The cast of the hit FOX television comedy GLEE is...

The cast of the hit FOX television comedy GLEE is pictured here. On the bottom row from the left, are Kevin McHale, Naya Rivera, Mark Salling, Jenna Ushkowitz, Dianna Agron, Lea Michele and Jane Lynch. From the left of the middle row are Jessalyn Gilsig, Jayma Mays, Matthew Morrison and Cory Monteith; and in the top row from the left, Heather Morris, Chris Colfer and Amber Riley. Credit: Patrick Ecclesine/FOX/

"Glee" co-creator Ryan Murphy plans to gradually replace the cast of his hit high-school musical series, with his current McKinley High characters graduating by the end of the show's fourth season in 2013. "There's nothing more depressing than a high schooler with a bald spot," he said.

"Every year we're going to populate a new group," Murphy told the Melbourne, Australia, newspaper the Herald Sun. The process began this season, the show's second, with Chord Overstreet as transfer student Sam Evans.

"I think you have to be true to the fact that here is a group of people who come and go in these teachers' lives - they graduate and they're gone," he said. The current twentysomethings playing the teenage students on the Fox series include Dianna Agron, Chris Colfer, Cory Monteith, Amber Riley, Mark Salling, Jenna Ushkowitz, Naya Rivera, Heather Morris, Kevin McHale and Lea Michele.

Murphy said he's discussed his plan with fellow "Glee" creators and co-executive producers Ian Brennan and Brad Falchuk. "I was concerned about that because those kids caught on so quickly," he said, "but I think one of the things I'm very happy we've been able to do this year is [add] new characters. . . . I didn't know if people would want those characters, but they do."

Long-running shows about high schoolers have often kept large portions of their casts intact, even as some stars age into their 30s, as with "Beverly Hills 90210" (Fox 1990-2000) or "Happy Days" (ABC 1974-1984). Characters do age, but more slowly than in real life. Other shows, such as the current "Friday Night Lights," have brought in new cast members - in this case, by having the lead-character coach transfer to a new school.

"When some of them finish their run at high school it will be very teary episodes," Murphy said of his "Glee" characters. "For me it will be particularly tough, but a new crop will come in."

Fox did not comment when TVGuide.com inquired about Murphy's statements.

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