PTP1B is an effector of activin signaling and regulates neural specification of embryonic stem cells.

During embryogenesis, the Activin/Nodal pathway promotes the mesendodermal lineage and inhibits neural fate. The molecular mechanisms underlying this role of the Activin/Nodal pathway are not clear. In this study, we report a role for protein tyrosine phosphatase 1B (PTP1B) in Activin-mediated early fate decisions during ESC differentiation and show that PTP1B acts as an effector of the Activin pathway to specify mesendodermal or neural fate. We found that the Activin/ALK4 pathway directly recruits PTP1B and stimulates its release from the endoplasmic reticulum through ALK4-mediated cleavage. Subsequently, PTP1B suppresses p-ERK1/2 signaling to inhibit neural specification and promote mesendodermal commitment. These findings suggest that a noncanonical Activin signaling pathway functions in lineage specification of mouse and human embryonic stem cells.