chordin

Chordin is a secreted glycoprotein that acts as a critical antagonist of bone morphogenetic protein (BMP) signaling in early vertebrate development. It is encoded by the CHRD gene and is expressed predominantly in the dorsal region of the embryo, where it binds BMP ligands in the extracellular space, blocking their interaction with BMP receptors. By limiting BMP activity dorsally, chordin promotes neural tissue formation and helps establish the dorsal-ventral axis.

Chordin has a modular architecture characterized by multiple cysteine-rich repeats (CR domains) that mediate BMP binding. It is secreted and can be cleaved by tolloid metalloproteases, which releases BMPs and tunes the signaling gradient necessary for proper patterning during gastrulation.

Chordin interacts with other extracellular BMP antagonists, such as Noggin and Follistatin, and participates in a network that shapes morphogen gradients during development. Its function is conserved across vertebrates, and functional homologs exist in other phyla, notably the Drosophila protein Short gastrulation (Sog), illustrating a conserved strategy to modulate BMP signaling.

Disruption of CHRD or misregulation of chordin activity can perturb dorsal-ventral patterning and neural induction, as shown in model organisms. Chordin remains a key focus in studies of embryonic organizer activity and BMP transport, contributing to understanding of vertebrate axis formation.