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The Drosophila mitochondrial translation elongation factor G1 contains a nuclear localization signal and inhibits growth and DPP signaling.

Trivigno C, Haerry TE - PLoS ONE (2011)

Bottom Line: Expression of missense mutant forms of EF-G1 can accumulate in the nucleus and cause growth and patterning defects and animal lethality.We find that transgenes that encode mutant human EF-G1 proteins can rescue ico mutants, indicating that the underlying problem of the human disease is not just the loss of enzymatic activity.Our results are consistent with a model where EF-G1 acts as a retrograde signal from mitochondria to the nucleus to slow down cell proliferation if mitochondrial energy output is low.

View Article: PubMed Central - PubMed

Affiliation: Center for Molecular Biology and Biotechnology, Florida Atlantic University, Boca Raton, Florida, United States of America.

ABSTRACT
Mutations in the human mitochondrial elongation factor G1 (EF-G1) are recessive lethal and cause death shortly after birth. We have isolated mutations in iconoclast (ico), which encodes the highly conserved Drosophila orthologue of EF-G1. We find that EF-G1 is essential during fly development, but its function is not required in every tissue. In contrast to mutations, missense mutations exhibit stronger, possibly neomorphic phenotypes that lead to premature death during embryogenesis. Our experiments show that EF-G1 contains a secondary C-terminal nuclear localization signal. Expression of missense mutant forms of EF-G1 can accumulate in the nucleus and cause growth and patterning defects and animal lethality. We find that transgenes that encode mutant human EF-G1 proteins can rescue ico mutants, indicating that the underlying problem of the human disease is not just the loss of enzymatic activity. Our results are consistent with a model where EF-G1 acts as a retrograde signal from mitochondria to the nucleus to slow down cell proliferation if mitochondrial energy output is low.

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Expression of mutant EF-G1 forms reduces growth and affects patterning in wings.(A) Heterozygous A9-GAL4/+ female wing with wild type patterning. Longitudinal veins L1-L5 and the anterior and posterior crossveins are indicated (AC, PC). (B) Wings that express four CG4567-G538E transgenes encoding the EF-G1 protein of II032 mutants with ptc-GAL4 show normal proportions but exhibit reduced growth between L3 and L4 where the mutant protein is expressed. They also lack the anterior crossvein (arrow). (C) Overexpression of two wild type ico transgenes in wings using A9-GAL4 does not affect patterning but results in smaller wings. (D) In comparison, ubiquitous expression of two CG4567-G538E transgenes reduces growth and interferes with proper vein formation. (E) Expression of three EF-G1 transgenes that lack the C-terminal tail has no apparent effects on growth or patterning. (F) Compared to two full-length mutant transgenes (D), expression of three tailless mutant CG4567-G538E transgenes results in no major pattern defects but reduces the size of wings.
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pone-0016799-g005: Expression of mutant EF-G1 forms reduces growth and affects patterning in wings.(A) Heterozygous A9-GAL4/+ female wing with wild type patterning. Longitudinal veins L1-L5 and the anterior and posterior crossveins are indicated (AC, PC). (B) Wings that express four CG4567-G538E transgenes encoding the EF-G1 protein of II032 mutants with ptc-GAL4 show normal proportions but exhibit reduced growth between L3 and L4 where the mutant protein is expressed. They also lack the anterior crossvein (arrow). (C) Overexpression of two wild type ico transgenes in wings using A9-GAL4 does not affect patterning but results in smaller wings. (D) In comparison, ubiquitous expression of two CG4567-G538E transgenes reduces growth and interferes with proper vein formation. (E) Expression of three EF-G1 transgenes that lack the C-terminal tail has no apparent effects on growth or patterning. (F) Compared to two full-length mutant transgenes (D), expression of three tailless mutant CG4567-G538E transgenes results in no major pattern defects but reduces the size of wings.

Mentions: To further investigate the deleterious effects of EF-G1 missense mutant proteins, we expressed the II032 mutant form CG4567-G538E in various tissues. While animals that ubiquitously express two wild type ico transgenes with daughterless-GAL4 develop normally, we find that wild type animals that express two copies of CG4567-G538E all die before pupation, further supporting the idea that full-length mutant EF-G1 proteins can cause additional defects. When expressed in wings, a tissue that is not essential for viability, we find that CG4567-G538E transgenes cause growth and pattern defects. Compared to wild type wings (Figure 5A), wings that express two or four CG4567-G538E transgenes under the control of ptc-GAL4 exhibit normal proportions but show reduced growth in the area between longitudinal veins 3 and 4 where the mutant proteins are expressed (Figure 5B). In addition, the mutant transgenes also prevent the formation of the anterior crossvein in this area (Figure 5B, arrow). When expressed ubiquitously with the wing driver A9-GAL4, two copies of CG4567-G538E clearly disrupt wing growth, which leads to patterning defects such as ectopic vein formation and the merging of longitudinal veins (Figure 5D). In comparison, we noticed that ubiquitous expression of two wild type CG4567 transgenes also reduces growth (Figure 5C). Although we did not quantify the average reduction in growth, the major difference between wild type and mutant transgenes is the absence of pattern defects in wings that express wild type transgenes.


The Drosophila mitochondrial translation elongation factor G1 contains a nuclear localization signal and inhibits growth and DPP signaling.

Trivigno C, Haerry TE - PLoS ONE (2011)

Expression of mutant EF-G1 forms reduces growth and affects patterning in wings.(A) Heterozygous A9-GAL4/+ female wing with wild type patterning. Longitudinal veins L1-L5 and the anterior and posterior crossveins are indicated (AC, PC). (B) Wings that express four CG4567-G538E transgenes encoding the EF-G1 protein of II032 mutants with ptc-GAL4 show normal proportions but exhibit reduced growth between L3 and L4 where the mutant protein is expressed. They also lack the anterior crossvein (arrow). (C) Overexpression of two wild type ico transgenes in wings using A9-GAL4 does not affect patterning but results in smaller wings. (D) In comparison, ubiquitous expression of two CG4567-G538E transgenes reduces growth and interferes with proper vein formation. (E) Expression of three EF-G1 transgenes that lack the C-terminal tail has no apparent effects on growth or patterning. (F) Compared to two full-length mutant transgenes (D), expression of three tailless mutant CG4567-G538E transgenes results in no major pattern defects but reduces the size of wings.
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Related In: Results  -  Collection

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pone-0016799-g005: Expression of mutant EF-G1 forms reduces growth and affects patterning in wings.(A) Heterozygous A9-GAL4/+ female wing with wild type patterning. Longitudinal veins L1-L5 and the anterior and posterior crossveins are indicated (AC, PC). (B) Wings that express four CG4567-G538E transgenes encoding the EF-G1 protein of II032 mutants with ptc-GAL4 show normal proportions but exhibit reduced growth between L3 and L4 where the mutant protein is expressed. They also lack the anterior crossvein (arrow). (C) Overexpression of two wild type ico transgenes in wings using A9-GAL4 does not affect patterning but results in smaller wings. (D) In comparison, ubiquitous expression of two CG4567-G538E transgenes reduces growth and interferes with proper vein formation. (E) Expression of three EF-G1 transgenes that lack the C-terminal tail has no apparent effects on growth or patterning. (F) Compared to two full-length mutant transgenes (D), expression of three tailless mutant CG4567-G538E transgenes results in no major pattern defects but reduces the size of wings.
Mentions: To further investigate the deleterious effects of EF-G1 missense mutant proteins, we expressed the II032 mutant form CG4567-G538E in various tissues. While animals that ubiquitously express two wild type ico transgenes with daughterless-GAL4 develop normally, we find that wild type animals that express two copies of CG4567-G538E all die before pupation, further supporting the idea that full-length mutant EF-G1 proteins can cause additional defects. When expressed in wings, a tissue that is not essential for viability, we find that CG4567-G538E transgenes cause growth and pattern defects. Compared to wild type wings (Figure 5A), wings that express two or four CG4567-G538E transgenes under the control of ptc-GAL4 exhibit normal proportions but show reduced growth in the area between longitudinal veins 3 and 4 where the mutant proteins are expressed (Figure 5B). In addition, the mutant transgenes also prevent the formation of the anterior crossvein in this area (Figure 5B, arrow). When expressed ubiquitously with the wing driver A9-GAL4, two copies of CG4567-G538E clearly disrupt wing growth, which leads to patterning defects such as ectopic vein formation and the merging of longitudinal veins (Figure 5D). In comparison, we noticed that ubiquitous expression of two wild type CG4567 transgenes also reduces growth (Figure 5C). Although we did not quantify the average reduction in growth, the major difference between wild type and mutant transgenes is the absence of pattern defects in wings that express wild type transgenes.

Bottom Line: Expression of missense mutant forms of EF-G1 can accumulate in the nucleus and cause growth and patterning defects and animal lethality.We find that transgenes that encode mutant human EF-G1 proteins can rescue ico mutants, indicating that the underlying problem of the human disease is not just the loss of enzymatic activity.Our results are consistent with a model where EF-G1 acts as a retrograde signal from mitochondria to the nucleus to slow down cell proliferation if mitochondrial energy output is low.

View Article: PubMed Central - PubMed

Affiliation: Center for Molecular Biology and Biotechnology, Florida Atlantic University, Boca Raton, Florida, United States of America.

ABSTRACT
Mutations in the human mitochondrial elongation factor G1 (EF-G1) are recessive lethal and cause death shortly after birth. We have isolated mutations in iconoclast (ico), which encodes the highly conserved Drosophila orthologue of EF-G1. We find that EF-G1 is essential during fly development, but its function is not required in every tissue. In contrast to mutations, missense mutations exhibit stronger, possibly neomorphic phenotypes that lead to premature death during embryogenesis. Our experiments show that EF-G1 contains a secondary C-terminal nuclear localization signal. Expression of missense mutant forms of EF-G1 can accumulate in the nucleus and cause growth and patterning defects and animal lethality. We find that transgenes that encode mutant human EF-G1 proteins can rescue ico mutants, indicating that the underlying problem of the human disease is not just the loss of enzymatic activity. Our results are consistent with a model where EF-G1 acts as a retrograde signal from mitochondria to the nucleus to slow down cell proliferation if mitochondrial energy output is low.

Show MeSH