RESUMEN
Recent data shows that the effects of ionizing radiation are not restricted to the directly exposed parental germ cells, but can also manifest in their nonexposed offspring, resulting in elevated mutation rates and cancer predisposition. The mechanisms underlying these transgenerational changes remain poorly understood. One of the most important steps in elucidating these mechanisms is to investigate the initial cellular events that trigger genomic instability. Here we have analyzed the effects of paternal treatment by ethylnitrosourea, an alkylating agent which is known to form specific types of DNA adducts, on the transgenerational effects in the first-generation (F1) offspring of exposed CBA/Ca and BALB/c male mice. Mutation rates at two expanded simple tandem repeat loci were significantly elevated in the F1 germline of both strains. Pre and postmeiotic exposures resulted in similar increases in mutation rate in the F1 germline. Within each strain mutation rates were equally elevated in the germline of male and female F1 offspring of the directly exposed males. The results of our study suggest that transgenerational instability is not attributed to a specific sub-set of DNA lesions, such as double strand breaks, and is most probably triggered by a stress-like response to a generalized DNA damage.
Asunto(s)
Alquilantes/toxicidad , ADN/efectos de los fármacos , Etilnitrosourea/toxicidad , Inestabilidad Genómica , Exposición Paterna/efectos adversos , Animales , ADN/genética , Masculino , Ratones , Ratones Endogámicos BALB C , Ratones Endogámicos CBARESUMEN
Murine severe combined immunodeficiency (scid) cells are characterized by defective Prkdc (DNA-PKcs), one of the key genes involved in the repair of DNA double-strand breaks. Interestingly, scid mice are not null mutants and their cells are likely to show low DNA-PKcs activity. Prkdc is also involved in telomere maintenance and in contrast to mice genetically engineered to lack Prkdc (i.e. null mutants), which show complete absence of DNA-PKcs activity, loss of telomere capping function and normal telomere length, cells from scid mice show not only loss of telomere capping function but also abnormally elongated telomeres. Here we demonstrate that telomere elongation observed in murine scid cells can be reversed by expressing mutant hRAD54, a protein involved in homologous recombination. In addition, we measured recombination rates at telomeres using chromosome orientation fluorescence in situ hybridization (CO-FISH) and found that these are elevated in scid cells in comparison with control cells, or significantly reduced in scid cells expressing mutant hRAD54. Similarly, recombination rates at telomeres are reduced in scid cells following introduction of functional Prkdc. Since expression of mutant hRAD54 and restoration of functional Prkdc in scid cells cause the same effects, i.e. telomere shortening and reduced recombination rates at telomeres, these results argue that telomere elongation in scid cells is a complex trait resulting from interactions between homologous recombination mechanisms and DNA-PKcs.