Mitochondrial gene transcription and genome copy number in freeze tolerant larvae of the Arctic woolly bear caterpillar, Gynaephor groenlandica, and the Goldenrod gall fly, Eurosta solidaginis
Date
2001
Authors
Barber, Sarah Anne
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Abstract
The Arctic woolly bear caterpillar, Gynaephora groenlandica, and Goldenrod gall fly, Eurosta solidaginis, are two species of freeze tolerant insects. Both use a system of cryoprotectants and reduced metabolism characteristic of diapause to enhance cold hardiness. Mitochondrial degradation was previously suggested as an adaptive response to cold in Gynaephora, and postulated to occur in Eurosta. Molecular analyses were used to examine mitochondrial gene transcription and to analyze changes in mitochondrial copy number during cold hardiness in both species. Epifluorescent microscopy using bisbenzimide, a DNA specific chromophore, showed increased maximum mitochondrial density in fat body cells of winter collected Eurosta larvae held at l0°C compared to cells from fall collected larvae. Northern analysis using mitochondrial specific probes, cytochrome oxidase and 16S ribosomal RNA, demonstrated increased high molecular weight transcripts in winter collected Eurosta larvae, while in Gynaephora processed mitochondrial transcripts were more abundant in cold adapted larvae. Northern blot results were consistent with increased RNA stability with cold adaptation in both Eurosta and Gynaephora, although different mechanisms were suggested. Dot blot analyses indicated that mitochondrial genome copy number was reduced in cold adapted Gynaephora larvae, but that there was no decrease in copy number in Eurosta cold adapted larvae. Restriction digests of total DNA from Eurosta, Gynaephora, and Drosophila hybridized with mitochondrial probes indicated the presence of mitochondrial derived sequences in nuclear genomes.