Zooey Deschanel and Joseph Gordon-Levitt are in negotiations to play the leads in Fox Searchlight’s romantic comedy 500 Days of Summer, sources say. Gordon-Levitt, who will next be seen in Paramount’s Iraq-war drama Stop-Loss (out March 28) will play a guy who falls in love with a girl (Deschanel, soon to appear in M. Night Shyamalan’s The Happening) who doesn’t believe in love. Acclaimed music video director Marc Webb will make his feature directorial debut from a script by Michael H. Weber and Scott Neustadter (The Pink Panther 2). The movie is expected to begin filming this spring. Fox Searchlight declined comment.