Identification of the alternative oxidase gene and its expression in the copepod Tigriopus californicus

Abstract

In addition to the typical electron transport system (ETS) in animal mitochondria responsible for oxidative phosphorylation, in some species there exists an alternative oxidase (AOX) pathway capable of catalyzing the oxidation of ubiquinol and the reduction of oxygen to water. The discovery of AOX in animals is recent and further investigations into its expression, regulation, and physiological role have been hampered by the lack of a tractable experimental model organism. Our recent DNA database searches using bioinformatics revealed an AOX sequence in several marine copepods including Tigriopus californicus. This species lives in tidepools along the west coast of North America and is subject to a wide variety of daily environmental stresses. Here we verify the presence of the AOX gene in T. californicus and the expression of AOX mRNA and AOX protein in various life stages of the animal. We demonstrate that levels of the AOX protein increase in T. californicus in response to cold and heat stress compared to normal rearing temperature. We predict that a functional AOX pathway is present in T. californicus, propose that this species will be a useful model organism for the study of AOX in animals, and discuss future directions for animal AOX research.

The tardigradeHypsibius exemplarisas an emerging model to study the mitochondrial alternative oxidase at animal organismal level

“…Thus, the available data indicates that functional studies of animal AOX are based on models that do not contain native AOX with exception of T. californicus, C. gigas, A. franciscana and L. vannamei enzyme. The molecular weight (MW) detected for the AOX protein reported for T. californicus is not convincing and its predicted amino acid sequence does not contain the proper C-terminus motif [34]. In the case of C. gigas, AOX contribution to the oyster adjustments to short-term hypoxia and re-oxygenation was considered in isolated mitochondria [17] but the presented data do not allow for clear conclusions as the observed AA-resistant respiration was not shown to be eliminated by AOX inhibitor, for example by benzohydroxamic acid (BHAM) [35].…”

“…The second one was heterologously expressed in mitochondria of cultured human cells [9,[20][21] as well as in the fruit fly Drosophila (Sophophora) melanogaster [22] [23][24][25][26][27] and mouse [9,12,[28][29]. Additionally, some experimental data concerning AOX protein are available for crustaceans, the brine shrimp Artemia franciscana [30], the white shrimp Litopenaeus vannamei [31] [32] and the marine copepod Tigriopus californicus [33] [34]. In the case of both the shrimps the data concerns AOX activity in isolated mitochondria whereas in the case of the copepod amounts of AOX mRNA and protein in various life stages of the animal and under stress temperature conditions were studied.…”

“…Thus, data concerning animal AOX expression and activity regulation is still scarce (e.g. [1,3,34]).…”

The Tardigrade Hypsibius Exemplaris as an Emerging Model to Study the Mitochondrial Alternative Oxidase at Animal Organismal Level

“…The second one was heterologously expressed in mitochondria of cultured human cells [9,[20][21] as well as in the fruit y Drosophila (Sophophora) melanogaster [22] [23][24][25][26][27] and mouse [9,12,[28][29]. Additionally, some experimental data concerning AOX protein are available for crustaceans, the brine shrimp Artemia franciscana [30], the white shrimp Litopenaeus vannamei [31] [32] and the marine copepod Tigriopus californicus [33] [34]. In the case of both the shrimps the data concerns AOX activity in isolated mitochondria whereas in the case of the copepod amounts of AOX mRNA and protein in various life stages of the animal and under stress temperature conditions were studied.…”

“…Thus, data concerning animal AOX expression and activity regulation is still scarce (e.g. [1,3,34]).…”