scholarly journals Induction and patterning of the primitive streak, an organizing center of gastrulation in the amniote

2004 ◽  
Vol 229 (3) ◽  
pp. 422-432 ◽  
Author(s):  
Takashi Mikawa ◽  
Alisa M. Poh ◽  
Kristine A. Kelly ◽  
Yasuo Ishii ◽  
David E. Reese
Keyword(s):  
Primitive Streak ◽  
Organizing Center

Nuclear beta-catenin and the development of bilateral symmetry in normal and LiCl-exposed chick embryos

Development ◽  
1999 ◽  
Vol 126 (13) ◽  
pp. 2955-2965 ◽  
Author(s):  
T. Roeser ◽  
S. Stein ◽  
M. Kessel
Keyword(s):  
Molecular Markers ◽  
Nuclear Localization ◽  
Symmetric Domain ◽  
Primitive Streak ◽  
Bilateral Symmetry ◽  
Beta Catenin ◽  
Developmental Constraints ◽  
Organizing Center ◽  
Developing Area ◽  
Further Development

Studies in Xenopus laevis and zebrafish suggest a key role for beta-catenin in the specification of the axis of bilateral symmetry. In these organisms, nuclear beta-catenin demarcates the dorsalizing centers. We have asked whether beta-catenin plays a comparable role in the chick embryo and how it is adapted to the particular developmental constraints of chick development. The first nuclear localization of beta-catenin is observed in late intrauterine stages of development in the periphery of the blastoderm, the developing area opaca and marginal zone. Obviously, this early, radially symmetric domain does not predict the future organizing center of the embryo. During further development, cells containing nuclear beta-catenin spread under the epiblast and form the secondary hypoblast. The onset of hypoblast formation thus demarcates the first bilateral symmetry in nuclear beta-catenin distribution. Lithium chloride exposure also causes ectopic nuclear localization of beta-catenin in cells of the epiblast in the area pellucida. Embryos treated before primitive streak formation become completely radialized, as shown by the expression of molecular markers, CMIX and GSC. Lithium treatments performed during early or medium streak stages cause excessive development of the anterior primitive streak, node and notochord, and lead to a degeneration of prospective ventral and posterior structures, as shown by the expression of the molecular markers GSC, CNOT1, BMP2 and Ch-Tbx6L. In summary, we found that in spite of remarkable spatiotemporal differences, beta-catenin acts in the chick in a manner similar to that in fish and amphibia.

A Novel Biomimetic Model for Studying Mechanics of Embryonic Morphogenesis and Differentiation

2010 ◽  
Author(s):  
Julia A. Henkels ◽  
Evan A. Zamir
Keyword(s):  
Epithelial To Mesenchymal Transition ◽  
Primitive Streak ◽  
Mitotic Cell ◽  
Embryonic Cells ◽  
Mesenchymal Transition ◽  
Genetics Research ◽  
Undifferentiated Cells ◽  
Organizing Center ◽  
Important Time ◽  
Anterior Posterior

Before the explosion of genetics research in the last century, embryonic development was largely studied from a mechanical perspective. Paired with genetic advances in understanding developmental signaling pathways and induction mechanisms, an important goal for understanding morphogenesis is to discover how the genome codes for changes in the mechanical movements of the embryonic cells. After formation of the zygote, a phase of rapid mitotic cell division is followed by epithelialization resulting in a cohesive sheet of cells termed the epiblast. During the next major phase of triploblastic development called gastrulation, a group of undifferentiated cells in the epiblast moves collectively to the embryonic midline and eventually gives rise to the three primary germ layers: endoderm, mesoderm, and ectoderm. At the primitive streak—the “organizing center” in amniotes (reptiles, birds, and mammals) which delineates anterior-posterior polarity—prospective endodermal and mesodermal precursors undergo epithelial-to-mesenchymal transition (EMT), internalization, and eventually organogenesis. “It is not birth, marriage, or death, but gastrulation which is truly the most important time in your life” (Lewis Wolpert, 1986).

Formation of the avian primitive streak from spatially restricted blastoderm: evidence for polarized cell division in the elongating streak

Development ◽  
2000 ◽  
Vol 127 (1) ◽  
pp. 87-96 ◽  
Author(s):  
Y. Wei ◽  
T. Mikawa
Keyword(s):  
Cell Division ◽  
Posterior Margin ◽  
Marginal Zone ◽  
Primitive Streak ◽  
Precursor Cells ◽  
In Ovo ◽  
Daughter Cells ◽  
Organizing Center ◽  
First Time ◽  
Inductive Signal

Gastrulation in the amniote begins with the formation of a primitive streak through which precursors of definitive mesoderm and endoderm ingress and migrate to their embryonic destinations. This organizing center for amniote gastrulation is induced by signal(s) from the posterior margin of the blastodisc. The mode of action of these inductive signal(s) remains unresolved, since various origins and developmental pathways of the primitive streak have been proposed. In the present study, the fate of chicken blastodermal cells was traced for the first time in ovo from prestreak stages XI-XII through HH stage 3, when the primitive streak is initially established and prior to the migration of mesoderm. Using replication-defective retrovirus-mediated gene transfer and vital dye labeling, precursor cells of the stage 3 primitive streak were mapped predominantly to a specific region where the embryonic midline crosses the posterior margin of the epiblast. No significant contribution to the early primitive streak was seen from the anterolateral epiblast. Instead, the precursor cells generated daughter cells that underwent a polarized cell division oriented perpendicular to the anteroposterior embryonic axis. The resulting daughter cell population was arranged in a longitudinal array extending the complete length of the primitive streak. Furthermore, expression of cVg1, a posterior margin-derived signal, at the anterior marginal zone induced adjacent epiblast cells, but not those lateral to or distant from the signal, to form an ectopic primitive streak. The cVg1-induced epiblast cells also exhibited polarized cell divisions during ectopic primitive streak formation. These results suggest that blastoderm cells located immediately anterior to the posterior marginal zone, which secretes an inductive signal, undergo spatially directed cytokineses during early primitive streak formation.

Dynamic Movement of Sub-Epiblastic ECM During Primitive Streak Formation

2008 ◽  
Author(s):  
Evan A. Zamir ◽  
Brenda J. Rongish ◽  
Charles D. Little
Keyword(s):  
Electron Microscopy ◽  
Extracellular Matrix ◽  
Primitive Streak ◽  
Ventral Surface ◽  
Text Book ◽  
Classical Text ◽  
Relative Paucity ◽  
Dynamic Movement ◽  
Immunofluorescence Studies ◽  
Organizing Center

A well known “Polonaise” pattern of epiblast cell movements accompanies formation of the amniote primitive streak (PS), which is the organizing center for gastrulation. Although the movements observed in classical (text book) and modern studies appear similar, the biophysical mechanisms driving these movements are unknown. In comparison to studies of dynamic cellular movements during PS formation, and more generally, gastrulation, there is a relative paucity of data regarding movement of the extracellular matrix (ECM) lying adjacent to the ventral surface of the epiblast. Electron microscopy and immunofluorescence studies demonstrated decades ago the presence of a nascent basement membrane-like structure, which we refer to as the sub-epiblastic ECM (SE ECM), containing, at least, fibronectin [1] and collagen [1]. Using ultrastructural markers, Sanders [2] found that the SE ECM is transported medially to the PS with the epiblast cells. Almost two decades later, Bortier et al. [3] grafted radiolabeled quail cells into the epiblasts of chicken blastoderms, and concluded that whole groups of epiblast cells slide across (move relative to) the SE ECM — thus, contradicting Sanders’ earlier findings.

The Role of Actomyosin Contractility During Early Avian Gastrulation

2010 ◽  
Author(s):  
Drew Owen ◽  
Evan Zamir
Keyword(s):  
Cell Movement ◽  
Primitive Streak ◽  
Higher Order ◽  
Specific Role ◽  
Germ Layers ◽  
Morphogenetic Movements ◽  
Actomyosin Contractility ◽  
Organizing Center ◽  
Cell Intercalation

Actin-myosin contraction has been shown to play a major role in early morphogenetic movements in Drosophila (fly) and Xenopus (frog) [1,2]. However, the specific role of actomyosin contractility in amniote embryos (reptiles, birds, and mammals) during primitive streak (PS) formation, the “organizing center” for gastrulation (formation of three primary germ layers), is not known. Current theories regarding primitive streak formation in higher order amniotes center around cell-cell intercalation or chemotactic cell movement [3,4]. We hypothesize that contraction via actin-myosin (AM) filaments is conserved from anamniotes and drives formation of the PS and the associated morphogenetic cell movements.

Three-Dimensional reconstruction of isolated centrosomes by automated electron tomography

1994 ◽  
Vol 52 ◽  
pp. 310-311
Author(s):  
M.B. Braunfeld ◽  
M. Moritz ◽  
B.M. Alberts ◽  
J.W. Sedat ◽  
D.A. Agard
Keyword(s):  
Electron Tomography ◽  
Three Dimensional ◽  
Vital Role ◽  
Complex Nature ◽  
Animal Cells ◽  
Microtubule Organizing Center ◽  
Nucleation Sites ◽  
Dimensional Reconstruction ◽  
Organizing Center ◽  
Resolution Model

In animal cells, the centrosome functions as the primary microtubule organizing center (MTOC). As such the centrosome plays a vital role in determining a cell's shape, migration, and perhaps most importantly, its division. Despite the obvious importance of this organelle little is known about centrosomal regulation, duplication, or how it nucleates microtubules. Furthermore, no high resolution model for centrosomal structure exists.We have used automated electron tomography, and reconstruction techniques in an attempt to better understand the complex nature of the centrosome. Additionally we hope to identify nucleation sites for microtubule growth.Centrosomes were isolated from early Drosophila embryos. Briefly, after large organelles and debris from homogenized embryos were pelleted, the resulting supernatant was separated on a sucrose velocity gradient. Fractions were collected and assayed for centrosome-mediated microtubule -nucleating activity by incubating with fluorescently-labeled tubulin subunits. The resulting microtubule asters were then spun onto coverslips and viewed by fluorescence microscopy.

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