i'm telling ya- it's induction.
induction, in
biology, refers to the initiation or cause of a change or process, such as the production of a specific
morphogenetic effect in the developing
embryo.
http://en.wikipedia.org/wiki/induction_(biology)
i remember a q similar to this on my dat.
Check this paper out
teeth were lost in birds 7080 million years ago. Current thinking holds that it is the avian cranial neural crest-derived mesenchyme that has lost odontogenic capacity, whereas the oral epithelium retains the signaling properties required to
induce odontogenesis. To investigate the odontogenic capacity of ectomesenchyme, we have used neural tube transplantations from mice to chick embryos to replace the chick neural crest cell populations with mouse neural crest cells. The mouse/chick chimeras obtained show evidence of tooth formation showing that avian oral epithelium
is able to induce a nonavian developmental program in mouse neural crest-derived mesenchymal cells.
Tooth development, in common with the formation of many other vertebrate organs, involves reciprocal series of epithelialmesenchymal interactions (
1). These inductive interactions are mediated by diffusible factors between oral epithelium and neural crest-derived mesenchyme (
2,
3). In the mouse embryo, the initiation period of tooth development extends from embryonic day (e) 8, when crest cells first emerge from the cranial neural folds, to e11, when local thickenings of the oral epithelium are formed (
4
6). The epithelium then invaginates into the underlying mesenchyme to form the tooth bud (e12.513).
Classical tissue recombination experiments and more recent molecular analysis have identified the oral epithelium as providing the instructive information for the initiation of mouse tooth development. The e911 presumptive dental epithelium can elicit tooth formation even in neural crest-derived mesenchyme that does not normally form teeth, but is not
able to induce tooth formation in a nonneural crest-derived mesenchyme, such as the limb mesenchyme (
4,
7). By e12, the odontogenic potential shifts to the mesenchyme, which can instruct any kind of epithelium to form tooth-specific structures (
7
9). These experiments point to the importance of epithelial signals in the initiation of mouse tooth formation.
http://www.pnas.org/content/100/11/6541.full