Even sharks — which have existed for more than half a billion years— have the recipe for fingers in their genetic cookbook — not to eat them, but to grow them.
While studying the mechanisms of development in shark embryos, UF scientists identified a spurt of genetic activity that is required for digit development in limbed animals.
Previous work suggested that the transition from fins to limbs involved the addition of a late phase of gene activity during embryonic development, something thought to be absent during the development of fish fins.
The finding shows what was thought to be a relatively recent evolutionary innovation existed eons earlier than previously believed, shedding light on how life on Earth developed and potentially providing insight for scientists seeking ways to cure human birth defects, which affect about 150,000 infants annually in the United States.
“We’ve uncovered a surprising degree of genetic complexity in place at an early point in the evolution of appendages,” said developmental biologist Martin Cohn, Ph.D., an associate professor with the UF departments of zoology and anatomy and cell biology and a member of the UF Genetics Institute. “Genetic processes were not simple in early aquatic vertebrates only to become more complex as the animals adapted to terrestrial living. They were complex from the outset. Some major evolutionary innovations, like digits at the end of limbs, may have been achieved by prolonging the activity of a genetic program that existed in a common ancestor of sharks and bony fishes.”
Researchers say the same genes that produced ancient fins likely enlarged their role about 365 million years ago in amphibians struggling to adapt to swamps and terrestrial living, creating a distinct burst of development and more versatile appendages.
Using molecular markers to study the formation of skeletal cartilage in embryos of the spotted catshark, UF scientists isolated and tracked the activity of Hox genes, a group of genes that control how and where body parts develop in all animals, including people.They discovered a phase of gene expression in sharks that was thought until recently to occur only when digits began to form in limbed animals.
Why, then, don’t sharks have fingers?
Renata Freitas and GuangJun Zhang, co-authors of the paper and graduate students in the zoology department of the College of Liberal Arts and Sciences, speculate that sharks and many other types of fish do not form more dramatic appendages during this late phase of Hox gene expression because it occurs briefly and only in a narrow band of cells, compared with the more extended time frame and larger anatomical area needed to prefigure the hand and foot in limbed animals.
“We know when this particular Hox gene is mutated in humans, it results in malformations of fingers and toes,” Cohn said. “Until now it was thought these mutations were affecting a relatively recent innovation in the genetic process of limb development. Our results show that this phase of Hox expression is much more ancient and suggest that if the origin of digits involved a prolonged activity of Hox genes, a truncated period could result in defective digits.”
In a parallel study, researchers at the University of Chicago found this second phase of gene expression in paddlefish, a primitive living descendant of early fish with the first bony skeletons.
Finding the second phase in sharks, which have skeletons consisting not of bone but of cartilage, means the genetic processes necessary to muster fingers and toes existed more than 500 million years ago in the common ancestor of fish with cartilaginous skeletons and bony fish — more than 135 million years before digits debuted in the earliest limbed animals.
“The leap from aquatic life to terrestrial life is an extremely dramatic, important point in evolution that has captured the interest of many,” said Marie Kmita, Ph.D., director of the Genetics and Development Research Unit at the Institut de Recherches Cliniques de Montréal who was not involved in the research. “Understanding how changes in gene regulation modify the body architecture is of extreme interest to scientists who are trying to find ways to improve human health by learning from developmental processes. This work shows a late phase of gene regulation seems fated to the emergence of digits.”
Citation: Freitas R, Zhang GJ, Cohn MJ (2007) Biphasic Hoxd Gene Expression in Shark Paired Fins Reveals an Ancient Origin of the Distal Limb Domain. PLoS ONE 2(8): e754. doi:10.1371/journal.pone.0000754
Andrew Hyde | alfa
'Y' a protein unicorn might matter in glaucoma
23.10.2017 | Georgia Institute of Technology
Microfluidics probe 'cholesterol' of the oil industry
23.10.2017 | Rice University
Salmonellae are dangerous pathogens that enter the body via contaminated food and can cause severe infections. But these bacteria are also known to target...
University of Maryland researchers contribute to historic detection of gravitational waves and light created by event
On August 17, 2017, at 12:41:04 UTC, scientists made the first direct observation of a merger between two neutron stars--the dense, collapsed cores that remain...
Seven new papers describe the first-ever detection of light from a gravitational wave source. The event, caused by two neutron stars colliding and merging together, was dubbed GW170817 because it sent ripples through space-time that reached Earth on 2017 August 17. Around the world, hundreds of excited astronomers mobilized quickly and were able to observe the event using numerous telescopes, providing a wealth of new data.
Previous detections of gravitational waves have all involved the merger of two black holes, a feat that won the 2017 Nobel Prize in Physics earlier this month....
Material defects in end products can quickly result in failures in many areas of industry, and have a massive impact on the safe use of their products. This is why, in the field of quality assurance, intelligent, nondestructive sensor systems play a key role. They allow testing components and parts in a rapid and cost-efficient manner without destroying the actual product or changing its surface. Experts from the Fraunhofer IZFP in Saarbrücken will be presenting two exhibits at the Blechexpo in Stuttgart from 7–10 November 2017 that allow fast, reliable, and automated characterization of materials and detection of defects (Hall 5, Booth 5306).
When quality testing uses time-consuming destructive test methods, it can result in enormous costs due to damaging or destroying the products. And given that...
Using a new cooling technique MPQ scientists succeed at observing collisions in a dense beam of cold and slow dipolar molecules.
How do chemical reactions proceed at extremely low temperatures? The answer requires the investigation of molecular samples that are cold, dense, and slow at...
23.10.2017 | Event News
17.10.2017 | Event News
10.10.2017 | Event News
23.10.2017 | Life Sciences
23.10.2017 | Physics and Astronomy
23.10.2017 | Health and Medicine