Yasuda G K, Baker J, Schubiger G
Department of Genetics, University of Washington, Seattle 98195.
Genes Dev. 1991 Oct;5(10):1800-12. doi: 10.1101/gad.5.10.1800.
The Drosophila embryo undergoes a developmental transition during cycle 14 when it initiates asynchronous mitotic cycles and markedly increases its rate of zygotic transcription. The nucleo-cytoplasmic ratio has been proposed to be the single factor that temporally regulates this developmental transition. We altered the ratio in the embryo and analyzed the consequences on the cell cycle program and on the transcripts of specific genes. These genes were chosen because their transcripts normally undergo changes in pattern during cycle 14. We found evidence that the nucleo-cytoplasmic ratio is read and interpreted locally to regulate the cell cycle program. Based on the response of the transcripts to changes in the ratio, we found evidence that at least two classes of temporal regulatory mechanisms control these transcripts. We therefore propose two corresponding classes of transcripts: (1) nucleo-cytoplasmic ratio dependent; and (2) nucleo-cytoplasmic ratio independent or time correlated. The temporal regulation of the ratio-independent transcripts may be dependent on developmental time. We conclude that multiple modes of temporal regulation underlie the events of the developmental transition in Drosophila embryogenesis.
果蝇胚胎在第14个细胞周期期间经历发育转变，此时它开始进行异步有丝分裂周期，并显著提高其合子转录速率。核质比被认为是在时间上调节这种发育转变的单一因素。我们改变了胚胎中的核质比，并分析了其对细胞周期程序以及特定基因转录本的影响。选择这些基因是因为它们的转录本在第14个细胞周期期间通常会发生模式变化。我们发现有证据表明，核质比在局部被读取和解读，以调节细胞周期程序。基于转录本对核质比变化的反应，我们发现有证据表明至少两类时间调节机制控制这些转录本。因此，我们提出两类相应的转录本：（1）核质比依赖性；（2）核质比独立性或时间相关性。非核质比依赖性转录本的时间调节可能依赖于发育时间。我们得出结论，多种时间调节模式是果蝇胚胎发育过程中发育转变事件的基础。
