Loss of alkyladenine DNA glycosylase alters gene expression in developing mouse brain and leads to reduced anxiety and increased exploratory behavior
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 ?H2AX 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. Overall design: To characterize brain development in Aag-/- versus WT, mice at postnatal day five (P5), juvenile mice at six weeks (6W) and adult mice from four to six months (6M) were evaluated. Hippocampus and pre-frontal cortex were isolated from P5, 6W and 6M male mice (4 animals per time point) for further RNA extraction. Total RNA from hippocampus and pre-frontal cortex was then compared between the KO (Aag-/-) and WT genotypes in addition to comparisons at the 3 different time points.