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AID can restrict L1 retrotransposition suggesting a dual role in innate and adaptive immunity.

MacDuff DA, Demorest ZL, Harris RS - Nucleic Acids Res. (2009)

Bottom Line: We found that AID can inhibit the retrotransposition of L1 through a DNA deamination-independent mechanism.This mechanism may manifest in the cytoplasmic compartment co- or posttranslationally.Together with evidence for AID expression in the ovary, our data combined to suggest that AID has innate immune functions in addition to its integral roles in creating antibody diversity.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry, Molecular Biology and Biophysics, Institute for Molecular Virology, Center for Genome Engineering, University of Minnesota, Minneapolis, MN 55455, USA.

ABSTRACT
Retrotransposons make up over 40% of the mammalian genome. Some copies are still capable of mobilizing and new insertions promote genetic variation. Several members of the APOBEC3 family of DNA cytosine deaminases function to limit the replication of a variety of retroelements, such as the long-terminal repeat (LTR)-containing MusD and Ty1 elements, and that of the non-LTR retrotransposons, L1 and Alu. However, the APOBEC3 genes are limited to mammalian lineages, whereas retrotransposons are far more widespread. This raises the question of what cellular factors control retroelement transposition in species that lack APOBEC3 genes. A strong phylogenetic case can be made that an ancestral activation-induced deaminase (AID)-like gene duplicated and diverged to root the APOBEC3 lineage in mammals. Therefore, we tested the hypothesis that present-day AID proteins possess anti-retroelement activity. We found that AID can inhibit the retrotransposition of L1 through a DNA deamination-independent mechanism. This mechanism may manifest in the cytoplasmic compartment co- or posttranslationally. Together with evidence for AID expression in the ovary, our data combined to suggest that AID has innate immune functions in addition to its integral roles in creating antibody diversity.

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Effect of AID on Ty1 retrotransposition. (A) The transposition frequency of Ty1 in yeast cells expressing the indicated untagged AID or A3 (A3F, A3G) proteins or empty vector. The transposition frequency was calculated as the number of HIS+ colonies per viable cell. The vector control was normalized to 1 for each experiment. Histogram bars represent the mean of the medians from four independent experiments (actual mean for vector = 2.8 × 10−6) and error bars represent the standard deviation. (B) Yeast-based CANR assay for DNA mutation. Each ‘x’ represents the mutation frequency of an independent culture, calculated as the number of CANR colonies per viable cell. Six independent cultures were assayed for each AID variant, and the median mutation frequencies are indicated by the horizontal bars. Vector represents the background level of mutation in UNG-deficient yeast.
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Figure 7: Effect of AID on Ty1 retrotransposition. (A) The transposition frequency of Ty1 in yeast cells expressing the indicated untagged AID or A3 (A3F, A3G) proteins or empty vector. The transposition frequency was calculated as the number of HIS+ colonies per viable cell. The vector control was normalized to 1 for each experiment. Histogram bars represent the mean of the medians from four independent experiments (actual mean for vector = 2.8 × 10−6) and error bars represent the standard deviation. (B) Yeast-based CANR assay for DNA mutation. Each ‘x’ represents the mutation frequency of an independent culture, calculated as the number of CANR colonies per viable cell. Six independent cultures were assayed for each AID variant, and the median mutation frequencies are indicated by the horizontal bars. Vector represents the background level of mutation in UNG-deficient yeast.

Mentions: We considered that HeLa and 293 cells (non-B cells) may contain an inhibitor of AID that is interfering with its function. We therefore opted to use an extremely heterologous system: transposition of a yeast LTR-retroelement, Ty1 (26,28). Retrotransposition of the Ty1 genome results in the removal of an intron from a HIS3 reporter gene, conferring a HIS+ phenotype to yeast cells with a newly retrotransposed Ty1 element. The replication of Ty1, and therefore the formation of HIS+ colonies, was largely unaffected by the presence of any of the AID proteins, in contrast to human A3G and A3F [Figure 7A; (26,28)].Figure 7.


AID can restrict L1 retrotransposition suggesting a dual role in innate and adaptive immunity.

MacDuff DA, Demorest ZL, Harris RS - Nucleic Acids Res. (2009)

Effect of AID on Ty1 retrotransposition. (A) The transposition frequency of Ty1 in yeast cells expressing the indicated untagged AID or A3 (A3F, A3G) proteins or empty vector. The transposition frequency was calculated as the number of HIS+ colonies per viable cell. The vector control was normalized to 1 for each experiment. Histogram bars represent the mean of the medians from four independent experiments (actual mean for vector = 2.8 × 10−6) and error bars represent the standard deviation. (B) Yeast-based CANR assay for DNA mutation. Each ‘x’ represents the mutation frequency of an independent culture, calculated as the number of CANR colonies per viable cell. Six independent cultures were assayed for each AID variant, and the median mutation frequencies are indicated by the horizontal bars. Vector represents the background level of mutation in UNG-deficient yeast.
© Copyright Policy - creative-commons
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2665220&req=5

Figure 7: Effect of AID on Ty1 retrotransposition. (A) The transposition frequency of Ty1 in yeast cells expressing the indicated untagged AID or A3 (A3F, A3G) proteins or empty vector. The transposition frequency was calculated as the number of HIS+ colonies per viable cell. The vector control was normalized to 1 for each experiment. Histogram bars represent the mean of the medians from four independent experiments (actual mean for vector = 2.8 × 10−6) and error bars represent the standard deviation. (B) Yeast-based CANR assay for DNA mutation. Each ‘x’ represents the mutation frequency of an independent culture, calculated as the number of CANR colonies per viable cell. Six independent cultures were assayed for each AID variant, and the median mutation frequencies are indicated by the horizontal bars. Vector represents the background level of mutation in UNG-deficient yeast.
Mentions: We considered that HeLa and 293 cells (non-B cells) may contain an inhibitor of AID that is interfering with its function. We therefore opted to use an extremely heterologous system: transposition of a yeast LTR-retroelement, Ty1 (26,28). Retrotransposition of the Ty1 genome results in the removal of an intron from a HIS3 reporter gene, conferring a HIS+ phenotype to yeast cells with a newly retrotransposed Ty1 element. The replication of Ty1, and therefore the formation of HIS+ colonies, was largely unaffected by the presence of any of the AID proteins, in contrast to human A3G and A3F [Figure 7A; (26,28)].Figure 7.

Bottom Line: We found that AID can inhibit the retrotransposition of L1 through a DNA deamination-independent mechanism.This mechanism may manifest in the cytoplasmic compartment co- or posttranslationally.Together with evidence for AID expression in the ovary, our data combined to suggest that AID has innate immune functions in addition to its integral roles in creating antibody diversity.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry, Molecular Biology and Biophysics, Institute for Molecular Virology, Center for Genome Engineering, University of Minnesota, Minneapolis, MN 55455, USA.

ABSTRACT
Retrotransposons make up over 40% of the mammalian genome. Some copies are still capable of mobilizing and new insertions promote genetic variation. Several members of the APOBEC3 family of DNA cytosine deaminases function to limit the replication of a variety of retroelements, such as the long-terminal repeat (LTR)-containing MusD and Ty1 elements, and that of the non-LTR retrotransposons, L1 and Alu. However, the APOBEC3 genes are limited to mammalian lineages, whereas retrotransposons are far more widespread. This raises the question of what cellular factors control retroelement transposition in species that lack APOBEC3 genes. A strong phylogenetic case can be made that an ancestral activation-induced deaminase (AID)-like gene duplicated and diverged to root the APOBEC3 lineage in mammals. Therefore, we tested the hypothesis that present-day AID proteins possess anti-retroelement activity. We found that AID can inhibit the retrotransposition of L1 through a DNA deamination-independent mechanism. This mechanism may manifest in the cytoplasmic compartment co- or posttranslationally. Together with evidence for AID expression in the ovary, our data combined to suggest that AID has innate immune functions in addition to its integral roles in creating antibody diversity.

Show MeSH
Related in: MedlinePlus