Abstract
SummaryUpon implantation, mammalian embryos undergo major morphogenesis and key developmental processes such as body axis specification and gastrulation. However, limited accessibility obscures the study of these crucial processes. Here, we develop an ex vivo Matrigel-collagen-based culture to recapitulate mouse development from E4.5 to E6.0. Our system not only recapitulates embryonic growth, axis initiation, and overall 3D architecture in 49% of the cases, but its compatibility with light-sheet microscopy also enables the study of cellular dynamics through automatic cell segmentation. We find that, upon implantation, release of the increasing tension in the polar trophectoderm is necessary for its constriction and invagination. The resulting extra-embryonic ectoderm plays a key role in growth, morphogenesis, and patterning of the neighboring epiblast, which subsequently gives rise to all embryonic tissues. This 3D ex vivo system thus offers unprecedented access to peri-implantation development for in toto monitoring, measurement, and spatiotemporally controlled perturbation, revealing a mechano-chemical interplay between extra-embryonic and embryonic tissues.
Highlights
Implantation is a unique event in mammalian development whereby an exchange interface is established between the embryo and the maternal tissues (Hemberger et al, 2020; Wang and Dey, 2006)
We found that the polar trophectoderm cells do not invaginate and fail to form the extra-embryonic ectoderm (ExE) after 6 h in culture, unlike E4.75 embryos developed in utero (Figures 1A and S1; Christodoulou et al, 2019; Copp, 1979)
Actin and bi-phosphorylated myosin regulatory light chain were enriched at the apical surface of the polar trophectoderm (pTE) cells before and during invagination in in utero developed embryos, whereas they were localized at cell-cell junctions in those developed ex vivo (Figures 1C and 1D)
Summary
Implantation is a unique event in mammalian development whereby an exchange interface is established between the embryo and the maternal tissues (Hemberger et al, 2020; Wang and Dey, 2006). The extra-embryonic portion of the embryo, consisting of TE and PrE-derived cells, engages the maternal tissue in a complex interplay that eventually forms the placenta. Ex vivo culture of peri-implantation mouse embryos so far relied on embryonic growth on 2D surfaces (Bedzhov and Zernicka-Goetz, 2014; Hsu, 1971, 1972; Morris et al, 2012; Pienkowski et al, 1974; Tachi, 1992). This culture typically induces adhesion and spread of trophoblast cells over the surface, disrupting embryonic morphogenesis. Recapitulation of in vivo development is limited with current methods, both in terms of efficiency and physiological relevance
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