Molecular mechanism underlying venation patterning in butterflies

Abstract

AbstractThe mechanism of wing vein differentiation in Drosophila is a classic text-book example of pattern formation using a system of positional-information, yet very little is known about how this mechanism differs in species with a different number of veins and how insect venation patterns evolved. Here, we examine the expression patterns of genes previously implicated in vein differentiation in Drosophila in two butterfly species with more complex venation, the African squinting bush brown Bicyclus anynana and the Asian cabbage white, Pieris canidia. We also test the function of one of these genes, spalt (sal), with CRISPR-Cas9 in B. anynana. We identify both conserved as well as new domains of decapentaplegic (dpp), engrailed (en), invected (inv) and sal gene expression in B. anynana, and propose how the simplified venation in Drosophila might have evolved via loss of dpp and sal gene expression domains, silencing of vein inducing programs at Sal-expression boundaries, and changes in gene expression of vein maintenance genes.Summary statementThe paper describes new domains of venation patterning genes in butterflies and proposes how simplified venation in other insect lineages might have evolved.