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Combinatorial effects of transposable elements on gene expression and phenotypic robustness in Drosophila melanogaster development.

Clemmons AW, Wasserman SA - G3 (Bethesda) (2013)

Bottom Line: We determine that the mutant lines have in common a retrotransposon insertion upstream of the tube transcription start site.Genetic and molecular approaches demonstrate that this insertion dramatically reduces maternal expression of tube, thereby uncovering the inherent variability in gene expression.We further find that additional transposable element insertions near the tube gene synergistically enhance the phenotype caused by the sensitizing upstream insertion.

View Article: PubMed Central - PubMed

Affiliation: Section of Cell & Developmental Biology, University of California San Diego, La Jolla, California 92093-0349.

ABSTRACT
Embryonic patterning displays remarkable consistency from individual to individual despite frequent environmental perturbations and diverse genetic contexts. Stochastic influences on the cellular environment may cause transcription rates to fluctuate, but these fluctuations rarely lead to developmental defects or disease. Here we characterize a set of recessive alleles of the Toll pathway component tube that destabilize embryonic dorsoventral patterning in Drosophila melanogaster. Females bearing these tube alleles generate embryos of an unusually wide range of dorsalized phenotypes, with the distributions across this range being unique for each allele. We determine that the mutant lines have in common a retrotransposon insertion upstream of the tube transcription start site. Genetic and molecular approaches demonstrate that this insertion dramatically reduces maternal expression of tube, thereby uncovering the inherent variability in gene expression. We further find that additional transposable element insertions near the tube gene synergistically enhance the phenotype caused by the sensitizing upstream insertion. These studies document how phenotypic variability can arise from normally occurring fluctuations around reduced mean expression and illustrate the contribution of transposons, individually and combinatorially, to such a state.

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Immune function of tube appears unaffected in tubvar adults. (A) Survival of adult males of specified genotype after septic wounding with F. oxysporum spores. Analysis of tub7 was performed in trans to tub2, a strong hypomorphic allele. Error bars represent SEM. (B) Quantitation of tube mRNA in adults. Quantitative RT-PCR data of tube expression in adult males of the specified genotype. Expression data were normalized to rp49 expression and are presented as a fraction of tub+/tub expression, with tub+/tub set to 0.5. Error bars represent SEM. **P < 0.01, ***P < 0.001, n.s. = not significant.
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fig4: Immune function of tube appears unaffected in tubvar adults. (A) Survival of adult males of specified genotype after septic wounding with F. oxysporum spores. Analysis of tub7 was performed in trans to tub2, a strong hypomorphic allele. Error bars represent SEM. (B) Quantitation of tube mRNA in adults. Quantitative RT-PCR data of tube expression in adult males of the specified genotype. Expression data were normalized to rp49 expression and are presented as a fraction of tub+/tub expression, with tub+/tub set to 0.5. Error bars represent SEM. **P < 0.01, ***P < 0.001, n.s. = not significant.

Mentions: The aforementioned findings indicate that the presence of the opus insertion alters tube expression. Because Tube is required for Toll pathway function in both embryonic patterning and innate immunity, we wondered whether tubvar mutants also display immune defects. To answer this question, we assayed tubvar/tub, tub/tub, and wild-type adult males for survival after septic injury with the fungus Fusarium oxysporum, a specific inducer of Toll signaling. We found that although tub/tub males died within 2 d after infection, tubvar/tub males survived on average for 4 d following infection, indistinguishable from wild-type males (Figure 4A). Thus, the tubvar chromosomes detectably disrupt Toll signaling in embryos but not in adult immune tissues.


Combinatorial effects of transposable elements on gene expression and phenotypic robustness in Drosophila melanogaster development.

Clemmons AW, Wasserman SA - G3 (Bethesda) (2013)

Immune function of tube appears unaffected in tubvar adults. (A) Survival of adult males of specified genotype after septic wounding with F. oxysporum spores. Analysis of tub7 was performed in trans to tub2, a strong hypomorphic allele. Error bars represent SEM. (B) Quantitation of tube mRNA in adults. Quantitative RT-PCR data of tube expression in adult males of the specified genotype. Expression data were normalized to rp49 expression and are presented as a fraction of tub+/tub expression, with tub+/tub set to 0.5. Error bars represent SEM. **P < 0.01, ***P < 0.001, n.s. = not significant.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3755913&req=5

fig4: Immune function of tube appears unaffected in tubvar adults. (A) Survival of adult males of specified genotype after septic wounding with F. oxysporum spores. Analysis of tub7 was performed in trans to tub2, a strong hypomorphic allele. Error bars represent SEM. (B) Quantitation of tube mRNA in adults. Quantitative RT-PCR data of tube expression in adult males of the specified genotype. Expression data were normalized to rp49 expression and are presented as a fraction of tub+/tub expression, with tub+/tub set to 0.5. Error bars represent SEM. **P < 0.01, ***P < 0.001, n.s. = not significant.
Mentions: The aforementioned findings indicate that the presence of the opus insertion alters tube expression. Because Tube is required for Toll pathway function in both embryonic patterning and innate immunity, we wondered whether tubvar mutants also display immune defects. To answer this question, we assayed tubvar/tub, tub/tub, and wild-type adult males for survival after septic injury with the fungus Fusarium oxysporum, a specific inducer of Toll signaling. We found that although tub/tub males died within 2 d after infection, tubvar/tub males survived on average for 4 d following infection, indistinguishable from wild-type males (Figure 4A). Thus, the tubvar chromosomes detectably disrupt Toll signaling in embryos but not in adult immune tissues.

Bottom Line: We determine that the mutant lines have in common a retrotransposon insertion upstream of the tube transcription start site.Genetic and molecular approaches demonstrate that this insertion dramatically reduces maternal expression of tube, thereby uncovering the inherent variability in gene expression.We further find that additional transposable element insertions near the tube gene synergistically enhance the phenotype caused by the sensitizing upstream insertion.

View Article: PubMed Central - PubMed

Affiliation: Section of Cell & Developmental Biology, University of California San Diego, La Jolla, California 92093-0349.

ABSTRACT
Embryonic patterning displays remarkable consistency from individual to individual despite frequent environmental perturbations and diverse genetic contexts. Stochastic influences on the cellular environment may cause transcription rates to fluctuate, but these fluctuations rarely lead to developmental defects or disease. Here we characterize a set of recessive alleles of the Toll pathway component tube that destabilize embryonic dorsoventral patterning in Drosophila melanogaster. Females bearing these tube alleles generate embryos of an unusually wide range of dorsalized phenotypes, with the distributions across this range being unique for each allele. We determine that the mutant lines have in common a retrotransposon insertion upstream of the tube transcription start site. Genetic and molecular approaches demonstrate that this insertion dramatically reduces maternal expression of tube, thereby uncovering the inherent variability in gene expression. We further find that additional transposable element insertions near the tube gene synergistically enhance the phenotype caused by the sensitizing upstream insertion. These studies document how phenotypic variability can arise from normally occurring fluctuations around reduced mean expression and illustrate the contribution of transposons, individually and combinatorially, to such a state.

Show MeSH
Related in: MedlinePlus