Differential expression of cold- and diet-specific genes encoding two isoforms of the ∆9-acyl-CoA desaturase in carp liver

Carp respond to cold by the up-regulated expression of ∆9-acyl CoA desaturase. Here we report the cloning and characterisation of Cds2, a second ∆9-acyl CoA desaturase expressed in carp liver. Both Cds1 and Cds2 complemented the ole1 mutation in Saccharomyces cerevisiae, permitting the synthesis of ∆9 monounsaturates, confirming their identity as ∆9-desaturases. We demonstrate that under a standard feeding regime it is the Cds2, and not Cds1, transcript that is transiently up-regulated during the first few days of cooling from 30oC to 10oC, the period when cold-induced membrane restructuring occurs. Cds2 exists as two differentially spliced transcripts, differing by a small segment from the 3' untranslated region, the ratio of which varies with temperature. Feeding a diet enriched in saturated fats produced a four-fold increase in Cds1 transcript levels, which was blocked by cooling to 15oC. Cds2 transcript levels, however, showed no substantial response to the saturated diet. Thus carp liver uniquely expresses two isoforms of ∆9-acyl CoA desaturase, possibly formed by a recent duplication event, that are differentially regulated by cooling and dietary treatment.