Oh Yeah, Developmental Biology!
RSSPosts tagged with "Evolution"
Top 10: Dinosaur Myths
Dinosaurs are fascinating, but half-truths and myths about them are common. New Scientist nails 10 of the most common.
1. Humans lived alongside dinosaurs
2. Mammals only came into being after the dinosaurs died out
3. Dinosaurs died out because mammals ate their eggs
4. An asteroid impact alone killed the dinosaurs
5. Dinosaurs died out because they were unsuccessful in evolutionary terms
6. All dinosaurs died out 65 million years ago
7. Dinosaurs were slow and sluggish animals
8. All large land reptiles from prehistoric times were dinosaurs
9. Marine reptiles - for example, plesiosaurs and ichthyosaurs - were dinosaurs
Belief is for ghost stories and R. Kelly songs about flying.
We go for testable hypotheses followed by careful observation, data collection and refinement of said hypothesis based on our current level of ignorance/knowledge on the subject at hand around these here parts. Now let’s talk about that grammar and use of two different fonts …
(source unknown)
Research Suggests How Fins Became Legs
Vertebrates’ transition to living on land, instead of only in water, represented a major event in the history of life. Now, researchers provide new evidence that the development of hands and feet occurred through the gain of new DNA elements that activate particular genes.
In order to understand how fins may have evolved into limbs, researchers led by José Luis Gómez-Skarmeta and Fernando Casares introduced extra Hoxd13, a gene known to play a role in distinguishing body parts, at the tip of a zebrafish embryo’s fin. Surprisingly, this led to the generation of new cartilage tissue and the reduction of fin tissue – changes that strikingly recapitulate key aspects of land-animal limb development. The researchers wondered whether novel Hoxd13 control elements may have increased Hoxd13 gene expression in the past to cause similar effects during limb evolution. They turned to a DNA control element that is known to regulate the activation of Hoxd13 in mouse embryonic limbs and that is absent in fish.
“We found that in the zebrafish, the mouse Hoxd13 control element was capable of driving gene expression in the distal fin rudiment. This result indicates that molecular machinery capable of activating this control element was also present in the last common ancestor of finned and legged animals and is proven by its remnants in zebrafish,” Casares said.
More:
• Fins to limbs with flip of genetic switch
• They came from the sea: the gene behind limb evolution
• Zebrafish made to grow pre-hands instead of fins
• Turning Fins Into Hands
Turing model for embryonic development of fingers and toes confirmed
Scientists have identified the mechanism responsible for generating our fingers and toes, and revealed the importance of gene regulation in the transition of fins to limbs during evolution. By combining genetic studies with mathematical modeling, the scientists provided experimental evidence supporting a theoretical model for pattern formation known as the Turing mechanism. In 1952, mathematician Alan Turing proposed mathematical equations for pattern formation, which describes how two uniformly-distributed substances, an activator and a repressor, trigger the formation of complex shapes and structures from initially-equivalent cells.
“The Turing model for pattern formation has long been debated, mostly due to the lack of experimental data supporting it,” explained Rushikesh Sheth, co-first author of the study. “By studying the role of Hox genes during limb development, we were able to show, for the first time, that the patterning process that generates our fingers and toes relies on a Turing-like mechanism.”
In humans, as in other mammals, the embryo’s development is controlled, in part, by Hox genes. These genes are essential to the proper positioning of the body’s architecture, and define the nature and function of cells that form organs and skeletal elements.
“Our genetic study suggested that Hox genes act as modulators of a Turing-like mechanism, which was further supported by mathematical tests,” added Marie Kmita, one of the team leaders. “Moreover, we showed that drastically reducing the dose of Hox genes in mice transforms fingers into structures reminiscent of the extremities of fish fins. These findings further support the key role of Hox genes in the transition of fins to limbs during evolution, one of the most important anatomical innovations associated with the transition from aquatic to terrestrial life.”
I have a special place in my heart for all things Turing as he was the subject of my final year dissertation.
Paddlefish’s doubled genome may question theories on limb evolution
The American paddlefish — known for its bizarre, protruding snout and eggs harvested for caviar — duplicated its entire genome about 42 million years ago, according to a new study published in the journal Genome Biology and Evolution. This finding may add a new twist to the way scientists study how fins evolved into limbs since the paddlefish is often used as a proxy for a more representative ancestor shared by humans and fishes.
“We found that paddlefish have had their own genome duplication,” said Karen Crow, assistant professor of biology at San Francisco State University. “This creates extra genetic material that adds complexity to comparative studies. It may change the way we interpret studies on limb development.”
In order to study how human limbs develop, scientists compare the limb-building genes found in mice with fin-building genes found in fishes. Previous research on paddlefish has suggested that fishes possessed the genetic toolkit required to grow limbs long before the evolution of the four-limbed creatures (tetrapods) that developed into reptiles, birds, amphibians and mammals.
In the last decade, paddlefish have become a useful benchmark in evolutionary studies because their position on the evolutionary tree makes them a reasonably good proxy for the ancestor of the bony fishes that evolved into tetrapods such as humans. However, the fact that paddlefish underwent a genome duplication could complicate what its genes tell us about the fin-to-limb transition, says Crow.
More sophisticated wiring, not just a bigger brain, helped humans evolve beyond chimps
from UCLA Newsroom:
Human and chimp brains look anatomically similar because both evolved from the same ancestor millions of years ago. But where does the chimp brain end and the human brain begin?A new UCLA study pinpoints uniquely human patterns of gene activity in the brain that could shed light on how we evolved differently than our closest relative. The identification of these genes could improve understanding of human brain diseases like autism and schizophrenia, as well as learning disorders and addictions.The research appears Aug. 22 in the advance online edition of the journal Neuron.“Scientists usually describe evolution in terms of the human brain growing bigger and adding new regions,” said principal investigator Dr. Daniel Geschwind, the Gordon and Virginia MacDonald Distinguished Professor of Human Genetics and a professor of neurology at the David Geffen School of Medicine at UCLA. “Our research suggests that it’s not only size but the rising complexity within brain centers that led humans to evolve into their own species.”Full paper in Neuron here. For free, if I’m not mistaken!
Clint Eastwood helps reveal secrets of brain evolution
Clint Eastwood might sound like an unlikely candidate to help investigate the evolution of the brain, but he has lent a helping hand to researchers doing just that. It turns out that brain regions that do the same job in monkeys and humans aren’t always found in the same part of the skull.
Previous studies comparing brains across species tended to assume that human brains were just blown-up versions of monkey brains and that functions are carried out by anatomically similar areas.
To test this idea, Wim Vanduffel of Harvard Medical School in Boston and the Catholic University of Leuven (KUL) in Belgium, and colleagues scanned the brains of 24 people and four rhesus monkeys while they watched The Good, The Bad and The Ugly. They compared the brain responses of each individual to the same sensory stimulation, and identified which brain areas had similar functions.
The majority of the human and monkey brain maps lined up, but some areas with a similar function were in completely different places.
The team say the discovery is crucial to building more accurate models of our evolution. “You can’t assume that because A and B are close together in the monkey brain, they need to be close together in the human brain,” Vanduffel says.
Five things humans no longer need.
Vestigial organs are parts of the body that once had a function but are now more-or-less useless. Probably the most famous example is the appendix, though it is now an open question whether the appendix is really vestigial. The idea that we are carrying around useless relics of our evolutionary past has long fascinated scientists and laypeople alike.
This week we tackle vestigial organs in a feature article that looks at how the idea has changed over the years, and how it has come under attack from creationists anxious to deny that vestigial organs (and hence evolution) exist at all. To accompany the article, here is our list of the five organs and functions most likely to be truly vestigial……
Why don’t our arms grow from the middle of our bodies? The question isn’t as trivial as it appears. Vertebrae, limbs, ribs, tailbone … in only two days, all these elements take their place in the embryo, in the right spot and with the precision of a Swiss watch.
During the development of an embryo, everything happens at a specific moment. In about 48 hours, it will grow from the top to the bottom, one slice at a time — scientists call this the embryo’s segmentation. “We’re made up of thirty-odd horizontal slices,” explains Denis Duboule, a professor at EPFL and Unige. “These slices correspond more or less to the number of vertebrae we have.”
Every hour and a half, a new segment is built. The genes corresponding to the cervical vertebrae, the thoracic vertebrae, the lumbar vertebrae and the tailbone become activated at exactly the right moment one after another. “If the timing is not followed to the letter, you’ll end up with ribs coming off your lumbar vertebrae,” jokes Duboule. How do the genes know how to launch themselves into action in such a perfectly synchronized manner? “We assumed that the DNA played the role of a kind of clock. But we didn’t understand how.”
When DNA acts like a mechanical clock
Very specific genes, known as “Hox,” are involved in this process. Responsible for the formation of limbs and the spinal column, they have a remarkable characteristic. “Hox genes are situated one exactly after the other on the DNA strand, in four groups. First the neck, then the thorax, then the lumbar, and so on,” explains Duboule. “This unique arrangement inevitably had to play a role.”
The process is astonishingly simple. In the embryo’s first moments, the Hox genes are dormant, packaged like a spool of wound yarn on the DNA. When the time is right, the strand begins to unwind. When the embryo begins to form the upper levels, the genes encoding the formation of cervical vertebrae come off the spool and become activated. Then it is the thoracic vertebrae’s turn, and so on down to the tailbone. The DNA strand acts a bit like an old-fashioned computer punchcard, delivering specific instructions as it progressively goes through the machine.
“A new gene comes out of the spool every ninety minutes, which corresponds to the time needed for a new layer of the embryo to be built,” explains Duboule. “It takes two days for the strand to completely unwind; this is the same time that’s needed for all the layers of the embryo to be completed.”
This system is the first “mechanical” clock ever discovered in genetics. And it explains why the system is so remarkably precise.
…
The Hox clock is a demonstration of the extraordinary complexity of evolution. One notable property of the mechanism is its extreme stability, explains Duboule. “Circadian or menstrual clocks involve complex chemistry. They can thus adapt to changing contexts, but in a general sense are fairly imprecise. The mechanism that we have discovered must be infinitely more stable and precise. Even the smallest change would end up leading to the emergence of a new species.”(via From blue whales to earthworms, a common mechanism gives shape to living beings)
This is why developmental biology (and evolution and molecular biology and everything) is awesome.
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