Crescent is an Inhibitor of Tolloid Proteases

PLOPER, DIEGO; DE ROBERTIS, EDWARD M.

Lake Arrowhead, CA

Encuentro; Biological Chemistry Retreat; 2009

University of California, Los Angeles

The Spemann organizer, a group of cells on the dorsal side of the gastrula embryo, expresses the BMP antagonist Chordin. Crescent, a secreted frizzled related protein (sFRP), is also expressed at early gastrula by this group of cells. The key step in dorso-ventral patterning is the digestion of Chordin by Tolloid enzymes (called Xolloid-related, Xolloid, and BMP1). This causes the release of BMPs made on more dorsal regions of the embryo on the ventral side. Tolloid enzymes have been shown to be regulated by Sizzled (Szl), another sFRP expressed in the Ventral Organizing Center. Szl inhibits Tolloid cleavage of Chordin. We now report that Crescent is also an inhibitor of the extracellular proteolytic reaction that regulates BMP signalling. We found through Biacore analyses that Crescent binds to Tolloid enzymes with high affinity, and from enzyme kinetic assays that Crescent is a competitive inhibitor of the cleavage of Chordin. Microinjection experiments show that Crescent is capable of dosalizing embryos, and that this dorsalization is dependent on Chordin. Furthermore, coinjections of Chordin and Crescent have synergistic effects. Injections with a Crescent mutant protein mimicking the Ogon mutation in Sizzled, which does not bind Tolloid enzymes, was much less dorsalizing. We suggest a model in which the digestion of the BMP antagonist Chordin by Tolloid enzymes is regulated from both the Ventral and Dorsal Organizing Centers, by Sizzled on the ventral and Crescent on the dorsal side.