Embryonic stem cell cultures are thought to self-organize into embryoid bodies, able to undergo symmetry-breaking, germ layer specification and even morphogenesis. Yet, it is unclear how to reconcile this remarkable self-organization capacity with classical experiments demonstrating key roles for extrinsic biases by maternal factors and/or extraembryonic tissues in embryogenesis. Here, we show that zebrafish embryonic tissue explants, prepared prior to germ layer induction and lacking extraembryonic tissues, can specify all germ layers and form a seemingly complete mesendoderm anlage. Importantly, explant organization requires polarized inheritance of maternal factors from dorsal-marginal regions of the blastoderm. Moreover, induction of endoderm and head-mesoderm, which require peak Nodal-signaling levels, is highly variable in explants, reminiscent of embryos with reduced Nodal signals from the extraembryonic tissues. Together, these data suggest that zebrafish explants do not undergo bona-fide self-organization, but rather display features of genetically encoded self-assembly, where intrinsic genetic programs control the emergence of order.
All data generated and analyzed in the manuscript are provided as Source Data Files. The Custom Script used has been uploaded as Source code 1.
- Carl-Philipp Heisenberg
- Alexandra Schauer
- Diana Pinheiro
- Diana Pinheiro
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
Animal experimentation: All animal experiments in this study were performed in strict accordance with the guidelines of the Ethics and Animal Welfare Committee (ETK) in Austria. The respective approval number that covers the performed experiments is 66.018/0010-WF/II/3b/2014.
- Ashley Bruce
© 2020, Schauer et al.
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