Fig. 9. Biosynthesis and processing of muscle RGMc. (A) Diagram of RGMc proteins found on the cell membrane of differentiating skeletal muscle cells and released into the culture medium. Green box, RGD motif; yellow box, partial von Willebrandt factor type D domain; gray stars, asparagine-linked sugars; jagged line, GPI-anchor; S-S, disulfide bonds. (B) Model for biosynthesis and processing of RGMc. The arrows designate different processing paths: (1) intracellular proteolytic processing of RGMc (indicated by red scissors) targeted to the cell membrane by a GPI moiety; (2) full-length, glycosylated RGMc is targeted to the cell membrane by a GPI sequence; release of full-length, glycosylated RGMc from the membrane by a phospholipase (3) or protease (4) (black scissors).