Abstract: There is growing evidence that defective DNA repair in neurons with accumulation of DNA lesions and loss of genome
integrity underlies aging and many neurodegenerative disorders. An important challenge is to understand how neurons
can tolerate the accumulation of persistent DNA lesions without triggering the apoptotic pathway. Here we study the
impact of the accumulation of unrepaired DNA on the chromatin architecture, kinetics of the DNA damage response
and transcriptional activity in rat sensory ganglion neurons exposed to 1-to-3 doses of ionizing radiation (IR). In particular,
we have characterized the structural, molecular and transcriptional compartmentalization of unrepaired DNA in
persistent DNA damaged foci (PDDF). IR induced the formation of numerous transient foci, which repaired DNA
within the 24 h post-IR, and a 1-to-3 PDDF. The latter concentrate DNA damage signaling and repair factors,
including ?H2AX, pATM, WRAP53 and 53BP1. The number and size of PDDF was dependent on the doses of IR
administered. The proportion of neurons carrying PDDF decreased over time of post-IR, indicating that a slow DNA
repair occurs in some foci. The fine structure of PDDF consisted of a loose network of unfolded 30 nm chromatin fiber
intermediates, which may provide a structural scaffold accessible for DNA repair factors. Furthermore, the transcription
assay demonstrated that PDDF are transcriptionally silent, although transcription occurred in flanking euchromatin.
Therefore, the expression of ?H2AX can be used as a reliable marker of gene silencing in DNA damaged neurons.
Moreover, PDDF were located in repressive nuclear environments, preferentially in the perinucleolar domain where they
were frequently associated with Cajal bodies or heterochromatin clumps forming a structural triad. We propose that the
sequestration of unrepaired DNA in discrete PDDF and the transcriptional silencing can be essential to preserve genome
stability and prevent the synthesis of aberrant mRNA and protein products encoded by damaged genes.
Otras publicaciones de la misma revista o congreso con autores/as de la Universidad de Cantabria