Differential gene expression in two cold hardy insects in response to low temperatures
The two cold hardy gall insects, Epiblema scudderiana andEurosta solidaginis, employ freeze avoidance and freeze tolerance, respectively, in coping with low seasonal temperatures. Biochemical and metabolic changes in these animals in response to low temperatures have been well documented, but the possibility that cold and subzero temperatures could upregulate genes in these animals has not been investigated. In this study, cDNA library screening and differential display PCR were used to address this question. Animals were sampled over a successive cold (2 weeks at 4°C) and subzero temperature (one week at -20°C) time course. Differential screening/PCR against RNA from control (15°C) animals and Northern analyses revealed a number of upregulated transcripts. All clones were sequenced, and all but two were unidentifiable through GenBank database comparisons, due to the novel and incomplete nature of their sequences. The two identifiable sequences had strong homologies to Drosophila genes mlp6OA andrpAl, encoding respectively, a factor crucial for myogenesis and an acidic ribosomal protein. Implicated in embryonic and adult development, the upregulation of these genes suggests a unique developmental regime in E. scudderiana and F. solidaginis,both of which overwinter as final instar larvae. These animals may be preparing in advance for impending morphogenic changes, allowing for a head-start with the onset of spring.