Heart of our evolution discovered: 380-million-year-old heart

Researchers have discovered a 380-million-year-old heart -- the oldest ever found -- alongside a separate fossilised stomach, intestine and liver in an ancient jawed fish, shedding new light on the evolution of our own bodies.

The new research, published today in Science, found that the position of the organs in the body of arthrodires -- an extinct class of armoured fishes that flourished through the Devonian period from 419.2 million years ago to 358.9 million years ago -- is similar to modern shark anatomy, offering vital new evolutionary clues.

Lead researcher John Curtin Distinguished Professor Kate Trinajstic, from Curtin's School of Molecular and Life Sciences and the Western Australian Museum, said the discovery was remarkable given that soft tissues of ancient species were rarely preserved and it was even rarer to find 3D preservation.

"As a palaeontologist who has studied fossils for more than 20 years, I was truly amazed to find a 3D and beautifully preserved heart in a 380-million-year-old ancestor," Professor Trinajstic said.

"Evolution is often thought of as a series of small steps, but these ancient fossils suggest there was a larger leap between jawless and jawed vertebrates. These fish literally have their hearts in their mouths and under their gills -- just like sharks today."

This research presents -- for the first time -- the 3D model of a complex s-shaped heart in an arthrodire that is made up of two chambers with the smaller chamber sitting on top.

Professor Trinajstic said these features were advanced in such early vertebrates, offering a unique window into how the head and neck region began to change to accommodate jaws, a critical stage in the evolution of our own bodies.

"For the first time, we can see all the organs together in a primitive jawed fish, and we were especially surprised to learn that they were not so different from us," Professor Trinajstic said.

"However, there was one critical difference -- the liver was large and enabled the fish to remain buoyant, just like sharks today. Some of today's bony fish such as lungfish and birchers have lungs that evolved from swim bladders but it was significant that we found no evidence of lungs in any of the extinct armoured fishes we examined, which suggests that they evolved independently in the bony fishes at a later date."

The Gogo Formation, in the Kimberley region of Western Australia where the fossils were collected, was originally a large reef.

Enlisting the help of scientists at the Australian Nuclear Science and Technology Organisation in Sydney and the European Synchrotron Radiation Facility in France, researchers used neutron beams and synchrotron x-rays to scan the specimens, still embedded in the limestone concretions, and constructed three-dimensional images of the soft tissues inside them based on the different densities of minerals deposited by the bacteria and the surrounding rock matrix.

This new discovery of mineralised organs, in addition to previous finds of muscles and embryos, makes the Gogo arthrodires the most fully understood of all jawed stem vertebrates and clarifies an evolutionary transition on the line to living jawed vertebrates, which includes the mammals and humans.

Co-author Professor John Long, from Flinders University, said: "These new discoveries of soft organs in these ancient fishes are truly the stuff of palaeontologists' dreams, for without doubt these fossils are the best preserved in the world for this age. They show the value of the Gogo fossils for understanding the big steps in our distant evolution. Gogo has given us world firsts, from the origins of sex to the oldest vertebrate heart, and is now one of the most significant fossil sites in the world. It's time the site was seriously considered for world heritage status."

Co-author Professor Per Ahlberg, from Uppsala University, said: "What's really exceptional about the Gogo fishes is that their soft tissues are preserved in three dimensions. Most cases of soft-tissue preservation are found in flattened fossils, where the soft anatomy is little more than a stain on the rock. We are also very fortunate in that modern scanning techniques allow us to study these fragile soft tissues without destroying them. A couple of decades ago, the project would have been impossible."

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Your stomach may be the secret to fighting obesity

Scientists believe a stomach-specific protein plays a major role in the progression of obesity, according to new research in Scientific Reports. The study co-authored by an Indiana University School of Medicine researcher, could help with development of therapeutics that would help individuals struggling with achieving and maintaining weight loss.

Researchers focused on Gastrokine-1 (GKN1) -- a protein produced exclusively and abundantly in the stomach. Previous research has suggested GKN1 is resistant to digestion, allowing it to pass into the intestine and interact with microbes in the gut.

In the Scientific Reports study, researchers show that inhibiting GKN1 produced significant differences in weight and levels of body fat in comparison to when the protein was expressed.

"While diet and exercise are critical to maintaining a healthy weight, some individuals struggle with weight loss -- even in cases of bariatric surgery, maintaining weight loss can be a challenge," said David Boone, PhD, associate professor of microbiology and immunology at IU School of Medicine, an adjunct professor in the Department of Biology at the University of Notre Dame and a co-author of the study. "These results are an example of how a better understanding of the gut microbiome and the physiological aspects of obesity -- how our bodies regulate metabolism and accumulate body fat -- could help inform new therapies."

Data from the Centers for Disease Control show adult obesity rates have increased to 42.4 percent in the United States. In addition to increasing an individual's risk of stroke, diabetes, certain cancers and other health issues, obesity can also increase the risk of severe illness due to COVID-19.

Boone and his team conducted a microbiome analysis of mouse models with and without the GKN1 protein expressed. Researchers measured food intake, caloric extraction, blood sugar, insulin and triglyceride levels. They used magnetic resonance imagining to monitor body composition. The team also calculated energy expenditure and observed inflammation levels.

Models without GKN1 weighed less and had lower levels of total body fat and higher percentages of lean mass -- despite consuming the same amount of food. When put on a high-fat diet, models without GKN1 showed a resistance to weight gain, increased body fat and hepatic inflammation, which can lead to liver disease. Researchers also found no evidence of adverse effects such as cancer, diabetes, loss of appetite, malabsorption or inflammation -- and results were consistent in male and female models.

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Thinking with your stomach? The brain may have evolved to regulate digestion

Many life forms use light as an important biological signal, including animals with visual and non-visual systems. But now, researchers from Japan have found that neuronal cells may have initially evolved to regulate digestion according to light information.

In a study published this month in BMC Biology, researchers from the University of Tsukuba have revealed that sea urchins use light to regulate the opening and closing of the pylorus, which is an important component of the digestive tract.

Light-dependent systems often rely on the activity of proteins in the Opsin family, and these are found across the animal kingdom, including in organisms with visual and non-visual systems. Understanding the function of Opsins in animals from different taxonomic groups may provide important clues regarding how visual/non-visual systems evolved in different creatures to use light as an external signal. The function of Opsins in the Ambulacraria groups of animals, which include sea urchins, has not been characterized, something the researchers aimed to address.

"The functions of eyes and visual systems have been well-characterized," says senior author of the study Professor Shunsuke Yaguchi. "However, the way in which light dependent systems were acquired and diversified throughout evolution is unclear especially in deuterostomes because of the lack of data regarding the signaling pathway in the Ambulacraria group."

To address this, the researchers tested whether light exposure caused changes in digestive tract activity in sea urchins. They then conducted micro-surgical and genetic knockdown experiments to test whether Opsin cells in the sea urchin digestive system mediated the effect of light.

"The results provided new information about the role of Opsins in sea urchins," explains Professor Yaguchi. "Specifically, we found that stimulation of sea urchin larvae via light caused changes in digestive system function, even in the absence of food stimuli."

Furthermore, the researchers identified brain serotonergic neurons near the Opsin-expressing cells that were essential for mediating the light-stimulated release of nitric oxide, which acts as a neurotransmitter.

"Our results have important implications for understanding the process of evolution, specifically, that of light-dependent systems controlled via neurotransmitters," says Professor Yaguchi.

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