[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

RE: Chicken embryo grows dino-snout




Take two.


----- Forwarded Message -----
> From: Jura <pristichampsus@yahoo.com>
> To: "dinosaur@usc.edu" <dinosaur@usc.edu>
> Cc: 
> Sent: Thursday, 18 August 2011 11:25 PM
> Subject: Re: Chicken embryo grows dino-snout
> 
> Newscientist apparently want to be annoying and insist on registration just 
> to 
> read their articles. It's free, but pointless. Below is the article in its 
> entirety:
> 
> *crosses fingers and hopes the truncation demon is sleeping*
> 
> ______________________________________________________________________________
> 
> 
> Reverse evolution: Chicken revisits its dinosaur past 17 August 2011 by 
> Sujata 
> Gupta
> 
> 
> Evolution has been rewound to create a "snouted" chicken. That means 
> we might also be able to fast-forward it to create the animals of the future 
> ARHAT ABZHANOV cuts a square hole in  the shell of a chicken egg, drops in a 
> small gelatinous bead and watches the embryo develop. By day 14, the chick 
> has 
> formed not a beak but something more snoutish - a feature, he says, "modern 
> birds have not seen since the Cretaceous". Abzhanov has rewound evolution. 
> Chickens share a common ancestor with alligators and are descended from 
> dinosaurs, raising the question of how they and other birds switched from 
> snouts 
> to beaks. Because chick and gator embryos start out looking strikingly 
> similar, 
> Abzhanov, an evolutionary biologist at Harvard University, suspected the key 
> might be found in developing embryos. In his open-egg experiment he tweaked a 
> few of the embryo's genes to make them behave more like identical genes do 
> in an alligator embryo.
> 
> If rewinding evolution has a certain Frankenstein-esque quality, the opposite 
> is 
> even more intriguing. Fast-forwarding evolution to create the chickens of the 
> future may also lie within grasp. And that, in theory, could lead to the 
> creation of species better equipped to handle a changing climate.Mounting 
> evidence shows that small modifications in when and where genes are switched 
> on 
> are all that'
s in anatomy. These 
> changes can lead to the appearance of beaks, turtle shells and jaws (see 
> "Qucks and duails"). Generally, the genes that control these major 
> anatomical changes produce signalling molecules. In a developing embryo, 
> these 
> switch on genes controlling the formation of structures such as limbs, organs 
> and facial features. Other genes dictate where the molecules are produced and 
> therefore where they take effect, ensuring that embryos don't grow digits in 
> the wrong places, misshapen bones or an extra pair of
> eyes.Abzhanov's "snouted" chicken provides a striking 
> demonstration of just how easy it can be to provoke major evolutionary 
> changes, 
> says Craig Albertson, a developmental biologist at the University of 
> Massachusetts in Amherst. Before such experiments were possible, explanations 
> for how creatures evolved "relied on the fossil record, which is 
> incomplete, and mathematical modelling, which is boring".
> 
> So how did he do it? Abzhanov started by trying to pinpoint the gene changes 
> that led to the myriad beak shapes of Galapagos finches. In 2004, he showed 
> that 
> all the finches share a handful of genes crucial to beak development, but 
> instructions for the signalling molecules they control vary from bird to bird 
> (Science, vol 305, p 1462). Abzhanov realised that a similar process might 
> underlie the much bigger evolutionary shift from snouts to beaks.The tip of 
> an 
> alligator snout is made of a separate set of paired bones called the 
> premaxillary, but in birds, these have fused with the main of the upper jaw 
> to 
> form a single, sharp bone.
> Abzhanov scanned signalling molecules in alligator and chick embryos and 
> found 
> that two of them - known as sonic hedgehog and fibroblast growth factor 8 - 
> show 
> up before the snout and beak form. In gators, however, the molecules were 
> only 
> present along the sides of the face. Chicks express them both at the sides 
> and 
> centre of the developing face. What would happen, he wondered, if he turned 
> that
proteins that stick to the signalling molecules 
> and deactivate them. As the molecules arrived at the centre of the embryonic 
> chick face - around day 5 - Abzhanov added his bead to the mix. Sure enough, 
> the 
> chicks developed paired bones. "It looks exactly like a snout looks in an 
> alligator [at this stage]," says Abzhanov, who presented his findings on 23 
> July at the Jackson Laboratory in Bar Harbor, Maine. Ethics regulations mean 
> no 
> such eggs can be hatched.
> 
> Long term Abzhanov, dreams of turning chickens back into Maniraptora, small 
> dinosaurs thought to have given rise to the 10,000 species of birds around 
> today. Others have similar musings. Palaeontologist Jack Horner described the 
> basic principles in a book he co-wrote with James Gorman, How to Build a 
> Dinosaur (Dutton Books, 2009), and regularly speaks of a future 
> "chickenosaurus". "We are interested in finding a way to extend 
> the tail and create a hand in the chicken," Horner told New Scientist, but 
> would not elaborate.The realisation that all it takes to create novel traits 
> is 
> a little genetic fine-tuning raises the possibility of engineering those 
> shifts 
> ourselves. Could we build the creatures of the future?
> 
> To a degree, we are already doing that, says Albertson. He and others are 
> crossing closely related species - those that could conceivably pair on their 
> own - and studying the resulting genetic changes. Sometimes those crosses 
> result 
> in novel creatures. For instance, Albertson crossed blue cichlid fish from 
> neighbouring but separate populations and was surprised to find some of the 
> offspring were red. He is trying to identify the genes and molecules 
> involved, 
> and says there is a possible advantage to the change. Some lakes that are 
> home 
> to cichlids are becoming increasingly murky, making it difficult for males to 
> attract females with their colourful scales. Could it be that the bright red 
> fish might have the edge, allowing the species to survive a more polluted 
> world?
> 
> A
sh, may still 
> be some way off, says Richard Schneider, of the University of California at 
> San 
> Francisco. So far, there are no ways to turn signalling pathways on; we can 
> only 
> rewind, not fast-forward evolution.Understanding these subtleties could have 
> a 
> huge impact on medicine. Many developmental abnormalities - cleft palate for 
> instance - arise from changes in gene signalling. Could we tweak them in a 
> developing embryo? "I can envision a day when we eliminate such defects in 
> the womb," says Jill Helms, a stem cell biologist at Stanford University in 
> Califorina.
> 
> 
> Qucks and duails
> ______________
> 
> It's a perplexing fact that species as dissimilar as flies and humans share 
> most of the same DNA. What could possibly trigger the huge differences in 
> body 
> structures? The first real clue emerged in the late 1970s, when Edward Lewis 
> and 
> colleagues discovered genes in the fruit fly that are now known to control 
> development in all animals. Specifically, Lewis found that genes in the 
> "bithorax complex" give rise to flies' body segments. By tweaking 
> them, Lewis grew a mutant fruit fly with an extra segment - giving them an 
> extra 
> pair of wings. Since then, Richard Schneider and Jill Helms have crossed 
> quails 
> and ducks to isolate the genes responsible for developing the beak. When they 
> transplanted the cells that give rise to beaks from one bird to the other, 
> they 
> swapped beaks. Quails grew wide bills and ducks grew pointy little quail 
> beaks - 
> the team had made qucks and duails. That suggested the cells were 
> pre-programmed 
> to build a specific beak and were
> simply following instructions in the host body. This led to the realisation 
> that 
> key evolutionary stages may have happened when changes in existing genes 
> switched on new pathways - a theory Scott Gilbert, an evolutionary 
> developmental 
> biologist at Swarthmore College in Pennsylvania, all but confirmed with his 
> work 
> in turtles. Gilbert showed that turtles had tapped into an ancient evolutionar
m limbs in other 
> animals - to their skin. In effect, turtles flipped their ribcage inside out 
> to 
> produce a shell. "A small gene change," says Gilbert, "can give 
> you birth defects or evolution."
>