Spemann organizer activity of Smad10.

The Spemann organizer induces neural tissue, dorsalizes mesoderm and generates a second dorsal axis. We report the isolation and characterization of Smad10, which has all three of these Spemann activities. Smad10 is expressed at the appropriate time to transduce Spemann signals endogenously. Like the organizer, Smad10 generates anterior and posterior neural tissues. Smad10 appears to function downstream of the Spemann organizer, consistent with a role in mediating organizer-derived signals. Interestingly, Smad10, unlike previously characterized mediators of Spemann activity, does not appear to block BMP signals. This finding, coupled with the functional activity and expression profile, suggests that Smad10 mediates Spemann action in a novel manner.