Knockdowns of red Malphigian tubules reveal pigmentation roles in the milkweed bug

Abstract

Classical Drosophila eye color mutations have unearthed a toolkit of genes that have permitted candidate gene studies of the outstanding diversity of coloration patterns in other insects. The gene underlying the eye color phenotypes of the red Malphigian tubules (red) fly mutant was mapped to a LysM domain gene of unknown molecular function.

Genome editing of thevermilionlocus generates a visible eye color marker forOncopeltus fasciatus

“…Here, we used RNAi to assess roles of selected genes encoding candidate visible markers, testing for detrimental consequences of gene knockdown before proceeding to genome editing. Our experiments verified the role of Of-v in eye color 47,48 and identified a novel role of the Of - xdh / ry gene in body color. We generated three independent Of-v null mutations, each of which has been maintained in lab colony for multiple generations without discernable impact on development.…”

“…Recently, RNAi knockdown demonstrated a role for Of - red Malpighian Tubules ( red ) in eye color, while also contributing somewhat to body pigmentation. This gene likely encodes a protein involved in intracellular pigment trafficking and, accordingly, knockdown impacted both ommochrome and pteridine pathways 48 .…”

Genetics of continuous colour variation in a pair of sympatric sulphur butterflies

“…The chromosome 18 LOD interval is 500 kb and contains 29 annotated genes ( Table S1 ), including a homolog of the gene red Malpighian tubules ( red ). The red gene is a compelling candidate gene for pterin pigment variation in butterflies, as mutant and knockdown phenotypes in Drosophila and Oncopeltus have suggested a role of this gene in the biogenesis of pigment granule formation, including pterinosomes (Francescutti et al, 2022; Grant et al, 2016). No coding variants were detected in whole genome resequenced individuals from Buckeystown, MA.…”

“…The D. melanogaster red mutant shows an accumulation of red ommochromes in the Malpighian Tubules (MTs), and a reduction of ommochromes and pterins in the eyes (Aslaksen and Hadorn, 1957; Ferré et al, 1986; Wessing and Bonse, 1966). In the milkweed bug Oncopeltus fasciatus , RNAi-mediated knockdown of red causes a reduction in pterins in pigmented cuticles, legs, and abdomens, as well as a reduction of ommochromes in the eye (Francescutti et al, 2022). Wing pigmentation is primarily pterin-based in Colias , with no contribution from ommochromes (Wijnen et al, 2007), but the dual effects on both ommochromes and pterins in Drosophila and Oncopeltus suggest that red acts at the level of a biological process that is shared between these pathways.…”

“…First, the unique pigment profile of red mutant flies is strikingly similar to the ones observed with two eye-colour mutant alleles of the chocolate (cho) / VhaAC39 gene (Ferré et al, 1986; Grant et al, 2016; Tearle, 1991), which encodes a v-ATPase proton pump essential for endosomal acidification and membrane trafficking in LROs (Allan et al, 2005; Sun-Wada et al, 2003; Yan et al, 2009). Second, homologs of Red contain a LysM domain, and it is their only annotated feature (Francescutti et al, 2022; Grant et al, 2016). The molecular function of this domain is poorly understood in insects, but there is mounting evidence in vertebrates that the LysM domains of several genes interact with the v-ATPase to modulate vacuolar pH across a variety of endosomal organelles (Merkulova et al, 2015; Castroflorio et al, 2021; Eaton et al, 2021; Tan et al, 2022).…”