Sea lamprey studies show remarkably conserved gene expression patterns in jawless vs. jawed vertebrates
If you never understood what "ontogeny recapitulates phylogeny" meant in high school, don't worry: biologists no longer think that an animal's "ontogeny", that is, its embryonic development, replays its entire evolutionary history.
This shows the morphology of an adult sea lamprey (top); the ventral view of the unique oral disc, adapted for a parasitic lifestyle (bottom left); and a transient transgenic lamprey embryo (bottom right).
Credit: Image courtesy of Krumlauf Lab, Stowers Institute for Medical Research and Bronner Lab, California Institute of Technology
Instead, the new way to figure out how animals evolved is to compare regulatory networks that control gene expression patterns, particularly embryonic ones, across species. An elegant study published in the September 14, 2014 advance online issue of Nature from the Stowers Institute for Medical Research shows just how humbling and exhilarating that pursuit can be.
In the study, Investigator and Scientific Director Robb Krumlauf, Ph.D. and colleagues show that the sea lamprey Petromyzon marinus, a survivor of ancient jawless vertebrates, exhibits a pattern of gene expression that is reminiscent of its jawed cousins, who evolved much, much later. Those genes, called Hox genes, function like a molecular ruler, determining where along the anterior-posterior (AP) axis an animal will place a particular feature or appendage. The new study means that that the genetic program used by jawed vertebrates, including fish, mice, and us, was up and running ages before a vertebrate ever possessed a recognizable face.
"Hox genes regulate a tissue's character or shape, as in head or facial features. Our work in the past has addressed how factors make unique structures, for example, what makes an arm different from a leg," says Krumlauf. "Now, we are excited by the common role that similar sets of genes play in creating a basic structural plan."
The team at Stowers, collaborating with Marianne Bronner, Ph.D., professor of biology at Caltech, focused on the sea lamprey because the fossil record shows that its ancestors emerged from Cambrian silt approximately 500 million years ago, 100 million years before jawed fish ever swam onto the scene. The question was, could the hindbrain gene regulatory network that constructs the "modern" vertebrate head have originated in animals that lack those structures?
To answer it, the researchers created so-called "reporter" genes from stretches of regulatory DNA flanking a specific Hox gene in zebrafish or mice and linked them to fluorescent tags. When inserted into an experimental animal these types of reporters glow in tissues where the gene is activated, or "expressed". The researchers chose this particular battery of Hox reporters because when inserted in embryos of a jawed fish they fluoresce in adjacent rainbow stripes up and down the embryonic hindbrain.
The paper's startling finding came when they inserted the very same reporters into lamprey embryos using a technique developed by Hugo Parker, Ph.D., a postdoctoral fellow in the Krumlauf lab and the study's first author: the lamprey embryos displayed the same rainbow pattern of Hox reporters as did jawed fish, in exactly the same order along the AP axis of the hindbrain.
"We were surprised to see any reporter expression in lamprey, much less a pattern that resembles the pattern in a mouse or fish," says Parker, who pioneered the lamprey reporter approach as a graduate student at London's Queen Mary University. "That means that the gene regulatory network that governs segmental patterning of the hindbrain likely evolved prior to divergence of jawed vertebrates."
Researchers knew that in mouse and zebrafish short stretches of DNA in one Hox reporter (Hoxb3) formed a landing pad recognized by a DNA-binding protein that flips on the gene. As you would expect, when inserted into zebrafish embryos, reporters mutant in those sequences were inactive (they didn't glow) in the hindbrain. Remarkably, the mutant reporter was inactive in lamprey embryos also, meaning that this control switch has been around for a very long time.
"These results suggest that regulatory circuits controlling hindbrain patterning were likely 'fixed in place' in ancient vertebrates," says Bronner. Some may find this surprising, as adult mammals (like us!) bear absolutely no resemblance to lampreys. "However, embryos of lamprey and other vertebrates show many striking similarities, so it makes sense that there are features common to all."
This study was funded by the Stowers Institute and by grants from the National Institutes of Health (R01NS086907 and R01DE017911). The content is solely the responsibility of the authors and does not necessarily represent the official views of the NIH.
About the Stowers Institute for Medical Research
The Stowers Institute for Medical Research is a non-profit, basic biomedical research organization dedicated to improving human health by studying the fundamental processes of life. Jim Stowers, founder of American Century Investments, and his wife, Virginia, opened the Institute in 2000. Since then, the Institute has spent over one billion dollars in pursuit of its mission.
Currently, the Institute is home to nearly 550 researchers and support personnel; over 20 independent research programs; and more than a dozen technology-development and core facilities.
Kim Bland | Eurek Alert!
Rutgers-led innovation could spur faster, cheaper, nano-based manufacturing
14.02.2018 | Rutgers University
New study from the University of Halle: How climate change alters plant growth
12.01.2018 | Martin-Luther-Universität Halle-Wittenberg
For the first time, a team of researchers at the Max-Planck Institute (MPI) for Polymer Research in Mainz, Germany, has succeeded in making an integrated circuit (IC) from just a monolayer of a semiconducting polymer via a bottom-up, self-assembly approach.
In the self-assembly process, the semiconducting polymer arranges itself into an ordered monolayer in a transistor. The transistors are binary switches used...
Breakthrough provides a new concept of the design of molecular motors, sensors and electricity generators at nanoscale
Researchers from the Institute of Organic Chemistry and Biochemistry of the CAS (IOCB Prague), Institute of Physics of the CAS (IP CAS) and Palacký University...
For photographers and scientists, lenses are lifesavers. They reflect and refract light, making possible the imaging systems that drive discovery through the microscope and preserve history through cameras.
But today's glass-based lenses are bulky and resist miniaturization. Next-generation technologies, such as ultrathin cameras or tiny microscopes, require...
Scientists from the University of Zurich have succeeded for the first time in tracking individual stem cells and their neuronal progeny over months within the intact adult brain. This study sheds light on how new neurons are produced throughout life.
The generation of new nerve cells was once thought to taper off at the end of embryonic development. However, recent research has shown that the adult brain...
Theoretical physicists propose to use negative interference to control heat flow in quantum devices. Study published in Physical Review Letters
Quantum computer parts are sensitive and need to be cooled to very low temperatures. Their tiny size makes them particularly susceptible to a temperature...
15.02.2018 | Event News
13.02.2018 | Event News
12.02.2018 | Event News
20.02.2018 | Life Sciences
20.02.2018 | Medical Engineering
20.02.2018 | Physics and Astronomy