Distinct GATA6- and laminin-dependent mechanisms regulate endodermal and ectodermal embryonic stem cell fates.

This study investigates the establishment of alternative cell fates during embryoid body differentiation when ES cells diverge into two epithelia simulating the pre-gastrulation endoderm and ectoderm. We report that endoderm differentiation and endoderm-specific gene expression, such as expression of laminin 1 subunits, is controlled by GATA6 induced by FGF. Subsequently, differentiation of the non-polar primitive ectoderm into columnar epithelium of the epiblast is induced by laminin 1. Using GATA6 transformed Lamc1-null endoderm-like cells, we demonstrate that laminin 1 exhibited by the basement membrane induces epiblast differentiation and cavitation by cell-to-matrix/matrix-to-cell interactions that are similar to the in vivo crosstalk in the early embryo. Pharmacological and dominant-negative inhibitors reveal that the cell shape change of epiblast differentiation requires ROCK, the Rho kinase. We also show that pluripotent ES cells display laminin receptors; hence, these stem cells may serve as target for columnar ectoderm differentiation. Laminin is not bound by endoderm derivatives; therefore, the sub-endodermal basement membrane is anchored selectively to the ectoderm, conveying polarity to its assembly and to the differentiation induced by it. Unique to these interactions is their flow through two cell layers connected by laminin 1 and their involvement in the differentiation of two epithelia from the same stem cell pool: one into endoderm controlled by FGF and GATA6; and the other into epiblast regulated by laminin 1 and Rho kinase.