Vol 363 (1495) ◽  
pp. 1317-1332 ◽  
Author(s):  
Ray Keller ◽  
David Shook
Keyword(s):  
Marginal Zone ◽  
Epithelial Mesenchymal Transition ◽  
The Body ◽  
Dynamic Features ◽  
Cell Behaviour ◽  
Mesenchymal Transition ◽  
Tissue Organization ◽  
Hoop Stresses ◽  
Cell Intercalation ◽  
Anterior Posterior

We review the dynamic patterns of cell behaviours in the marginal zone of amphibians with a focus on how the progressive nature and the geometry of these behaviours drive blastopore closure. Mediolateral cell intercalation behaviour and epithelial–mesenchymal transition are used in different combinations in several species of amphibian to generate a conserved pattern of circumblastoporal hoop stresses. Although these cell behaviours are quite different and involve different germ layers and tissue organization, they are expressed in similar patterns. They are expressed progressively along presumptive lateral–medial and anterior–posterior axes of the body plan in highly ordered geometries of functional significance in the context of the biomechanics of blastopore closure, thereby accounting for the production of similar patterns of circumblastoporal forces. It is not the nature of the cell behaviour alone, but the context, the biomechanical connectivity and spatial and temporal pattern of its expression that determine specificity of morphogenic output during gastrulation and blastopore closure. Understanding the patterning of these dynamic features of cell behaviour is important and will require analysis of signalling at much greater spatial and temporal resolution than that has been typical in the analysis of patterning tissue differentiation.

Lithium dorsalizes but also mechanically disrupts gastrulation of Xenopus laevis

Development ◽  
1988 ◽  
Vol 102 (4) ◽  
pp. 677-686 ◽  
Author(s):  
C.M. Regen ◽  
R.A. Steinhardt
Keyword(s):  
Xenopus Laevis ◽  
Marginal Zone ◽  
Lithium Treatment ◽  
Leading Edge ◽  
Spatial Layout ◽  
Cell Group ◽  
Axis Formation ◽  
Convergent Extension ◽  
Distinct Effect ◽  
Group Movements

The discovery that lithium treatment at blastula stages can induce axis formation suggested that it might act by respecifying the cytoplasmic rearrangement-generated dorsoventral pattern, so that ventral cells behave like their dorsal counterparts. We have studied the effects of Li+ treatment on the spatial layout of the cell-group movements of gastrulation to see whether this is the case. We find that involution of the chordamesoderm and associated archenteron roof is retarded by Li+, an effect which does not suggest dorsal respecification. However, in both migration of the leading edge mesoderm and convergent extension of the marginal zone, ventral regions clearly do show dorsal-type movement. Because of this, and because of examples where disruption of involution and effects on axis differentiation do not correlate, we propose that failure of involution represents a distinct effect of Li+ involving disruption of mechanical relationships at the blastopore. Thus archenteron formation poorly reflects the dorsoventral pattern. Extension of sandwich explants of the ventral marginal zone is proposed as a reliable quantitative assay for alterations to the dorsoventral pattern.

scholarly journals Cortical microtubule nucleation can organise the cytoskeleton of Drosophila oocytes to define the anteroposterior axis

eLife ◽  
2015 ◽  
Vol 4 ◽  
Author(s):  
Philipp Khuc Trong ◽  
Hélène Doerflinger ◽  
Jörn Dunkel ◽  
Daniel St Johnston ◽  
Raymond E Goldstein
Keyword(s):  
Theoretical Model ◽  
Cortical Microtubule ◽  
Three Dimensional ◽  
Axis Formation ◽  
Experimental Measurements ◽  
Dimensional Model ◽  
Three Dimensional Model ◽  
Microtubule Nucleation ◽  
And Function ◽  
Anterior Posterior

Many cells contain non-centrosomal arrays of microtubules (MTs), but the assembly, organisation and function of these arrays are poorly understood. We present the first theoretical model for the non-centrosomal MT cytoskeleton in Drosophila oocytes, in which bicoid and oskar mRNAs become localised to establish the anterior-posterior body axis. Constrained by experimental measurements, the model shows that a simple gradient of cortical MT nucleation is sufficient to reproduce the observed MT distribution, cytoplasmic flow patterns and localisation of oskar and naive bicoid mRNAs. Our simulations exclude a major role for cytoplasmic flows in localisation and reveal an organisation of the MT cytoskeleton that is more ordered than previously thought. Furthermore, modulating cortical MT nucleation induces a bifurcation in cytoskeletal organisation that accounts for the phenotypes of polarity mutants. Thus, our three-dimensional model explains many features of the MT network and highlights the importance of differential cortical MT nucleation for axis formation.

Induction of notochord cell intercalation behavior and differentiation by progressive signals in the gastrula of Xenopus laevis

Development ◽  
1995 ◽  
Vol 121 (10) ◽  
pp. 3311-3321 ◽  
Author(s):  
C. Domingo ◽  
R. Keller
Keyword(s):  
Xenopus Laevis ◽  
Behavioral Changes ◽  
Cell Behavior ◽  
Convergent Extension ◽  
Notochordal Cell ◽  
Cell Behaviors ◽  
Notochord Cell ◽  
Light Fluorescence ◽  
Cell Intercalation ◽  
Somitic Mesoderm

We show that notochord-inducing signals are present during Xenopus laevis gastrulation and that they are important for both inducing and organizing cell behavior and differentiation in the notochord. Previous work showed that convergent extension of prospective notochordal and somitic mesoderm occurs by mediolateral cell intercalation to produce a longer, narrower tissue. Mediolateral cell intercalation is driven by bipolar, mediolaterally directed protrusive activity that elongates cells and then pulls them between one another along the mediolateral axis. This cell behavior, and subsequent notochordal cell differentiation, begins anteriorly and spreads posteriorly along the notochordal-somitic boundary, and from this lateral boundary progresses medially towards the center of the notochord field. To examine whether these progressions of cell behaviors and differentiation are induced and organized during gastrulation, we grafted labeled cells from the prospective notochordal, somitic and epidermal regions of the gastrula into the notochordal region and monitored their behavior by low light, fluorescence videomicroscopy. Prospective notochordal, epidermal and somitic cells expressed mediolateral cell intercalation behavior in an anterior-to-posterior and lateral-to-medial order established by the host notochord. Behavioral changes were induced first and most dramatically among cells grafted next to the notochordal-somitic boundary, particularly those in direct contact with the boundary, suggesting that the boundary may provide signals that both induce and organize notochordal cell behaviors. By physically impeding normal convergent extension movements, notochordal cell behaviors and differentiation were restricted to the anteriormost notochordal region and to the lateral notochordal-somitic boundary. These results show that mediolateral cell intercalation behavior and notochordal differentiation can be induced in the gastrula stage, among cells not normally expressing these characteristics, and that these characteristics are induced progressively, most likely by signals emanating from the notochordal-somitic boundary. In addition, they show that morphogenetic movements during gastrulation are necessary for complete notochord formation and that the prospective notochord region is not determined by the onset of gastrulation.

scholarly journals Single-cell morphometrics reveals ancestral principles of notochord development

2020 ◽  
Author(s):  
Toby GR Andrews ◽  
Wolfram Ponisch ◽  
Ewa K Paluch ◽  
Benjamin Steventon ◽  
Elia Benito-Gutierrez
Keyword(s):  
Single Cell ◽  
Cell Shape ◽  
Cell Length ◽  
Spatial And Temporal Variation ◽  
Second Phase ◽  
Convergent Extension ◽  
Novel Approach ◽  
Specific Shape ◽  
Cell Intercalation ◽  
Anterior Posterior

During development, embryonic tissues are formed by the dynamic behaviours of their constituent cells, whose collective actions are tightly regulated in space and time. To understand such cell behaviours and how they have evolved, it is necessary to develop quantitative approaches to map out morphogenesis, so comparisons can be made across different tissues and organisms. With this idea in mind, here we sought to investigate ancestral principles of notochord development, by building a quantitative portrait of notochord morphogenesis in the amphioxus embryo, a basally-branching member of the chordate phylum. To this end, we developed a single-cell morphometrics pipeline to comprehensively catalogue the morphologies of thousands of notochord cells, and to project them simultaneously into a common mathematical space termed morphospace. This approach revealed complex patterns of cell-type specific shape trajectories, akin to those obtained using single-cell genomic approaches. By spatially mapping single-cell shape trajectories in whole segmented notochords, we found evidence of spatial and temporal variation in developmental dynamics. Such variations included temporal gradients of morphogenesis across the anterior-posterior embryonic axis, divergence of trajectories to different morphologies, and the convergence of different trajectories onto common morphologies. Through geometric simulations, we also identified an antagonistic relationship between cell shape regulation and growth that enables convergent extension to occur in two steps. First, by allowing growth to counterbalance loss of anterior-posterior cell length during cell intercalation. Secondly, by allowing growth to further increase cell length once cells have intercalated and aligned to the axial midline, thereby facilitating a second phase of tissue elongation. Finally, we show that apart from a complex coordination of individual cellular behaviours, posterior addition from proliferating progenitors is essential for full notochord elongation in amphioxus, a mechanism previously described only in vertebrates. This novel approach to quantifying morphogenesis paves the way towards comparative studies, and mechanistic explanations for the emergence of form over developmental and evolutionary time scales.

Development and Function of the Splenic Marginal Zone

2004 ◽  
Vol 24 (6) ◽  
pp. 16 ◽  
Author(s):  
Reina E. Mebius ◽  
Martijn A. Nolte ◽  
Georg Kraal
Keyword(s):  
Marginal Zone ◽  
And Function
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