The regulation of a pigmentation gene in the formation of complex color patterns in Drosophila abdomens

Changes in cis-regulatory modules (CRMs) that control developmental gene expression patterns have been implicated in the evolution of animal morphology1-6. However, the genetic mechanisms underlying complex morphological traits remain largely unknown. Here we investigated the molecular mechanisms that induce the pigmentation gene yellow (y) in a complex spot and shade pattern on the abdomen of the quinaria group species Drosophila guttifera. We show that the y expression pattern is controlled by only one CRM, which contains a stripe-inducing CRM at its core. We identified several developmental genes that may collectively interact with the CRM to orchestrate the patterning in the pupal abdomen of D. guttifera. We further show that the core CRM is conserved among D. guttifera and the closely related quinaria group species Drosophila deflecta, which displays a similarly spotted abdominal pigment pattern. Our data suggest that besides direct activation of patterns in distinct spots, abdominal spot patterns in Drosophila species may have evolved through partial repression of an ancestral stripe pattern, leaving isolated spots behind. Abdominal pigment patterns of extant quinaria group species support the partial repression hypothesis and further emphasize the modularity of the D. guttifera pattern.

Environmental UVR Levels and Skin Pigmentation Gene Variants Associated with Folate and Homocysteine Levels in an Elderly Cohort

Ultraviolet radiation (UVR) is a ubiquitous exposure which may contribute to decreased folate levels. Skin pigmentation mediates the biological effect of UVR exposure, but its relationship to folate levels is unexamined. Interactions may exist between UVR and pigmentation genes in determining folate status, which may, in turn, impact homocysteine levels, a potential risk factor for multiple chronic diseases. Therefore, independent and interactive influences of environmental UVR and genetic variants related to skin pigmentation (MC1R-rs1805007, IRF4-rs12203592 and HERC2-rs12913832) on folate (red blood cell (RBC) and serum) and homocysteine levels were examined in an elderly Australian cohort (n = 599). Genotypes were assessed by RT/RFLP-PCR, and UVR exposures were assessed as the accumulated erythemal dose rate accumulated over 4 months (4M-EDR). Multivariate analysis found significant negative associations between 4M-EDR and RBC folate (p < 0.001, β = −0.19), serum folate (p = 0.045, β = −0.08) and homocysteine levels (p < 0.001, β = −0.28). Significant associations between MC1R-rs1805007 and serum folate levels (p = 0.020), and IRF4-rs12203592 and homocysteine levels (p = 0.026) occurred but did not remain significant following corrections with confounders. No interactions between 4M-EDR and pigmentation variants in predicting folate/homocysteine levels were found. UVR levels and skin pigmentation-related variants are potential determinants of folate and homocysteine status, although, associations are mixed and complex, with further studies warranted.