Stauber M, Taubert H, Schmidt-Ott U
Max-Planck-Institut für Biophysikalische Chemie, Abteilung Molekulare Entwicklungsbiologie, Am Fassberg 11, D-37077 Göttingen, Germany.
Proc Natl Acad Sci U S A. 2000 Sep 26;97(20):10844-9. doi: 10.1073/pnas.190095397.
The Drosophila gene bicoid functions at the beginning of a gene cascade that specifies anterior structures in the embryo. Its transcripts are localized at the anterior pole of the oocyte, giving rise to a Bicoid protein gradient, which regulates the spatially restricted expression of target genes along the anterior-posterior axis of the embryo in a concentration-dependent manner. The morphogen function of Bicoid requires the coactivity of the zinc finger transcription factor Hunchback, which is expressed in a Bicoid-dependent fashion in the anterior half of the embryo. Whereas hunchback is conserved throughout insects, bicoid homologs are known only from cyclorrhaphan flies. Thus far, identification of hunchback and bicoid homologs rests only on sequence comparison. In this study, we used double-stranded RNA interference (RNAi) to address the function of bicoid and hunchback homologs in embryos of the lower cyclorrhaphan fly Megaselia abdita (Phoridae). Megaselia-hunchback RNAi causes hunchback-like phenotypes as observed in Drosophila, but Megaselia-bicoid RNAi causes phenotypes different from corresponding RNAi experiments in Drosophila and bicoid mutant embryos. Megaselia-bicoid is required not only for the head and thorax but also for the development of four abdominal segments. This difference between Megaselia and Drosophila suggests that the range of functional bicoid activity has been reduced in higher flies.
果蝇的双尾基因在决定胚胎前部结构的基因级联反应开始时发挥作用。其转录本定位于卵母细胞的前极，产生双尾蛋白梯度，该梯度以浓度依赖的方式调节胚胎前后轴上靶基因的空间限制表达。双尾的形态发生素功能需要锌指转录因子驼背的协同作用，驼背在胚胎前半部分以双尾依赖的方式表达。虽然驼背在整个昆虫中是保守的，但双尾同源物仅在环裂亚目蝇类中已知。到目前为止，驼背和双尾同源物的鉴定仅基于序列比较。在这项研究中，我们使用双链RNA干扰（RNAi）来研究双尾和驼背同源物在低等环裂亚目蝇类大跗鬃蝇（蚤蝇科）胚胎中的功能。大跗鬃蝇驼背RNAi会导致类似果蝇中观察到的驼背样表型，但大跗鬃蝇双尾RNAi会导致与果蝇相应RNAi实验和双尾突变胚胎不同的表型。大跗鬃蝇双尾不仅对头和胸的发育是必需的，而且对四个腹节的发育也是必需的。大跗鬃蝇和果蝇之间的这种差异表明，在高等蝇类中，功能性双尾活性的范围已经缩小。
