a Key Laboratory of Insect Developmental and Evolutionary Biology , Institute of Plant Physiology and Ecology, Chinese Academy of Sciences , Shanghai , China.
b Department of Neurosciences , College of Life Sciences, Shanghai University , Shanghai , China.
Cell Cycle. 2017;16(21):2156-2167. doi: 10.1080/15384101.2017.1376148. Epub 2017 Sep 21.
Integuments are the first line to protect insects from physical damage and pathogenic infection. In lepidopteran insects, they undergo distinct morphology changes such as scale formation during metamorphosis. However, we know little about integument development and scale formation during this stage. Here, we use the silkworm, Bombyx mori, as a model and show that stem cells in the integument of each segment, but not intersegmental membrane, divide into two scale precursor cells during the spinning stage. In young pupae, the scale precursor cell divides again. One of the daughter cells becomes a mature scale-secreting cell that undergoes several rounds of DNA duplication and the other daughter cell undergoes apoptosis later on. This scale precursor cell division is crucial to the development and differentiation of scale-secreting cells because scale production can be blocked after treatment with the cell division inhibitor paclitaxel. Subsequently, the growth of scale-secreting cells is under the control of 20-hydroxyecdysone but not juvenile hormone since injection of 20-hydroxyecdysone inhibited scale formation. Further work demonstrated that 20-hydroxyecdysone injection inhibits DNA duplication in scale-secreting cells while the expression of scale-forming gene ASH1 was down-regulated by BR-C Z2. Therefore, this research demonstrates that the scale cells of the silkworm develops through stem cell division prior to pupation and then another wave of cell division differentiates these cells into scale secreting cells soon after entrance into the pupal stage. Additionally, DNA duplication and scale production in the scale-secreting cells were found to be under the regulation of 20-hydroxyecdysone.
表皮是昆虫抵御物理损伤和病原感染的第一道防线。在鳞翅目昆虫中，它们在变态过程中经历明显的形态变化，如鳞片形成。然而，我们对这一阶段的表皮发育和鳞片形成知之甚少。在这里，我们以家蚕为模型，表明每个体节的表皮干细胞，但不是节间膜，在吐丝期分裂为两个鳞片前体细胞。在幼蛹中，鳞片前体细胞再次分裂。一个子细胞成为一个成熟的分泌鳞片的细胞，经历几次 DNA 复制，另一个子细胞随后凋亡。这种鳞片前体细胞分裂对于分泌鳞片细胞的发育和分化至关重要，因为用细胞分裂抑制剂紫杉醇处理后可以阻止鳞片的产生。随后，分泌鳞片细胞的生长受 20-羟基蜕皮酮的控制，而不是保幼激素，因为注射 20-羟基蜕皮酮抑制了鳞片的形成。进一步的工作表明，20-羟基蜕皮酮注射抑制了分泌鳞片细胞的 DNA 复制，而 BR-C Z2 下调了形成鳞片基因 ASH1 的表达。因此，这项研究表明，家蚕的鳞片细胞在化蛹前通过干细胞分裂发育，然后在进入蛹期后，又经历一波细胞分裂将这些细胞分化为分泌鳞片的细胞。此外，还发现分泌鳞片细胞中的 DNA 复制和鳞片产生受 20-羟基蜕皮酮的调节。
