Mark Lammers (Vrije Universiteit Amsterdam)
in: 'Frontiers in Ecology and Evolution': "Gene regulatory mechanisms underlying the evolutionary loss of a polygenic trait"
by Mark Lammers (Vrije Universiteit Amsterdam)
In almost all organisms, storage of diet-acquired energy in the form of lipids is essential for survival. This molecular process is the result of a conserved network consisting of several interconnected pathways, its enzymes encoded by a conserved set of genes across the animal kingdom. However, most parasitoid insects have lost the ability to convert dietary sugars into lipids. The model species Nasonia vitripennis has been shown to lack lipogenesis, despite the presence of all required genes in its genome without signs of degradation. This suggests that loss of lipogenesis is caused by changes in gene regulation, rather than gene decay. We performed genome-wide transcriptional profiling aimed at discovering the regulatory mechanism of the evolutionary loss of lipogenesis. Gene expression levels were compared between sugar-fed and starved individuals. All key genes involved in lipogenesis were transcribed at normal levels (compared to Drosophila melanogaster), confirming a lack of gene degradation. Several changes in expression levels in response to sugar-feeding were discovered in key genes coding for enzymes in the parasitoid’s acetyl-CoA metabolism. Their combined action likely shifts the energetic balance in carbon metabolism away from lipogenesis. We verified this hypothesis by generating knockdown wasps using RNA interference. Our results suggest that modification of expression levels of only a few genes is sufficient to enable complete loss of lipogenesis in Nasonia vitripennis. We conclude that evolutionary changes in universal physiological processes can be the consequence of gene regulatory alterations.