Hand, S. C.. University of Colorado, Hands@spot.colorado.edu
, . C.. ,
ARREST OF GENE EXPRESSION DURING ANOXIA: LESSONS FROM INVERTEBRATE DORMANCY.
With one exception, all major invertebrate phyla contain species that possess dormant states, a feature that affords tolerance to extreme environmental conditions. Embryos of the brine shrimp can survive oxygen deprivation for several years at room temperature by entering anaerobic quiescence. Transcription and translation are both depressed markedly in response to anoxia and represent two events in a suite of energy-saving measures. Transcriptional run-on assays performed with nuclei isolated from aerobic versus anoxic embryos show that the capacity for mRNA synthesis is lowered 80% as a result of anoxic exposure. Transcriptional capacity of isolated mitochondria is reduced about 50% by oxygen removal in vitro. Additionally, intracellular pH declines rapidly by over 1.0 pH unit during anoxia, and evidence indicates this acidification depresses transcription even further.
pH-sensitive translational components exist within the cytoplasm and the mitochondrial matrix.
However, oxygen deprivation in the absence of a pH change depresses protein synthesis 80% in isolated mitochondria. Surprisingly, chemical anoxia produces only a modest effect. Such a cyanide- and antimycin-insensitive, but hypoxia-sensitive, inhibitory signature suggests a molecular oxygen sensor within this organelle. Signalling mechanisms, based on protons and molecular oxygen, exist in these embryos that downregulate metabolic processes under anoxia. (NSF grant IBN-9723746)
Day: Tuesday, Feb. 2
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