Snee Mark J, Harrison Dianne, Yan Nan, Macdonald Paul M
Section of Molecular, Cell, and Developmental Biology, Institute for Cellular and Molecular Biology, University of Texas, Austin, TX 78712, USA.
Differentiation. 2007 Mar;75(3):246-55. doi: 10.1111/j.1432-0436.2006.00136.x.
In Drosophila, posterior embryonic body patterning and germ cell formation rely on Oskar, a protein that is concentrated at the posterior pole of the oocyte. A program of mRNA localization and translational regulation ensures that Oskar is only expressed at the proper location. One key regulatory factor is Bruno, which represses translation of oskar mRNA before its localization. Ectopic expression of a bruno cDNA prolongs repression, even after oskar mRNA is localized, and posterior body patterning is efficiently and selectively blocked. Surprisingly, the initial accumulation of Oskar, while frequently reduced, is not eliminated, arguing that levels of Oskar previously thought to be sufficient for patterning do not suffice, or that Bruno acts at a downstream step in patterning. Expression of the bruno cDNA does not inhibit posterior patterning when Oskar is expressed independent of Bruno-mediated regulation, ruling out a downstream requirement for Bruno. Notably, an Oskar::GFP reporter protein reveals continual accumulation during the late phases of oogenesis. Taken together, these results strongly argue that a late phase in accumulation of Osk protein, typically not monitored because of imperviousness of late stage oocytes to antibodies, is crucial for body patterning.
在果蝇中，胚胎身体后部的模式形成和生殖细胞的形成依赖于 Oskar 蛋白，该蛋白集中在卵母细胞的后极。一个 mRNA 定位和翻译调控程序确保 Oskar 仅在合适的位置表达。一个关键的调控因子是 Bruno，它在 oskar mRNA 定位之前抑制其翻译。即使在 oskar mRNA 定位后，Bruno cDNA 的异位表达仍会延长抑制作用，并且身体后部的模式形成会被有效且选择性地阻断。令人惊讶的是，Oskar 的初始积累虽然经常减少，但并未消除，这表明之前认为足以进行模式形成的 Oskar 水平并不足够，或者 Bruno 在模式形成的下游步骤起作用。当 Oskar 独立于 Bruno 介导的调控进行表达时，Bruno cDNA 的表达不会抑制身体后部的模式形成，排除了 Bruno 在下游的需求。值得注意的是，一个 Oskar::GFP 报告蛋白显示在卵子发生的后期阶段持续积累。综上所述，这些结果有力地表明，由于晚期卵母细胞对抗体不敏感，通常未被监测到的 Osk 蛋白积累的后期阶段对于身体模式形成至关重要。
