Regulatory evolution tuning pigmentation intensity quantitatively in Drosophila

Quantitative variation in attributes such as color, texture, or stiffness dominates morphological diversification. It results from combinations of alleles at many Mendelian loci. Here, we identify an additional source of quantitative variation among species, continuous evolution in a gene regulatory region. Specifically, we examined the modulation of wing pigmentation in a group of fly species and showed that inter-species variation correlated with the quantitative expression of the pigmentation gene yellow. This variation results from an enhancer of yellow determining darkness through species-specific activity. We mapped the divergent activities between two sister species and found the changes to be broadly distributed along the enhancer. Our results demonstrate that enhancers can act as dials fueling quantitative morphological diversification by modulating trait properties.

Revisiting the developmental and cellular role of the pigmentation gene yellow in Drosophila using a tagged allele

Pigmentation is a diverse and ecologically relevant trait in insects. Pigment formation has been studied extensively at the genetic and biochemical levels. The temporality of pigment formation during animal development, however, is more elusive. Here, we examine this temporality, focusing on yellow, a gene involved in the formation of black melanin. We generated a protein-tagged yellow allele in the fruit fly Drosophila melanogaster, which allowed us to precisely describe Yellow expression pattern at the tissue and cellular levels throughout development. We found Yellow expressed in the pupal epidermis in patterns prefiguring black pigmentation. We also found Yellow expressed in a few central neurons from the second larval instar to adult stages, including a subset of neurons adjacent to the clock neurons marked by the gene Pdf. We then specifically examined the dynamics of Yellow expression domain and subcellular localization in relationship to pigment formation. In particular, we showed how a late step of re-internalization is regulated by the large low-density lipoprotein receptor-related protein Megalin. Finally we suggest a new function for Yellow in the establishment of sharp pigmentation pattern boundaries, whereby this protein may assume a structural role, anchoring pigment deposits or pigmentation enzymes in the cuticle.