Synchronized Expression of Two Caspase Family Genes, ice-2 and ice-5, in Hydrogen Peroxide-Induced Cells of the Silkworm, Bombyx mori

Caspase family proteins play important roles in different stages of the apoptotic pathway. To date, however, functions of Bombyx mori L. (Lepidoptera: Bombycidae) caspase family genes are poorly known. This paper focuses on the morphology, mitochondrial membrane potential, and expression profiles of two novel B. mori caspase family genes (ice-2 and ice-5) in 3 µM hydrogen peroxide (H(2)O(2)) damaged B. mori cells, which were separated from the ovary of B. mori. In addition, comparisons were made between damage caused by H(2)O(2) and by ultraviolet (UV) irradiation. The results showed that the potential change of the mitochondrial membrane occurred at 0.5 h after H(2)O(2) stimulation, which was sooner than occurred in the UV treated model where the obvious decrease appeared at 6 h after stimulation. In addition, the total change in the potential of the mitochondrial membrane in H(2)O(2) treated B. mori cells was larger than with UV treated cells during the whole process. Analysis of fluorescent quantitative real-time PCR demonstrated that ice-2 and ice-5 might be involved in both H(2)O(2) and UV-induced apoptosis in B. mori cells. Notably, after exposure to H(2)O(2), the expression patterns of ice-5 were remarkably higher than those of ice-2, while the result was the opposite after exposure to UV irradiation. The data indicate that apoptosis induced by H(2)O(2) was directly related to the mitochondrial pathway. The two isoforms of B. mori ice may play different roles in the mitochondrion associated apoptotic pathway in B. mori cells, and the apoptotic pathway in H(2)O(2) induced B. mori cells is different from the UV induced apoptotic pathway.