Good day, Prof. Leonardo!
We appreciate your comments on our presentation. Here are the answers to your questions:
1. Please elaborate on gastruloid and embryoid. What are they composed of exactly and how reliable are they in reflecting the embryologic processes you are interested in? The gastruloid is composed of the ectoderm fate and primitive streak fate, while the embryoid is composed of the epiblast fate and the primitive streak fate. For both bodies, embryonic stem cells aggregates are cultured unconstrained and undergo symmetry breaking to establish the primitive streak-like domain.
In this research, we are interested in observing the effects of external signals in the development of the embryoid and gastruloid. Then, we determine the importance and actual role of extraembryonic tissues in these processes, so the embryoids and gastruloids are reliable for assessing their ability to break the radial symmetry and give rise to primitive streak fate in the absence of extraembryonic tissues, which are important for signaling and morphogenesis during gastrulation.
Therefore, using the gastruloid and embryoid bodies, the formation of embryonic stem cells can be traced while also accounting for the external input. With this, an intact embryo's self-organization, decision-making, and patterning processes can be deduced.
2. Please explain the brachyury expression in relation to embryologic development. How sensitive is this to destabilization? The expression of transcription factor Brachyury regulates the posterior mesoderm formation and notochord development (Chen et al., 2020). It mainly affects the formation and development of the structure of the embryo wherein 2D embryonic stem cell (ESC) colony geometry affects the positioning of these brachyury-expressing cells, which will later trigger the rise to the primitive streak. For example, in colonies with an ellipsoid shape, the brachyury-expressing cells prefer to localize on the tips of colonies which was an effect of shape-dependent differences in cell densities.
The specific geometry of stem cell colonies affects colony patterning by inducing differential tension along the colony boundary, with high tension promoting brachyury expression. Thus, if destabilization occurs in brachyury expression, it would significantly affect the formation and development of the structure of the embryo.
Reference (not included in the journal article):
Chen, M., Wu, Y., Zhang, H., Li, S., Zhou, J., & Shen, J. (2020). The roles of embryonic transcription factor BRACHYURY in tumorigenesis and progression. Frontiers in Oncology, 10, 961.
