A Tgfbr1/Snai1-dependent developmental module at the core of vertebrate axial elongation

Formation of the vertebrate postcranial body axis follows two sequential but distinct phases. The first phase generates pre-sacral structures (the so-called primary body) through the activity of the primitive streak on axial progenitors within the epiblast. The embryo then switches to generate the secondary body (post-sacral structures), which depends on axial progenitors in the tail bud. Here we show that the mammalian tail bud is generated through an independent functional developmental module, concurrent but functionally different from that generating the primary body. This module is triggered by convergent Tgfbr1 and Snai1 activities that promote an incomplete epithelial to mesenchymal transition on a subset of epiblast axial progenitors. This EMT is functionally different from that coordinated by the primitive streak, as it does not lead to mesodermal differentiation but brings axial progenitors into a transitory state, keeping their progenitor activity to drive further axial body extension.

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A TgfβRI/Snai1-dependent developmental module at the core of vertebrate axial elongation

10.1101/2020.03.09.983809 ◽

2020 ◽

Author(s):

André Dias ◽

Anastasiia Lozovska ◽

Filip J. Wymeersch ◽

Ana Nóvoa ◽

Anahi Binagui-Casas ◽

...

Keyword(s):

Epithelial To Mesenchymal Transition ◽

Primitive Streak ◽

Body Axis ◽

Tail Bud ◽

Mesenchymal Transition ◽

Axial Elongation ◽

The Core ◽

Primary Body ◽

Transitory State

ABSTRACTFormation of the vertebrate postcranial body axis follows two sequential but distinct phases. The first phase generates pre-sacral structures (the so-called primary body) through the activity of the primitive streak (PS) on axial progenitors within the epiblast. The embryo then switches to generate the secondary body (post-sacral structures), which depends on axial progenitors in the tail bud. Here we show that the mammalian tail bud is generated through an independent developmental module, concurrent but functionally different to that generating the primary body. This module is triggered by convergent TgfβRI and Snai1 activities that promote an incomplete epithelial to mesenchymal transition (EMT) on a subset of epiblast axial progenitors. This EMT is functionally different to that coordinated by the PS, as it does not lead to mesodermal differentiation but brings axial progenitors into a transitory state, keeping their progenitor activity to drive further axial body extension.

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Molecular mechanism of symmetry breaking in a 3D model of a human epiblast

10.1101/330704 ◽

2018 ◽

Cited By ~ 2

Author(s):

Mijo Simunovic ◽

Jakob J. Metzger ◽

Fred Etoc ◽

Anna Yoney ◽

Albert Ruzo ◽

...

Keyword(s):

Symmetry Breaking ◽

Axial Symmetry ◽

3D Model ◽

Epithelial To Mesenchymal Transition ◽

Embryonic Stem ◽

Primitive Streak ◽

Molecular Evidence ◽

Axis Formation ◽

Mesenchymal Transition

ABSTRACTBreaking the anterior-posterior (AP) symmetry in mammals takes place at gastrulation. Much of the signaling network underlying this process has been elucidated in the mouse, however there is no direct molecular evidence of events driving axis formation in humans. Here, we use human embryonic stem cells to generate an in vitro 3D model of a human epiblast whose size, cell polarity, and gene expression are similar to a 10-day human epiblast. A defined dose of bone mor-phogenetic protein 4 (BMP4) spontaneously breaks axial symmetry, and induces markers of the primitive streak and epithelial to mesenchymal transition. By gene knockouts and live-cell imaging we show that, downstream of BMP4, WNT3 and its inhibitor DKK1 play key roles in this process. Our work demonstrates that a model human epiblast can break axial symmetry despite no asymmetry in the initial signal and in the absence of extraembryonic tissues or maternal cues. Our 3D model opens routes to capturing molecular events underlying axial symmetry breaking phenomena, which have largely been unexplored in model human systems.

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BMP4-induced symmetry breaking in a 3D model of the human epiblast

10.21203/rs.2.9730/v1 ◽

2019 ◽

Cited By ~ 1

Author(s):

Mijo Simunovic ◽

Ali H. Brivanlou ◽

Eric D. Siggia

Keyword(s):

Live Cell Imaging ◽

3D Model ◽

Epithelial To Mesenchymal Transition ◽

Cell Imaging ◽

Embryonic Stem ◽

Primitive Streak ◽

Mesenchymal Transition ◽

Pluripotency Markers ◽

Anterior Posterior

Abstract We describe the protocol of generating a 3D stem-cell-based model of the human pre-gastrulation epiblast by culturing human embryonic stem cells in a mix of hydrogel and Matrigel. Much like the epiblast of an in vitro attached day-10 human embryo, this model is an epithelial sphere with a cavity at its center, it is expressing key pluripotency markers, and it displays apico-basal polarity. The 3D colonies can further be differentiated with morphogens and in the case of intermediate concentrations of BMP4, they break the anterior-posterior symmetry characterized by an asymmetric expression of a primitive streak marker and showing signs of epithelial to mesenchymal transition. The protocol described here is suitable for immunofluorescence staining and for live-cell imaging.

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Mouse primitive streak forms in situ by initiation of epithelial to mesenchymal transition without migration of a cell population

Developmental Dynamics ◽

10.1002/dvdy.23711 ◽

2011 ◽

Vol 241 (2) ◽

pp. 270-283 ◽

Cited By ~ 70

Author(s):

Margot Williams ◽

Carol Burdsal ◽

Ammasi Periasamy ◽

Mark Lewandoski ◽

Ann Sutherland

Keyword(s):

Cell Population ◽

Epithelial To Mesenchymal Transition ◽

Primitive Streak ◽

Mesenchymal Transition ◽

A Cell

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

ASME 2010 Summer Bioengineering Conference, Parts A and B ◽

10.1115/sbc2010-19608 ◽

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).

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Self-organization of a functional human organizer by combined WNT and NODAL signalling

10.1101/234633 ◽

2017 ◽

Cited By ~ 3

Author(s):

I. Martyn ◽

T.Y. Kanno ◽

A. Ruzo ◽

E.D. Siggia ◽

A.H. Brivanlou

Keyword(s):

Epithelial To Mesenchymal Transition ◽

Embryonic Stem ◽

Primitive Streak ◽

Model Organisms ◽

Detailed Characterization ◽

Mesenchymal Transition ◽

Neural Fate ◽

Secondary Axis ◽

Human Embryology ◽

Emt Markers

In amniotes, the development of the primitive streak (PS) and its accompanying “organizer” define the first stages of gastrulation. Despite detailed characterization in model organisms, the analogous human structures remain a mystery. We have previously shown that when stimulated with BMP4, micropatterned colonies of human embryonic stem cells (hESCs) self-organize to generate early embryonic germ layers1. Here we show that in the same type of colonies WNT signalling is sufficient to induce a PS, and WNT with ACTIVIN is sufficient to induce an organizer, as characterized by embryo-like sharp boundary formation, epithelial-to-mesenchymal transition (EMT) markers, and expression of the organizer specific transcription factor GSC. Moreover, when grafted into chick embryos, WNT and ACTIVIN treated human cells induce and contribute autonomously to a secondary axis while inducing neural fate in the host. This fulfills the most stringent functional criteria for an organizer, and its discovery represents a major milestone in human embryology.

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