Baehrecke E H, Thummel C S
Howard Hughes Medical Institute, University of Utah, Salt Lake City 84112.
Dev Biol. 1995 Sep;171(1):85-97. doi: 10.1006/dbio.1995.1262.
Pulses of ecdysteroids induce dramatic changes in gene expression that direct the early stages of Drosophila metamorphosis. This gene activity is reflected by the appearance of early and late puffs in the salivary gland polytene chromosomes. Curiously, the early puff genes that have been studied to date are induced by both the late larval and prepupal pulses of ecdysteroids and are expressed in many ecdysteroid target tissues, raising the question of how the hormone directs the complex stage- and tissue-specific responses associated with metamorphosis. In an effort to address this question, we have isolated and characterized the E93 gene responsible for the stage-specific 93F early puff. The E93 mRNA displays no response to ecdysteroids in late larval salivary glands but is directly induced 12 hr later by the prepupal ecdysteroid pulse, identical to the response of the 93F puff. In tissues other than the salivary gland, however, E93 displays complex spatial and temporal regulation. E93 spans at least 55 kb of genomic DNA and encodes a 146-kDa protein that has no matches in the sequence databases, but displays several characteristics of known Drosophila transcription factors. We propose that E93 acts in a stage-specific regulatory hierarchy in the salivary gland to direct its histolysis in response to the prepupal ecdysteroid pulse.
蜕皮甾类脉冲会引发基因表达的显著变化，这些变化指导着果蝇变态发育的早期阶段。这种基因活性通过唾液腺多线染色体上早期和晚期胀泡的出现得以体现。奇怪的是，迄今为止所研究的早期胀泡基因是由蜕皮甾类的晚期幼虫期脉冲和蛹前期脉冲共同诱导产生的，并且在许多蜕皮甾类靶组织中表达，这就引发了一个问题：激素是如何指导与变态发育相关的复杂的阶段特异性和组织特异性反应的。为了解决这个问题，我们分离并鉴定了负责阶段特异性93F早期胀泡的E93基因。E93 mRNA在晚期幼虫唾液腺中对蜕皮甾类没有反应，但在蛹前期蜕皮甾类脉冲12小时后被直接诱导，这与93F胀泡的反应相同。然而，在唾液腺以外的组织中，E93表现出复杂的时空调节。E93跨越至少55 kb的基因组DNA，编码一种146 kDa的蛋白质，该蛋白质在序列数据库中没有匹配项，但具有已知果蝇转录因子的几个特征。我们提出，E93在唾液腺中以阶段特异性的调控层级发挥作用，以响应蛹前期蜕皮甾类脉冲来指导其组织溶解。
