The “Msx1, a feedback activator of Bmp4 expression” with the Osr2 control gene has been discovered to switch between single vs multiple sets of teeth. E.g. distinguishing between humans and sharks. This efficient compact control mechanism appears to fit well within an ID Design paradigm. The serious cleft pallet defects caused by errors further suggest an irreducibly complex system.
What evidence might there be for random mutation and “selection” to form such a complex yet elegant control system so “early” in evolution?
Finding genes that make teeth grow all in a row By LAURAN NEERGAARD, AP Thursday, February 26, 2009
Ever wonder why sharks get several rows of teeth and people only get one? . . .A single gene appears to be in charge, preventing additional tooth formation in species destined for a limited set. When the scientists bred mice that lacked that gene, the rodents developed extra teeth next to their first molars _ backups like sharks and other non-mammals grow, University of Rochester scientists reported Thursday. . . .Also intriguing: All the mice born without this gene, called Osr2, had cleft palates severe enough to kill. So better understanding of this gene might play a role in efforts to prevent that birth defect, the Rochester team reported in the journal Science.
Teeth may not be visible until long after birth, but they start to form early in embryo development. Teeth ultimately erupt from a thickened band of tissue along the jaw line called the dental lamina, a band that forms in a top layer of the gum called the epithelium.
. . . All the action takes place instead in a deeper cell layer called the mesenchyme.
Think of the Osr2 gene as a control switch, a kind of gene that turns on and off the downstream actions of other genes and proteins. In that mesenchymal tissue, the Osr2 gene works in concert with two other genes to make sure budding teeth form in the right spot, said lead researcher Dr. Rulang Jiang, a geneticist at Rochester’s Center for Oral Biology.
See: full article.
Antagonistic Actions of Msx1 and Osr2 Pattern Mammalian Teeth into a Single Row
Zunyi Zhang, Yu Lan, Yang Chai, Rulang Jiang
Science 27 February 2009: Vol. 323. no. 5918, pp. 1232 – 1234;
Mammals have single-rowed dentitions, whereas many nonmammalian vertebrates have teeth in multiple rows. Neither the molecular mechanism regulating iterative tooth initiation nor that restricting mammalian tooth development in one row is known. We found that mice lacking the transcription factor odd-skipped related-2 (Osr2) develop supernumerary teeth lingual to their molars because of expansion of the odontogenic field. Osr2 was expressed in a lingual-to-buccal gradient and restricted expression of bone morphogenetic protein 4 (Bmp4), an essential odontogenic signal, in the developing tooth mesenchyme. Expansion of odontogenic field in Osr2-deficient mice required Msx1, a feedback activator of Bmp4 expression. These findings suggest that the Bmp4-Msx1 pathway propagates mesenchymal activation for sequential tooth induction and that spatial modulation of this pathway provides a mechanism for patterning vertebrate dentition.