Abstract

Introduction

Materials & Methods

Results

Discussion & Conclusion

References

Discussion
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The intertidal environment is a wildly fluctuating habitat. Species inhabiting these areas are faced with daily and seasonal variations in water and oxygen availability, temperature and salinity. Consequently, these animals have an equally flexible metabolism. Littorina littorea is one such tolerant species. This marine gastropod is both freeze-tolerant and anoxia resistant

Anoxia Survival

At low tide, intertidal gill breathers are exposed to open air and are faced with a lack of oxygen. Survival then depends on the animals' ability to tolerate anoxic conditions for extended time periods. Most intertidal invertebrates tolerate anoxia thanks to a combination of strategies, including the ability to drop metabolic rate to less than 10% of the resting aerobic rate. They also enhance anaerobic production of ATP via fermentative reactions linked to succinate and volatile fatty acid production (deZwaan, 1983; Storey and Storey, 1990; Storey 1992).

Freezing

At higher latitudes, intertidal animals are also faced with sub-zero temperatures when exposed to air. Survival depends on strategies in place to endure or avoid freezing. L. littorea employs freeze tolerance, permitting and even encouraging ice to form in extracellular spaces, while preventing the freezing of intracellular fluids. Unique proteins are synthesized in animals that survive freezing temperatures. Thermal hysteresis (antifreeze) and ice-nucleating proteins are synthesized by many freeze-avoiding and freeze-tolerant species respectively in response to environmental cues. Although antifreeze proteins have not been found in L littorea, such proteins suggest a strong genetic component to the induction and maintenance of freezing survival strategies.

Genetic alterations in response to freezing and low oxygen tension and approach to be used for genetic studies of L. littorea

The genetic response to freezing has not been investigated extensively and most of what little research there is, has been obtained from plants. In contrast, a huge volume of work has been accumulated in the field of hypoxia. A large number of studies have demonstrated that oxygen can modulate gene expression (see reviews by Bunn and Poyton, 1996 and Fandrey, 1995) with up-regulated genes ranging from transcription factors to glycolytic enzymes to structural proteins. However the vast majority of these studies have been conducted on systems that are intolerant to stress rather than the anoxia and freezing tolerant species I have described. In addition, the broad range of induced genes makes it impossible to hypothesize which will be up-regulated in L. littorea.

The aim of this on-going study is therefore to identify the genes that are induced or up-regulated in the frozen and anoxic condition of L. littorea. To do this, cDNA libraries constructed from the foot-muscle of freeze- and anoxia- exposed animals were differentially screened with 32P-labelled, single stranded cDNA probes from control vs stressed animals. Presented in this poster are some preliminary results.

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