Required for left-right asymmetry determination of organ systems in mammals. At the primitive streak stage (7.0 dpc), expressed in the emerging mesoderm. By 8.0 dpc, expressed exclusively on the left side of developing embryos with expression predominantly in the lateral-plate mesoderm (LPM). Weak expression in the prospective floor plate (PFP). The processing of the protein may also occur at the second R-X-X-R site located at AA 132-135. Processing appears to be regulated in a cell-type specific manner. Belongs to the TGF-beta family.