Evolutionary modification of development in mammalian teeth: quantifying gene expression patterns and topography.
The study of mammalian evolution often relies on detailed analysis of dental morphology. For molecular patterning to play a role in dental evolution, gene expression differences should be linkable to corresponding morphological differences. Because teeth, like many other structures, are complex and evolution of new shapes usually involves subtle changes, we have developed topographic methods by using Geographic Information Systems. We investigated how genetic markers for epithelial signaling centers known as enamel knots are associated with evolutionary divergence of molar teeth in two rodent species, mouse and vole. Our analysis of expression patterns of Fgf4, Lef1, p21, and Shh genes in relation to digital elevation models of developing tooth shapes shows that molecular prepatterns predict the lateral cusp topography more than a day in advance. A heterotopic shift in the molecular prepatterns can be implicated in the evolution of mouse molar, changing locations from which historically homologous cusps form. The subtle but measurable heterotopic shifts may play a large role in the evolution of tooth cusp topographies. However, evolutionary increase in the number of longitudinal cusps in vole molar has involved accelerated longitudinal growth and iterative addition of new cusps without changes in lateral cusp topography. The iterative addition of cusps after the establishment of lateral cusp topography may limit the independence of individual morphological features used in evolutionary studies. The diversity of mammalian molar patterns may largely result from the heterotopic and iterative processes.
Jernvall
J
J
Institute of Biotechnology, Viikki Biocenter, University of Helsinki, Post Office Box 56 Viikinkaariq, FIN-00014, Helsinki, Finland. jvakudaret@aol.com
Keränen
S V
SV
Thesleff
I
I
D000818:Animals; D003411:Arvicolinae; D005075:Biological Evolution; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics; D051519:Fibroblast Growth Factor 4; D005346:Fibroblast Growth Factors / Q000235:genetics; D020869:Gene Expression Profiling; D053823:Hedgehog Proteins; D051821:Lymphoid Enhancer-Binding Factor 1; D051379:Mice; D008963:Molar / Q000033:anatomy & histology / Q000254:growth & development* / Q000378:metabolism; D011506:Proteins / Q000235:genetics; D011518:Proto-Oncogene Proteins / Q000235:genetics; D014070:Tooth / Q000033:anatomy & histology / Q000254:growth & development* / Q000378:metabolism; D015534:Trans-Activators; D014157:Transcription Factors / Q000235:genetics
C493957:Cdkn1a protein, mouse; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D004268:DNA-Binding Proteins; C496446:Fgf4 protein, mouse; D051519:Fibroblast Growth Factor 4; D053823:Hedgehog Proteins; C497574:Lef1 protein, mouse; D051821:Lymphoid Enhancer-Binding Factor 1; D011506:Proteins; D011518:Proto-Oncogene Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D005346:Fibroblast Growth Factors