Enhances bone morphogenetic protein (BMP) signaling in a paracrine manner. In contrast, it inhibits both the activin-A and TGFB1-mediated signaling pathways. Interacts with BMP7 and, by doing so, enhances binding to the type I receptors that contains cytoplasmic serine-/threonine protein kinase domains. Also able to interact with activin-A and TGFB1. Weakly expressed in embryonic kidney and brain. Not expressed in adult tissues and several cell lines. Prominently expressed in two areas, the limb buds and the developing kidney, with diffuse staining in the central nervous system. At 9.5 dpc the limb bud mesenchyme is positive. Expression in the kidney region could be detected as early as 9 dpc in the intermediate mesoderm. By 10 dpc, the mesonephric tubules and nephric ducts are clearly positive. At later stages, high levels are localized to the developing tubules. At 18.5 dpc, it is localized to more mature renal tubules located in the developing cortex with little expression detected in the nephrogenic zone. By renal stresses.