Yamada Nobuto, Okamoto Naoki, Kataoka Hiroshi, Mizoguchi Akira
Division of Biological Science, Graduate School of Science, Nagoya University, Nagoya, Japan.
Department of Integrated Biosciences, Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa, Chiba, Japan.
PLoS One. 2016 Jan 8;11(1):e0146619. doi: 10.1371/journal.pone.0146619. eCollection 2016.
Diapause, a programmed developmental arrest at a specific stage, is common in insects and is regulated by hormones. It is well established that in pupal diapause, cessation of ecdysteroid secretion from the prothoracic glands (PGs) after pupal ecdysis leads to diapause initiation, while resumption of its secretion induces post-diapause development. However, what regulates the activity of the glands is poorly understood, especially for the glands of diapause-terminated pupae. In the present study, we investigate the mechanisms by which post-diapause development is regulated in the cabbage armyworm Mamestra brassicae. We demonstrate that the brain is necessary for the initiation of post-diapause development and that the factor in the brain responsible for the activation of the PGs is the prothoracicotropic hormone (PTTH). Further, through measuring the hemolymph PTTH titers by time-resolved fluoroimmunoassay, we show that PTTH is actually released into the hemolymph prior to the activation of the PGs. Although its peak titer is much lower than expected, this low concentration of PTTH is most likely still effective to activate the PGs of post-diapause pupae, because the responsiveness to PTTH of the glands at this stage is very high compared to that of nondiapause pupal PGs. These results strongly suggest that in M. brassicae, PTTH serves as a trigger to initiate pupa-adult development after diapause termination by stimulating the PGs to secrete ecdysteroid.
滞育是昆虫在特定阶段发生的一种程序性发育停滞现象，受激素调节。众所周知，在蛹滞育过程中，蛹化后前胸腺（PGs）停止分泌蜕皮甾体激素会导致滞育开始，而其分泌的恢复则会诱导滞育后发育。然而，对于调节腺体活性的机制我们了解甚少，尤其是滞育结束后的蛹的腺体。在本研究中，我们探究了甘蓝夜蛾滞育后发育的调节机制。我们证明，大脑对于滞育后发育的启动是必需的，且大脑中负责激活前胸腺的因子是促前胸腺激素（PTTH）。此外，通过时间分辨荧光免疫分析法测量血淋巴中PTTH的滴度，我们发现PTTH实际上在激活前胸腺之前就已释放到血淋巴中。尽管其峰值滴度远低于预期，但这种低浓度的PTTH很可能仍能有效激活滞育后蛹的前胸腺，因为与非滞育蛹的前胸腺相比，此阶段腺体对PTTH的反应性非常高。这些结果有力地表明，在甘蓝夜蛾中，PTTH通过刺激前胸腺分泌蜕皮甾体激素，作为滞育结束后启动蛹到成虫发育的触发因子。
