BackgroundRotifers are microscopic aquatic invertebrates that reproduce both sexually and asexually. Though rotifers are phylogenetically distant from humans, and have specialized reproductive physiology, this work identifies a surprising conservation in the control of reproduction between humans and rotifers through the estrogen receptor. Until recently, steroid signaling has been observed in only a few invertebrate taxa and its role in regulating invertebrate reproduction has not been clearly demonstrated. Insights into the evolution of sex signaling pathways can be gained by clarifying how receptors function in invertebrate reproduction.ResultsIn this paper, we show that a ligand-activated estrogen-like receptor in rotifers binds human estradiol and regulates reproductive output in females. In other invertebrates characterized thus far, ER ligand binding domains have occluded ligand-binding sites and the ERs are not ligand activated. We have used a suite of computational, biochemical and biological techniques to determine that the rotifer ER binding site is not occluded and can bind human estradiol.ConclusionsOur results demonstrate that this mammalian hormone receptor plays a key role in reproduction of the ancient microinvertebrate Brachinous manjavacas. The presence and activity of the ER within the phylum Rotifera indicates that the ER structure and function is highly conserved throughout animal evolution.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-017-0909-z) contains supplementary material, which is available to authorized users.
Hypoxia extends lifespan of Brachionus manjavacas (Rotifera)Work by Maria Rosa Miracle's group in 1989 described the adaptation of natural Brachionus plicatilis populations to low oxygen in oxyclines of meromictic lakes. This adaptation was accomplished by slowing metabolism in hypoxia, altering reproductive schedules and extending generation times. Many years later, Miracle's work inspired us to examine whether hypoxia could extend rotifer longevity and reproduction in our study of the biology of aging. In this paper we show that exposure of rotifers to four days of an atmosphere of 1.6 % O 2 extended mean lifespan 107 % over controls in normoxia (20.9 % O 2 ), whose mean lifespan was 7.9 days. Alternating days of hypoxia and normoxia also markedly extended rotifer lifespan by 53 %. Exposure to 1.6 % O 2 hypoxia nearly doubled lifetime reproduction of females (24.3 vs 12.4 offspring in control). Hypoxia exposure protected rotifers from subsequent oxidative and UV stress, but not starvation, osmotic or heat stress. The 0-4 day age-classes responded best to hypoxia exposure as compared to hypoxia exposure days 4-8 or 8-12. The protective effects of two days of hypoxia exposure persisted through day 6, then vanished by day 8. Rotifer diapausing eggs are especially resistant to hypoxia and hatch in atmospheres containing as little as 1.6 % O 2 after a one day delay. Our conclusion is that exposure to hypoxia for four days in the youngest age classes extends rotifer longevity and enhances lifetime reproduction. This response has adaptive value in anoxic sediments where most rotifer diapausing eggs are deposited.
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