bioRxiv preprint doi: https://doi.org/10.1101/2020.12.18.423440; this version posted December 19, 2020. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY-ND 4.0 International license. Differential compartmentalization of BMP4/NOGGIN requires NOGGIN trans-epithelial transport Tien Phan-Everson1-2 +, Fred Etoc1 +, Ali H. Brivanlou1 *, Eric D. Siggia2 * 1 Laboratory of Stem Cell Biology and Molecular Embryology, The Rockefeller University, New York, New York 10065, USA. 2 Laboratory of Physical, Mathematical, and Computational Biology, The Rockefeller University, New York, New York 10065, USA. + Co-first Authors * Joint Corresponding Authors Correspondence:
[email protected];
[email protected] Summary Using self-organizing human models of gastrulation, we previously showed that (i) BMP4 initiates the cascade of events leading to gastrulation; (ii) BMP4 signal-reception is restricted to the basolateral domain; and (iii) in a human-specific manner, BMP4 directly induces the expression of NOGGIN. Here, we report the surprising discovery that in human epiblasts, NOGGIN and BMP4 were secreted into opposite extracellular spaces. Interestingly, apically-presented NOGGIN could inhibit basally-delivered BMP4. Apically-imposed microfluidic flow demonstrated that NOGGIN traveled in the apical extracellular space. Our co-localization analysis detailed the endocytotic route that trafficked NOGGIN from the apical space to the basolateral intercellular space where BMP4 receptors were located. This apical-to-basal transcytosis was indispensable for NOGGIN inhibition. Taken together, the segregation of activator/inhibitor into distinct extracellular spaces challenges classical views of morphogen movement.