Eukaryotic cells contain a range of secretory organelles, including secretory granules, that store condensed cargo at high concentrations and mediate their release through exocytosis in response to extracellular stimuli. Although in mammalian cells the sorting of aggregated cargo can occur through a unique pathway, there has been interest in whether this is always the case for all cargo and in other systems. Here, the authors use expression profiling in the ciliate Tetrahymena thermophila to show that sorting of non-aggregated cargo in a specific type of secretory organelle, mucocysts, relies on receptors of the sortilin (also known as VPS10) family that are better known for their role in lysosome biogenesis. They propose that different types of cargo may be delivered to secretory granules through distinct means.
References
Briguglio, J. S., Kumar, S. & Turkewitz, A. P. Lysosomal sorting receptors are essential for secretory granule biogenesis in Tetrahymena. J. Cell Biol. http://dx.doi.org/10.1083/jcb.201305086 (2013)
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Schuldt, A. A sortilin for secretory granules. Nat Rev Mol Cell Biol 14, 751 (2013). https://doi.org/10.1038/nrm3711
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DOI: https://doi.org/10.1038/nrm3711