Prasad Mohit, Bajpai Ruchi, Shashidhara L S
Centre for Cellular and Molecular Biology, Uppal Road, Hyderabad, 500 007, India.
Development. 2003 Apr;130(8):1537-47. doi: 10.1242/dev.00393.
In the third thoracic segment of Drosophila, wing development is suppressed by the homeotic selector gene Ultrabithorax (Ubx) in order to mediate haltere development. Previously, we have shown that Ubx represses dorsoventral (DV) signaling to specify haltere fate. Here we examine the mechanism of Ubx-mediated downregulation of DV signaling. We show that Wingless (Wg) and Vestigial (Vg) are differentially regulated in wing and haltere discs. In wing discs, although Vg expression in non-DV cells is dependent on DV boundary function of Wg, it maintains its expression by autoregulation. Thus, overexpression of Vg in non-DV cells can bypass the requirement for Wg signaling from the DV boundary. Ubx functions, at least, at two levels to repress Vestigial expression in non-DV cells of haltere discs. At the DV boundary, it functions downstream of Shaggy/GSK3 beta to enhance the degradation of Armadillo (Arm), which causes downregulation of Wg signaling. In non-DV cells, Ubx inhibits event(s) downstream of Arm, but upstream of Vg autoregulation. Repression of Vg at multiple levels appears to be crucial for Ubx-mediated specification of the haltere fate. Overexpression of Vg in haltere discs is enough to override Ubx function and cause haltere-to-wing homeotic transformations.
在果蝇的第三胸节中，同源异型选择基因超双胸（Ubx）抑制翅膀发育，以介导平衡棒发育。此前，我们已经表明Ubx抑制背腹（DV）信号传导以确定平衡棒命运。在此，我们研究Ubx介导的DV信号传导下调的机制。我们发现，无翅（Wg）和残翅（Vg）在翅盘和平衡棒盘中受到不同的调控。在翅盘中，虽然非DV细胞中的Vg表达依赖于Wg的DV边界功能，但它通过自我调节维持其表达。因此，在非DV细胞中过表达Vg可以绕过对来自DV边界的Wg信号的需求。Ubx至少在两个水平上发挥作用，以抑制平衡棒盘非DV细胞中的残翅表达。在DV边界，它在蓬乱/糖原合成酶激酶3β的下游发挥作用，以增强犰狳（Arm）的降解，从而导致Wg信号传导的下调。在非DV细胞中，Ubx抑制Arm下游但Vg自我调节上游的事件。在多个水平上抑制Vg似乎对Ubx介导的平衡棒命运的确定至关重要。在平衡棒盘中过表达Vg足以超越Ubx的功能并导致平衡棒向翅膀的同源异型转化。
