Chen G, Handel K, Roth S
Max-Planck-Institut für Entwicklungsbiologie, Spemannstrasse 35/II, D-72076 Tübingen, Germany.
Development. 2000 Dec;127(23):5145-56. doi: 10.1242/dev.127.23.5145.
In the long-germ insect Drosophila melanogaster dorsoventral polarity is induced by localized Toll-receptor activation which leads to the formation of a nuclear gradient of the rel/ NF-kappaB protein Dorsal. Peak levels of nuclear Dorsal are found in a ventral stripe spanning the entire length of the blastoderm embryo allowing all segments and their dorsoventral subdivisions to be synchronously specified before gastrulation. We show that a nuclear Dorsal protein gradient of similar anteroposterior extension exists in the short-germ beetle, Tribolium castaneum, which forms most segments from a posterior growth zone after gastrulation. In contrast to Drosophila, (i) nuclear accumulation is first uniform and then becomes progressively restricted to a narrow ventral stripe, (ii) gradient refinement is accompanied by changes in the zygotic expression of the Tribolium Toll-receptor suggesting feedback regulation and, (iii) the gradient only transiently overlaps with the expression of a potential target, the Tribolium twist homolog, and does not repress Tribolium decapentaplegic. No nuclear Dorsal is seen in the cells of the growth zone of Tribolium embryos, indicating that here dorsoventral patterning occurs by a different mechanism. However, Dorsal is up-regulated and transiently forms a nuclear gradient in the serosa, a protective extraembryonic cell layer ultimately covering the whole embryo.
在长胚昆虫黑腹果蝇中，背腹极性是由局部Toll受体激活诱导的，这导致rel/NF-κB蛋白背侧（Dorsal）形成核梯度。在横跨胚盘胚胎全长的腹侧条带中发现了核背侧（Dorsal）的峰值水平，使得所有体节及其背腹亚区在原肠胚形成之前能够同步确定。我们发现，在短胚甲虫赤拟谷盗中存在类似前后延伸的核背侧（Dorsal）蛋白梯度，它在原肠胚形成后从后生长区形成大多数体节。与果蝇不同的是：（i）核积累最初是均匀的，然后逐渐局限于一条狭窄的腹侧条带；（ii）梯度细化伴随着赤拟谷盗Toll受体合子表达的变化，提示存在反馈调节；（iii）该梯度仅与潜在靶标赤拟谷盗twist同源物的表达短暂重叠，且不抑制赤拟谷盗的十体节基因（decapentaplegic）。在赤拟谷盗胚胎生长区的细胞中未观察到核背侧（Dorsal），这表明此处的背腹模式形成是通过不同的机制进行的。然而，背侧（Dorsal）在浆膜（一种最终覆盖整个胚胎的保护性胚外细胞层）中上调并短暂形成核梯度。
