Heads or tails: How different species of flies repurpose genes to determine which end is up
Animals have many genes in common, but up to one third of the genes in a given species are only found in that species or its close relatives. One might think that those “orphan genes” are what truly distinguish a species, i.e., genes that control the body shape, size, or behavior. But a new study by scientists from the University of Chicago shows how even genes with a fundamental role early development of an embryo can change over relatively short time without changing the resulting body parts and functions of the fly.
One of the most consequential developments in the life of an insect is determining its polarity, or which end of an egg will develop the head and which will develop the tail. In Drosophila, the common fruit fly studied as a model species by biologists the world over, a gene called bicoid controls embryo polarity. The gene produces messenger RNA that congregates in one end of the egg, which becomes the head. In another type of fly, the common midge Chironomus, a gene called panish fills this role. The bicoid and panish genes are dedicated to establishing embryo polarity. Most fly species don’t have these genes, though, and yet they all manage to produce offspring with a head and tail. So, how did these new genes acquire the job of controlling embryo polarity?
In a new study published in eLife, biologist Urs Schmidt-Ott, PhD, and his collaborators, including Yoseop Yoon, a graduate student in Schmidt-Ott’s lab and first author of the study, identified three older genes that adopted this function in other fly species. They found genes with other, unrelated functions took on the job of establishing head-to-tail polarity in developing embryos by stashing their RNA in the anterior end of the egg (the part that ultimately forms the head).