Hormones control growth, metabolism, reproduction and many other important biological processes. In humans, and all other vertebrates, the chemical signals are produced by specialised brain centres such as the hypothalamus and secreted into the blood stream that distributes them around the body. Researchers from the European Molecular Biology Laboratory (EMBL) now reveal that the hypothalamus and its hormones are not purely vertebrate inventions, but have their evolutionary roots in marine, worm-like ancestors. In this weeks issue of the journal Cell they report that hormone-secreting brain centres are much older than expected and likely evolved from multifunctional cells of the last common ancestor of vertebrates, flies and worms.
Hormones mostly have slow, long-lasting and body-wide effects, rendering them the perfect complement to the fast and precise nervous system of vertebrates. Also insects and nematode worms rely on the secretion of hormones to transmit information, but the compounds they use are often very different from the vertebrate counterparts.
This suggested that hormone-secreting brain centres have arisen after the evolution of vertebrates and invertebrates had split, says Detlev Arendt, whose group studies development and evolution of the brain at EMBL. But then vertebratetype hormones were found in annelid worms and molluscs, indicating that these centres might be much older than expected.
Scientist Kristin Tessmar-Raible from Arendts lab directly compared two types of hormone-secreting nerve cells of zebrafish, a vertebrate, and the annelid worm Platynereis dumerilii, and found some stunning similarities. Not only were both cell types located at the same positions in the developing brains of the two species, but they also looked similar and shared the same molecular makeup. One of these cell types secretes vasotocin, a hormone controlling reproduction and water balance of the body, the other secretes a hormone called RF-amide.
Contact: Anna-Lynn Wegener
European Molecular Biology Laboratory