Spontaneous long-range calcium waves in developing butterfly wings.

Yoshikazu Ohno,Joji M Otaki

doi:10.1186/s12861-015-0067-8

Abstract

BackgroundButterfly wing color patterns emerge as the result of a regular arrangement of scales produced by epithelial scale cells at the pupal stage. These color patterns and scale arrangements are coordinated throughout the wing. However, the mechanism by which the development of scale cells is controlled across the entire wing remains elusive. In the present study, we used pupal wings of the blue pansy butterfly, Junonia orithya, which has distinct eyespots, to examine the possible involvement of Ca2+ waves in wing development.ResultsHere, we demonstrate that the developing pupal wing tissue of the blue pansy butterfly displayed spontaneous low-frequency Ca2+ waves in vivo that propagated slowly over long distances. Some waves appeared to be released from the immediate peripheries of the prospective eyespot and discal spot, though it was often difficult to identify the specific origins of these waves. Physical damage, which is known to induce ectopic eyespots, led to the radiation of Ca2+ waves from the immediate periphery of the damaged site. Thapsigargin, which is a specific inhibitor of Ca2+-ATPases in the endoplasmic reticulum, induced an acute increase in cytoplasmic Ca2+ levels and halted the spontaneous Ca2+ waves. Additionally, thapsigargin-treated wings showed incomplete scale development as well as other scale and color pattern abnormalities.ConclusionsWe identified a novel form of Ca2+ waves, spontaneous low-frequency slow waves, which travel over exceptionally long distances. Our results suggest that spontaneous Ca2+ waves play a critical role in the coordinated development of scale arrangements and possibly in color pattern formation in butterflies.Electronic supplementary materialThe online version of this article (doi:10.1186/s12861-015-0067-8) contains supplementary material, which is available to authorized users.

Highlights

Wing color patterns emerge as the result of a regular arrangement of scales produced by epithelial scale cells at the pupal stage
We investigated the potential involvement of Ca2+ waves in butterfly wing development using the blue pansy butterfly Junonia orithya, which has large eyespots on its wings (Figure 1a, b)
This study detected, for the first time, spontaneously produced Ca2+ waves that travel slowly over long distances during butterfly wing development. These findings were made possible by our technological advancements in butterfly wing live imaging

Summary

Introduction

Wing color patterns emerge as the result of a regular arrangement of scales produced by epithelial scale cells at the pupal stage. The role of ions as signaling molecules is possible partially because their distribution and trafficking in cells, tissues and organs are tightly regulated by membranous structures. Among these signaling ions, calcium ions (Ca2+) are known to contribute to numerous cellular processes in both excitable and non-excitable cells during development and differentiation [1,2,3]. In the central nervous system, glial Ca2+ signals waves have been well studied in the blowfly salivary gland [15]; the developmental roles of Ca2+ waves in insect tissues have not been elucidated [16] We examined these processes using pupal wing tissues of butterflies. Each scale has a single color that is produced by a

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