A mouse homologue of FAST-1 transduces TGF beta superfamily signals and isexpressed during early embryogenesis

The transcription factor FAST-1 has recently been shown to play a key role in the specification of mesoderm by TGF beta superfamily signals in the ear ly Xenopus embryo. We have cloned Fast1, a mouse homologue of Xenopus FAST- 1; and characterized its expression during embryogenesis and function in ac tivin/TGF beta signal transduction. In vitro, Fast1 associates with Smads i n response to an activin/TGF beta signal to form a complex that recognizes the Xenopus activin responsive element (ARE.) targeted by Xenopus FAST-1. I n intact cells, introduction of Fast1 confers activin/TGF beta regulation o f an ARE-luciferase reporter. In embryos, Fast1 is expressed predominantly throughout the epiblast before gastrulation and declines as development pro gresses. We propose that mouse Fast1, Like Xenopus FAST-1, mediates TGF bet a superfamily signals specifying developmental fate during early embryogene sis. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.