The survival of motor neurons protein determines the capacity for snRNP assembly: biochemical deficiency in spinal muscular atrophy.
Reduction of the survival of motor neurons (SMN) protein levels causes the motor neuron degenerative disease spinal muscular atrophy, the severity of which correlates with the extent of reduction in SMN. SMN, together with Gemins 2 to 7, forms a complex that functions in the assembly of small nuclear ribonucleoprotein particles (snRNPs). Complete depletion of the SMN complex from cell extracts abolishes snRNP assembly, the formation of heptameric Sm cores on snRNAs. However, what effect, if any, reduction of SMN protein levels, as occurs in spinal muscular atrophy patients, has on the capacity of cells to produce snRNPs is not known. To address this, we developed a sensitive and quantitative assay for snRNP assembly, the formation of high-salt- and heparin-resistant stable Sm cores, that is strictly dependent on the SMN complex. We show that the extent of Sm core assembly is directly proportional to the amount of SMN protein in cell extracts. Consistent with this, pulse-labeling experiments demonstrate a significant reduction in the rate of snRNP biogenesis in low-SMN cells. Furthermore, extracts of cells from spinal muscular atrophy patients have a lower capacity for snRNP assembly that corresponds directly to the reduced amount of SMN. Thus, SMN determines the capacity for snRNP biogenesis, and our findings provide evidence for a measurable deficiency in a biochemical activity in cells from patients with spinal muscular atrophy.
Wan
Lili
L
Howard Hughes Medical Institute, Department of Biochemistry & Biophysics, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-6148, USA.
Battle
Daniel J
DJ
Yong
Jeongsik
J
Gubitz
Amelie K
AK
Kolb
Stephen J
SJ
Wang
Jin
J
Dreyfuss
Gideon
G
D000818:Animals; D019921:Biotinylation; D002457:Cell Extracts / Q000032:analysis; D002460:Cell Line; D002461:Cell Line, Transformed; D002472:Cell Transformation, Viral; D002645:Chickens; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism*; D003593:Cytoplasm / Q000737:chemistry; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism; D006367:HeLa Cells; D004854:Herpesvirus 4, Human; D006801:Humans; D007700:Kinetics; D008954:Models, Biological; D009046:Motor Neurons / Q000378:metabolism; D009134:Muscular Atrophy, Spinal / Q000235:genetics* / Q000473:pathology; D009419:Nerve Tissue Proteins / Q000172:deficiency* / Q000378:metabolism*; D010761:Phosphorus Radioisotopes; D011485:Protein Binding; D012342:RNA, Small Nuclear / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000378:metabolism*; D017411:Ribonucleoproteins, Small Nuclear / Q000032:analysis / Q000378:metabolism*; D055532:SMN Complex Proteins; D012680:Sensitivity and Specificity; D014158:Transcription, Genetic
D002457:Cell Extracts; D017362:Cyclic AMP Response Element-Binding Protein; D009419:Nerve Tissue Proteins; D010761:Phosphorus Radioisotopes; D012342:RNA, Small Nuclear; D016601:RNA-Binding Proteins; D017411:Ribonucleoproteins, Small Nuclear; D055532:SMN Complex Proteins