Endo-fin-ally a SARA for BMP receptors.

Bone morphogenetic proteins (BMPs) control numerous processes in developing and adult organisms by binding to receptors on various cell types. The signals are relayed to the nucleus by signaling molecules called Smads. How the Smads are recruited to BMP receptors has been difficult to establish. In a paper appearing in this issue of Journal of Cell Science, Shi and colleagues show that a lipid-binding protein present in intracellular endosomal compartments is the crucial link (Shi et al., 2007). The protein also appears to act as a switch that can shut off signaling.