The Drosophila Medea gene is required downstream of dpp and encodes a functional homolog of human Smad4.
Hudson JB, Podos SD, Keith K, Simpson SL, Ferguson EL. The Drosophila Medea gene is required downstream of dpp and encodes a functional homolog of human Smad4. Development. 1998 Apr; 125(8):1407-20.