Tauchman Seth J, Lorch Jeffrey M, Orth Anthony P, Goodman Walter G
Department of Entomology, University of Wisconsin-Madison, Madison, WI 53706, USA.
Insect Biochem Mol Biol. 2007 Aug;37(8):847-54. doi: 10.1016/j.ibmb.2007.05.015. Epub 2007 Jun 2.
External stressors disrupt physiological homeostasis; in insects, the response to stress may result in delayed development as the animal attempts to restore homeostasis before proceeding with its complex life cycle. Previous studies have demonstrated that exposure to stress leads to increased levels of the juvenile hormone (JH), a hormone responsible for maintaining the insect larval state. In Manduca sexta, JH is transported to target tissue by a high-affinity binding protein, hemolymph JH binding protein (hJHBP). Since JH titers are elevated in stressed Manduca, we examined levels of hJHBP to better understand (1) the role of JH in regulating hJHBP levels and (2) the hJHBP-regulated bioavailability of hormone at the target site. Fourth stadium Manduca (48 h post-ecdysis) were exposed for 24h to various stressors including nutritional deprivation, microbial infection, cutaneous injury, episodic movement, and temperature elevation. Insects raised on diets lacking nutritional content exhibited mean hJHBP levels that were less than half (45%) those of control insects. Similarly, insects injected with Escherichia coli demonstrated a 47% reduction in hJHBP titers. Cutaneous injury, episodic movement, and temperature elevation lowered hJHBP levels by 47%, 43%, and 38%, respectively. Total hemolymph protein concentration was not affected. After a stress event (injury), a 50% reduction in abundance of fat body hJHBP mRNA was observed within 4h; hJHBP levels did not drop until 24h after injury. Stress in the fourth stadium was manifest in fifth instars, with 100% of the injured insects displaying an extended larval stadium or failing to pupate. Computational modeling of the JH-hJHBP interaction indicates that unbound JH doubles in stressed insects. These results indicate that in response to stress larval hJHBP titers are significantly reduced, increasing JH bioavailability at the target site and thereby impacting development and survival of the insect. Treatment of unstressed insects with physiological doses of JH I did not affect hJHBP levels, suggesting that elevated JH levels were not solely responsible for the observed down-regulation in stressed insects.
外部应激源会破坏生理稳态；在昆虫中，应激反应可能导致发育延迟，因为动物在继续其复杂的生命周期之前会试图恢复稳态。先前的研究表明，暴露于应激会导致保幼激素（JH）水平升高，保幼激素是一种负责维持昆虫幼虫状态的激素。在烟草天蛾中，JH通过一种高亲和力结合蛋白——血淋巴JH结合蛋白（hJHBP）被转运到靶组织。由于应激状态下烟草天蛾的JH滴度会升高，我们检测了hJHBP的水平，以便更好地了解（1）JH在调节hJHBP水平中的作用，以及（2）hJHBP调节的激素在靶位点的生物利用度。将处于第四龄期的烟草天蛾（蜕皮后48小时）暴露于各种应激源24小时，这些应激源包括营养剥夺、微生物感染、皮肤损伤、间歇性运动和温度升高。以缺乏营养成分的饲料饲养的昆虫，其hJHBP平均水平不到对照昆虫的一半（45%）。同样，注射大肠杆菌的昆虫hJHBP滴度降低了47%。皮肤损伤、间歇性运动和温度升高分别使hJHBP水平降低了47%、43%和38%。血淋巴总蛋白浓度未受影响。在应激事件（损伤）后，4小时内脂肪体hJHBP mRNA丰度降低了50%；hJHBP水平直到损伤后24小时才下降。第四龄期的应激在第五龄期表现出来，100%的受伤昆虫出现幼虫龄期延长或无法化蛹。JH-hJHBP相互作用的计算模型表明，应激昆虫中未结合的JH增加了一倍。这些结果表明，作为对应激的反应，幼虫hJHBP滴度显著降低，增加了激素在靶位点的生物利用度，从而影响昆虫的发育和存活。用生理剂量的JH I处理未受应激的昆虫不会影响hJHBP水平，这表明JH水平升高并非应激昆虫中观察到的下调的唯一原因。
