Modeling early stages of endoderm development in epiblast stem cell aggregates with supply of extracellular matrices

• Published in: Development, growth & differentiation growth & differentiation, 2020-05, Vol.62 (4), p.243-259
• Main Authors: Inamori, Sachiko, Fujii, Mai, Satake, Sayaka, Iida, Hideaki, Teramoto, Machiko, Sumi, Tomoyuki, Meno, Chikara, Ishii, Yasuo, Kondoh, Hisato
• Format: Article
• Language: English
• Subjects: Animals; Cell culture; Cell migration; Developmental stages; Embedding; Embryos; Endoderm; Endoderm - cytology; Endoderm - metabolism; epiblast stem cells; extracellular matrix; Extracellular Matrix - metabolism; FOXA2; Gastrulation; Germ Layers - cytology; Germ Layers - metabolism; Green fluorescent protein; Laminin; Mice; Mice, Inbred DBA; Models, Biological; Mouse Embryonic Stem Cells - cytology; Mouse Embryonic Stem Cells - metabolism; Oct-4 protein; Original; Stem cells; Transcription activation
• ISSN: 0012-1592; 1440-169X
• DOI: 10.1111/dgd.12663

Endoderm precursors expressing FoxA2 and Sox17 develop from the epiblast through the gastrulation process. In this study, we developed an experimental system to model the endoderm‐generating gastrulation process using epiblast stem cells (EpiSCs). To this end, we established an EpiSC line i22, in which enhanced green fluorescent protein is coexpressed with Foxa2. Culturing i22 EpiSCs as aggregates for a few days was sufficient to initiate Foxa2 expression, and further culturing of the aggregates in Matrigel promoted the sequential activation of transcription factor genes involved in endoderm precursor development, e.g., Eomes, Gsc, and Sox17. In aggregation culture of i22 cells for 3 days, all cells expressed POU5F1, SOX2, and E‐cadherin, a signature of the epiblast, whereas expression of GATA4 and SOX17 was also activated moderately in dispersed cells, suggesting priming of these cells to endodermal development. Embedding the aggregates in Matrigel for further 3 days elicited migration of the cells into the lumen of laminin‐rich matrices covering the aggregates, in which FOXA2 and SOX17 were expressed at a high level with the concomitant loss of E‐cadherin, indicating the migratory phase of endodermal precursors. Prolonged culturing of the aggregates generated three segregating cell populations found in post‐gastrulation stage embryos: (1) definitive endoderm co‐expressing high SOX17, GATA4, and E‐cadherin, (2) mesodermal cells expressing a low level of GATA4 and lacking E‐cadherin, and (3) primed epiblast cells expressing POU5F1, SOX2 without E‐cadherin. Thus, aggregation of EpiSCs followed by embedding of aggregates in the laminin‐rich matrix models the gastrulation‐dependent endoderm precursor development. Changes in the distribution of SOX17‐expressing cells in the EpiSC aggregates. The SOX17‐expressing cells initially arises at scattered positions in simple aggregates of EpiSCs. Embedding the aggregates in laminin‐rich Matrigel increased the fraction of SOX17‐expressing endoderm precursor cells, and these SOX17‐expressing cells migrated out in the laminin‐rich mantle zone, and eventually settled in the mantle zone forming epitheloid endodermal tissues.