Extreme anti-oxidant protection against ionizing radiation in bdelloid rotifers

Abstract

Bdelloid rotifers, a class of freshwater invertebrates, are extraordinarily resistant to ionizing radiation (IR). Their radioresistance is not caused by reduced susceptibility to DNA double-strand breakage for IR makes double-strand breaks (DSBs) in bdelloids with essentially the same efficiency as in other species, regardless of radiosensitivity. Instead, we find that the bdelloid Adineta vaga is far more resistant to IR-induced protein carbonylation than is the much more radiosensitive nematode Caenorhabditis elegans. In both species, the dose-response for protein carbonylation parallels that for fecundity reduction, manifested as embryonic death. We conclude that the great radioresistance of bdelloid rotifers is a consequence of an unusually effective system of anti-oxidant protection of cellular constituents, including those required for DSB repair, allowing bdelloids to recover and continue reproducing after doses of IR causing hundreds of DSBs per nucleus. Bdelloid rotifers therefore offer an advantageous system for investigation of enhanced anti-oxidant protection and its consequences in animal systems.

Fig. 1.

(A) Dose–response for fecundity. ●, A. vaga; ◆, C. elegans. Dose rate was 26–38 Gy/min. ○, A. vaga; □, P. roseola; △, E. dilatata. Dose rate was 2.3 Gy/min; data represented by unfilled symbols are from ref. . Curve is drawn to fit data for A. vaga. (B) Dose–response for motion in response to touch 24 h after irradiation. Dose rate was 38 Gy/min.

Fig. 2.

(A) Dose–response for fecundity and protein carbonylation assayed by ELISA. Dose rate was 26–38 Gy/min. Fecundity: ●, A. vaga; ◆, C. elegans. Carbonylation: ○, A. vaga; ◇, C. elegans. The indicated degree of carbonylation was obtained by comparison with the provided albumin standards and should be regarded as only proportional to the actual value because the composition of the experimental samples differs from that of the standard. No difference in carbonylation is found between extracts made soon after irradiation and extracts from animals kept on ice an additional 3 h, whereas, if kept 3 h at room temperature, nearly half of the carbonylated protein is lost. It may therefore be concluded that proteolysis of carbonylated protein during irradiation is negligible. (B) Dose dependence for protein carbonylation visualized on Western blots with silver-stain loading controls beneath.

Fig. 3.

Saturation of IR-induced protein carbonylation at high dose observed by Western blotting. (A) A. vaga. (B) C. elegans. Relative amounts of extract assayed: 1, solid symbols; 1/2, shaded symbols; 1/4, open symbols. Doses: 0, 200, 2,500 and 5,000 Gy. The observation of plateaus by quantitative Western blotting shows that they are not an artifact peculiar to OxyELISA.