Fig. 6. Cleavage mutant forms of Xnr2 are secreted and can act non-cell autonomously. (A-D) DCM-Xnr2 induces mesoderm non-cell autonomously. Four-cell embryos were injected at the animal pole with (A) 100 pg xnr2 + 200 pg ß-galactosidase, (B) 2 ng DCM-xnr2 + ß-galactosidase or (C) lacZ/adr2 mRNA. lacZ expression was visualized by red-gal staining and xbra expression was detected by in situ hybridization. (D) Control embryos. (E) CM-Xnr2 and DCM-Xnr2 are secreted from oocytes while CM-Der is not. Mature oocytes were injected with 25 ng of the indicated mRNAs and labeled with [35S]methionine. CM-Xnr2 and DCM-Xnr2 are efficiently secreted while CM-Der is retained within the oocyte lysate (asterisk). Both Xnr2 and CM-Xnr2 undergo proteolytic processing, as indicated by the presence of the proB domain (arrowhead). Mutation of both cryptic and canonical sites in DCM-Xnr2 abolishes all proteolytic processing.
