The evolutionary origin of the gutSeptember 11, 2017
How did the gut, the skin and musculature evolve? This question concerns scientists for more than a century. Through the investigation of the embryonic development of sea anemones, a very old animal lineage, researchers from the University of Vienna have now come to conclusions which challenge the 150 year-old hypothesis of the homology (common evolutionary origin) of the germ layers that form all later organs and tissues.
According to a 150 year-old hypothesis, all tissues and organs in our body derive from one of three germ layers that are established during early embryogenesis. This "germ layer hypothesis" states that skin and nervous system derive from the outer ectoderm layer, the gut and some inner organs, like the pancreas, derive from the inner endoderm layer, while muscles and gonads stem from the middle layer, the mesoderm. Early on, researchers noted a fundamental difference in the number of germ layers in different animal groups.
While most animals, like humans, insects and worms, develop from three germ layers, the cnidarians (corals, sea anemones or jellyfish) lack the intermediate layer and present only two cell layers during development and throughout life. The emergence of mesoderm as the third intermediate germ layer is considered a key event during the evolution of complex animals. So far, however, it was controversial how mesoderm has evolved, and how the two cnidarian germ layers relate to the three layers in most other animals. A new publication from the laboratory of Ulrich Technau at the Department for Molecular Evolution and Development of the University of Vienna presents a fundamentally new view of the evolution of germ layers.
The inner-most, gut-forming endoderm has always been considered as evolutionary related between cnidarians and other animals. In their study, Technau and colleagues have now tested this hypothesis by tracing the embryonic origin of digestive enzyme-producing cells as well as their developmental regulator genes typical of the gut and pancreas in a sea anemone. The authors show that in sea anemones, against all previous beliefs, digestive enzyme- and insulin-producing gland cells do not develop from endoderm but from the ectodermal part of the mouth, the pharynx. "I was puzzled when I first saw that all endoderm derivatives of sea anemones are totally devoid of digestive gland cells. That was not what is taught in biology textbooks" explains Patrick Steinmetz, who contributed most of the experiments and is now a group leader at the University of Bergen in Norway.
"The results completely change the way we think of the origin of germ layers. It means that 'endoderm' in sea anemones and vertebrates, although they are called the same, are actually not evolutionary related" adds Ulrich Technau. If the mouth ectoderm of the sea anemone and not the endoderm corresponds to the vertebrate gut and pancreas, then what is the vertebrate correlate of the sea anemone endoderm? When Steinmetz and Technau dwelled deeper into this question, they found strong similarities between the cnidarian endoderm and the intermediate mesoderm layer: both share a large number of regulatory genes, and both give rise to similar cell types such as muscle or gonad cells. The sea anemone thus shows a clear correlate of mesoderm, but not in an intermediate position as found in three-layered animals. Positioning, and not novel emergence, of tissue in-between the gut and skin was thus the key event that led to the evolution of three-layered animals.
"An overwhelming majority of animals nowadays develop three germ layers, and we have taken a big step towards the understanding of one of the most crucial events underlying this evolutionary success story" concludes Steinmetz.
Univ.-Prof. Dr. Ulrich Technau
Department for Molecular Evolution and Development
Centre for Organismal Systems Biology
University of Vienna
1090 Vienna, Althanstrasse 14
T +43-(1) 4277-57000
Mag. Alexandra Frey
Press office of the University of Vienna
Research and Teaching
1010 Vienna, Universitätsring 1
T +43-1-4277-175 33
M +43-664-602 77-175 33
University of Vienna
Related Evolution Articles:
The evolution of cells and organisms is thought to have been preceded by a phase in which informational molecules like DNA could be replicated selectively.
A new study by University of Arizona biologists helps explain why different groups of animals differ dramatically in their number of species, and how this is related to differences in their body forms and ways of life.
A genome project, comprising six evolutionary biologists from Professor Axel Meyer's research team from Konstanz and researchers from China and Singapore, sequenced and analyzed the genome of the tiger tail seahorse.
Rapid evolution of other species happens all around us all the time -- and many of the most extreme examples are associated with human influences.
Landscapes are formed by a combination of uplift and erosion.
How enzymes -- the biological proteins that act as catalysts and help complex reactions occur -- are 'tuned' to work at a particular temperature is described in new research from groups in New Zealand and the UK, including the University of Bristol.
On Nov. 11, 1954, Syuiti Mori turned out the lights on a small group of fruit flies.
A team of researchers, among them a zoologist from the University of Cologne, has succeeded in reconstructing a 160 million year old compound eye of a fossil crustacean found in southeastern France visible.
Evolution may be more intelligent than we thought, according to a University of Southampton professor.
Organized opposition to the teaching of evolution in public schoolsin the United States began in the 1920s, leading to the famous Scopes Monkey trial.
Related Evolution Reading:
Evolutions: Fifteen Myths That Explain Our World
by Oren Harman (Author)
A brilliant lyrical exploration of how modern science illuminates what it means to be human, from the award-winning author of The Price of Altruism
We no longer think, like the ancient Chinese did, that the world was hatched from an egg, or, like the Maori, that it came from the tearing-apart of a love embrace. The Greeks told of a tempestuous Hera and a cunning Zeus, but we now use genes and natural selection to explain fear and desire, and physics to demystify the workings of the universe.
On a brisk winter morning in 2004, after leaving early from their final exams for the fall semester, four 19 and 20-year-old college students park an unmarked van outside of the Transylvania University Private Collections Museum. Home to a collection of some of the most valuable rare books and paintings in the world, including John James Audubon’s Birds of America and Charles Darwin’s On The Origin of Species, the four young men enter the building with the intention to steal history.
As one of the most audacious art heists in U.S. history unfolds, this... View Details
Evolution: The Cutting-Edge Guide to Breaking Down Mental Walls and Building the Body You've Always Wanted
by Joe Manganiello (Author)
Joe Manganiello first gained recognition around the world for his incredible, sculpted body while winning both popular and critical praise as the star of HBO's True Blood. Now, from the man that Magic Mike director Steven Soderbergh called “walking CGI,” comes the cutting-edge guide to achieving the perfect body and therefore enhancing your overall quality of life.
With a build that men envy and women adore, Joe Manganiello is more than qualified to write the end-all guide to sculpting the perfect body. His fit physique catapulted him to the top of the list of... View Details
Evolution: A Visual Record
by Robert Clark (Author)
Stunning images to reawaken us to the scientific process that drives the amazing diversity of life on earth
Evidence of evolution is everywhere. Through 200 revelatory images, award-winning photographer Robert Clark makes one of the most important foundations of science clear and exciting to everyone. Evolution: A Visual Record transports readers from the near-mystical(human ancestors) to the historic (the famous 'finches' Darwin collected on the Galapagos Islands that spurred his theory); the recently understood (the link between dinosaurs and modern birds)... View Details
Why Evolution Is True
by Jerry A. Coyne (Author)
"Coyne's knowledge of evolutionary biology is prodigious, his deployment of it as masterful as his touch is light." -Richard Dawkins
In the current debate about creationism and intelligent design, there is an element of the controversy that is rarely mentioned-the evidence. Yet the proof of evolution by natural selection is vast, varied, and magnificent. In this succinct and accessible summary of the facts supporting the theory of natural selection, Jerry A. Coyne dispels common misunderstandings and fears about evolution and clearly confirms the scientific truth that... View Details
Evolution: The Human Story
by DK (Author)
How did we develop from simple animals inhabiting small pockets of forest in Africa to the dominant species on Earth? Traveling back almost eight million years to our earliest primate relatives, Evolution: The Human Story charts the development of our species from tree-dwelling primates to modern humans.
Investigating each of our ancestors in detail and in context, from the anatomy of their bones to the environment they lived in, Evolution: The Human Story profiles every human relative and ancestor discovered to date, and illustrates them in lifelike form.
Amazingly... View Details
by Douglas J. Futuyma (Author), Mark Kirkpatrick (Author)
Extensively rewritten and reorganized, this new edition of Evolution--featuring a new coauthor: Mark Kirkpatrick (The University of Texas at Austin)--offers additional expertise in evolutionary genetics and genomics, the fastest-developing area of evolutionary biology. Directed toward an undergraduate audience, the text emphasizes the interplay between theory and empirical tests of hypotheses, thus acquainting students with the process of science. It addresses major themes--including the history of evolution, evolutionary processes, adaptation, and evolution as an explanatory... View Details
Evolution: How We and All Living Things Came to Be
by Daniel Loxton (Author), Daniel Loxton (Illustrator)
Evolution is the process that created the terrible teeth of Tyrannosaurus rex and the complex human brain, clever enough to understand the workings of nature. Young readers will learn how a British naturalist named Charles Darwin studied nature and developed his now-famous concepts of natural selection and survival of the fittest. And how modern-day science has added to our understanding of the theory of evolution.
Can something as complex and wondrous as the natural world be explained by a simple theory? The answer is yes, and now Evolution explains how in a way that makes it easy... View Details
Evolution: Making Sense of Life
by Carl Zimmer (Author), Douglas J. Emlen (Author)
Science writer Carl Zimmer and evolutionary biologist Douglas Emlen have produced a thoroughly revised new edition of their widely praised evolution textbook. Emlen, an award-winning evolutionary biologist at the University of Montana, has infused Evolution: Making Sense of Life with the technical rigor and conceptual depth that today’s biology majors require. Zimmer, an award-winning New York Times columnist, brings compelling storytelling to the book, bringing evolutionary research to life. Students will learn the fundamental concepts of evolutionary theory, such as natural... View Details
Evolution 2.0: Breaking the Deadlock Between Darwin and Design
by Perry Marshall (Author)
When Charles Darwin wrote "Origin of Species," cells were considered gobs of goo. But today we know NASA astronaut Scott Kelly's body altered its own gene expressions in just one year (!) when he traveled to space and back. His body executed a direct evolutionary response to the rigors of the International Space Station.
Such new discoveries demonstrate how obsolete Neo-Darwinian ideas about random mutation were. New knowledge was resisted for decades. Why? Because it overturned entrenched norms, popular beliefs, accepted paradigms.
The old-school Darwinism of... View Details