Heat Inducible Expression of Antifreeze Protein Genes from the Beetles Tenebrio molitor and Microdera punctipennis

BACKGROUND: Antifreeze proteins (AFPs) play important roles in protecting poikilothermic organisms from cold damage. The expression of AFP genes (afps) is induced by low temperature. However, it is reported that heat can influence the expression of afps in the desert beetle Microdera punctipennis. OBJECTIVE: To further detect whether heat also induce the expression of afps in other insects, and to determine the expression profiling of insect afps at different temperatures. MATERIALS AND METHODS: The expression of antifreeze protein genes in the two beetles, Microdera punctipennis and Tenebrio molitor that have quite different living environment, under different temperatures were studied by using real–time quantitative PCR. RESULTS: Mild low temperatures (5°C∼15°C), high temperature (38°C∼47°C for M. punctipennis, or 37°C∼42°C for T. molitor) and temperature difference (10°C∼30°C) all stimulated strongly to the expression of AFP genes (Mpafps) in M. punctipennis which lives in the wild filed in desert. The mRNA level of Mpafps after M. punctipennis were exposed to these temperatures for 1h∼5h was at least 30-fold of the control at 25°C. For T. molitor which is breeding in door with wheat bran all these temperatures stimulated significantly to the expression of Tmafps, while the extent and degree of the temperature stimulation on Tmafps expression were much lower than on Mpafps. After T. molitor were exposed to 5°C and 15°C for 1h∼5h, the mRNA level of Tmafps was over 6-fold and 45-fold of the control at 25°C. High temperature (37°C∼42°C) for 1h∼3h treatments increased Tmafps mRNA level 4.8-fold of the control. Temperature difference of 10°C was effective in stimulating Tmafps expression. CONCLUSION: The expression of insect antifreeze protein genes both in M. punctipennis and T. molitor was induced by heat, suggesting that this phenomenon may be common in insects; the extent and degree of the influence differ in species that have different living conditions. The heat inducible expression of antifreeze protein genes hints that antifreeze proteins may involve in other functions except for antifreeze.