The present invention relates to the finding that Syndecans (Sdc) are receptors of Rspondin-2 (Rspo2) and Rspondin-3 (Rspo3). Thus, the present invention relates to the identification of Rspo2, Rspo3 and/or Sdc activity modulators by determining if a test compound has the ability to modulate the binding of an Rspo2 and/or Rspo3 polypeptide to an Sdc polypeptide. Further, the invention refers to novel uses for antagonists of Rspo2 and/or Rspo3 in the treatment of Sdc-associated disorders and for Sdc antagonists in the treatment of Rspo2- and/or Rspo3-associated disorders.
