FIGURE 6.

Follistatin-like domain 7 can be replaced by domains 1 and 6 but not by domain 8. To determine if other follistatin-like domains of TM-agrin also have process-inducing activity when placed at the appropriate position, constructs were generated where the seventh follistatin-like domain was replaced by either the first follistatin-like domain (construct TMFD6+FD1-GFP), by the sixth follistatin-like domain (construct TMFD6+FD6-GFP), or by the eighth follistatin-like domain (construct TMFD6+FD8-GFP). Although the first and sixth follistatin-like domains can functionally substitute for the seventh follistatin-like domain, replacing follistatin-like domain 7 with the eighth follistatin-like domain resulted in a severe reduction of the number of processes extended by the transfected cells. Moreover, a critical distance of the seventh follistatin-like domain to the plasma membrane appears to be necessary for process formation, because deletion of the first and second follistatin-like domain (construct TMFD3–8-GFP) resulted in a loss of the process-formation activity, whereas deletion of only the first follistatin-like domain (construct TMFD2–8-GFP) did not influence process formation.