Georg-August-Universität Göttingen, Johann-Friedrich-Blumenbach-Institut für Zoologie und Anthropologie, Abteilung für Entwicklungsbiologie, GZMB Ernst-Caspari-Haus, Justus-von-Liebig-Weg 11, 37077 Göttingen, Germany.
Dev Biol. 2012 Oct 15;370(2):264-72. doi: 10.1016/j.ydbio.2012.08.005. Epub 2012 Aug 18.
The evolution of a mechanism to generate a proximal-distal axis perpendicular to the anterior-posterior body axis was a key event in arthropod evolution and facilitated the formation of multi-functional limbs. The study of proximodistal limb patterning in extant arthropods can provide insight into the origin and evolution of the proximal-distal axis. In Drosophila melanogaster, proximal-distal patterning is mainly organized by Wg/Dpp signaling. Egfr signaling is also involved, but is restricted to late stages and distal leg parts (tarsus and pretarsus). Here we study the role of Epidermal growth factor receptor (Egfr), spitz (spi), and pointed (pnt) in leg development in the beetle Tribolium castaneum. We show that Egfr signaling has a more complex role in T. castaneum than in D. melanogaster and is not only required in the distal leg, but is also involved in formation of the medial leg (including femur and tibia). Egfr and spi are required for the regulation of clawless (cll), Distal-less (Dll) and dachshund (dac), and RNAi leads to thickened and fused leg segments. Intriguingly, regulation of Dll and dac by Egfr signaling appears functionally separate from its role in cll regulation, because it is not mediated by the transcription factor Pnt. This suggests that Egfr signaling has a dual role with separate mediators in proximodistal axis patterning. While the regulation of distal factors like cll is evolutionarily conserved, regulation of Dll and dac appears to function in parallel or redundant with Wg/Dpp signaling, thus providing a possible explanation why this role is less evolutionarily conserved in the insects.
一个生成垂直于体轴的近-远轴机制的进化是节肢动物进化中的一个关键事件，并促进了多功能肢体的形成。对现存节肢动物近-远肢体模式的研究可以深入了解近-远轴的起源和进化。在黑腹果蝇中，近-远模式主要由 Wg/Dpp 信号组织。Egfr 信号也参与其中，但仅限于晚期和远端腿部（跗节和前跗节）。在这里，我们研究了表皮生长因子受体（Egfr）、Spitz（spi）和 pointed（pnt）在鞘翅目甲虫 Tribolium castaneum 腿部发育中的作用。我们表明，Egfr 信号在 T. castaneum 中的作用比在 D. melanogaster 中更为复杂，不仅在远端腿部需要，而且还参与了中腿（包括股骨和胫骨）的形成。Egfr 和 spi 对于调控无爪（cll）、远端缺失（Dll）和达克斯犬（dac）是必需的，而 RNAi 导致腿部节段变厚和融合。有趣的是，Egfr 信号对 Dll 和 dac 的调控似乎与其在 cll 调控中的作用在功能上是分开的，因为它不是由转录因子 Pnt 介导的。这表明 Egfr 信号在近-远轴模式形成中具有双重作用和独立的介质。虽然像 cll 这样的远端因子的调控在进化上是保守的，但 Dll 和 dac 的调控似乎与 Wg/Dpp 信号平行或冗余，因此提供了一个可能的解释，即为什么在昆虫中这个作用在进化上不太保守。
