Division of Life Sciences, Graduate School of Natural Science and Technology, Kanazawa University, Kakumamachi, Kanazawa 920-1192, Japan.
J Insect Physiol. 2011 Dec;57(12):1715-22. doi: 10.1016/j.jinsphys.2011.09.013. Epub 2011 Sep 25.
In holometabolus insects, morphology of the larval fat body is remodeled during metamorphosis. In higher Diptera, remodeling of the fat body is achieved by cell death of larval fat body cells and differentiation of the adult fat body from primordial cells. However, little is known about remodeling of the fat body at pupal metamorphosis in Lepidoptera. In this study, we found that cell death of the larval fat body in Bombyx mori occurs at shortly after pupation. About 30% of the fat body cells underwent cell death on days 1 and 2 after pupation. The cell death involved genomic DNA fragmentation, a characteristic of apoptosis. Surgical manipulation and in vitro culture of fat body cells revealed that 20-hydroxyecdysone and juvenile hormone had no effect on either initiation or progression of cell death. During cell death, a large increase in activity of caspase-3, a key enzyme of cell death, was observed. Western blot analysis of the active form of caspase-3-like protein revealed that the length of caspase-3 of B. mori was much larger than that of caspase-3 in other species. The results suggest that larval fat body cells of B. mori are removed through cell death, which is mediated by a caspase probably categorized in a novel family.
在全变态昆虫中，幼虫脂肪体的形态在变态期间会发生重塑。在较高等的双翅目昆虫中，脂肪体的重塑是通过幼虫脂肪体细胞的细胞死亡和原始细胞分化为成虫脂肪体来实现的。然而，关于鳞翅目昆虫蛹变态时脂肪体的重塑，人们知之甚少。在本研究中，我们发现家蚕幼虫脂肪体的细胞死亡发生在刚化蛹后不久。大约 30%的脂肪体细胞在化蛹后第 1 天和第 2 天发生细胞死亡。细胞死亡涉及基因组 DNA 片段化，这是凋亡的特征。对脂肪体细胞的手术操作和体外培养表明，20-羟基蜕皮酮和保幼激素对细胞死亡的起始或进展均无影响。在细胞死亡过程中，观察到 caspase-3（细胞死亡的关键酶）的活性大大增加。对家蚕活性形式的 caspase-3 样蛋白的 Western blot 分析表明，家蚕 caspase-3 的长度比其他物种的 caspase-3 长得多。这些结果表明，家蚕幼虫脂肪体细胞通过可能属于新型家族的 caspase 介导的细胞死亡被清除。
