ABSTRACT
The biogenesis of splicing snRNPs (small nuclear ribonucleoproteins) is a complex process, beginning and ending in the nucleus of the cell but including key stages that take place in the cytoplasm. In particular, the SMN (survival motor neuron) protein complex is required for addition of the core Sm proteins to the snRNP. Insufficiency of SMN results in the inherited neurodegenerative condition, spinal muscular atrophy (SMA). Details of the physical organization of the cytoplasmic stages of snRNP biogenesis are unknown. Here, we use time-resolved quantitative proteomics to identify proteins that associate preferentially with either newly assembled or mature splicing snRNPs. We identified highly mobile SmB protein-trafficking vesicles in neural cells, which are dependent on the cellular levels of SMN and SmB for their morphology and mobility. We propose that these represent a family of related vesicles, some of which play a role in snRNP biogenesis and some that might play more diverse roles in cellular RNA metabolism.
Footnotes
Competing interests
The authors declare no conflict of interests.
Author contributions
ARP acquired and interpreted the correlative light/electron microscopy images and helped to edit the final manuscript. AB assisted with acquiring and analyzing data and with drafting the article. JJ assisted with acquiring and analyzing data. LTM analyzed the AP/MS data, generated the related tables and figures and helped to edit the final manuscript. JES came up with the original concept, designed all experiments, carried out imaging, affinity purification and Western blot experiments and generated the related figures, analyzed data and prepared the manuscript.
Funding
L.T.M. holds a Canadian Institutes of Health Research (CIHR) New Investigator Salary Support Award. This work was supported in part by the Royal Society via a University Research Fellowship to J.E.S.
Supplementary material available online at http://jcs.biologists.org/lookup/suppl/doi:10.1242/jcs.137703/-/DC1
- Received June 30, 2013.
- Accepted November 30, 2013.
- © 2014. Published by The Company of Biologists Ltd
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