Suzuki Takumi, Sakurai Sho, Iwami Masafumi
Division of Life Sciences, Graduate School of Natural Science and Technology, Kanazawa University, Kakuma-machi, Kanazawa 920-1192, Japan.
J Insect Physiol. 2009 Mar;55(3):250-4. doi: 10.1016/j.jinsphys.2008.11.014. Epub 2009 Jan 4.
Holometabolous insects do not excrete but store metabolic wastes during the pupal period. The waste is called meconium and is purged after adult emergence. Although the contents of meconium are well-studied, the developmental and physiological regulation of meconium accumulation is poorly understood. In Bombyx mori, meconium is accumulated in the rectal sac; thereby, the rectal sac distends at the late pupal stage. Here, we show that rectal sac distention occurs between 4 and 5 days after pupation. The distention is halted by brain-removal just after larval-pupal ecdysis but not by brain-removal 1 day after pupation. In the pupae, brain-removal just after ecdysis kept the hemolymph ecdysteroid titer low during early and mid-pupal stages. An injection of 20-hydroxyecdysone (20E) evoked the distention that was halted by brain-removal in a dose-dependent manner. Therefore, brain-removal caused the lack of ecdysteroid, and rectal sac distention did not appear in the brain-removed pupae because of the lack of ecdysteroid. We conclude that rectal sac distention is one of the developmental events regulated by 20E during the pupal period in B. mori.
全变态昆虫在蛹期并不排泄，而是储存代谢废物。这些废物被称为蛹便，在成虫羽化后排出。尽管对蛹便的成分已有充分研究，但对蛹便积累的发育和生理调节却知之甚少。在家蚕中，蛹便积聚在直肠囊中；因此，直肠囊在蛹后期会膨胀。在此，我们表明直肠囊膨胀发生在化蛹后4至5天之间。刚在幼虫-蛹蜕皮后摘除脑会阻止这种膨胀，但在化蛹1天后摘除脑则不会。在蛹中，蜕皮后立即摘除脑会使蛹早期和中期的血淋巴蜕皮甾类激素滴度保持较低水平。注射20-羟基蜕皮酮（20E）会引发一种膨胀，这种膨胀会被摘除脑以剂量依赖的方式阻止。因此，摘除脑导致蜕皮甾类激素缺乏，并且由于缺乏蜕皮甾类激素，在摘除脑的蛹中直肠囊膨胀并未出现。我们得出结论，直肠囊膨胀是家蚕蛹期由20E调节的发育事件之一。
