While this initial observation might not have been entirely surprising, since previous reports showed that MuRF1 expression is only up-regulated during the relatively acute stages of atrophy (i.e., <14 days), a subsequent experiment in WT mice demonstrated a lack of acute upregulation of MuRF1 in space as well (Supplemental Fig. 5); this lack of upregulation of MuRF1 on its own distinguishes spaceflight induced muscle atrophy from all Earth-based models studied, including hind-limb suspension. This evidence concerns the gene TRIM63 and muscle atrophy.