Differential subcellular localization of the survival motor neuron protein in spinal cord and skeletal muscle

To compare the expression pattern of the survival motor neuron (SMN) protein in spinal cord and skeletal muscle, we generated a sheep polyclonal antibody against a bacterially expressed human SMN-fusion protein. On Western blots, the affinity purified anti-SMN antibody recognized a approximately 38 kDa protein band in extracts prepared from the mouse skeletal muscle, spinal cord, and brain that co-migrated with the bacterially expressed SMN protein. In immunohistochemical studies, the anti-SMN antibody labeled mostly the cytoplasm of the motor neurons in the anterior horn of mouse spinal cord. In contrast, predominant uniform labeling of the nuclei was observed in the mouse skeletal muscle. Thus, our results for the first time demonstrate that the SMN protein is differentially localized in mouse spinal cord and skeletal muscle.