DETERMINING WHETHER UBE4B ACTIVITY EFFECTS SKELETAL MUSCLE PERFORMANCE Jeremy Boutin, Sarah Spinette, Department of Biology, Rhode Island College, Providence, RI RI-INBRE Summer Undergraduate Research Fellowship Program Skeletal muscle tissue develops through a complex process called myogenesis that is controlled in part by the regulated degradation of specific proteins. These substrates are degraded by the proteasome after being marked by the cell's ubiquitin conjugation system that is composed of three levels of enzymes (E1, E2 and E3). Ube4b is an E3 ligase enzyme that mediates ubiquitin conjugation through its U-box domain. To determine whether or not the function of Ube4b plays a crucial role in skeletal muscle development and function, we developed transgenic mice whose Ube4b U-box domain was removed in skeletal muscle when iCre-recombinase expression is controlled by the MyoD promoter. Removal of the U-box domain, leads to expression of an inactive E3 ligase. Mice lacking active Ube4b in their skeletal muscle exhibit reduced postnatal growth, skeletal muscle size and loss of sarcomere structure within many skeletal muscle fibers. These observations have led us to hypothesize that the Ube4b mutant mice should have diminished performance when tested with strength assays. In order to test this hypothesis, mutant and control littermates were subjected to two strength assays: the hanging wire and grip strength tests. The two strength assays showed that mice lacking Ube4b performed worse at two and four weeks old, but better at three weeks old. The data collected so far has not underlined an overall trend. Thus far only small groups (n=3-5) of mutant and control mice have been tested and none of the results were significant. Given the high variability in these assays they will be continued in order to increase the sample size and allow statistical analysis.
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