Five things we learned in Week 1, No. 4

USC’s out on spring break this week and not practicing, but each weekday through Friday, we’ll bring you one thing we learned from the first three days of practice last week and what it might mean for the future.

Our first item covered Marqise Lee‘s continued progress, our second the new-look Aundrey Walker and third the situation at backup QB.

Fourth is this: All options will be explored in the interior of the defensive line.

It doesn't necessarily reflect the talent levels of the players who created them, but USC's biggest hole this offseason -- by far -- is at nose tackle.

Nick Perry had a natural replacement, as did DaJohn Harris in George Uko. Matt Kalil had a qualified candidate to replace him at left tackle, too, in Kevin Graf.

But Christian Tupou's spot? The natural person to step in would be J.R. Tavai, but it's clear he's not being looked at as an every-down option. Then there's Antwaun Woods, whose playing time seems to largely depend on his physical condition.

So what next? Ed Orgeron and the Trojans are looking every which way for potential options to fill the hole created by Tupou's departure. Defensive end Wes Horton worked out at tackle last season, but Orgeron said last week that was a failed experiment and will no longer be tried.

Now, defensive end Greg Townsend Jr. is getting time at the three-technique, which could presumably push Uko to nose if it works out. Redshirt freshman Christian Heyward is sitting out the spring after undergoing shoulder surgery, but he'll get a long look come fall camp to determine if he can contribute 20 or snaps a game.

One thing is clear: The nose tackle spot is going to be USC's biggest 2012 weakness, unless someone unexpectedly emerges. Tupou wasn't a high-profile contributor, but he rarely made mistakes and he was consistently on the field when healthy.

The Trojans could use a similar player this season, since Uko, Horton and Devon Kennard -- the other starting defensive linemen -- have the ability to produce enough quarterback pressure on their own.

Check back later Friday for the fifth and final thing we learned from the spring.