Pankratz M J, Hoch M, Seifert E, Jäckle H
Institut für Genetik und Mikrobiologie, München, FRG.
Nature. 1989 Sep 28;341(6240):337-40. doi: 10.1038/341337a0.
Segmental pattern formation in Drosophila proceeds in a hierarchical manner whereby the embryo is stepwise divided into progressively finer regions until it reaches its final metameric form. Maternal genes initiate this process by imparting on the egg a distinct antero-posterior polarity and by directing from the two polar centres the activities of the zygotic genes. The anterior system is strictly dependent on the product of the maternal gene bicoid (bcd), without which all pattern elements in the anterior region of the embryo fail to develop. The posterior system seems to lack such a morphogen. Rather, the known posterior maternal determinants simply define the boundaries within which abdominal segmentation can occur, and the process that actively generates the abdominal body pattern may be entirely due to the interactions between the zygotic genes. The most likely candidates among the zygotic genes that could fulfil the role of initiating the posterior pattern-forming process are the gap genes, as they are the first segmentation genes to be expressed in the embryo. Here we describe the interactions between the gap genes Krüppel (Kr), knirps (kni) and tailless (tll). We show that kni expression is repressed by tll activity, whereas it is directly enhanced by Kr activity. Thus, Kr activity is present throughout the domain of kni expression and forms a long-range protein gradient, which in combination with kni activity is required for abdominal segmentation of the embryo.
果蝇的体节模式形成以一种分级的方式进行，胚胎在此过程中被逐步划分为越来越精细的区域，直至达到其最终的体节形式。母体基因通过赋予卵子明显的前后极性，并从两个极性中心指导合子基因的活性来启动这一过程。前部系统严格依赖于母体基因双胸（bcd）的产物，没有该产物，胚胎前部区域的所有模式元素都无法发育。后部系统似乎缺乏这样一种形态发生素。相反，已知的后部母体决定因素只是定义了腹部体节形成可以发生的边界，而积极产生腹部身体模式的过程可能完全归因于合子基因之间的相互作用。在合子基因中，最有可能发挥启动后部模式形成过程作用的候选基因是间隙基因，因为它们是胚胎中最早表达的体节基因。在这里，我们描述了间隙基因克虏伯（Kr）、无尾（kni）和无尾（tll）之间的相互作用。我们表明，kni的表达受到tll活性的抑制，而它直接受到Kr活性的增强。因此，Kr活性存在于kni表达的整个区域，并形成一个长距离的蛋白质梯度，该梯度与kni活性一起是胚胎腹部体节形成所必需的。
