University of Puerto Rico, Humacao Campus
“Analysis of the Function of the MUSA1 Ubiquitin E3 Ligase during Muscle Development in Xenopus laevis””
MUSA1, also known as FBX030, is an F-Box containing protein that is conserved throughout vertebrates. F-Box proteins bind specific phosphorylated proteins and induce their ubiquitination by the SCF ubiquitin ligase. Protein ubiquitination leads to their degradation. Recently, MUSA1 was shown to function as a negative regulator in the maintenance of muscle mass in adult mice. Protein ubiquitination mediated by MUSA1 is thought to promote muscle atrophy. MUSA1 might exert its role as an effector of growth and differentiation factors (GDFs) such as myostatin. In contrast, BMP13 and BMP14 signaling counteracts MUSA1 action, protecting against atrophy. To understand MUSA1’s role during development, we pursued
the characterization of MUSA1 using the Xenopus laevis amphibian model system. We have discovered two MUSA1 homolog genes in X. laevis, MUSA1-A and MUSA1-B. The MUSA1-A and MUSA1-B proteins are 91% identical to each other, and share 64% and 63% identity with their Homo sapiens protein homolog, respectively. We have found through RT-PCR and in situ hybridization that MUSA1-A and MUSA1-B are maternally expresed, with their mRNAs present in the animal pole of unfertilized eggs. The mRNAs persist during cleavage, decrease once gastrulation starts, and reappear during organogenesis in the developing somites. The somites are the precursors of muscle, suggesting that MUSA1 not only regulates muscle mass in the adult, but could also regulate the production of muscle fibers during development. Using monoclonal antibodies, we localized the MUSA1-A protein in the nuclei of cells at the gastrula stage. To continue our studies we propose: 1. To study the abundance, distribution, and subcellular localization of MUSA1-A and MUSA1-B during somitogenesis and muscle development. 2. To determine the effects of MUSA1-A and MUSA1-B depletion and overexpression in muscle development.