In this movie, you can for example see that the full ablation of the hypoblast completely inhibits primitive streak formation, while a partial ablation that leaves a piece of posterior hypoblast on each side leads to the formation of two embryonic axes (forming conjoined twins).

By intercalating a porous filter between the epiblast and the hypoblast, we further showed that the hypoblast requires physical contact with the epiblast to achieve counter-rotating flows. Thus, forces generated in the epiblast propagate by mechanical coupling to the hypoblast, setting it in motion.

By generating a two-color chimera, we observed that the counter-rotating flows of the epiblast and hypoblast are highly synchronized. As a result, the hypoblast and epiblast move very little in relation to each other.

We have adapted live-imaging techniques previously used to characterize tissue flows in the avian epiblast to describe, this time, tissue flows in the hypoblast. This allowed us to discover that, like the epiblast, the hypoblast exhibits counter-rotating flows (also known as Polonaise movements).