HIF-1α involvement in low temperature and anoxia survival by a freeze tolerant insect

Winter survival for many insect species relies on the ability to endure the freezing of extracellular body fluids. Because freezing impedes oxygen delivery to tissues, one component of natural freeze tolerance is a well-developed anoxia/ischemia resistance. The present study explores the responses of the hypoxia-inducible factor-1 alpha (HIF-1 alpha) to cold, freezing and anoxia exposures in the freeze tolerant goldenrod gall fly larva, Eurosta solidaginis. Reverse transcription-PCR was used to quantify hif-1 alpha transcript levels; transcripts were significantly elevated by similar to 70% in chilled (3 degrees C), frozen (-16 degrees C) and thawed (returned to 3 degrees C) insects, compared with 15 degrees C controls. Transcripts also rose by similar to 3-fold in insects given anoxia exposure under a nitrogen gas atmosphere. Cold and freezing exposure also elevated HIF-1 alpha protein content in the larvae and HIF-1 alpha levels increased over the winter months in insects sampled from an outdoor population; levels peaked in February at 2.1-fold higher than in September. A partial sequence of HIF-1 alpha that covers the bHLH and PAS domains of the protein was obtained from E. solidaginis and sequence analysis revealed that this segment shared 62% identity overall with Drosophila melanogaster HIF-1 alpha and higher percent identities within specific domains: 76% within the bHLH domain and 70% within the PAS domain. The data provide the first documentation of a potential role for HIF-1 in regulating the expression of genes that can aid freezing survival in a cold-hardy animal.