The bristle patterning genes hairy and extramacrochaetae regulate the development of structures required for flight in Diptera

Pigmentation pattern and developmental constraints: flight muscle attachment sites delimit the thoracic trident of Drosophila melanogaster

In their seminal paper published in 1979, Gould and Lewontin argued that some traits arise as by-products of the development of other structures and not for direct utility in themselves. We show here that this applies to the trident, a pigmentation pattern observed on the thorax of Drosophila melanogaster. Using reporter constructs, we show that the expression domain of several genes encoding pigmentation enzymes follows the trident shape. This domain is complementary to the expression pattern of stripe (sr), which encodes an essential transcription factor specifying flight muscle attachment sites. We demonstrate that sr limits the expression of these pigmentation enzyme genes to the trident by repressing them in its own expression domain, i.e. at the flight muscle attachment sites. We give evidence that repression of not only yellow but also other pigmentation genes, notably tan, is involved in the trident shape. The flight muscle attachment sites and sr expression patterns are remarkably conserved in dipterans reflecting the essential role of sr. Our data suggest that the trident is a by-product of flight muscle attachment site patterning that arose when sr was co-opted for the regulation of pigmentation enzyme coding genes.

Canalization of gene expression is a major signature of regulatory cold adaptation in temperate Drosophila melanogaster

BACKGROUND

Transcriptome analysis may provide means to investigate the underlying genetic causes of shared and divergent phenotypes in different populations and help to identify potential targets of adaptive evolution. Applying RNA sequencing to whole male Drosophila melanogaster from the ancestral tropical African environment and a very recently colonized cold-temperate European environment at both standard laboratory conditions and following a cold shock, we seek to uncover the transcriptional basis of cold adaptation.

RESULTS

In both the ancestral and the derived populations, the predominant characteristic of the cold shock response is the swift and massive upregulation of heat shock proteins and other chaperones. Although we find ~25 % of the genome to be differentially expressed following a cold shock, only relatively few genes (n = 16) are up- or down-regulated in a population-specific way. Intriguingly, 14 of these 16 genes show a greater degree of differential expression in the African population. Likewise, there is an excess of genes with particularly strong cold-induced changes in expression in Africa on a genome-wide scale.

CONCLUSIONS

The analysis of the transcriptional cold shock response most prominently reveals an upregulation of components of a general stress response, which is conserved over many taxa and triggered by a plethora of stressors. Despite the overall response being fairly similar in both populations, there is a definite excess of genes with a strong cold-induced fold-change in Africa. This is consistent with a detrimental deregulation or an overshooting stress response. Thus, the canalization of European gene expression might be responsible for the increased cold tolerance of European flies.

Emerging developmental genetic model systems in holometabolous insects

The number of insect species that are amenable to functional genetic studies is growing rapidly and provides many new research opportunities in developmental and evolutionary biology. The holometabolous insects represent a disproportionate percentage of animal diversity and are thus well positioned to provide model species for a wide variety of developmental processes. Here we discuss emerging holometabolous models, and review some recent breakthroughs. For example, flies and midges were found to use structurally unrelated long-range pattern organizers, butterflies and moths revealed extensive pattern formation during oogenesis, new imaging possibilities in the flour beetle Tribolium castaneum showed how embryos break free of their extraembryonic membranes, and the complex genetics governing interspecies difference in head shape were revealed in Nasonia wasps.