Mechano-biochemical marine stimulation of inversion, gastrulation, and endomesoderm specification in multicellular Eukaryota

Abstract

The evolutionary emergence of the primitive gut in Metazoa is one of the decisive events that conditioned the major evolutionary transition, leading to the origin of animal development. It is thought to have been induced by the specification of the endomesoderm (EM) into the multicellular tissue and its invagination (i.e., gastrulation). However, the biochemical signals underlying the evolutionary emergence of EM specification and gastrulation remain unknown. Herein, we find that hydrodynamic mechanical strains, reminiscent of soft marine flow, trigger active tissue invagination/gastrulation or curvature reversal via a Myo-II-dependent mechanotransductive process in both the metazoan Nematostella vectensis (cnidaria) and the multicellular choanoflagellate Choanoeca flexa. In the latter, our data suggest that the curvature reversal is associated with a sensory-behavioral feeding response. Additionally, like in bilaterian animals, gastrulation in the cnidarian Nematostella vectensis is shown to participate in the biochemical specification of the EM through mechanical activation of the β-catenin pathway via the phosphorylation of Y654-βcatenin. Choanoflagellates are considered the closest living relative to metazoans, and the common ancestor of choanoflagellates and metazoans dates back at least 700 million years. Therefore, the present findings using these evolutionarily distant species suggest that the primitive emergence of the gut in Metazoa may have been initiated in response to marine mechanical stress already in multicellular pre-Metazoa. Then, the evolutionary transition may have been achieved by specifying the EM via a mechanosensitive Y654-βcatenin dependent mechanism, which appeared during early Metazoa evolution and is specifically conserved in all animals.

Tissue tension permits β-catenin phosphorylation to drive mesoderm specification in human embryonic stem cells

“…Our current results now provide definitive mechanistic evidence linking tissue mechanics and tension to β-catenin Y654 phosphorylation and the EMT and mesoderm specification in this gastruloid model. Our findings are consistent with prior work showing that tension-dependent modulation of β-catenin phosphorylation and Wnt-regulated development is a conserved mesoderm signaling mechanism in a range of species, including zebrafish 9 , Drosophila 19 the cnidarian N. vectensis and choanoflagellates 20 . Homozygous phosphomimetic mutants (Y654E) have been shown to cause embryonic lethality in mice, further implicating the importance of phosphorylation of this residue in higher organism development 42 .…”

“…Interestingly, we also noted that inhibiting GSK3β activity using CHIR99021 (CHIR) similarly rescued T-mNeongreen expression and restored the spatial distribution of mesoderm induction, indicating that preventing β-catenin degradation to artificially elevate cytosolic and nuclear β-catenin can bypass the effects of the mutation on Wnt signaling. We thus arrive at a model in our human gastrulation system where tension-dependent accessibility of AJ β-catenin permits its Src-mediated phosphorylation at residue Y654 β-catenin to facilitate Wnt signaling and direct mesoderm specification is mechanically activated 11,19,20 .…”

“…β-catenin, a key developmental protein 13,14 , has been implicated in such mechanical signaling 9,10,[15][16][17][18] . Mechanical tension at adherens junctions (AJ) has been implicated in β-catenin phosphorylation of the C-terminus tyrosine 654 (Y654) in Drosophila, zebrafish, sea anemone and choanoflagellates 19,20 . This force-dependent βcatenin exposure is predicted to be permissive for Src-dependent Y654 phosphorylation, which reduces β-catenin binding to E-cadherin 21 , leading to loss of AJ β-catenin 22 , nuclear accumulation, and a Wnt-dependent mesodermal gene expression program 23,24 .…”