Chapter 21
Xenopus Deep Cell Aggregates: A 3D Tissue Model
for Mesenchymal-to-Epithelial Transition
Hye Young Kim and Lance A. Davidson
Abstract
Mesenchymal-to-epithelial transition (MET) describes the ability of loosely associated migratory cells to
form a more adherent sheet-like assembly of cells. MET is a conserved motif occurring throughout
organogenesis and plays a key role in regeneration and cancer metastasis, and is the first step in producing
induced pluripotent stem cells (iPSCs). To resolve fundamental biological questions about MET, its
relation to epithelial-to-mesenchymal transition, and to explore MET’s role in tissue assembly and remodeling requires live models for MET that are amenable to experimentation. Many cases of clinically
important MET are inferred since they occur deep with the body of the embryo or adult. We have
developed a tractable model for MET, where cellular transitions can be directly observed under conditions
where molecular, mechanical, and cellular contexts can be controlled experimentally. In this chapter, we
introduce a 3-dimensional (3D) tissue model to study MET using Xenopus laevis embryonic mesenchymal
cell aggregates.
Key words Mesenchymal-to-epithelial transition, 3D aggregate, Mesenchyme, Immunofluorescence,
Dissociation, Microsurgery
1 Introduction
Cells in our body are highly plastic with regard to both their
phenotype and their mechanical properties. For instance, a tightly
adherent epithelial cell in a sheet may undergo a transition into a
loosely bound mesenchymal cell allowing it to migrate into surrounding tissues (e.g., an epithelial-to-mesenchymal transition or
EMT). Conversely, motile mesenchymal cells can undergo a
mesenchymal-to-epithelial transition (MET) during which they
aggregate and form an organized epithelium. METs involve largescale changes at the level of transcription, the cytoarchitecture, and
cell behavior [1]. MET appears to have evolved as a revolutionary
strategy in the metazoan lineage [2] where it plays a fundamental
role in many tissue-shaping processes including cancer [3], development [4, 5] and stem cell reprogramming [6, 7]. METs are key
Kyra Campbell and Eric Theveneau (eds.), The Epithelial-to Mesenchymal Transition: Methods and Protocols,
Methods in Molecular Biology, vol. 2179, https://doi.org/10.1007/978-1-0716-0779-4_21,
© Springer Science+Business Media, LLC, part of Springer Nature 2021
275
Xenopus Deep Cell Aggregates: A 3D Tissue Model
for Mesenchymal-to-Epithelial Transition
Hye Young Kim and Lance A. Davidson
Abstract
Mesenchymal-to-epithelial transition (MET) describes the ability of loosely associated migratory cells to
form a more adherent sheet-like assembly of cells. MET is a conserved motif occurring throughout
organogenesis and plays a key role in regeneration and cancer metastasis, and is the first step in producing
induced pluripotent stem cells (iPSCs). To resolve fundamental biological questions about MET, its
relation to epithelial-to-mesenchymal transition, and to explore MET’s role in tissue assembly and remodeling requires live models for MET that are amenable to experimentation. Many cases of clinically
important MET are inferred since they occur deep with the body of the embryo or adult. We have
developed a tractable model for MET, where cellular transitions can be directly observed under conditions
where molecular, mechanical, and cellular contexts can be controlled experimentally. In this chapter, we
introduce a 3-dimensional (3D) tissue model to study MET using Xenopus laevis embryonic mesenchymal
cell aggregates.
Key words Mesenchymal-to-epithelial transition, 3D aggregate, Mesenchyme, Immunofluorescence,
Dissociation, Microsurgery
1 Introduction
Cells in our body are highly plastic with regard to both their
phenotype and their mechanical properties. For instance, a tightly
adherent epithelial cell in a sheet may undergo a transition into a
loosely bound mesenchymal cell allowing it to migrate into surrounding tissues (e.g., an epithelial-to-mesenchymal transition or
EMT). Conversely, motile mesenchymal cells can undergo a
mesenchymal-to-epithelial transition (MET) during which they
aggregate and form an organized epithelium. METs involve largescale changes at the level of transcription, the cytoarchitecture, and
cell behavior [1]. MET appears to have evolved as a revolutionary
strategy in the metazoan lineage [2] where it plays a fundamental
role in many tissue-shaping processes including cancer [3], development [4, 5] and stem cell reprogramming [6, 7]. METs are key
Kyra Campbell and Eric Theveneau (eds.), The Epithelial-to Mesenchymal Transition: Methods and Protocols,
Methods in Molecular Biology, vol. 2179, https://doi.org/10.1007/978-1-0716-0779-4_21,
© Springer Science+Business Media, LLC, part of Springer Nature 2021
275