A mouse homologue of FAST-1 transduces TGFβ superfamily signals and is expressed during early embryogenesis

The transcription factor FAST-1 has recently been shown to play a key role in the specification of mesoderm by TGFβ superfamily signals in the early Xenopus embryo. We have cloned Fast1, a mouse homologue of Xenopus FAST-1, and characterized its expression during embryogenesis and function in activin/TGFβ signal transduction. In vitro, Fast1 associates with Smads in response to an activin/ TGFβ signal to form a complex that recognizes the Xenopus activin responsive element (ARE) targeted by Xenopus FAST-1. In intact cells, introduction of Fast1 confers activin/TGFβ regulation of an ARE-luciferase reporter. In embryos, Fast1 is expressed predominantly throughout the epiblast before gastrulation and declines as development progresses. We propose that mouse Fast1, like Xenopus FAST1, mediates TGFβ superfamily signals specifying developmental fate during early embryogenesis.