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Contents:

1) Birds that make teeth (Press Release)

Gone does not necessarily mean forgotten, especially in biology. A recent finding by researchers at the University of Wisconsin, Madison, and colleagues from the University of Manchester have found new evidence that the ability to form previously lost organs--in this case, teeth--can be maintained millions of years after the last known ancestor possessed them.

Birds do not have teeth. However, their ancestors did--about 70 - 80 million years ago. The evolutionary loss of teeth corresponded to the formation of the beak that is present in all living birds. Nonetheless, it has been known that if mouse tooth-forming tissue is in contact with bird jaw tissue, the bird tissue is able to follow the instructions given by the mouse tissue and participate in making teeth, and that these teeth look very much like those of mammals. However, Drs. Matthew Harris and John F. Fallon and colleagues have found that modern birds retain the ability to make teeth even without instruction from their tooth-bearing cousins.

Full text at:

http://www.eurekalert.org/pub_releases/2006-02/cp-btm021506.php


2) The Development of Archosaurian First-Generation Teeth in a Chicken Mutant

[Harris et al., Current Biology, Feb '06]

Summary:

Modern birds do not have teeth. Rather, they develop a specialized keratinized structure, called the rhamphotheca, that covers the mandible, maxillae, and premaxillae. Although recombination studies have shown that the avian epidermis can respond to tooth-inductive cues from mouse or lizard oral mesenchyme and participate in tooth formation 1; 2, attempts to initiate tooth development de novo in birds have failed. Here, we describe the formation of teeth in the talpid2 chicken mutant, including the developmental processes and early molecular changes associated with the formation of teeth. Additionally, we show recapitulation of the early events seen in talpid2 after in vivo activation of β-catenin in wild-type embryos. We compare the formation of teeth in the talpid2 mutant with that in the alligator and show the formation of decidedly archosaurian (crocodilian) first-generation teeth in an avian embryo. The formation of teeth in the mutant is coupled with alterations in the specification of the oral/aboral boundary of the jaw. We propose an epigenetic model of the developmental modification of dentition in avian evolution; in this model, changes in the relative position of a lateral signaling center over competent odontogenic mesenchyme led to loss of teeth in avians while maintaining tooth developmental potential.

Summary available at:

http://www.current-biology.com/content/article/abstract?uid=PIIS0960982206000649

One of the authors (John F. Fallon) sent me a copy of the full paper yesterday. His email address is at the link above. Contact me here if you have any difficulty.

John Latter

Model of an Internal Evolutionary Mechanism
http://members.aol.com/jorolat/index.html

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technorati tags: birds, mandible, epidermis, mouse, lizard, tooth+formation, teeth, chicken, evolution, developmental, molecular, embryo, alligator, formation, epigenetic, jaw, recapitulation, biology, university, wisconsin, madison, manchester, organs, ancestor, mutant, avian

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