Ametabolic embryos of Artemia franciscana accumulate DNA damage during prolonged anoxia

Encysted embryos of the brine shrimp Artemia franciscana are able to survive prolonged periods of anoxia even when fully hydrated. During this time there is no metabolism, raising the question of how embryos tolerate spontaneous, hydrolytic DNA damage such as depurination. When incubated at 28 degrees C and 40 degrees C for several weeks, hydrated anoxic embryos were found to accumulate abasic sites in their DNA with k=5.8x10(-11) s(-1) and 2.8x10(-10) s(-1), respectively. In both cases this is about 3-fold slower than expected from published observations on purified DNA. However, purified calf thymus DNA incubated under similar anoxic conditions at pH 6.3, the intracellular pH of anoxic cysts, also depurinated more slowly than predicted (about 1.7-fold), suggesting that cysts may in fact accumulate abasic sites only slightly more slowly than purified DNA. Upon reoxygenation of cysts stored under N(2) for 30 weeks at 28 degrees C, the number of abasic sites per 10(4) bp DNA fell from 21.1+/-4.0 to 9.8+/-2.0 by 12 h and to 6.2+/-2.1 by 24 h. Larvae hatched after 48 h and 72 h had only 0.59+/-0.17 and 0.48+/-0.07 abasic sites per 10(4) bp, respectively, suggesting that repair of these lesions had largely taken place before hatching commenced. Thus, unlike bacterial spores, Artemia cysts appear to have no specific protective mechanism beyond what might be afforded by chromatin structure to limit spontaneous depurination, and rely on the repair of accumulated lesions during the period between reoxygenation and hatching.