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Lysosomal sorting receptors are essential for secretory granule biogenesis in Tetrahymena.

Briguglio JS, Kumar S, Turkewitz AP - J. Cell Biol. (2013)

Bottom Line: We show that assembly of mucocysts depends on proteins classically associated with lysosome biogenesis.In addition, sortilins are required for delivery of a key protease involved in T. thermophila mucocyst maturation.Our results suggest potential similarities in the formation of regulated secretory organelles between even very distantly related eukaryotes.

View Article: PubMed Central - HTML - PubMed

Affiliation: Molecular Genetics and Cell Biology, The University of Chicago, Chicago, IL 60637.

ABSTRACT
Secretory granules, such as neuronal dense core vesicles, are specialized for storing cargo at high concentration and releasing it via regulated exocytosis in response to extracellular stimuli. Here, we used expression profiling to identify new components of the machinery for sorting proteins into mucocysts, secretory granule-like vesicles in the ciliate Tetrahymena thermophila. We show that assembly of mucocysts depends on proteins classically associated with lysosome biogenesis. In particular, the delivery of nonaggregated, but not aggregated, cargo proteins requires classical receptors of the sortilin/VPS10 family, which indicates that dual mechanisms are involved in sorting to this secretory compartment. In addition, sortilins are required for delivery of a key protease involved in T. thermophila mucocyst maturation. Our results suggest potential similarities in the formation of regulated secretory organelles between even very distantly related eukaryotes.

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The T. thermophila sortilins fall into two major groups. A maximum likelihood phylogeny of the ciliate VPS10 domains shown in Fig. 2 B, together with the most highly related homologues (as judged by BLAST scores) present in a variety of organisms from the other major eukaryotic lineages. VPS10 domain–containing genes appear to have been entirely lost in numerous organisms including A.thaliana and D. melanogaster. In some fungi, VPS10 domains are present as tandem repeats, depicted as h1 and h2. Species are abbreviated as follows: Aspergillus nidulans (An), Coccomyxa subellipsoidea (Cs), Daphnia pulex (Dap), Dictyostelium discoideum (Dd), Dictyostelium fasciculatum (Df), Dictyostelium purpureum (Dp), Homo sapiens (Hs), Ichthyophthirius multifiliis (Im), M. pusilla (Mp), Micromonas sp. RCC299 (Mr), Mus musculus (Mm), Naegleria gruberi (Ng), Naumovozyma castellii (Nac), Ostreococcus lucimarinus (Ol), Ostreococcus tauri (Ot), Paracoccidioides brasiliensis (Pab), P. tetraurelia (Pt), Polysphondylium pallidum (Pp), Punctularia strigosozonata (Ps), S. cerevisiae (Sc), T. thermophila (Tt), Trichoplax adhaerens (Tra), Xenopus (Silurana) tropicalis (Xt), Yarrowia lipolytica (Yl). See also Table S1 for a list of accession numbers for the sequences used to assemble this phylogeny.
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fig1: The T. thermophila sortilins fall into two major groups. A maximum likelihood phylogeny of the ciliate VPS10 domains shown in Fig. 2 B, together with the most highly related homologues (as judged by BLAST scores) present in a variety of organisms from the other major eukaryotic lineages. VPS10 domain–containing genes appear to have been entirely lost in numerous organisms including A.thaliana and D. melanogaster. In some fungi, VPS10 domains are present as tandem repeats, depicted as h1 and h2. Species are abbreviated as follows: Aspergillus nidulans (An), Coccomyxa subellipsoidea (Cs), Daphnia pulex (Dap), Dictyostelium discoideum (Dd), Dictyostelium fasciculatum (Df), Dictyostelium purpureum (Dp), Homo sapiens (Hs), Ichthyophthirius multifiliis (Im), M. pusilla (Mp), Micromonas sp. RCC299 (Mr), Mus musculus (Mm), Naegleria gruberi (Ng), Naumovozyma castellii (Nac), Ostreococcus lucimarinus (Ol), Ostreococcus tauri (Ot), Paracoccidioides brasiliensis (Pab), P. tetraurelia (Pt), Polysphondylium pallidum (Pp), Punctularia strigosozonata (Ps), S. cerevisiae (Sc), T. thermophila (Tt), Trichoplax adhaerens (Tra), Xenopus (Silurana) tropicalis (Xt), Yarrowia lipolytica (Yl). See also Table S1 for a list of accession numbers for the sequences used to assemble this phylogeny.

Mentions: Sortilins are Type I transmembrane proteins first characterized in Saccharomyces cerevisiae as the product of the VPS10 gene, which functions as a sorting receptor for vacuolar hydrolases (Marcusson et al., 1994). Although the sortilin gene family has undergone broad expansions throughout the major eukaryotic supergroups, the family has been lost in several lineages that include Arabidopsis thaliana, D. melanogaster, and C. elegans. (Fig. 1 and Fig. S1). Sortilins in vertebrates are receptors for sorting to lysosome-related organelles, in addition to other functions (Hermey, 2009). In T. thermophila, all four of the sortilin genes have similar expression profiles, which are also strikingly similar to those of known mucocyst-associated genes (Fig. 2 A and Fig. S2 A). The four T. thermophila sortilins, called SOR1–SOR4, have diverged significantly from one another as judged by amino acid sequence (∼30% identity within the VPS10 domains; ∼12% identity within the cytosolic tails). The four genes fall into two clades. SOR1 and -3 belong to a clade including members from non-ciliates, whereas SOR2 and -4 belong to a ciliate-restricted clade, and therefore are likely to have arisen via gene duplications that occurred within the ciliate lineage (Fig. 1 and Fig. 2 B).


Lysosomal sorting receptors are essential for secretory granule biogenesis in Tetrahymena.

Briguglio JS, Kumar S, Turkewitz AP - J. Cell Biol. (2013)

The T. thermophila sortilins fall into two major groups. A maximum likelihood phylogeny of the ciliate VPS10 domains shown in Fig. 2 B, together with the most highly related homologues (as judged by BLAST scores) present in a variety of organisms from the other major eukaryotic lineages. VPS10 domain–containing genes appear to have been entirely lost in numerous organisms including A.thaliana and D. melanogaster. In some fungi, VPS10 domains are present as tandem repeats, depicted as h1 and h2. Species are abbreviated as follows: Aspergillus nidulans (An), Coccomyxa subellipsoidea (Cs), Daphnia pulex (Dap), Dictyostelium discoideum (Dd), Dictyostelium fasciculatum (Df), Dictyostelium purpureum (Dp), Homo sapiens (Hs), Ichthyophthirius multifiliis (Im), M. pusilla (Mp), Micromonas sp. RCC299 (Mr), Mus musculus (Mm), Naegleria gruberi (Ng), Naumovozyma castellii (Nac), Ostreococcus lucimarinus (Ol), Ostreococcus tauri (Ot), Paracoccidioides brasiliensis (Pab), P. tetraurelia (Pt), Polysphondylium pallidum (Pp), Punctularia strigosozonata (Ps), S. cerevisiae (Sc), T. thermophila (Tt), Trichoplax adhaerens (Tra), Xenopus (Silurana) tropicalis (Xt), Yarrowia lipolytica (Yl). See also Table S1 for a list of accession numbers for the sequences used to assemble this phylogeny.
© Copyright Policy - openaccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC3824020&req=5

fig1: The T. thermophila sortilins fall into two major groups. A maximum likelihood phylogeny of the ciliate VPS10 domains shown in Fig. 2 B, together with the most highly related homologues (as judged by BLAST scores) present in a variety of organisms from the other major eukaryotic lineages. VPS10 domain–containing genes appear to have been entirely lost in numerous organisms including A.thaliana and D. melanogaster. In some fungi, VPS10 domains are present as tandem repeats, depicted as h1 and h2. Species are abbreviated as follows: Aspergillus nidulans (An), Coccomyxa subellipsoidea (Cs), Daphnia pulex (Dap), Dictyostelium discoideum (Dd), Dictyostelium fasciculatum (Df), Dictyostelium purpureum (Dp), Homo sapiens (Hs), Ichthyophthirius multifiliis (Im), M. pusilla (Mp), Micromonas sp. RCC299 (Mr), Mus musculus (Mm), Naegleria gruberi (Ng), Naumovozyma castellii (Nac), Ostreococcus lucimarinus (Ol), Ostreococcus tauri (Ot), Paracoccidioides brasiliensis (Pab), P. tetraurelia (Pt), Polysphondylium pallidum (Pp), Punctularia strigosozonata (Ps), S. cerevisiae (Sc), T. thermophila (Tt), Trichoplax adhaerens (Tra), Xenopus (Silurana) tropicalis (Xt), Yarrowia lipolytica (Yl). See also Table S1 for a list of accession numbers for the sequences used to assemble this phylogeny.
Mentions: Sortilins are Type I transmembrane proteins first characterized in Saccharomyces cerevisiae as the product of the VPS10 gene, which functions as a sorting receptor for vacuolar hydrolases (Marcusson et al., 1994). Although the sortilin gene family has undergone broad expansions throughout the major eukaryotic supergroups, the family has been lost in several lineages that include Arabidopsis thaliana, D. melanogaster, and C. elegans. (Fig. 1 and Fig. S1). Sortilins in vertebrates are receptors for sorting to lysosome-related organelles, in addition to other functions (Hermey, 2009). In T. thermophila, all four of the sortilin genes have similar expression profiles, which are also strikingly similar to those of known mucocyst-associated genes (Fig. 2 A and Fig. S2 A). The four T. thermophila sortilins, called SOR1–SOR4, have diverged significantly from one another as judged by amino acid sequence (∼30% identity within the VPS10 domains; ∼12% identity within the cytosolic tails). The four genes fall into two clades. SOR1 and -3 belong to a clade including members from non-ciliates, whereas SOR2 and -4 belong to a ciliate-restricted clade, and therefore are likely to have arisen via gene duplications that occurred within the ciliate lineage (Fig. 1 and Fig. 2 B).

Bottom Line: We show that assembly of mucocysts depends on proteins classically associated with lysosome biogenesis.In addition, sortilins are required for delivery of a key protease involved in T. thermophila mucocyst maturation.Our results suggest potential similarities in the formation of regulated secretory organelles between even very distantly related eukaryotes.

View Article: PubMed Central - HTML - PubMed

Affiliation: Molecular Genetics and Cell Biology, The University of Chicago, Chicago, IL 60637.

ABSTRACT
Secretory granules, such as neuronal dense core vesicles, are specialized for storing cargo at high concentration and releasing it via regulated exocytosis in response to extracellular stimuli. Here, we used expression profiling to identify new components of the machinery for sorting proteins into mucocysts, secretory granule-like vesicles in the ciliate Tetrahymena thermophila. We show that assembly of mucocysts depends on proteins classically associated with lysosome biogenesis. In particular, the delivery of nonaggregated, but not aggregated, cargo proteins requires classical receptors of the sortilin/VPS10 family, which indicates that dual mechanisms are involved in sorting to this secretory compartment. In addition, sortilins are required for delivery of a key protease involved in T. thermophila mucocyst maturation. Our results suggest potential similarities in the formation of regulated secretory organelles between even very distantly related eukaryotes.

Show MeSH
Related in: MedlinePlus