Jim Carrey has been cast as Horton and Steve Carell has been cast as the mayor of Who-ville in Dr. Seuss' HORTON HEARS A WHO, a CGI-animated feature film from 20th Century Fox Animation, says The Hollywood Reporter.

HORTON HEARS A WHO marks the first time Carrey will voice a CGI-animated character. He previously inhabited Seuss' world as the title character in Universal Pictures' "Dr. Seuss' How the Grinch Stole Christmas."

HORTON HEARS A WHO centers on an imaginative elephant who hears a cry for help coming from a tiny speck of dust floating through the air. Suspecting that there might be life on that speck and despite a surrounding community that thinks he has lost his mind, Horton is determined to help.