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Aag glycosylase and impact on gene expression changes

ABSTRACT: We are investigating the transcriptional response of mice that are wt or null for Aag in response to alkylating agent MMS We used microarrays to detail the global programme of gene expression response due to MMS exposure in a DNA repair proficient or deficient mouse Keywords: timepoint

ORGANISM(S): Mus musculus

PROVIDER: GSE11252 | GEO | 2009/02/04

SECONDARY ACCESSION(S): PRJNA106761

REPOSITORIES: GEO

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Project description:Neurodevelopment is a tightly coordinated process, in which genome is exposed to spectra of endogenous agents at different stages of differentiation. Increasing body of evidence suggests that DNA damage is an important feature of developing brain, tightly linked to gene expression programs and neuronal activity. Some of the most frequent DNA damage includes changes to DNA bases, recognized by DNA glycosylases and repaired through base excision repair (BER). The only mammalian DNA glycosylase able to remove frequent alkylated DNA based is alkyladenine DNA glycosylase (Aag, aka Mpg). Recently we showed that, besides participation in DNA repair, AAG affects expression of neurodevelopmental genes in human cells. Aag was further proposed to act as reader of epigenetic marks, including 5-hydroxymethylcytosine (5hmC), in the mouse brain. Despite the evidence of potential Aag involvement in the key brain processes, the impact of Aag loss on developing brain remains unknown. Here, by using Aag knockout (Aag-/-) mice, we show that Aag absence leads to reduced DNA damage levels, evident in lowered number of γH2AX foci in P5 hippocampi. This is accompanied by changes in 5hmC signal intensity in different hippocampal regions. Analysis of gene expression in hippocampus and prefrontal cortex, at multiple developmental stages, indicates that lack of Aag results in altered gene expression, primarily of genes involved in regulation of response to stress. One of the most prominent genes deregulated in Aag-dependent manner, at all tested developmental stages, is aldehyde dehydrogenase 2 (Aldh2). In line with the changes in hippocampal DNA damage levels and the gene expression, adult Aag-/- mice exhibit altered behavior, evident in decreased anxiety in the Elevated Zero Maze and increased alternations in the Elevated T Maze tests. Taken together these results suggests that Aag has functions in modulation of genome dynamics during brain development, important for animal behavior.

Project description:Alkylation damage to DNA occurs when cells encounter alkylating agents in the environment or when active alkylators are generated by nitrosation of amino acids in metabolic pathways. To cope with DNA alkylation damage, cells have evolved genes that encode proteins with alkylation-specific DNA repair activities. It is notable that these repair systems are conserved from bacteria to humans. In Escherichia coli, cells exposed to a low concentration of an alkylating agent, such as N-methyl-Nâ-nitro-N-nitrosoguanidine (MNNG) or methyl methanesulfonate (MMS), show a remarkable increase in resistance to both the lethal and mutagenic effects of subsequent high-level challenge treatments with the same or other alkylating agents. This increased resistance has been known as âadaptive responseâ to alkylation damage in DNA. To date, four genes have been identified as components of this response, ada, alkA, alkB and aidB. The ada gene encodes the Ada protein, which has the dual function of a transcriptional regulator for the genes involved in the adaptive response, and a methyltransferase that demethylates two methylated bases (O6meG and O4meT) and methylphosphotriesters produced by methylating agents in the sugar phosphate backbone. The differences between the wild-type and mutant strains were characterized at transcriptome levels. In addition, the global changes in gene expressions in response to alkylating agents (MMS), in E. coli K-12 W3110 and ada mutant strains were also analyzed. The analysis of time- and strain-dependent adaptive responses revealed the regulatory and physiological characteristics of the Ada-dependent adaptive response in E. coli. In order to examine the intracellular changes that are induced by the ada gene deletion in the MMS-untreated, normal growth condition, the expression levels of genes of ada mutant cells were compared with those of wild-type cells at the mid-log growth phase (at 0.5 h sampling point). Cells were cultivated at 37oC and 250 rpm in 100 mL of Luria-Bertani (LB) medium (10 g/L tryptone, 5 g/L yeast extract, and 5 g/L NaCl) in 250-mL Erlenmeyer flasks. Transcriptome analysis were also performed for the samples (E. coli wildtype and ada mutant strains) taken at 0.5, 1.5 and 3.9 h following MMS treatment for both MMS-treated and -untreated control cultures, and the expression levels were compared.

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Aag glycosylase and impact on gene expression changes

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