Researchers from Skoltech, Koltzov Institute of Developmental Biology of the Russian Academy of Sciences, and Engelhardt Institute of Molecular Biology of the Russian Academy of Sciences have studied gene expression dynamics during metamorphosis in two species of flies. The study aims to identify patterns of changes in gene activity during insect development that undergo complete metamorphosis — from egg to larva, pupa, and adult. The results were published in the Genome Biology and Evolution journal.

Every day we are surrounded by thousands of flies, mosquitoes, beetles, butterflies, and many other insects that go through several stages of development — for example, a caterpillar transforming into a beautiful butterfly. Each stage activates different sets of genes, allowing these insects to adapt to various environments. In their new study, scientists investigated how gene activity levels change at different developmental stages of two fly species — Drosophila melanogaster and Drosophila virilis.

“In our previous work, we showed that metamorphosis is similar to embryogenesis—that is, organism development from fertilized egg cell to fully formed embryo. Both processes involve organ and tissue formation since there is significant restructuring from larvae to adults during metamorphosis. During embryogenesis, the hourglass hypothesis suggests that different species exhibit striking similarities at a mid-developmental stage, forming a ‘narrow neck’ where gene activation patterns converge. We tested whether this hypothesis applies to metamorphosis,” commented Alexandra Ozerova, the lead author of the paper and PhD student at Skoltech’s Life Sciences program.

Results of the new study revealed a completely different scenario — the dynamic of gene activity resembles a spindle rather than an hourglass. Instead of a narrow point with similarities between species, diversity increases over time.

“We conducted RNA sequencing experiments for both drosophila species, collecting samples at different life cycle stages: embryos, larvae, various pupal stages, and adults. For analysis, we used bioinformatics methods. We found that genes which emerged relatively recently in insect evolution begin actively expressing themselves during the mid-pupal period, their expression level sharply rises. It can be assumed that they help the organism carry out necessary physiological transformations leading to adulthood,” added a study co-author, Professor Mikhail Gelfand, the vice president for biomedical research at Skoltech.

Insects undergoing full transformation cycles are more evolutionarily successful — they include the most numerous groups by number of species (e.g. beetles, mosquitoes, flies, bees, ants, butterflies). Many of them turn out to be pests. A better understanding of biological processes at different stages of development opens up new prospects for developing effective control measures against them. Knowing specifics about gene expression could lead to designing drugs targeting vulnerable stages of insect development.