Li Yao-Feng, Chen Xiang-Yun, Zhang Chun-Dong, Tang Xiao-Fang, Wang La, Liu Tai-Hang, Pan Min-Hui, Lu Cheng
State Key Laboratory of Silkworm Genome Biology, Southwest University, Chongqing, China.
Department of Biochemistry and Molecular Biology, Chongqing Medical University, Chongqing, China.
Insect Sci. 2016 Aug;23(4):569-78. doi: 10.1111/1744-7917.12199. Epub 2015 May 6.
Silk gland cells of silkworm larvae undergo multiple cycles of endomitosis for the synthesis of silk proteins during the spinning phase. In this paper, we analyzed the endomitotic DNA synthesis of silk gland cells during larval development, and found that it was a periodic fluctuation, increasing during the vigorous feeding phase and being gradually inhibited in the next molting phase. That means it might be activated by a self-regulating process after molting. The expression levels of cyclin E, cdt1 and pcna were consistent with these developmental changes. Moreover, we further examined whether these changes in endomitotic DNA synthesis resulted from feeding or hormonal stimulation. The results showed that DNA synthesis could be inhibited by starvation and re-activated by re-feeding, and therefore appears to be dependent on nutrition. DNA synthesis was suppressed by in vivo treatment with 20-hydroxyecdysone (20E). However, there was no effect on DNA synthesis by in vitro 20E treatment or by either in vivo or in vitro juvenile hormone treatment. The levels of Akt and 4E-BP phosphorylation in the silk glands were also reduced by starvation and in vivo treatment with 20E. These results indicate that the activation of endomitotic DNA synthesis during the intermolt stages is related to feeding and DNA synthesis is inhibited indirectly by 20E.
家蚕幼虫的丝腺细胞在吐丝阶段会经历多次核内有丝分裂周期以合成丝蛋白。在本文中，我们分析了幼虫发育过程中丝腺细胞的核内有丝分裂DNA合成情况，发现其呈周期性波动，在旺盛摄食阶段增加，在下一次蜕皮阶段逐渐受到抑制。这意味着它可能在蜕皮后通过自我调节过程被激活。细胞周期蛋白E、cdt1和增殖细胞核抗原的表达水平与这些发育变化一致。此外，我们进一步研究了这些核内有丝分裂DNA合成的变化是由摄食还是激素刺激引起的。结果表明，饥饿可抑制DNA合成，重新喂食可使其重新激活，并因此似乎依赖于营养。体内用20-羟基蜕皮酮（20E）处理可抑制DNA合成。然而，体外20E处理或体内或体外保幼激素处理对DNA合成均无影响。饥饿和体内用20E处理也会降低丝腺中Akt和4E-BP的磷酸化水平。这些结果表明，蜕皮间期核内有丝分裂DNA合成的激活与摄食有关，且DNA合成受到20E的间接抑制。
