Increased levels of mitochondrial gene transcripts in the thermally selected rainbow trout (Oncorhynchus mykiss) strain during embryonic development.

To investigate molecular mechanisms involved in thermal resistance of rainbow trout, Oncorhynchus mykiss, embryos from thermally selected strain in various developmental stages were treated at 22 degrees C for 30 min and subsequently developed at 12 degrees C using the Donaldson strain as a reference. The embryos were evaluated for their hatching rate along with the ratio of embryos having an abnormal appearance and subjected to mRNA arbitrarily primed reverse transcription-polymerase chain reaction (RAP RT-PCR). One of the genes dominantly expressed in the thermally selected strain (COX II) coded for cytochrome c oxidase subunit II. Northern blot analysis revealed that the accumulated levels of COX II transcripts were more abundant in embryos and unfertilized eggs from the thermally selected strain than those from the Donaldson strain. Furthermore, the differential expression patterns of the ATPase 6-8 gene were similar to those of the COX II gene, whereas the ATP synthase beta-subunit gene showed no significant differences between the two strains.