May be involved in dorsoventral axis formation. Seems to antagonize BMP signaling by forming ternary complexes with CHRD and BMPs, thereby preventing BMPs from binding to their receptors. In addition to the anti-BMP function, also has pro-BMP activity, partly mediated by cleavage and degradation of CHRD, which releases BMPs from ternary complexes. May be an important modulator of BMP-regulated cartilage development and chondrocyte differentiation. May play a role in thymocyte development (By similarity). Interacts with CHRD and BMP4. This interaction enhances CHRD/BMP4 complex formation. Interacts with BMP7 (By similarity). The N-terminal domain is sufficient to interact with BMP4. Belongs to the twisted gastrulation protein family.