Experimental Selection for Drosophila Survival in Extremely Low O2 Environment

Abstract

BackgroundCellular hypoxia, if severe enough, results usually in injury or cell death. Our research in this area has focused on the molecular mechanisms underlying hypoxic tissue injury to explore strategies to prevent injury or enhance tolerance. The current experiments were designed to determine the genetic basis for adaptation to long term low O2 environments.Methodology/Principal FindingsWith long term experimental selection over many generations, we obtained a Drosophila melanogaster strain that can live perpetually in extremely low, normally lethal, O2 condition (as low as 4% O2). This strain shows a dramatic phenotypic divergence from controls, including a decreased recovery time from anoxic stupor, a higher rate of O2 consumption in hypoxic conditions, and a decreased body size and mass due to decreased cell number and size. Expression arrays showed that about 4% of the Drosophila genome altered in expression and about half of the alteration was down-regulation. The contribution of some altered transcripts to hypoxia tolerance was examined by testing the survival of available corresponding P-element insertions (and their excisions) under extremely low O2 conditions. We found that down-regulation of several candidate genes including Best1, broad, CG7102, dunce, lin19-like and sec6 conferred severe hypoxia tolerance in Drosophila.Conclusions/SignificanceWe have identified a number of genes that play an important role in the survival of a selected Drosophila strain in extremely low O2 conditions, selected by decreasing O2 availability over many generations. Because of conservation of pathways, we believe that such genes are critical in hypoxia adaptation in physiological or pathological conditions not only in Drosophila but also in mammals.

Flies developed small bodies and small cells in warm and in thermally fluctuating environments.

“…Consistent with this idea, flies that developed in a hypoxic environment produced small cells in two types of tissues (Heinrich et al, 2011). Furthermore, experimental evolution of D. melanogaster in hypoxic conditions led to small cells that consumed oxygen faster than did large cells (Zhou et al, 2007). Importantly, the superior diffusion of oxygen through the hydrocarbon phase of membranes is more pronounced at high temperatures, suggesting that small cells especially benefit a warm organism (Subczynski et al, 1989).…”

Systematic Identification of Gene Activities Promoting Hypoxic Death

“…Previous forward mutagenesis screens, candidate screens, existing mutant screens, and multigenerational selections have identified genes that regulate hypoxic sensitivity in C. elegans (Jiang et al 2001;Padilla et al 2002;Scott et al 2002;Nystul et al 2003;Shen et al 2005;Mendenhall et al 2006;Samokhvalov et al 2008;Anderson et al 2009;) and/or Drosophila (Ma et al 2001;Chen et al 2002;Zhou et al 2007; . In Drosophila, most of these hypoxic sensitivity genes function to reduce hypoxic sensitivity and would not have been expected to be found in our screen.…”

“…In Drosophila, most of these hypoxic sensitivity genes function to reduce hypoxic sensitivity and would not have been expected to be found in our screen. However, the hypoxia-resistance phenotype of a P-element insertion in Drosophila sec6 and phenotypic reversion by precise P-element excision showed that sec6 promotes hypoxic organismal death in Drosophila (Zhou et al 2007) as does its C. elegans ortholog, sec-6 (Table 1, supplemental Table 2-Channels/transport). Thus, the role of SEC-6 in promoting hypoxic sensitivity appears to be evolutionarily conserved.…”

Experimental selection of hypoxia-tolerant Drosophila melanogaster

“…Many studies have investigated the mechanisms that lead to injury when cells are deprived of O 2 , but to potentially treat or prevent the consequences of hypoxia necessitates also the understanding of the inherent tissue mechanisms that are critical for tolerance and survival. To do so, we use a long-term laboratory selection strategy that unmasks mechanisms that play an important role in hypoxia tolerance in a genetic model, Drosophila melanogaster (1,2). In this attempt, starting with 27 isofemale D. melanogaster strains, and applying decreasing levels of O 2 over >200 generations, we generated Drosophila populations that tolerate severe levels of hypoxia, which are lethal to the original parental lines.…”