this article was in my morning news.
http://my.earthlink.net/article/hea?guid=20090226/49a621d0_3ca6_1552620090226219486010

Very interesting Maureen, Thanks for sharing!

Thanks for bringing that interesting article to my attention, Maureen. The evolutionary explanation for why sharks, reptiles, etc. can replace teeth indefinitely and mammals cannot has to do with the complex pattern of projections and hollows in mammalian teeth. Mammals are the only vertebrates that have the jaw musculature to chew extensively because of how the bones in the skull are restructured (actually lost) to form the zygomatic arch to which the powerful jaw muscles attach. So our having only two sets of teeth is related to the fundamentals of how our teeth do their job. So the challenge may be getting teeth that are able to fit against those of the other jaw. As for the source of teeth, from the underlying tissue, that's am interesting tale, too. Of course, nobirds have teeth, but you can get a chicken embryo to grow teeth if you transplant a piece of the underlying tissue from an embryonic mouse jaw into the mouth of a chicken embryo. The teeth that form are not mouse teeth, but chicken teeth! This is interpreted that the underlying tissue produces a signal that says "make teeth" and that birds lost the ability to make this signal. But the tooth-forming tissues have not lost the ability to respond, and the mouse signal is so similar to the ancestral bird signal that it still works.

Sorry-just saw a chance to share one of my favorite stories about developmental biology!

What I found interesting is the link they seem to have discovered between missing teeth as one expression of the decreased influence of this piece of DNA and cleft palates from the absence of it. It sort of gives another reason to consider whether incomplete dentition is an undesirable genetic trait.

As I have said for years, the worst thing a dog with missing teeth can produce is NOT just more missing teeth. I have had bad bites in multiple litters from dogs with missing premolars - in two different breeds! Now I have to wonder if the incidence of cleft palates in some lines is related as well.

I have a girl with 6 missing teeth who has had multiple puppies with missing teeth- no cleft palates. She also has produced dogs with full dentition.

I have never had a cleft palate, but have used several stud dogs (of different breeds) that have missing teeth and only produced one pup ever with a missing tooth. BOTH of the dogs, however, produced undershot mouths in over 50% of the litters from bitches with good bites and full dentition. It sort of cured me of doing that

I just found the link between clefts and the gene that seems to control dentition interesting. Another thing to make you go... Hmmmmmm.

No undershot mouths either. Ther sound you hear is me knocking on wood.

Makes me go Hmmmmm... since cleft palates are considered to be neural tube defects and can be prevented with folic acid supplementation, one has to wonder how the Osr2 gene would be affected if given this supplement. I am no scientist, but if these mice were given the folic acid and then got no clefts, then one could possibly ascertain that there is no correlation as thought. Would be interesting to explore.

"Makes me go Hmmmmm... since cleft palates are considered to be neural tube defects and can be prevented with folic acid supplementation"

Actually, your comment is missing one word .... SOME. SOME cleft palates are considered to be hereditary, but the mechanism had not been identified previously. This new research seems to shed a different light on SOME of the genetic factors. SOME cleft palates are influenced/prevented by folic acid supplementation. SOME are caused by the teratogenic effects of vitamin A supplementation or toxins. There seem to be a variety of factors involved with suture-line defects. This research deals with just one of them.