A novel nuclear structure containing the survival of motor neurons protein

Abstract

Spinal muscular atrophy (SMA) is a common, often fatal, autosomal recessive disease leading to progressive muscle wasting and paralysis as a result of degeneration of anterior horn cells of the spinal cord. A gene termed survival of motor neurons (SMN), at 5q13, has been identified as the determining gene of SMA. The SMN gene is deleted in >98% of SMA patients, but the function of the SMN protein is unknown, In searching for hnRNP-interacting proteins we found that SMN interacts with the RGG box region of hnRNP U, with itself, with fibrillarin and with several novel proteins. We have produced monoclonal antibodies to the SMN protein, and we report here on its striking cellular localization pattern. Immunelocalization studies using SMN monoclonal antibodies show several intense dots in HeLa cell nuclei. These structures are similar in number (2-6) and size (0.1-1.0 μm) to coiled bodies, and frequently are found near or associated with coiled bodies. We term these prominent nuclear structures gems, for Gemini of coiled bodies.