Gain of cis -regulatory activities underlies novel domains of wingless gene expression in Drosophila

Abstract

Changes in gene expression during animal development are largely responsible for the evolution of morphological diversity. However, the genetic and molecular mechanisms responsible for the origins of new gene-expression domains have been difficult to elucidate. Here, we sought to identify molecular events underlying the origins of three novel features of wingless (wg) gene expression that are associated with distinct pigmentation patterns in Drosophila guttifera. We compared the activity of cis-regulatory sequences (enhancers) across the wg locus in D. guttifera and Drosophila melanogaster and found strong functional conservation among the enhancers that control similar patterns of wg expression in larval imaginal discs that are essential for appendage development. For pupal tissues, however, we found three novel wg enhancer activities in D. guttifera associated with novel domains of wg expression, including two enhancers located surprisingly far away in an intron of the distant Wnt10 gene. Detailed analysis of one enhancer (the vein-tip enhancer) revealed that it overlapped with a region controlling wg expression in wing crossveins (crossvein enhancer) in D. guttifera and other species. Our results indicate that one novel domain of wg expression in D. guttifera wings evolved by co-opting pre-existing regulatory sequences governing gene activity in the developing wing. We suggest that the modification of existing enhancers is a common path to the evolution of new gene-expression domains and enhancers.enhancers | novelty | gene regulation | development | pigmentation

The Genetic Basis of Pigmentation Differences Within and Between Drosophila Species

“…It is not yet known whether Bab proteins directly bind to enhancers of any pigment synthesis genes, but it is clear that Bab proteins affect expression of pigment synthesis genes in some manner (Kopp 2009). Similarly, Omb (Brisson et al 2004) and Wingless (Wg, a ligand for a signal transduction pathway) (Werner et al 2010; Koshikawa et al 2015) have also been shown to influence expression of at least one pigment synthesis gene (Figure 1), although questions remain about the precise molecular mechanisms by which they do so. Additional transcription factors with effects on abdominal pigmentation in Drosophila melanogaster have been identified in recent RNAi screens (Kalay 2012; Rogers et al 2013a), but the ways in which they alter expression of pigment synthesis genes remains unknown.…”

Morphological Evolution Repeatedly Caused by Mutations in Signaling Ligand Genes

“…Wnt1; wg) and its tandem paralogs Wnt6 and Wnt10 (Fig. 4.3c), show that three novel, tissue-specific cis-regulatory elements drive wingless expression and underlie novel color patterns on the wings and thorax of Drosophila guttifera fruit flies (Werner et al 2010;Koshikawa et al 2015). While these studies lack the phylogenetic resolution and replication observed in butterflies, they provide one of the most detailed mechanistic accounts of truly novel traits, where the deployment of Wnt expression in three different body regions is driven by independent cis-regulatory changes.…”

“…While these studies lack the phylogenetic resolution and replication observed in butterflies, they provide one of the most detailed mechanistic accounts of truly novel traits, where the deployment of Wnt expression in three different body regions is driven by independent cis-regulatory changes. Of note, wg is also associated to color patterns and wing contours in both flies and butterflies (Macdonald et al 2010;Martin and Reed 2010;Koshikawa et al 2015), and a redeployment of this gene to new body regions is likely to drive the evolution of new patterns as well, as it seemed to have occurred during the evolution of larval cuticle patterns in Lepidoptera (Yamaguchi et al 2013). We note that while Koshikawa et al did not detect any pattern-related Wnt6 and Wnt10 expression in D. guttifera developing wings ; S. Koshikawa, personal communication), these two paralogs are co-deployed with wg in butterflies where they may underlie a more complex architecture, with partially redundant ligand activities (Martin and Reed 2014).…”

Drosophila guttifera as a Model System for Unraveling Color Pattern Formation

“…These novel enhancer activities are thought to have been involved in the evolution of the novel pigmentation pattern . This study provided unique insights into the evolution of novel traits, illustrating how gains of novel enhancer activities at developmental regulatory gene were associated with derived expression domains and the emergence of novel traits (Rebeiz et al 2011;Koshikawa et al 2015;Rebeiz and Williams 2017).…”

“…Involvement of another transcription factor is assumed, but so far it has not been identified. Furthermore, we know yellow is involved in pigmentation, but overexpression of yellow alone does not cause additional pigmentation in D. melanogaster (Gompel et al 2005;Riedel et al 2011 Koshikawa et al (2015) and Koshikawa (2015)) repression of melanin synthesis-related genes and/or proper supply of melanin precursors, such as dopa and dopamine, could be required for artificial production of pigmentation in D. melanogaster wings.…”