19Proc. Arthropod. Embryol. Soc. Jpn. 54, 19–20 (2022)Ⓒ 2022 Arthropodan Embryological Society of Japan
ISSN 1341–1527

Developmental Origin of Wings
in the Two-spotted Cricket Gryllus bimaculatus
Suggests an Evolutionary Mechanism of the Insect Wing＊
Takahiro OHDE
Department of Applied Biosciences, Graduate School of Agriculture, Kyoto University, Kyoto, Kyoto 606–­8502, Japan
E-mail: ohde.takahiro.4n@kyoto-u.ac.jp

The classical hypotheses about the evolutionary
origin of the insect wing have claimed tergal or pleuralorigin and have drawn mutually exclusive evolutionaryscenarios (Clark-Hachtel and Tomoyasu, 2016). The
third hypothesis, the dual origin hypothesis, proposes
the evolution of the wing through the combined
contribution of the morphological elements of boththe tergum and pleuron, but there is no unified
view on the degree of contribution of each element(Clark-Hachtel and Tomoyasu, 2016). Where
does the insect wing come from? To answer thisquestion, we investigated the developmental originof the wing in the hemimetabolous insect, Gryllus
bimaculatus. Hemimetabolous insects develop into
adults without major changes in body plans formed
during embryogenesis. This feature could clarify
the contribution of the tergum and pleuron to wingdevelopment.
In order to find the homologous structure ofwings, we first investigated the expression pattern ofvestigial (vg), apterous (ap), and wingless (wg), whichplay a decisive role in the wing development processof Drosophila. In Gryllus embryos, ap was widelyexpressed in the tergal region, and vg and wg wereexpressed at the edge of the tergal plate. In addition,
ap and vg were also expressed in the pleural region.
Since vg is involved in determining the fate of wing
primordial cells in Drosophila embryos (Fuse et al.,1996), the fate of vg-expressing cells is important forunderstanding the developmental origin of cricket
wings. Therefore, a reporter line of vg expression
was created by genome editing, and the fate of vgexpressing cells was traced in Gryllus. Subsequently,
we performed functional analysis of vg and ap using
genome editing technology. In the vg mosaic knockout
individual, the formation of the nymphal tergal edge
was inhibited. Adult wing formation was significantly＊

inhibited in crickets lacking the nymphal tergal edge.
This result suggests that nymphal tergal cells contributeconsiderably to adult wing formation. Consistently,
physical ablation of the nymphal tergal edge
significantly inhibited adult wing growth. On the other
hand, we found that ap is required for vg expression
at the tergal margin by creating a mosaic knockout
individual of ap in the vg reporter cricket strain. From
the above results, we conclude that vg induced by ap inthe embryonic stage is required to form the tergal edge,
and a part of the tergal edge leads the growth of thewing in the postembryonic stage.
How do the cells of tergal edge grow wings in thecricket? To further understand this point, the nymphal
tergum was divided into two regions and a comparativetranscriptome analysis was performed. The analysis
revealed that the components of multiple signaling
pathways were highly expressed in the lateral region ofthe tergum, suggesting that this region could serve as asignaling center and control wing growth. In fact, RNAi
analysis revealed that the Wnt/Ft (Fat)/Hippo pathway
is involved in cricket wing growth. These pathways,
along with vg, have been reported to play a collaborativerole in Drosophila wing growth (Zecca and Struhl,2010), suggesting a correspondence between cricket
lateral tergum and Drosophila wing regions.
This study showed the instructive role of tergum
cells in the wing development of the hemimetabolous
insect. Together with a previous study (Niwa etal., 2010), this study suggests that the tergal edgeof apterygote and hemimetabolous insects arehomologous. Therefore, we conclude that activationof the growth mechanism mediated by Wnt/Ft/Hippo
pathways in the tergal margin cells of a winglessancestor might be a key step in the wingless-to-winged
transition.

Contribution to the symposium “Acquisition of Functional Diversity of Insects” in the 57th Annual Meeting of the Arthropodan EmbryologicalSociety of Japan, July 9–10, 2021, Ushiku-numa, Ibaraki, Japan.

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References
Clark-Hachtel, C.M. and Y. Tomoyasu (2016) Exploring theorigin of insect wings from an evo-devo perspective.
Current Opinion in Insect Science, 13, 77–85.
Fuse, N., S. Hirose and S. Hayashi (1996) Determination ofwing cell fate by the escargot and snail genes in Drosophila.
Development, 122, 1059–1067.
Niwa, N., A. Akimoto-Kato, T. Niimi, K. Tojo, R. Machida andS. Hayashi (2010) Evolutionary origin of the insect wing via
integration of two developmental modules. Evolution &Development, 12, 168–176.
Zecca, M. and G. Struhl (2010) A feed-forward circuit linking
Wingless, Fat-Dachsous signaling, and the Warts-Hippo
pathway to Drosophila wing growth. PLoS Biology, 8,e1000386.