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First published online 24 November 2004
doi: 10.1242/dev.01561

Development 132, 27-34 (2005)
Published by The Company of Biologists 2005
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Functional analyses of tiptop and Antennapedia in the embryonic development of Oncopeltus fasciatus suggests an evolutionary pathway from ground state to insect legs

Scott W. Herke, Nahum V. Serio and Bryan T. Rogers*

Louisiana State University, Department of Biological Sciences, Baton Rouge, LA 70803, USA Department of Biological Sciences, 202 Life Sciences Building, Louisiana State University, Baton Rouge, LA 70803, USA

* Author for correspondence (e-mail: broger2{at}lsu.edu)

Accepted 8 June 2004

In insects, selector genes are thought to modify the development of a default, or `ground state', appendage into a tagma-specific appendage such as a mouthpart, antenna or leg. In the best described example, Drosophila melanogaster, the primary determination of leg identity is thought to result from regulatory interactions between the Hox genes and the antennal-specifying gene homothorax. Based on RNA-interference, a functional analysis of the selector gene tiptop and the Hox gene Antennapedia in Oncopeltus fasciatus embryogenesis is presented. It is shown that, in O. fasciatus, tiptop is required for the segmentation of distal leg segments and is required to specify the identity of the leg. The distal portions of legs with reduced tiptop develop like antennae. Thus, tiptop can act as a regulatory switch that chooses between antennal and leg identity. By contrast, Antennapedia does not act as a switch between leg and antennal identity. This observation suggests a significant difference in the mechanism of leg specification between O. fasciatus and D. melanogaster. These observations also suggest a significant plasticity in the mechanism of leg specification during insect evolution that is greater than would have been expected based on strictly morphological or molecular comparisons. Finally, it is proposed that a tiptop-like activity is a likely component of an ancestral leg specification mechanism. Incorporating a tiptop-like activity into a model of the leg-specification mechanism explains several mutant phenotypes, previously described in D. melanogaster, and suggests a mechanism for the evolution of legs from a ground state.

Key words: Oncopeltus fasciatus, tiptop, Antennapedia, Leg development, Ground state, RNA-interference


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Development 2005 132: e101. [Full Text]  





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