CEDAR FALLS, Iowa - University of Northern Iowa assistant wrestling coach Derek Mountsier has resigned from the position, affective immediately, UNI head coach Brad Penrith announced recently.    Mountsier was in his fourth season with the Panthers and was the first assistant hired by Penrith when the latter was named UNI's head coach.  Mountsier is moving to Tulsa, Okla., to be near his fiancee and is entering private business.  The couple plans to wed next summer.    "Derek has been a huge part of our program," Penrith said.  "He will be truly missed and we are not only losing a great coach, but I am losing a great friend.  He needs to do what is best for his family and we wish him the best."    Mountsier, a native of Newton, Iowa, was an all-American wrestler at Iowa State in 1994 and '96.  In 1996, he was the Big Eight champion at 142 pounds, placed fourth at the NCAA Championships and captained the Cyclones to a NCAA runner-up team finish.  He also placed eighth at 134 pounds in 1994.  He qualified for the nationals each of his four years, placed at the Midlands Tournament each year and finished his career ranked second on the school's all-time win list with 128.  He's a three-time National Open Greco-Roman all-American (1997-99) and a three-time Greco-Roman World Team Trials place winner.  He also is a University National Greco-Roman champion.    Prior to being named Penrith's top assistant, he was the head assistant at Pennsylvania from 1999-00 and prior to that, spent a year as an assistant at Nebraska.  He also served two years with the Cyclone Wrestling Club prior to his stint at Nebraska.  Pennsylvania placed ninth at the 2000 NCAA Championships.  He also was instrumental in securing the Quakers' 2000 recruiting class, which was ranked seventh nationally by InterMat.    Current fourth-year assistant Randy Pugh is replacing Mountsier as head assistant.  Pugh is a UNI alum and finished fourth at the 2000 NCAA Tournament at 174 pounds, capping a senior season in which he compiled a 26-4 record.  He was ranked as high as third nationally after upending top-rated Otto Olson at the Virginia Duals.  He transferred to UNI in 1998 from the Naval Academy and went 16-8 his first year in a Panther singlet and finished his UNI career with 54-9, 70-17 overall.    While sitting beside Penrith and Mountsier, he also has been training for international competition as an 85 kg. freestyle wrestler.      UNI's other two assistants include Jose DeAnda and Tolly Thompson, who serves as head club coach and strength and conditioning coach.  DeAnda is in his fourth season and Thompson is in his third year.