Gu Shi-Hong, Chen Chien-Hung
Department of Biology, National Museum of Natural Science, Taichung, Taiwan, China.
Chung Hwa University of Medical Technology, Taiwan, China.
Insect Sci. 2017 Apr;24(2):248-258. doi: 10.1111/1744-7917.12301. Epub 2016 Apr 1.
Previous study showed that diapause in Bombyx mori eggs can be terminated by dechorionation and that activation in the mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) in dechorionated cultured eggs is involved in diapause termination. In the present study, the possible mechanism underlying activation of ERK upon dechorionation was further investigated. Results showed that mechanical injury of diapause eggs without medium incubation also resulted in rapid increase in the phospho-ERK levels and that injury increased the phospho-ERK levels at different stages of both diapause eggs and eggs in which diapause initiation was prevented by HCl. Effects of anaerobiosis on dechorionation-stimulated phospho-ERK levels showed that the mechanical injury itself but not the dramatic increase in oxygen uptake upon injury is involved in a rapid activation of ERK. Chemical anaerobiosis on dechorionation-stimulated phospho-ERK levels and the in vivo effect of anaerobiosis showed that the supply of oxygen also plays a role in ERK signaling. In addition, injury induced the phosphorylation of c-jun N-terminal kinases (JNKs) and p38 kinase, components of two parallel MAPK pathways. A kinase assay showed a dramatic increase in JNK kinase activity in egg lysates upon injury. When newly hatched first instar larvae were injured, an increase in the phospho-ERK levels similar to that in dechorionated eggs was observed. From the results, we hypothesize that the injury-induced rapid activation of MAPK signaling, which serves as a natural signal for embryonic development, is related to diapause termination in dechorionated eggs.
先前的研究表明，家蚕卵的滞育可通过去壳终止，且去壳培养卵中丝裂原活化蛋白激酶（MAPK）/细胞外信号调节激酶（ERK）的激活参与滞育终止。在本研究中，进一步探究了去壳后ERK激活的潜在机制。结果显示，未进行培养基孵育的滞育卵的机械损伤也导致磷酸化ERK水平迅速升高，并且损伤在滞育卵以及用盐酸阻止滞育起始的卵的不同阶段均增加了磷酸化ERK水平。无氧条件对去壳刺激的磷酸化ERK水平的影响表明，是机械损伤本身而非损伤后氧气摄取的显著增加参与了ERK的快速激活。化学无氧条件对去壳刺激的磷酸化ERK水平的影响以及无氧条件的体内效应表明，氧气供应在ERK信号传导中也起作用。此外，损伤诱导了c-jun氨基末端激酶（JNKs）和p38激酶（两条平行MAPK途径的组成部分）的磷酸化。激酶分析显示损伤后卵裂解物中JNK激酶活性显著增加。当新孵化的一龄幼虫受到损伤时，观察到磷酸化ERK水平的增加与去壳卵中的增加相似。根据这些结果，我们推测损伤诱导的MAPK信号的快速激活作为胚胎发育的天然信号，与去壳卵的滞育终止有关。
