# mTORC2-mediated cell-cell interactions promote BMP4-induced WNT activation and mesoderm differentiation

## TL;DR

This study shows that mTORC2 is not needed for stem cell renewal but is important for cell adhesion and activating WNT signals during differentiation into mesoderm and endoderm.

## Contribution

The study reveals a novel mechanism linking mTORC2 to WNT activation via cell-cell interactions during differentiation.

## Key findings

- mTORC2 deficiency impairs cell adhesion and Rho/Rac signaling in hESCs.
- Reduced cell-cell interactions in mTORC2-deficient hESCs hinder WNT activation and mesoderm/endoderm differentiation.
- Direct WNT activation rescues mesendoderm differentiation in mTORC2-deficient hESCs.

## Abstract

The mechanistic target of rapamycin complex 2 (mTORC2) is essential for embryonic development, but its underlying molecular mechanisms remain unclear. Here, we show that disruption of mTORC2 in human embryonic stem cells (hESCs) considerably alters the Rho/Rac signaling dynamics and reduces E-cadherin expression and cell adhesion. Despite this, mTORC2-deficient hESCs maintain self-renewal and expression of pluripotent markers when cultured in mouse embryonic fibroblast conditioned medium (MEF-CM) supplemented with bFGF. However, these hESCs exhibit significantly impaired mesoderm and endoderm differentiation in response to BMP4 and Activin treatment, respectively, possibly due to reduced WNT activation mediated by cell-cell interactions. Direct activation of the WNT pathway using a GSK3 inhibitor restores mesendoderm differentiation in mTORC2-deficient hESCs. Our study uncovers a novel mechanism by which mTORC2 regulates cell fate determination and highlights a critical link between the intercellular adhesion and the activation of canonical WNT genes.

•mTORC2 is not necessary for maintaining hESC self-renewal•Deficiency of mTORC2 impairs cell adhesion and cell-cell interactions•Mesoderm and endoderm formation are hindered in mTORC2-null hESCs•Cell-cell interactions are important for WNT signaling activation

mTORC2 is not necessary for maintaining hESC self-renewal

Deficiency of mTORC2 impairs cell adhesion and cell-cell interactions

Mesoderm and endoderm formation are hindered in mTORC2-null hESCs

Cell-cell interactions are important for WNT signaling activation

The role of mTORC2 in embryonic development and stem cells remains unclear. Tong et al. use mTORC2-knockout hESCs to demonstrate that mTORC2 is dispensable for maintaining hESC self-renewal, but its deficiency significantly damages cell adhesion due to imbalanced RhoA/Rac. Reduced cell adhesion by mTORC2 deficiency in hESCs impedes the activation of WNT signaling and reduces mesoderm and endoderm differentiation.