Abstract
Many species of marine mollusks demonstrate exceptional capacities for long term survival without oxygen. Analysis of gene expression under anoxic conditions, including the subsequent translational responses, allows examination of the functional mechanisms that support and regulate natural anaerobiosis and permit noninjurious transitions between aerobic and anoxic states. Identification of stress-specific gene expression can provide important insights into the metabolic adaptations that are needed for anoxia tolerance, with potential applications to anoxia-intolerant systems. Various methods are available to do this, including high throughput microarray screening and construction and screening of cDNA libraries. Anoxia-responsive genes have been identified in mollusks; some have known functions in other organisms but were not previously linked with anoxia survival. In other cases, completely novel anoxia-responsive genes have been discovered, some that show known motifs or domains that hint at function. Selected genes are expressed at different times over an anoxia-recovery time course with their transcription and translation being actively regulated to ensure protein expression at the optimal time. An examination of transcript status over the course of anoxia exposure and subsequent aerobic recovery identifies genes, and the proteins that they encode, that enhance cell survival under oxygen-limited conditions. Analysis of data generated from non-mainstream model systems allows for insight into the response by cells to anoxia stress.
Highlights
Humans view oxygen as essential for life but many organisms are excellent facultative anaerobes, able to take advantage of the high ATP yield from oxidative phosphorylation when oxygen is available but able to rely on fermentation reactions to generate energy when oxygen is lacking
Using a cDNA library prepared from L. littorea, we have identified a number of such genes in periwinkle hepatopancreas [14, 15, 18] that perform potentially novel functions under hypoxic or anoxic conditions
The roles of the proteins encoded by anoxia-responsive genes can be speculated upon based on whether: i) the protein shares key domains, motifs, secondary structure or other attributes known to be characteristic of a specific protein or protein family, ii) mRNA transcripts accumulate due to active transcription or due to protection from degradation, iii) the transcript is translated to produce the protein at the onset, during, or following anoxia exposure, and iv) the protein has a defined role(s) in other systems
Summary
Humans view oxygen as essential for life but many organisms are excellent facultative anaerobes, able to take advantage of the high ATP yield from oxidative phosphorylation when oxygen is available but able to rely on fermentation reactions to generate energy when oxygen is lacking. Analysis of gene expression during anoxia, including the subsequent translational responses, allows examination of the functional mechanisms that support and regulate natural anaerobiosis and gives us a better understanding of how many organisms on earth can make reversible transitions to life without oxygen.
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