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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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Tissue distribution of AID expression. (A) A quantitative analysis of AID mRNA expression in mouse spleen, heart, liver, testes and ovaries in relation to RPL13A (housekeeping gene control) mRNA in the same samples. Spleen was normalized to 1.0. Tissues from two or three animals were procured and each sample was analyzed in triplicate. The standard deviations are shown. (B) Agarose gel images of the PCR products from the qPCR. DNA marker sizes are indicated on the left in base pairs. RT, reverse transcriptase.
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Figure 8: Tissue distribution of AID expression. (A) A quantitative analysis of AID mRNA expression in mouse spleen, heart, liver, testes and ovaries in relation to RPL13A (housekeeping gene control) mRNA in the same samples. Spleen was normalized to 1.0. Tissues from two or three animals were procured and each sample was analyzed in triplicate. The standard deviations are shown. (B) Agarose gel images of the PCR products from the qPCR. DNA marker sizes are indicated on the left in base pairs. RT, reverse transcriptase.

Mentions: While the anti-L1 and anti-MusD activities of AID were certainly intriguing, we were unsure how a protein that is expressed in B lymphocytes could prevent the transposition of retroelements that replicate mostly in germ cells and/or early in embryogenesis (although reports of somatic mobilization of L1 are emerging) (75–78). However, several studies have suggested that AID may be expressed outside of the B-cell compartment in certain circumstances (58,79–82). Therefore, since a good anti-mouse AID antibody is not commercially available for protein detection, we performed quantitative RT-PCR to determine the relative levels of AID expression in various mouse tissues. We showed that AID is expressed in the spleen (as expected) and ovaries (∼60% compared with spleen), but only weakly in heart, and not at all in liver or testes (Figure 8A). These data were in accordance with another study that found high levels of AID expression in oocytes (82). Representative PCR reactions products were also visualized on an agarose gel to verify the qPCR data (Figure 8B). The AID amplicon was visible in the reaction from spleen and ovary cDNA, but not from heart, liver or testes cDNA. We confirmed specific amplification of AID by cloning and sequencing the qPCR product. RPL13A was used as the housekeeping gene control, and it amplified similarly in all samples. We concluded that AID is indeed expressed in a tissue relevant to L1 and MusD replication in vivo.Figure 8.


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

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

Tissue distribution of AID expression. (A) A quantitative analysis of AID mRNA expression in mouse spleen, heart, liver, testes and ovaries in relation to RPL13A (housekeeping gene control) mRNA in the same samples. Spleen was normalized to 1.0. Tissues from two or three animals were procured and each sample was analyzed in triplicate. The standard deviations are shown. (B) Agarose gel images of the PCR products from the qPCR. DNA marker sizes are indicated on the left in base pairs. RT, reverse transcriptase.
© Copyright Policy - creative-commons
Related In: Results  -  Collection

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

Figure 8: Tissue distribution of AID expression. (A) A quantitative analysis of AID mRNA expression in mouse spleen, heart, liver, testes and ovaries in relation to RPL13A (housekeeping gene control) mRNA in the same samples. Spleen was normalized to 1.0. Tissues from two or three animals were procured and each sample was analyzed in triplicate. The standard deviations are shown. (B) Agarose gel images of the PCR products from the qPCR. DNA marker sizes are indicated on the left in base pairs. RT, reverse transcriptase.
Mentions: While the anti-L1 and anti-MusD activities of AID were certainly intriguing, we were unsure how a protein that is expressed in B lymphocytes could prevent the transposition of retroelements that replicate mostly in germ cells and/or early in embryogenesis (although reports of somatic mobilization of L1 are emerging) (75–78). However, several studies have suggested that AID may be expressed outside of the B-cell compartment in certain circumstances (58,79–82). Therefore, since a good anti-mouse AID antibody is not commercially available for protein detection, we performed quantitative RT-PCR to determine the relative levels of AID expression in various mouse tissues. We showed that AID is expressed in the spleen (as expected) and ovaries (∼60% compared with spleen), but only weakly in heart, and not at all in liver or testes (Figure 8A). These data were in accordance with another study that found high levels of AID expression in oocytes (82). Representative PCR reactions products were also visualized on an agarose gel to verify the qPCR data (Figure 8B). The AID amplicon was visible in the reaction from spleen and ovary cDNA, but not from heart, liver or testes cDNA. We confirmed specific amplification of AID by cloning and sequencing the qPCR product. RPL13A was used as the housekeeping gene control, and it amplified similarly in all samples. We concluded that AID is indeed expressed in a tissue relevant to L1 and MusD replication in vivo.Figure 8.

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