25Proc. Arthropod. Embryol. Soc. Jpn. 50, 25 (2016)Ⓒ 2016 Arthropodan Embryological Society of Japan
ISSN 1341–1527

Regulatory Role of Homeotic Genes in Lepidopteran Proleg
Development*Shuichiro TOMITANational Institute of Agrobiological Sciences, Ohwashi, Tsukuba, Ibaraki, 305–0851, Japan
E-mail: tomita@affrc.go.jp

The basic body plan of the insect consists of threetagmata namely head, thorax and abdomen. Each thoracic
segment bares a pair of appendages and abdominal segments
in adult insects lack such a feature quite often. Prolegs areappendages that develop in the larval abdomen of Lepidoptera,
Mecoptera and Symphyta of Hymenoptera. The limited
distribution of proleg-baring species raises the question
whether prolegs are homologous structures or convergent
traits.
To address this issue we tried to analyze the molecularmechanisms underlying the proleg development in a
lepidopteran species, Bombyx mori. Prolegs of Bombyx aresegmented and bare crochets at their tips. Their ventrolateral position is in line with the thoracic legs and Dll
expression is detected at their tips during embryonicdevelopment where the expression domains of wg and dpp areoverlapped. These observations suggest geometricalinformation in developing prolegs in Bombyx is carried by thesame genetic network as Drosophila legs and prolegs ofBombyx are likely serially homologous to the thoracic legs.
The development of appendages in abdominal segments
in insects is suppressed by the expression of the homeotic
genes, Ubx, abd-A and Abd-B in this tagma, and permissive
expression of Dll in proleg-baring segments that is achievedby the “clearance” of abd-A expression is thought to result in
the development of lepidopteran prologs (Warren et al., 1994).
Strange enough, the abd-A null mutant strain of Bombyx, ECa* Abstract of paper read at the 51st Annual Meeting of the Arthropodan

animals fail to develop any prolegs (Ueno et al.,) and this isphenocopied by knocking down abd-A expression by injecting
dsRNA for abd-A into the embryo (Tomita and Kikuchi, 2009).
Moreover, Dll expression remains to be detected in the proleg
primodial region in ECa embryos. Knocking-down Dll made noeffects on proleg development while gnathal appendages andthoracic legs are greatly reduced. Abd-A protein wasaccumulated at the proleg primodial regions and this trend isconserved among the genetic mutants that develop extra
prologs. This strong expression of Abd-A is observed only inthe sixth abdominal segment of the embryo of a Geometridae
species (Milionia basalis) which bares prologs only on A6segment. These results strongly suggest that during thedevelopment of abdominal prologs of Lepidoptera abd-A plays
promotive, rather than suppressive role and Dll expression isdispensable.
References
Tomita, S. and A. Kikuchi (2009) Abd-B suppresses lepidopteranproleg development in posterior abdomen. Developmental Biology,328, 403–409.
Ueno, K., C. C. Hui, M, Fukuta and Y. Suzuki (1992) Molecularanalysis of the deletion mutants in the E homeotic complex of thesilkworm Bombyx mori. Development, 114, 555–563.
Warren, R. W., L. Nagy, J. Selegue, J. Gates and S. Carroll (1994)
Evolution of homeotic gene regulation and function in flies andbutterflies. Nature, 372, 458–461.

Embryological Society of Japan, June 12–13, 2015 (Urabandai, Fukushima)