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Mitochondrial function is required for secretion of DAF-28/insulin in C. elegans.

Billing O, Kao G, Naredi P - PLoS ONE (2011)

Bottom Line: We find that animals with reduced levels of the mitochondrial outer membrane translocase homologue TOMM-40 arrest growth as larvae and have decreased insulin signaling strength.We conclude that mitochondrial function is required for C. elegans to secrete DAF-28/insulin when food is abundant.This modulation of secretion likely represents an additional level of control over DAF-28/insulin function.

View Article: PubMed Central - PubMed

Affiliation: Department of Surgery and Perioperative Sciences, Umeå University, Umeå, Sweden.

ABSTRACT
While insulin signaling has been extensively studied in Caenorhabditis elegans in the context of ageing and stress response, less is known about the factors underlying the secretion of insulin ligands upstream of the insulin receptor. Activation of the receptor governs the decision whether to progress through the reproductive lifecycle or to arrest growth and enter hibernation. We find that animals with reduced levels of the mitochondrial outer membrane translocase homologue TOMM-40 arrest growth as larvae and have decreased insulin signaling strength. TOMM-40 acts as a mitochondrial translocase in C. elegans and in its absence animals fail to import a mitochondrial protein reporter across the mitochondrial membrane(s). Inactivation of TOMM-40 evokes the mitochondrial unfolded protein response and causes a collapse of the proton gradient across the inner mitochondrial membrane. Consequently these broadly dysfunctional mitochondria render an inability to couple food abundance to secretion of DAF-28/insulin. The secretion defect is not general in nature since two other neuropeptides, ANF::GFP and INS-22::VENUS, are secreted normally. RNAi against two other putative members of the TOMM complex give similar phenotypes, implying that DAF-28 secretion is sensitive to mitochondrial dysfunction in general. We conclude that mitochondrial function is required for C. elegans to secrete DAF-28/insulin when food is abundant. This modulation of secretion likely represents an additional level of control over DAF-28/insulin function.

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TOMM-40 is the C. elegans homologue of TOM40.(A) Amino acid sequence comparison of TOMM-40 homologues from C. elegans, H. sapiens, D. melanogaster and S. cerevisiae. Dark gray corresponds to 100% interspecies conservation, medium gray to 75% and light gray to 50%. (B) Phylogenetic tree analysis of TOMM-40 homologues. The scale indicates sequence difference, where 0.5 is 50% difference in residues. The tree was constructed using the neighbor-joining algorithm. (C) (From top to bottom) Scale bar, followed by the intron/exon structure of tomm-40. Boxes represent exons. The first methionine is indicated by an arrow. (Below) The tm4574 mutation deletes exon two, three and four and part of exon five and instead inserts 28 base pairs in the open reading frame of tomm-40 are indicated with a black bar. (Below) The Ptomm-40::gfp (pVB488OB) and the Ptomm-40::tomm-40::gfp (pVB518OB) constructs used in this study are shown.
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pone-0014507-g001: TOMM-40 is the C. elegans homologue of TOM40.(A) Amino acid sequence comparison of TOMM-40 homologues from C. elegans, H. sapiens, D. melanogaster and S. cerevisiae. Dark gray corresponds to 100% interspecies conservation, medium gray to 75% and light gray to 50%. (B) Phylogenetic tree analysis of TOMM-40 homologues. The scale indicates sequence difference, where 0.5 is 50% difference in residues. The tree was constructed using the neighbor-joining algorithm. (C) (From top to bottom) Scale bar, followed by the intron/exon structure of tomm-40. Boxes represent exons. The first methionine is indicated by an arrow. (Below) The tm4574 mutation deletes exon two, three and four and part of exon five and instead inserts 28 base pairs in the open reading frame of tomm-40 are indicated with a black bar. (Below) The Ptomm-40::gfp (pVB488OB) and the Ptomm-40::tomm-40::gfp (pVB518OB) constructs used in this study are shown.

Mentions: Based on sequence similarity to TOM40 homologues in Homo sapiens, Drosophila melanogaster and Saccharomyces cerevisiae, C. elegans TOMM-40 is predicted to be a mitochondrial translocase subunit [Figure 1A, B and [19]]. It shares 49% and 42% protein sequence identity with D. melanogaster and H. sapiens TOM40 respectively. The C. elegans tomm-40 gene (cosmid name: C18E9.6) contains seven exons, encoding a 301 amino acid protein. The cDNA was completely sequenced and shown to possess the predicted splicing pattern.


Mitochondrial function is required for secretion of DAF-28/insulin in C. elegans.

Billing O, Kao G, Naredi P - PLoS ONE (2011)

TOMM-40 is the C. elegans homologue of TOM40.(A) Amino acid sequence comparison of TOMM-40 homologues from C. elegans, H. sapiens, D. melanogaster and S. cerevisiae. Dark gray corresponds to 100% interspecies conservation, medium gray to 75% and light gray to 50%. (B) Phylogenetic tree analysis of TOMM-40 homologues. The scale indicates sequence difference, where 0.5 is 50% difference in residues. The tree was constructed using the neighbor-joining algorithm. (C) (From top to bottom) Scale bar, followed by the intron/exon structure of tomm-40. Boxes represent exons. The first methionine is indicated by an arrow. (Below) The tm4574 mutation deletes exon two, three and four and part of exon five and instead inserts 28 base pairs in the open reading frame of tomm-40 are indicated with a black bar. (Below) The Ptomm-40::gfp (pVB488OB) and the Ptomm-40::tomm-40::gfp (pVB518OB) constructs used in this study are shown.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3022011&req=5

pone-0014507-g001: TOMM-40 is the C. elegans homologue of TOM40.(A) Amino acid sequence comparison of TOMM-40 homologues from C. elegans, H. sapiens, D. melanogaster and S. cerevisiae. Dark gray corresponds to 100% interspecies conservation, medium gray to 75% and light gray to 50%. (B) Phylogenetic tree analysis of TOMM-40 homologues. The scale indicates sequence difference, where 0.5 is 50% difference in residues. The tree was constructed using the neighbor-joining algorithm. (C) (From top to bottom) Scale bar, followed by the intron/exon structure of tomm-40. Boxes represent exons. The first methionine is indicated by an arrow. (Below) The tm4574 mutation deletes exon two, three and four and part of exon five and instead inserts 28 base pairs in the open reading frame of tomm-40 are indicated with a black bar. (Below) The Ptomm-40::gfp (pVB488OB) and the Ptomm-40::tomm-40::gfp (pVB518OB) constructs used in this study are shown.
Mentions: Based on sequence similarity to TOM40 homologues in Homo sapiens, Drosophila melanogaster and Saccharomyces cerevisiae, C. elegans TOMM-40 is predicted to be a mitochondrial translocase subunit [Figure 1A, B and [19]]. It shares 49% and 42% protein sequence identity with D. melanogaster and H. sapiens TOM40 respectively. The C. elegans tomm-40 gene (cosmid name: C18E9.6) contains seven exons, encoding a 301 amino acid protein. The cDNA was completely sequenced and shown to possess the predicted splicing pattern.

Bottom Line: We find that animals with reduced levels of the mitochondrial outer membrane translocase homologue TOMM-40 arrest growth as larvae and have decreased insulin signaling strength.We conclude that mitochondrial function is required for C. elegans to secrete DAF-28/insulin when food is abundant.This modulation of secretion likely represents an additional level of control over DAF-28/insulin function.

View Article: PubMed Central - PubMed

Affiliation: Department of Surgery and Perioperative Sciences, Umeå University, Umeå, Sweden.

ABSTRACT
While insulin signaling has been extensively studied in Caenorhabditis elegans in the context of ageing and stress response, less is known about the factors underlying the secretion of insulin ligands upstream of the insulin receptor. Activation of the receptor governs the decision whether to progress through the reproductive lifecycle or to arrest growth and enter hibernation. We find that animals with reduced levels of the mitochondrial outer membrane translocase homologue TOMM-40 arrest growth as larvae and have decreased insulin signaling strength. TOMM-40 acts as a mitochondrial translocase in C. elegans and in its absence animals fail to import a mitochondrial protein reporter across the mitochondrial membrane(s). Inactivation of TOMM-40 evokes the mitochondrial unfolded protein response and causes a collapse of the proton gradient across the inner mitochondrial membrane. Consequently these broadly dysfunctional mitochondria render an inability to couple food abundance to secretion of DAF-28/insulin. The secretion defect is not general in nature since two other neuropeptides, ANF::GFP and INS-22::VENUS, are secreted normally. RNAi against two other putative members of the TOMM complex give similar phenotypes, implying that DAF-28 secretion is sensitive to mitochondrial dysfunction in general. We conclude that mitochondrial function is required for C. elegans to secrete DAF-28/insulin when food is abundant. This modulation of secretion likely represents an additional level of control over DAF-28/insulin function.

Show MeSH
Related in: MedlinePlus