Giant prehistoric flying reptile took off using similar method to bats, study finds

The pterosaur likely used all four limbs to propel itself in the air, as seen in bats today, researchers have found.

The findings, published today in PeerJ, provide new insights into how pterosaurs managed to take flight despite reaching sizes far larger than modern animals.

The research sheds new light on the flight initiating jumping ability of these animals, some of which had wingspans of over ten meters.

The study, carried out by scientists at the University of Bristol, Liverpool John Moores University, Universidade Federal do ABC and the University of Keele, follows years of analysis and modelling of how muscles interact with bones to create movement in other animals and is now being used to start answering the question of how the largest flying animals known managed to get off the ground.

The team created the first computer model for this kind of analysis of a pterosaur to test three different ways pterosaurs may have taken off: a vertical burst jump using just the legs like those used by primarily ground-dwelling birds, a less vertical jump using just the legs more similar to the jump used by birds that fly frequently, and a four-limbed jump using its wings as well in a motion more like the take-off jump of a bat.

By mimicking these motions, the researchers aimed to understand the leverage available to push the animal into the air.

"Larger animals have greater challenges to overcome in order to fly making the ability of animals as large as pterosaurs to do so especially fascinating." Dr Ben Griffin, the lead author of the study, said.

"Unlike birds which mainly rely on their hindlimbs, our models indicate that pterosaurs were more likely to rely on all four of their limbs to propel themselves into the air."

Read more at Science Daily

'Smart glove' can boost hand mobility of stroke patients

This month, a group of stroke survivors in B.C. will test a new technology designed to aid their recovery, and ultimately restore use of their limbs and hands.

Participants will wear a new groundbreaking "smart glove" capable of tracking their hand and finger movements during rehabilitation exercises supervised by Dr. Janice Eng, a leading stroke rehabilitation specialist and professor of medicine at UBC.

The glove incorporates a sophisticated network of highly sensitive sensor yarns and pressure sensors that are woven into a comfortable stretchy fabric, enabling it to track, capture and wirelessly transmit even the smallest hand and finger movements.

"With this glove, we can monitor patients' hand and finger movements without the need for cameras. We can then analyze and fine-tune their exercise programs for the best possible results, even remotely," says Dr. Eng.

Precision in a wearable device

UBC electrical and computer engineering professor Dr. Peyman Servati, PhD student Arvin Tashakori and their team at their startup, Texavie, created the smart glove for collaboration on the stroke project.

Dr. Servati highlighted a number of breakthroughs, described in a paper published last week in Nature Machine Intelligence.

"This is the most accurate glove we know of that can track hand and finger movement and grasping force without requiring motion-capture cameras. Thanks to machine learning models we developed, the glove can accurately determine the angles of all finger joints and the wrist as they move. The technology is highly precise and fast, capable of detecting small stretches and pressures and predicting movement with at least 99-per-cent accuracy -- matching the performance of costly motion-capture cameras."

Unlike other products in the market, the glove is wireless and comfortable, and can be easily washed after removing the battery.

Dr. Servati and his team have developed advanced methods to manufacture the smart gloves and related apparel at a relatively low cost locally.

Augmented reality and robotics

Dr. Servati envisions a seamless transition of the glove into the consumer market with ongoing improvements, in collaboration with different industrial partners.

The team also sees potential applications in virtual reality and augmented reality, animation and robotics.

Read more at Science Daily

First map of human limb development reveals unexpected growth processes and explains syndromes found at birth

Human fingers and toes do not grow outward; instead, they form from within a larger foundational bud, as intervening cells recede to reveal the digits beneath. This is among many processes captured for the first time as scientists unveil a spatial cell atlas of the entire developing human limb, resolved in space and time.

Researchers at the Wellcome Sanger Institute, Sun Yat-sen University, EMBL's European Bioinformatics Institute and collaborators applied cutting-edge single-cell and spatial technologies to create an atlas characterising the cellular landscape of the early human limb, pinpointing the exact location of cells.

This study is part of the international Human Cell Atlas initiative to map every cell type in the human body, to transform understanding of health and disease.

The atlas, published today (6 December) in Nature, provides an openly available resource that captures the intricate processes governing the limbs' rapid development during the early stages of limb formation.

The atlas also uncovers new links between developmental cells and some congenital limb syndromes, such as short fingers and extra digits.

Limbs are known to initially emerge as undifferentiated cell pouches on the sides of the body, without a specific shape or function.

However after 8 weeks of development, they are well differentiated, anatomically complex and immediately recognisable as limbs, complete with fingers and toes.

This requires a very rapid and precise orchestration of cells.

Any small disturbances to this process can have a downstream effect, which is why variations in the limbs are among the most frequently reported syndromes at birth, affecting approximately one in 500 births globally.

While limb development has been extensively studied in mouse and chick models, the extent to which they mirror the human situation remained unclear.

However, advances in technology now enable researchers to explore the early stages of human limb formation.

In this new study, scientists from the Wellcome Sanger Institute, Sun Yat-sen University, and their collaborators analysed tissues between 5 and 9 weeks of development.

This allowed them to trace specific gene expression programs, activated at certain times and in specific areas, which shape the forming limbs.

Special staining of the tissue revealed clearly how cell populations differentially arrange themselves into patterns of the forming digits.

As part of the study, researchers demonstrated that certain gene patterns have implications for how the hands and feet form, identifying certain genes, which when disrupted, are associated with specific limb syndromes like brachydactyly -- short fingers -- and polysyndactyly -- extra fingers or toes.

The team were also able to confirm that many aspects of limb development are shared between humans and mice.

Overall, these findings not only provide an in-depth characterisation of limb development in humans but also critical insights that could impact the diagnosis and treatment of congenital limb syndromes.

Professor Hongbo Zhang, senior author of the study from Sun Yat-sen University, Guangzhou, said: "Decades of studying model organisms established the basis for our understanding of vertebrate limb development. However, characterising this in humans has been elusive until now, and we couldn't assume the relevance of mouse models for human development. What we reveal is a highly complex and precisely regulated process. It is like watching a sculptor at work, chiselling away at a block of marble to reveal a masterpiece. In this case, nature is the sculptor, and the result is the incredible complexity of our fingers and toes."

Dr Sarah Teichmann, senior author of the study from the Wellcome Sanger Institute, and co-founder of the Human Cell Atlas, said: "For the first time, we have been able to capture the remarkable process of limb development down to single cell resolution in space and time. Our work in the Human Cell Atlas is deepening our understanding of how anatomically complex structures form, helping us uncover the genetic and cellular processes behind healthy human development, with many implications for research and healthcare. For instance, we discovered novel roles of key genes MSC and PITX1 that may regulate muscle stem cells. This could offer potential for treating muscle-related disorders or injuries."

Read more at Science Daily

Where do our limbs come from?

An international collaboration that includes scientists from the University of Colorado School of Medicine has uncovered new clues about the origin of paired appendages -- a major evolutionary step that remains unresolved and highly debated.

The researchers describe their study in an article published today in the journal Nature.

"This has become a topic that comes with bit of controversy, but it's really a very fundamental question in evolutionary biology: Where do our limbs come from?" says co-corresponding author Christian Mosimann, PhD, associate professor and Johnson Chair in the Department of Pediatrics, Section of Developmental Biology at CU School of Medicine.

That question -- where do our limbs come from? -- has been subject of debate for more than 100 years. In 1878, German scientist Carl Gegenbaur proposed that paired fins derived from a source called the gill arch, which are bony loops present in fish to support their gills. Other scientists favor the lateral fin fold hypothesis, concluding that lateral fins on the top and bottom of the fish are the source of paired fins.

"It is a highly active research topic because it's been an intellectual challenge for such a long time," Mosimann says. "Many big labs have studied the various aspects of how our limbs develop and have evolved." Among those labs are Dr. Mosimann's colleagues and co-authors, Tom Carney, PhD, and his team at the Lee Kong Chian School of Medicine at Nanyang Technological University in Singapore.

Chasing the odd cells

For Mosimann, the inquiry into where limbs come from is an offshoot of other research conducted by his laboratory on the CU Anschutz Medical Campus. In his laboratory, his team uses zebrafish as a model to understand the development from cells to organs. He and his team study how cells decide their fate, looking for explanations for how development can go awry leading to congenital anomalies, in particular cardiovascular and connective tissue diseases.

Along the way, Mosimann and his lab team observed how a peculiar cell type with features of connective tissue cells, so-called fibroblasts that share a developmental origin with the cardiovascular system, migrated into specific developing fins of the zebrafish. It turns out that these cells may support a connection between the competing theories of paired appendage evolution.

"We always knew these cells were odd," he says. "There were these fibroblast-looking cells that went into the so-called ventral fin, the fin at the belly of the developing zebrafish. Similar fibroblast cells didn't crawl into any other fin except the pectoral fin, which are the equivalent of our arms. So we kept noticing these peculiar fibroblasts, and we could never make sense of what these were for many years."

The Mosimann lab has developed several techniques to track cell fates during development in pursuit of their main topic, which is an improved understanding of how the embryonic cell layer, called the lateral plate mesoderm, contributes to diverse organs. The lateral plate mesoderm is the developmental origin of the heart, blood vessels, kidneys, connective tissue, as well as major parts of limbs.

The paired fins that form the equivalent of our arms and legs are seeded by cells from the lateral plate mesoderm, while other fins are not. Understanding how these particular fins became more limb-like has been at the core of a long-standing debate.

Developing new theories

Hannah Moran, who is pursuing her PhD in the Cell Biology, Stem Cells and Development program in the Mosimann lab, adapted a method of tracking lateral plate mesoderm cells that contribute to heart development so that researchers could track the peculiar fibroblasts related to limb development.

"My primary research project focuses on the development of the heart rather than limb development," Moran says, "but there was a genetic technique that I had adapted to map early heart cells, and so we were able to implement that into mapping where the mysterious cells of the ventral fin came from. And turns out, they are also from the lateral plate mesoderm."

This crucial discovery provides a new puzzle piece to the big picture of how we evolved our arms and legs. Increasing evidence supports a hypothesis of paired appendage evolution called the dual origin theory.

"Our data fit nicely into this combined theory, but it can also stand on its own with the lateral fin theory," says Robert Lalonde, PhD, postdoctoral fellow in the Mosimann lab. "While paired appendages arise from the lateral plate mesoderm, that does not rule out an ancient connection to unpaired, lateral fins."

By observing the mechanisms of embryonic development and comparing the anatomy of existing species, research groups like Mosimann's can develop theories on how embryonic structures may have evolved or have been modified over time.

"The embryo has features that are still ancient remnants that they have not lost yet, which provides insight into how animals have evolved," Mosimann says. "We can use the embryo to learn more about features that just persist today, allowing us to kind of travel back in time," Mosimann says. "We see that the body has a fundamental, inherent propensity to form bilateral, two-sided structures. Our study provides a molecular and genetic puzzle piece to resolve how we came to have limbs. It adds to this 100-plus year discussion, but now we have molecular insights."

International collaboration

Collaborations with colleagues in laboratories across the country and around the world are another important part of the study. Those scientists bring additional specializations and contribute data from other models, including paddlefish, African clawed frogs, and a variant of split-tail goldfish called Ranchu, to study embryonic development.

"There are labs on this on this paper that work on musculoskeletal diseases, toxicology, fibrosis. We work on cardiovascular, congenital anomalies, cardiopulmonary anomalies, limb development, all related to our interest on the lateral plate mesoderm," says Mosimann. "And then together, you get to make such fundamental discoveries. And that's where team science enables us to do something that is more than just the sum of the parts."

For all the considerable work and significance of the study, the Mosimann team recognizes that it is a key step, but not the end of the journey in the debate about paired appendages.

Read more at Science Daily

Dead fish breathes new life into the evolutionary origin of fins and limbs

A trove of fossils in China, unearthed in rock dating back some 436 million years, have revealed for the first time that the mysterious galeaspids, a jawless freshwater fish, possessed paired fins.

The discovery, by an international team, led by Min Zhu of the Institute of Vertebrate Palaeontology and Palaeoanthropology, Bejiing and Professor Philip Donoghue from the University of Bristol's School of Earth Sciences, shows the primitive condition of paired fins before they separated into pectoral and pelvic fins, the forerunner to arms and legs.

Until now, the only surviving fossils of galeaspids were heads, but these new fossils originating in the rocks of Hunan Province and Chongqing and named Tujiaaspis after the indigenous Tujia people who live in this region, contain their whole bodies.

Theories abound on the evolutionary beginnings of vertebrate fins and limbs -- the evolutionary precursors of arms and legs -- mostly based on comparative embryology. There is a rich fossil record, but early vertebrates either had fins or they didn't. There was little evidence for their gradual evolution.

First author Zhikun Gai, a University of Bristol alumnus, said: "The anatomy of galeaspids has been something of a mystery since they were first discovered more than half a century ago. Tens of thousands of fossils are known from China and Vietnam, but almost all of them are just heads -- nothing has been known about the rest of their bodies -- until now.

"The new fossils are spectacular, preserving the whole body for the first time and revealing that these animals possessed paired fins that extended continuously, all the way from the back of the head to the very tip of the tail. This is a great surprise since galeaspids have been thought to lack paired fins altogether."

Corresponding author Professor Donoghue said: "Tujiaaspis breathes new life into a century old hypothesis for the evolution of paired fins, through differentiation of pectoral (arms) and pelvic (legs) fins over evolutionary time from a continuous head-to-tail fin precursor.

"This 'fin-fold' hypothesis has been very popular but it has lacked any supporting evidence until now. The discovery to Tujiaaspis resurrects the fin-fold hypothesis and reconciles it with contemporary data on the genetic controls on the embryonic development of fins in living vertebrates."

Corresponding author Min Zhu of VPP, Beijing, added "Tujiaaspis shows the primitive condition for paired fins first evolved. Later groups, like the jawless osteostracans show the first evidence for the separation of muscular pectoral fins, retaining long pelvic fins that reduced to the short muscular fins in jawed vertebrates, such as in groups like placoderms and sharks. Nevertheless, we can see vestiges of elongate fin-folds in the embryos of living jawed fishes, which can be experimentally manipulated to reproduce them. The key question is why did fins first evolve in this way?"

Bristol's Dr Humberto Ferron used computational engineering approaches to simulate the behaviour of models of Tujiaaspis with and without the paired fins. The co-author said: "The paired fins of Tujiaaspis act as hydrofoils, passively generating lift for the fish without any muscular input from the fins themselves. The lateral fin-folds of Tujiaaspis allowed it to swim more efficiently."

Co-author Dr Joseph Keating at Bristol modelled the evolution of paired fins. He said: "Fossil jawless vertebrates display a dizzying array of fin types, which has provoked extensive debate about the evolution of paired fins.

Read more at Science Daily

New research challenges long-held beliefs about limb regeneration

Ken Muneoka is no stranger to disrupting the field of regeneration; for example, in a 2019 ground-breaking publication in Nature, the Texas A&M University College of Veterinary Medicine & Biomedical Sciences (CVMBS) professor proved for the first time that joint regeneration in mammals was possible.

Now, his team is again challenging other centuries-old beliefs about the fundamental science of the field, this time related to how mammals might regenerate damaged parts of the body.

In humans, the natural ability to regenerate is limited to tissues like the epidermis, the outermost layer of skin, and some organs, such as the liver.

Other species, most notably salamanders, have the ability to regenerate complex structures such as bones, joints, and even entire limbs. As a result, scientists have been studying these species for more than 200 years to try to understand the mechanisms behind limb regeneration in the hopes of someday translating those mechanisms to induce more extensive regeneration in humans.

That research has led to a common belief that the single biggest key for limb regeneration is the presence of nerves.

While that may be true for salamanders and other species, it isn't the case in mammals, according to two of Muneoka's recently published studies. The first study, published last year in the Journal of Bone and Mineral Research, established that mechanical loading (the ability to apply force to or with an affected area) is a requirement for mammals. The second, published earlier this year in Developmental Biology, established that the absence of nerves does not inhibit regeneration.

Together, these findings present a sizeable shift in the thinking of how regeneration could work in human medicine.

"What these two studies show counteracts the two-century-old dogma that you need nerves to regenerate," Muneoka said. "What replaces it in mammals is that you need mechanical loading, not nerves."

Importance Of Mechanical Load

Scientists have long believed that two things must be present in an affected area in order to induce regeneration in mammals. The first is growth factors, which are molecules that can stimulate cells to regrow and reconstruct parts of the body.

In natural regeneration, these growth factors, which vary from species to species and by area being regenerated, are produced by the body. For human-induced regeneration, these growth factors must be introduced to the area.

The second factor believed to be necessary was nerves. This belief was predicated by many previous human-induced mammal regeneration studies on areas, usually digit tips, without nerves, in which the whole limbs were also no longer usable.

Those studies would have the predicted outcome -- when growth factors were introduced regeneration did not take place-leading to the conclusion that, like in other species, nerves were a requirement for regeneration.

But the mechanical load aspect was ignored.

In their studies, Muneoka and colleagues decided to take a step back and ask the question, "is it really the nerves, or is lack of mechanical load part of the equation as well?"

Connor Dolan, a former graduate student in Muneoka's lab and first author on both new studies (who now works at the Walter Reed National Military Medical Center), came up with a way to test the denervation requirement in mammals that was inspired by astronauts.

The technique, called hindlimb suspension, has been used by NASA and other scientists for decades to test how mammals react to zero gravity environments. A similar process is used during medical procedures on legs of large animals to prevent the animals from putting weight on the affected limbs.

"Dolan found that when the limbs were suspended, even though they still had lots of nerves and could move around, they couldn't actually put pressure on their limbs so the digit tips wouldn't regenerate," Muneoka said. "It just completely inhibited regeneration."

As soon as the mechanical load returns, however, regeneration is rescued.

"Absolutely nothing happens during the suspension," Muneoka said. "But once the load returns, there will be a couple weeks of delay, but then they'll begin to regenerate."

That first step proved that even though nerves might be required, the mechanical loading was a critical component to regeneration.

Taking the research a step further, Dolan's second publication showed that nerves weren't required by demonstrating that if a mouse has no nerves in one of its digits but does in the others -- so that it's still exerting force on the denervated digit -- that digit will still regenerate.

"He found that they regenerate a little bit slower, but they regenerated perfectly normally," Muneoka said.

Ramifications Of The Research

Muneoka is quick to point out that their studies aren't saying that previous research is wrong, just that it doesn't directly apply to humans.

"There have been a number of studies in salamanders that prove that when you remove the nerves, they do not regenerate," Muneoka said. "Researchers have also been able to put growth factors they know are being produced by nerves into the cells and rescue regeneration.

"So, salamanders probably do need nerves to regenerate," he said. "But if we're going to regenerate limbs in humans, it's going to be a lot more like what happens in mice."

Since first beginning to look at regeneration more than 20 years ago, a number of Muneoka's ideas have pushed back against the generally accepted theories about regeneration. He said that getting these two papers published took almost three years because they originally tried to submit them together.

"Many scientists don't embrace this idea," he said. "A lot of people's careers are really dependent on their studies of nerves and how they affect regeneration. For a study to come out and say that for humans it's unlikely you'll need the nerves, the whole biomedical application of what people are doing in salamanders and fish kind of goes out the window."

Looking Down The Road

Nerves not being required for regeneration in mammals may seem like an academic point. After all, what would be the point of regenerating a limb if the person couldn't feel it or control it because it had no nerves. In that sense, nerves are still going to be an important part of the puzzle.

From Muneoka's perspective, the shift is that instead of thinking of nerves as a requirement for regeneration, nerves are a part of what needs to be regenerated.

Larry Suva, head of the CVMBS' Department of Veterinary Physiology & Pharmacology (VTPP), says the issue is that nobody was even thinking about the load aspect previously.

"Think of a blast injury where a soldier is left with a stump," Suva said. "No one, until this paper came out, was even thinking about a requirement from mechanical influences. You had people see that a denervated animal doesn't regenerate and they're thinking it's because the nerve was cut, but nobody was studying the mechanical load aspect."

As Suva puts it, science is full of people looking where the light is best.

"I work on bones, so when I see a problem, I look at the bone problem," he said. "People who work on nerves, all they look at are nerves. So it's very rare that someone like Dr. Muneoka will take a step back and take a more holistic view.

"That's what he brought to this idea, to this 200-year-old data," Suva said. "We now have to look at regeneration through a different lens because now we know the mechanical influences are extremely important."

One of the results of research focusing on nerves is that scientists have been able to recreate the growth factors that nerves produce, which has allowed researchers to start regeneration in salamanders, even if the nerves aren't present. Suva said that with these new findings, scientists will now know they have to do the same with the mechanical load aspect if they want to start regeneration in mammals.

"Scientists already have been able to trick the body into thinking nerves are still present," he said. "But now they know they'll also have to trick it into thinking there's a mechanical load, something that has not been done before."

Because cells react differently under mechanical load, somehow, that load is being translated biochemically inside the cell.

"There's a small number of labs looking at the biochemical basis for what mechanical load does to a cell," Muneoka said. "If we could understand that biochemical signal, then perhaps the physical force of mechanical load can be replaced by some sort of cocktail of molecules that will create the same signals in the cells."

The end of the road toward full human regeneration may still be a long way in the future, but Suva says that this kind of fundamental shift in thinking is a major marker on that road.

"Regeneration of a human limb may still be science fiction, but we know some facts about it, and now we know you have to have that mechanical load along with the growth factors," he said. "That changes how future scientists and engineers are going to solve this problem.

Read more at Science Daily

Scientists regrow frog's lost leg

For millions of patients who have lost limbs for reasons ranging from diabetes to trauma, the possibility of regaining function through natural regeneration remains out of reach. Regrowth of legs and arms remains the province of salamanders and superheroes.

But in a study published in the journal Science Advances, scientists at Tufts University and Harvard University's Wyss Institute have brought us a step closer to the goal of regenerative medicine.

On adult frogs, which are naturally unable to regenerate limbs, the researchers were able to trigger regrowth of a lost leg using a five-drug cocktail applied in a silicone wearable bioreactor dome that seals in the elixir over the stump for just 24 hours. That brief treatment sets in motion an 18-month period of regrowth that restores a functional leg.

Many creatures have the capability of full regeneration of at least some limbs, including salamanders, starfish, crabs, and lizards. Flatworms can even be cut up into pieces, with each piece reconstructing an entire organism. Humans are capable of closing wounds with new tissue growth, and our livers have a remarkable, almost flatworm-like capability of regenerating to full size after a 50% loss.

But loss of a large and structurally complex limb -- an arm or leg -- cannot be restored by any natural process of regeneration in humans or mammals. In fact, we tend to cover major injuries with an amorphous mass of scar tissue, protecting it from further blood loss and infection and preventing further growth.

Kickstarting Regeneration

The Tufts researchers triggered the regenerative process in African clawed frogs by enclosing the wound in a silicone cap, which they call a BioDome, containing a silk protein gel loaded with the five-drug cocktail.

Each drug fulfilled a different purpose, including tamping down inflammation, inhibiting the production of collagen which would lead to scarring, and encouraging the new growth of nerve fibers, blood vessels, and muscle. The combination and the bioreactor provided a local environment and signals that tipped the scales away from the natural tendency to close off the stump, and toward the regenerative process.

The researchers observed dramatic growth of tissue in many of the treated frogs, re-creating an almost fully functional leg. The new limbs had bone structure extended with features similar to a natural limb's bone structure, a richer complement of internal tissues (including neurons), and several "toes" grew from the end of the limb, although without the support of underlying bone.

The regrown limb moved and responded to stimuli such as a touch from a stiff fiber, and the frogs were able to make use of it for swimming through water, moving much like a normal frog would.

"It's exciting to see that the drugs we selected were helping to create an almost complete limb," said Nirosha Murugan, research affiliate at the Allen Discovery Center at Tufts and first author of the paper. "The fact that it required only a brief exposure to the drugs to set in motion a months-long regeneration process suggests that frogs and perhaps other animals may have dormant regenerative capabilities that can be triggered into action."

The researchers explored the mechanisms by which the brief intervention could lead to long-term growth. Within the first few days after treatment, they detected the activation of known molecular pathways that are normally used in a developing embryo to help the body take shape.

Activation of these pathways could allow the burden of growth and organization of tissue to be handled by the limb itself, similar to how it occurs in an embryo, rather than require ongoing therapeutic intervention over the many months it takes to grow the limb.

How the BioDome Works

Animals naturally capable of regeneration live mostly in an aquatic environment. The first stage of growth after loss of a limb is the formation of a mass of stem cells at the end of the stump called a blastema, which is used to gradually reconstruct the lost body part. The wound is rapidly covered by skin cells within the first 24 hours after the injury, protecting the reconstructing tissue underneath.

"Mammals and other regenerating animals will usually have their injuries exposed to air or making contact with the ground, and they can take days to weeks to close up with scar tissue," said David Kaplan, Stern Family Professor of Engineering at Tufts and co-author of the study. "Using the BioDome cap in the first 24 hours helps mimic an amniotic-like environment which, along with the right drugs, allows the rebuilding process to proceed without the interference of scar tissue."

Next Steps in Frogs and Mammals

Previous work by the Tufts team showed a significant degree of limb growth triggered by a single drug, progesterone, with the BioDome. However, the resulting limb grew as a spike and was far from the more normally shaped, functional limb achieved in the current study.

The five-drug cocktail represents a significant milestone toward the restoration of fully functional frog limbs and suggests further exploration of drug and growth factor combinations could lead to regrown limbs that are even more functionally complete, with normal digits, webbing, and more detailed skeletal and muscular features.

"We'll be testing how this treatment could apply to mammals next," said corresponding author Michael Levin, Vannevar Bush Professor of Biology in the School of Arts & Sciences, director of the Allen Discovery Center at Tufts, and associate faculty member of the Wyss Institute.

Read more at Science Daily

From fins to limbs

 When tetrapods (four-limbed vertebrates) began to move from water to land roughly 390 million years ago it set in motion the rise of lizards, birds, mammals, and all land animals that exist today, including humans and some aquatic vertebrates such as whales and dolphins.

The earliest tetrapods originated from their fish ancestors in the Devonian period and are more than twice as old as the oldest dinosaur fossils. They resembled a cross between a giant salamander and a crocodile and were about 1-2 meters long, had gills, webbed feet and tail fins, and were still heavily tied to water. Their short arms and legs had up to eight digits on each hand and foot and they were probably ambush predators, lurking in shallow water waiting for prey to come near.

Scientists know how the fins of fish transformed into the limbs of tetrapods, but controversies remain about where and how the earliest tetrapods used their limbs. And, while many hypotheses have been proposed, very few studies have rigorously tested them using the fossil record.

In a paper published January 22 in Science Advances an international team of researchers examined three-dimensional digital models of the bones, joints, and muscles of the fins and limbs of two extinct early tetrapods and a closely related fossil fish to reveal how function of the forelimb changed as fins evolved into limbs. The research led by Julia Molnar, Assistant Professor at New York Institute of Technology College of Osteopathic Medicine and Stephanie Pierce, Thomas D. Cabot Associate Professor of Organismic and Evolutionary Biology at Harvard University, discovered three distinct functional stages in the transition from fins to limbs, and that these early tetrapods had a very distinct pattern of muscle leverage that didn't look like a fish fin or modern tetrapod limbs.

To reconstruct how limbs of the earliest known tetrapods functioned, Molnar, Pierce and co-authors John Hutchinson (Royal Veterinary College), Rui Diogo (Howard University), and Jennifer Clack (University of Cambridge) first needed to figure out what muscles were present in the fossil animals. A challenging task as muscles are not preserved in fossils, and the muscles of modern fish fins are completely different from those of tetrapod limbs. The team spent several years trying to answer the question, how exactly did the few simple muscles of a fin become dozens of muscles that perform all sorts of functions in a tetrapod limb?

"Determining what muscles were present in a 360-million-year-old fossil took many years of work just to get to the point where we could begin to build very complicated musculoskeletal models," said Pierce. "We needed to know how many muscles were present in the fossil animals and where they attached to on the bones so we could test how they functioned."

They built three-dimensional musculoskeletal models of the pectoral fin in Eusthenopteron (a fish closely related to tetrapods that lived during the Late Devonian period about 385 million years ago) and the forelimbs of two early tetrapods, Acanthostega (365 million years old living towards the end of the Late Devonian period) and Pederpes (348-347 million years old living during the early Carboniferous period). For comparison, they also built similar models of the pectoral fins of living fishes (coelacanth, lungfish) and forelimbs of living tetrapods (salamander, lizard).

To determine how the fins and limbs worked, the researchers used computational software originally developed to study human locomotion. This technique had been used recently to study locomotion in the ancestors of humans and also dinosaurs like T. rex, but never in something as old as an early tetrapod.

Manipulating the models in the software, the team were able to measure two functional traits: the joint's maximum range of motion and the muscles' ability to move the fin or limb joints. The two measurements would reveal trade-offs in the locomotor system and allow the researchers to test hypotheses of function in extinct animals.

The team found the forelimbs of all terrestrial tetrapods passed through three distinct functional stages: a "benthic fish" stage that resembled modern lungfish, an "early tetrapod" stage unlike any extinct animal, and a "crown tetrapod" stage with characteristics of both lizards and salamanders.

"The fin from Eusthenopteron had a pattern that was reminiscent of the lungfish, which is one of the closest living relatives of tetrapods," said Pierce. "But the early tetrapod limbs showed more similarities to each other than either fish or modern tetrapods."

"That was perhaps the most surprising," said Molnar. "I thought Pederpes, and possibly Acanthostega, would fall pretty well within the range of modern tetrapods. But they formed their own distinct cluster that didn't look like a modern tetrapod limb or a fish fin. They were not smack dab in the middle but had their own collection of characteristics that probably reflected their unique environment and behaviors."

The results showed that early tetrapod limbs were more adapted for propulsion rather than weight bearing. In the water, animals use their limbs for propulsion to move themselves forward or backward allowing the water to support their body weight. Moving on land, however, requires the animal act against gravity and push downward with their limbs to support their body mass.

This doesn't mean that early tetrapods were incapable of moving on land, but rather they didn't move like a modern-day living tetrapod. Their means of locomotion was probably unique to these animals that were still very much tied to the water, but were also venturing onto land, where there were many opportunities for vertebrate animals but little competition or fear from predators.

"These results are exciting as they independently support a study I published last year using completely different fossils and methods," said Pierce. "That study, which focused on the upper arm bone, indicated that early tetrapods had some capacity for land movement but that they may not have been very good at it."

The researchers are closer to reconstructing the evolution of terrestrial locomotion, but more work is needed. They plan to next model the hind limb to investigate how all four limbs worked together. It has been suggested that early tetrapods were using their forelimbs for propulsion, but modern tetrapods get most of their propulsive power from the hind limb.

Read more at Science Daily