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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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Clonal analysis of ico mutants in the eye.Clones of homozygous ico alleles were generated with eyeless-Flipase in the eyes of females. Homozygous ico clones do not contain eye pigment and are white. Pigmented cells are heterozygous for ico. (A) Clones of the mutation II032 do not survive to adulthood. (B–D) Clones of the other three missense mutations exhibit a small numbers of white cells. In contrast, homozygous clones of the two  mutations develop normally (E and F), indicating that EF-G1 function is not required in the eye and that clones expressing C-terminally truncated proteins do not affect growth and patterning. The cause for the black patches of cells that can be clearly seen in GA1, BA18, and GA25 but are also present in the other alleles is not entirely clear. However, their presence does not affect the interpretation of the results. See text for details.
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pone-0016799-g004: Clonal analysis of ico mutants in the eye.Clones of homozygous ico alleles were generated with eyeless-Flipase in the eyes of females. Homozygous ico clones do not contain eye pigment and are white. Pigmented cells are heterozygous for ico. (A) Clones of the mutation II032 do not survive to adulthood. (B–D) Clones of the other three missense mutations exhibit a small numbers of white cells. In contrast, homozygous clones of the two mutations develop normally (E and F), indicating that EF-G1 function is not required in the eye and that clones expressing C-terminally truncated proteins do not affect growth and patterning. The cause for the black patches of cells that can be clearly seen in GA1, BA18, and GA25 but are also present in the other alleles is not entirely clear. However, their presence does not affect the interpretation of the results. See text for details.

Mentions: The absence of white cells in heterozygous II032 animals suggests that homozygous clones of this missense mutation do not survive to adulthood (Figure 4A). The size of the eyes is reduced and patterning is disrupted, since the recombined cells die and only non-recombined cells survive and proliferate. Compared to II032, a few small white clones appear in the eyes of GA1, BA18, and GA25 mutant animals (Figure 4B-D, arrow), indicating that these mutations severely affect cell proliferation or survival rates. GA25 mutant animals exhibit the largest number of white cells, suggesting that it is the weakest of the missense mutations (Figure 4D). In contrast to missense mutations, the eyes of the deletion mutations icoDel EY1 and icoDel EY2 show no pattern defects and contain large areas of white homozygous clones (Figure 4E and F). The finding that cellular clones of ico mutants that almost certainly represent mutations develop normally and do not disrupt patterning of the eyes indicates that the function of Drosophila EF-G1 is not required in the eye and possibly other tissues. Since elongation is an essential process and all eukaryotes encode a second highly conserved mitochondrial G factor, EF-G2, it is possible that Drosophila EF-G2 can compensate for the lack of EF-G1 in certain tissues like the eye. Taken together, our results demonstrate that the presence of ico missense mutations has deleterious effects on cell proliferation or survival even in tissues where Drosophila EF-G1 is apparently not required.


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)

Clonal analysis of ico mutants in the eye.Clones of homozygous ico alleles were generated with eyeless-Flipase in the eyes of females. Homozygous ico clones do not contain eye pigment and are white. Pigmented cells are heterozygous for ico. (A) Clones of the mutation II032 do not survive to adulthood. (B–D) Clones of the other three missense mutations exhibit a small numbers of white cells. In contrast, homozygous clones of the two  mutations develop normally (E and F), indicating that EF-G1 function is not required in the eye and that clones expressing C-terminally truncated proteins do not affect growth and patterning. The cause for the black patches of cells that can be clearly seen in GA1, BA18, and GA25 but are also present in the other alleles is not entirely clear. However, their presence does not affect the interpretation of the results. See text for details.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3045377&req=5

pone-0016799-g004: Clonal analysis of ico mutants in the eye.Clones of homozygous ico alleles were generated with eyeless-Flipase in the eyes of females. Homozygous ico clones do not contain eye pigment and are white. Pigmented cells are heterozygous for ico. (A) Clones of the mutation II032 do not survive to adulthood. (B–D) Clones of the other three missense mutations exhibit a small numbers of white cells. In contrast, homozygous clones of the two mutations develop normally (E and F), indicating that EF-G1 function is not required in the eye and that clones expressing C-terminally truncated proteins do not affect growth and patterning. The cause for the black patches of cells that can be clearly seen in GA1, BA18, and GA25 but are also present in the other alleles is not entirely clear. However, their presence does not affect the interpretation of the results. See text for details.
Mentions: The absence of white cells in heterozygous II032 animals suggests that homozygous clones of this missense mutation do not survive to adulthood (Figure 4A). The size of the eyes is reduced and patterning is disrupted, since the recombined cells die and only non-recombined cells survive and proliferate. Compared to II032, a few small white clones appear in the eyes of GA1, BA18, and GA25 mutant animals (Figure 4B-D, arrow), indicating that these mutations severely affect cell proliferation or survival rates. GA25 mutant animals exhibit the largest number of white cells, suggesting that it is the weakest of the missense mutations (Figure 4D). In contrast to missense mutations, the eyes of the deletion mutations icoDel EY1 and icoDel EY2 show no pattern defects and contain large areas of white homozygous clones (Figure 4E and F). The finding that cellular clones of ico mutants that almost certainly represent mutations develop normally and do not disrupt patterning of the eyes indicates that the function of Drosophila EF-G1 is not required in the eye and possibly other tissues. Since elongation is an essential process and all eukaryotes encode a second highly conserved mitochondrial G factor, EF-G2, it is possible that Drosophila EF-G2 can compensate for the lack of EF-G1 in certain tissues like the eye. Taken together, our results demonstrate that the presence of ico missense mutations has deleterious effects on cell proliferation or survival even in tissues where Drosophila EF-G1 is apparently not required.

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