Dorsal-Ventral Polarity in the Drosophila Embryo

果蝇模式形成的一个关键步骤是沿两个主要身体轴建立极性。至少有20个母系活性基因参与了背腹极性的形成。各种实验表明，背侧染色体代表了这一过程的最后一步，它作为腹侧形态原，将母体的位置信息与合子基因组联系起来。Steward博士克隆并鉴定了背侧基因，发现它与脊椎动物原癌基因c-rel密切相关。在野生型胚胎中，卵裂时细胞质中存在背侧蛋白。细胞核迁移到胚胎外围后，细胞核背侧蛋白的腹侧到背侧梯度建立。核梯度的形成在其他母体活跃的背-腹极性基因的突变胚胎中被破坏。在背侧化的突变胚中，只观察到细胞质蛋白，而在腹侧化的胚胎中，核梯度向背侧移动。背侧蛋白从细胞质到细胞核的重新定位似乎对背侧作为形态发生的功能至关重要。Steward博士提出了一系列的实验，以解决哪些基因与背侧相互作用以影响细胞质与核定位的问题，或者一旦蛋白质进入细胞核，哪些基因对背侧功能至关重要。具体来说，她将进行遗传筛选，以分离特定背侧突变的第二位点抑制子。

A critical step in pattern formation in Drosophila is the establishment of polarity along the two major body axes. At least 20 maternally active genes are involved in creating dorsal- ventral polarity. A variety of experiments have shown that dorsal represents the last step in the process, it acts as the ventral morphogen relating the maternal positional information to the zygotic genome. Dr. Steward has cloned and characterized the dorsal gene and found it is closely related to the vertebrate proto-oncogene c-rel. In wild type embryos, the dorsal protein is present in the cytoplasm during cleavage. After the nuclei migrate to the periphery of the embryo, a ventral to dorsal gradient of nuclear dorsal protein is established. The formation of the nuclear gradient is disrupted in mutant embryos from other maternally active dorsal-ventral polarity genes. In dorsalized mutant embryos, only cytoplasmic protein is observed, while in ventralized embryos, the nuclear gradient is shifted dorsally. Relocalization of the dorsal protein from the cytoplasm to the nucleus appears critical for dorsal to function as a morphogen. Dr. Steward proposes a number of experiments that address the question of what genes either interact with dorsal to effect the cytoplasmic versus nuclear localization or are essential for dorsal function once the protein is in the nucleus. Specifically she will perform genetic screens to isolate second site suppressors of specific dorsal mutations.