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Gene expression in alligators suggests birds have 'thumbs'
October 06, 2008The latest breakthrough in a 120 year-old debate on the evolution of the bird wing was published in the open-access journal PLoS ONE, October 3, by Alexander Vargas and colleagues at Yale University, the University of Wisconsin-Madison and Yale Peabody Museum of Natural History.
Bird wings only have three fingers, having evolved from remote ancestors that, like humans and most reptiles, had five fingers. Biologists have typically used embryology to identify the evolutionary origin (homology) of structures; the three fingers of the bird wing develop from cartilage condensations that are found in the same positions in the embryo as fingers two, three and four of humans (the index, middle and ring fingers). However, the morphology of the fingers of early birds such as Archaeopteryx corresponds to that of fingers one, two and three in other reptiles (thumb, index and middle finger). The fossil record clearly shows that fingers four and five (ring and pinky finger) were lost and reduced in the dinosaur ancestors of birds.
Further, the lack of expression of the HoxD-11 gene in the first finger of the wing makes it most similar to finger one (the "thumb") of the mouse, consistent with comparative morphology. However, the mouse is only distantly related to birds; crocodilians, in turn, are bird's closest living relatives.
To see whether the evidence from mouse HoxD-11 expression held up, Vargas and colleagues, working at the lab of Gunter Wagner at Yale, have examined the expression of this gene in alligators; they found the expression to be, as in mice, absent only in finger one (the "thumb").
Developmental and evolutionary biologists are familiar with the phenomenon of homeotic transformations, in which one structure begins to develop at a different position within the body. A famous example is the case of the fruitfly mutant antennapaedia, which develops legs on its head instead of antennae. The new work by Vargas et al. rekindles the hypothesis that a "hometic frameshift" occurred in the evolution of the bird wing, such that fingers one, two and three began to develop from the embryological positions of fingers two, three and four.
Public Library of Science
To see whether the evidence from mouse HoxD-11 expression held up, Vargas and colleagues, working at the lab of Gunter Wagner at Yale, have examined the expression of this gene in alligators; they found the expression to be, as in mice, absent only in finger one (the "thumb").
Developmental and evolutionary biologists are familiar with the phenomenon of homeotic transformations, in which one structure begins to develop at a different position within the body. A famous example is the case of the fruitfly mutant antennapaedia, which develops legs on its head instead of antennae. The new work by Vargas et al. rekindles the hypothesis that a "hometic frameshift" occurred in the evolution of the bird wing, such that fingers one, two and three began to develop from the embryological positions of fingers two, three and four.
Public Library of Science
Gene Expression Current Events and Gene Expression News RSSDeciphering the regulatory code
Embryonic development is like a well-organised building project, with the embryo's DNA serving as the blueprint from which all construction details are derived.
Experimental agent reduces breast cancer metastasis to bone
Researchers have reduced breast cancer metastasis to bone using an experimental agent to inhibit ROCK, a protein that was found to be over-expressed in metastatic breast cancer.
Geneticists Hunt for Scleroderma Triggers
At its most benign, the autoimmune disease scleroderma can discolor parts of the skin of its sufferers. At its most pernicious, it can thicken and harden their skin, their blood vessels, and their internal organs before, in many cases, killing them.
Hunting for the Prozac Gene
Prozac works wonders for some depressed people, but not for others. In some cases, patients derive little benefit and at worst, it can lead to bizarre hallucinations and fits of rage.
Changes in brain chemicals mark shifts in infant learning
When do you first leave the nest? Early in development infants of many species experience important transitions-such as learning when to leave the protective presence of their mother to start exploring the wider world.
Study finds mercury levels in children with autism and those developing typically are the same
In a large population-based study published online today, researchers at the UC Davis MIND Institute report that after adjusting for a number of factors, typically developing children and children with autism have similar levels of mercury in their blood streams. Mercury is a heavy metal found in other studies to adversely affect the developing nervous system.
A master mechanism for regeneration?
Biologists long have marveled at the ability of some animals to re-grow lost body parts. Newts, for example, can lose a leg and grow a new one identical to the original. Zebrafish can re-grow fins.
Checkered history of mother and daughter cells explains cell cycle differences
When mother and daughter cells are created each time a cell divides, they are not exactly alike. They have the same set of genes, but differ in the way they regulate them.
Small mechanical forces have big impact on embryonic stem cells
Applying a small mechanical force to embryonic stem cells could be a new way of coaxing them into a specific direction of differentiation, researchers at the University of Illinois report. Applications for force-directed cell differentiation include therapeutic cloning and regenerative medicine.
The food-energy cellular connection revealed
Our body's activity levels fall and rise to the beat of our internal drums-the 24-hour cycles that govern fundamental physiological functions, from sleeping and feeding patterns to the energy available to our cells.
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Gene Wilder Autographed 8x10 Photo Beautiful photograph. Printed on photographic paper from an actual negative. Add to your collection. Will look great on a media room wall. Please check out the rest of our collection. Will be adding more. |
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