Transcription factors underlying wing margin color patterns and pupal cuticle markings in butterflies

Robert D Reed,Jayne E Selegue,Linlin Zhang,Craig R Brunetti

doi:10.1186/s13227-020-00155-w

Abstract

BackgroundThe diversity of butterfly color patterns can be attributed to a relatively small number of pattern elements that are homologous across Lepidoptera. Although genes involved in patterning some of these elements have been identified, the development of several major elements remains poorly understood. To identify genes underlying wing pupal cuticle markings and wing margin color patterns, we examined expression of the candidate transcription factors Engrailed/Invected (En/Inv), Distal-less (Dll), Cubitus interruptus (Ci), and Spalt in two nymphalids: Junonia coenia and Bicyclus anynana.ResultsWe found that En/Inv, Dll, and Ci mark domains on the J. coenia last-instar forewing disc that closely correspond to the position and shape of pupal cuticle markings. We also found that Spalt demarcates wing margin color patterns in both J. coenia and B. anynana, and that CRISPR/Cas9 deletions in the spalt gene result in reduction and loss of wing margin color patterns in J. coenia. These data demonstrate a role for spalt in promoting wing margin color patterning, in addition to its previously described role in eyespot patterning.ConclusionOur observations support the model that a core set of regulatory genes are redeployed multiple times, and in multiple roles, during butterfly wing pattern development. Of these genes, spalt is of special interest as it plays a dual role in both eyespot and margin color pattern development.

Highlights

The diversity of butterfly color patterns can be attributed to a relatively small number of pattern elements that are homologous across Lepidoptera
Closer examination of J. coenia immunostains revealed that the expression patterns (Fig. 2a) are not consistent with typical round eyespot foci (Fig. 2b), rather they appear as chevrons and circles (Fig. 2a)
In this study we asked whether these genes may play some additional roles in wing patterning beyond eyespot development, and we presented new evidence for their likely roles in wing pupal cuticle marking and, in the case of Spalt, wing margin color pattern determination as well

Summary

Introduction

The diversity of butterfly color patterns can be attributed to a relatively small number of pattern elements that are homologous across Lepidoptera. As originally proposed by Schwanwitsch [1] and Süffert [2], and later refined by Nijhout [3], this spectacular diversity of color patterns is the product of a relatively simple ground plan of evolutionarily conserved pattern elements that are homologous across Lepidoptera. These elements, many of which are characterized as symmetry systems, include the marginal and submarginal bands, the border ocelli, the. Cells surrounding the focus would differentiate into colored scales based on their distance from the focus, due to positional differences in morphogen concentration

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Discussion

Conclusion