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.

Gephebase, a database of genotype-phenotype relationships for natural and domesticated variation in Eukaryotes.

Gephebase is a manually-curated database compiling our accumulated knowledge of the genes and mutations that underlie natural, domesticated and experimental phenotypic variation in all Eukaryotes-mostly animals, plants and yeasts. Gephebase aims to compile studies where the genotype-phenotype association (based on linkage mapping, association mapping or a candidate gene approach) is relatively well supported. Human clinical traits and aberrant mutant phenotypes in laboratory organisms are not included and can be found in other databases (e.g. OMIM, OMIA, Monarch Initiative). Gephebase contains more than 1700 entries. Each entry corresponds to an allelic difference at a given gene and its associated phenotypic change(s) between two species or two individuals of the same species, and is enriched with molecular details, taxonomic information, and bibliographic information. Users can easily browse entries and perform searches at various levels using boolean operators (e.g. transposable elements, snakes, carotenoid content, Doebley). Data is exportable in spreadsheet format. This database allows to perform meta-analyses to extract global trends about the living world and the research fields. Gephebase should also help breeders, conservationists and others to identify promising target genes for crop improvement, parasite/pest control, bioconservation and genetic diagnostic. It is freely available at www.gephebase.org.

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.

[The genetic walk of evolution]. / La marche génétique de l'évolution⋆

Genetic mutations are the main fuel of evolution. In each generation, they produce new variations, which may be sorted out by natural or sexual selection. Mutations are generated by chance; yet which are the mutations actually sorted out by evolution, and why? This review presents some recent advances regarding this question. First, we gather results obtained at molecular and cellular levels, through synthetic experiments and under artificial selection paradigms. Next, we highlight studies at the multi-cellular level, especially studies of repeated evolution, whereby independent lineages acquire similar traits. Recent meta-analysis and quantifications are being presented; together they suggest that evolutionary relevant mutations accumulate around hotspots, spanning different levels of genetic organization. Pioneering work suggests that many causes, corresponding to many biological contexts, may explain the existence of these genetic hotspots. We finally discuss methodological limits, empirical challenges and a few future potential directions for this domain of research dedicated to the genetic path of evolution.

Emergence and diversification of fly pigmentation through evolution of a gene regulatory module.

The typical pattern of morphological evolution associated with the radiation of a group of related species is the emergence of a novel trait and its subsequent diversification. Yet the genetic mechanisms associated with these two evolutionary steps are poorly characterized. Here, we show that a spot of dark pigment on fly wings emerged from the assembly of a novel gene regulatory module in which a set of pigmentation genes evolved to respond to a common transcriptional regulator determining their spatial distribution. The primitive wing spot pattern subsequently diversified through changes in the expression pattern of this regulator. These results suggest that the genetic changes underlying the emergence and diversification of wing pigmentation patterns are partitioned within genetic networks.