Helton announced that he had hired his younger brother, Tyson, as running backs coach and passing-game coordinator. Helton also hired Neil Callaway, who was offensive line coach under the Heltons' father, Kim, at Houston during a 37-year coaching career.
Tyson Helton was Western Kentucky's offensive coordinator and quarterbacks coach, although Coach Jeff Brohm called the plays. Callaway was offensive line coach.
Western Kentucky averaged 44.3 points per game this season, which ranks third nationally. The Hilltoppers rank first in passing efficiency, fourth in passing and ninth in total yards.
"We are very excited to welcome Tyson and Neil to the Trojan Family," Clay Helton said in a statement. "Their experience and knowledge will be a huge benefit to our players as well as our football program.
"Both have been highly successful coordinators and we look forward to the fresh energy and ideas they will bring."
The announcements marked Helton's first major staff moves since he promoted Tee Martin from receivers coach to offensive coordinator before the Holiday Bowl. The Trojans lost to Wisconsin, 23-21, in Clay Helton's final game as the Trojans' play-caller.
Helton has said that Martin will call plays next season.
Helton fired defensive coordinator Justin Wilcox, defensive line coach Chris Wilson, defensive backs coach Keith Heyward and offensive line coach Bob Connelly after the Trojans' loss to Stanford in the Pac-12 Conference title game.
Several graduate assistants, an administrative assistant and an assistant strength coach helped fill roles for the Holiday Bowl.
Helton said that most, if not all, full-time assistants would be in place by mid-January for the final recruiting push toward national signing day in February.
Johnny Nansen had been USC's running backs coach the last two seasons. He also has coached special teams, cornerbacks, linebackers and defensive linemen during his career, so he could be moved to another position on the staff.
Quarterbacks coach Marques Tuiasosopo and linebackers coach Peter Sirmon, who also is the recruiting coordinator, also are holdovers from a staff originally hired by former coach Steve Sarkisian.
Tyson Helton played quarterback at Houston, where his father was the coach. He also has worked at Hawaii, Memphis, Alabama Birmingham and Cincinnati during his 16-year coaching career.
Callaway, who played at Alabama, was head coach at Alabama Birmingham from 2007 to 2011. He was previously offensive coordinator at Georgia, offensive line coach and offensive coordinator at Alabama, offensive coordinator at Houston and offensive line coach at Auburn.