Edayoshi Mina, Yamaguchi Junichi, Fujiwara Haruhiko
Department of Integrated Biosciences, Graduate School of Frontier Sciences, University of Tokyo Bioscience, Kashiwa, Chiba, Japan.
PLoS One. 2015 Mar 27;10(3):e0121736. doi: 10.1371/journal.pone.0121736. eCollection 2015.
Spine-like or protruding structures, which may be aposematic for predators, are often observed in multiple segments of lepidopteran larvae (caterpillars). For example, the larvae of the Chinese wheel butterfly, Byasa alcinous, display many protrusions on their backs as a warning that they are toxic. Although these protrusions are formed by an integument lined with single-layered epidermal cells, the molecular mechanisms underlying their formation have remained unclear. In this study, we focused on a spontaneous mutant of the silkworm, Bombyx mori, Knobbed, which shows similar protrusions to B. alcinous and demonstrates that Wnt1 plays a crucial role in the formation of protrusion structures. Using both transgene expression and RNAi-based knockdown approaches, we showed that Wnt1 designates the position where epidermal cells excessively proliferate, leading to the generation of knobbed structures. Furthermore, in the B. alcinous larvae, Wnt1 was also specifically expressed in association with the protrusions. Our results suggest that Wnt1 plays a role in the formation of protrusions on the larval body, and is conserved broadly among diverse species in Lepidoptera.
在鳞翅目幼虫（毛虫）的多个体节中，常可观察到类似脊椎或突出的结构，这些结构可能对捕食者具有警戒作用。例如，中华虎凤蝶（Byasa alcinous）的幼虫背部有许多突出物，以此警示它们是有毒的。尽管这些突出物由单层表皮细胞构成的体壁形成，但其形成的分子机制仍不清楚。在本研究中，我们聚焦于家蚕（Bombyx mori）的一个自发突变体——瘤突（Knobbed），它表现出与中华虎凤蝶类似的突出物，并证明Wnt1在突出结构的形成中起关键作用。通过转基因表达和基于RNA干扰的敲低方法，我们表明Wnt1指定了表皮细胞过度增殖的位置，从而导致瘤突结构的产生。此外，在中华虎凤蝶幼虫中，Wnt1也与突出物特异性表达相关。我们的结果表明，Wnt1在幼虫身体突出物的形成中起作用，并且在鳞翅目的多种物种中广泛保守。
