Dna metabolism's role in neuronal activity-dependent processes

Resumen

Recently some studies demonstrate that adult neuronal genome is a genetic mosaic but the role of this mosaicism and how is generated are not well known. The two main mechanisms that could result in the neuronal mosaic genome are somatic recombination and the LINE-1 (L1) retrotransposition. Some evidences, alterations in central nervous system development found in knock-out (KO) mice for proteins related with DNA repair processes and L1 activation in neuronal precursors, suggest that neuronal genome mosaicism may be related with the generation of neuronal diversity during central nervous system development. However, if genome reorganization processes happen in the adult nervous system during neuronal plasticity events are not established. Recently, it has been reported that neuronal activity transiently provokes increase of neuronal DNA breaks in cerebral areas where long-term neuronal plasticity events takes place, in some case related with cognition. DNA breaks have been related with the initial steps of gene expression activation, but also can be compatible with genomic reorganization. The main objective of this PhD project was determinate the potential role of processes that may result in genomic reorganization during neuronal activation. Firstly, we studied the importance of adult L1 retrotransposition in neuronal activation processes. Our results showed an activity-dependent increase in genome de novo L1 insertions in the hippocampus. Also using systemic pharmacologic and intrahippocampal genetic approaches, we demonstrate that L1 activation in the adult hippocampus is required for long-term memory formation. Secondly, we looked for evidences of potential genome reorganization events induced by exploration of an enriched environment, a protocol that provokes neuronal activity-dependent events. Exploratory session provoked an increase in the number of neurons containing DNA breaks, measured as the number of cells with 53BP1 foci, and in gene expression of genes related with DNA metabolism and DNA breaks. Both events happen in a sequential temporal-dependent manner in hippocampus and prefrontal cortex. Thirdly, to clear up the possible physiological role of DNA metabolism proteins in cognition, we made transient knock down of tyrosil-DNA phosphodiesterases 1 and 2, and h2ax, by intrahippocampal administration with specific antisense oligonucleotides (ASOs), and passive avoidance, an hippocampal-dependent cognition test. Hippocampal knock down of these three proteins provoked impairment in long-term memory formation in passive avoidance test. Finally, using the H2AX-/- mice we studied the role of H2AX in central nervous system function. H2AX-/- mice showed morphological alterations in the amygdala and hippocampus compared with the wt mice. Also, at behavioral level H2AX-/- mice presented deficits in depressive, cognition and social behaviors. In conclusion, all these data together suggest activity-dependent neural DNA reorganizations in the adult hippocampus. In addition, genetic and pharmacological manipulations of DNA reorganizations events in adult brain seem to affect cognition processes such as memory formation. Finally, depletion of H2AX in the germinal line provokes alteration in central nervous system function.