Ismail S M, Satyanarayana K, Bradfield J Y, Dahm K H, Bhaskaran G
Department of Biology, Texas A&M University, College Station, USA.
Arch Insect Biochem Physiol. 1998;37(4):305-14. doi: 10.1002/(SICI)1520-6327(1998)37:4<305::AID-ARCH6>3.0.CO;2-P.
In the tobacco hornworm (Manduca sexta), vitellogenin (Vg), the major yolk protein precursor, and its mRNA are first detectable in the prepupal stage; and production of both can be enhanced by methoprene, a juvenile hormone (JH) analog. Competence to respond to methoprene is acquired after ecdysteroid-initiated commitment for metamorphosis. Here we show that acquisition of competence requires prior exposure to JH-II acid in addition to ecdysteroid. Application of 20-hydroxyecdysone or RH5992, an ecdysteroid analog, to isolated abdomens from feeding larvae (precommitment) results in exposure of the dorsal vessel (EDV), a sign of metamorphic commitment--but such abdomens do not make Vg in response to methoprene. However, injection of JH-II acid along with 20-hydroxyecdysone into isolated abdomens causes Vg production in response to methoprene. Methoprene acid similarly induces competence to respond to methoprene. Northern blot analysis confirmed that Vg transcripts are present in fat body only if isolated abdomens were pretreated with both ecdysteroid, and JH-II acid or methoprene acid. The latter two can induce competence even in precocious prepupae resulting from removal of the corpora allata (the glands that produce JH) from early penultimate larvae. JH-III acid and related metabolites such as farnesol, farnesoic acid, and methyl farnesoate do not induce competence. Hitherto, JH acids have been regarded as precursors or catabolites of JHs. Here we show for the first time that JH acid has a hormonal function that cannot be performed by JH itself.
在烟草天蛾（烟草天蛾）中，卵黄原蛋白（Vg）作为主要的卵黄蛋白前体，其及其mRNA最早在蛹前期可被检测到；并且两者的产生都可被甲氧普烯（一种保幼激素（JH）类似物）增强。对甲氧普烯作出反应的能力是在蜕皮甾类引发变态发育的决定之后获得的。在此我们表明，除了蜕皮甾类之外，获得这种能力还需要事先接触JH-II酸。将20-羟基蜕皮酮或蜕皮甾类类似物RH5992应用于取食幼虫（未决定变态发育）分离出的腹部会导致背血管暴露（EDV），这是变态发育决定的一个标志——但这样的腹部不会因甲氧普烯而产生Vg。然而，将JH-II酸与20-羟基蜕皮酮一起注射到分离出的腹部会导致因甲氧普烯而产生Vg。甲氧普烯酸同样可诱导对甲氧普烯作出反应的能力。Northern印迹分析证实，只有当分离出的腹部用蜕皮甾类以及JH-II酸或甲氧普烯酸进行预处理时，脂肪体中才会存在Vg转录本。后两者甚至可在因从倒数第二龄早期幼虫摘除咽侧体（产生JH的腺体）而导致的早熟蛹前期中诱导产生这种能力。JH-III酸以及相关代谢物如法尼醇、法尼酸和法尼酸甲酯不会诱导产生这种能力。迄今为止，JH酸一直被视为JH的前体或分解代谢产物。在此我们首次表明，JH酸具有一种JH自身无法行使的激素功能。
