Crossveinless-2 (CV-2), also known as bone morphogenetic protein-binding endothelial cell precursor-derived regulator (BMPER), is a secreted chordin-like protein that modulates the BMP signaling pathway (1 - 3). Human CV-2 is synthesized as a 685 amino acid (aa) residue precursor protein with a putative 39 aa signal peptide, five tandem chordin-like cysteine-rich (CR) domains, a partial von Willebrand factor type D domain (vWD), and a carboxyl trypsin inhibitor-like cysteine-rich domain (TIL) (1, 4). Secreted CV-2 is reported to be proteolytically cleaved to generate two fragments that are disulfide-linked (1, 2). The cleavage site of R&D Systems’ recombinant CV-2 is found to be between asp³⁶⁹ and pro³⁷⁰ in the GDPH sequence within the vWD domain. This cleavage is likely due to an autocatalytic mechanism triggered by low pH comparable to that of the late secretory pathway (5). The GDPH sequence is conserved in CV-2 from other species. It is also found in multiple proteins that undergo a similar type of cleavage (5). Human CV-2 message is detected in many tissues, with the highest expression detected in adult brain and adult and fetal lung (1). It is also expressed in flk-1⁺ endothelial cell precursors and in primary chondrocytes (2). During embryonic development, CV-2 is expressed in regions of high BMP signaling, such as the posterior primitive streak and the ventral tail bud (4). Human CV-2 shares 92% and 34% aa sequence identity with the mouse and Drosophila homologs, respectively (1, 4). Results from biochemical experiments using recombinant CV-2 show that CV-2 directly interacts with BMP-2, -4, and -6 to antagonize BMP signaling, which can regulate a wide range of differentiation processes (1, 2). In contrast, genetic data from Drosophila suggest that CV-2 potentiates BMP-signaling (6). It is possible that like TSG, CV-2 can positively and negatively modulate BMP signal transduction depending on the cell context (7).