evolution and development of primate teeth
diversity of mammalian teeth upper left molars buccal mesial distal lingual Jernvall & Salazar-Ciudad 07
trends in dental evolution many similar single-cusped teeth multi-cusped teeth different types of multi-cusped teeth I C P M M homodont evolution heterodont
questions morphology: nr. of teeth, tooth types nr. of cusps, cusp morphology and configuration patterns of variability dental structure and function evolution: homologies and homoplasies trends development: genetic background epigenetics dental morphogenesis and pattern formation
I3 C P1 P3 M1 primitive mammals dental formulae strepsirrhines platyrrhines catarrhines
tritubercular theory: E.D. Cope (1875) and H.F. Osborn (1888) H. F. Osborn (1888): The evolution of mammalian molars to and from the tritubercular type. The American Naturalist 22 (264), 1067-1079.
basic concept trigon buccal max. mesial talon evolution buccal mand. mesial talonid trigonid
hypothetical molars of primitive mammals buccal (lateral) Para- Meta- Proto- Hypo- mesial (anterior) maxillary mandibular distal (posterior) Proto- Para- Meta- Hypoconulid R -Cone -Conid Ento- lingual (medial) L
hypothetical molars of primitive mammals: tribosphenic occlusion buccal (lateral) mesial (anterior) distal (posterior) R lingual (medial) L
dual origin of tribosphenic mammals Luo et al. (2001) Nature 409, 53-57
Luo et al. (2001) Dual origin of tribosphenic mammals. Nature 409, 53-57
mammalian molars: evolutionary trends buccal (lateral) mesial (anterior) max. mand. distal (posterior) + - Hypoconus Paraconid lingual (medial) R L
mammalian molars: evolutionary trends and occlusion buccal (lateral) mesial (anterior) distal (posterior) R lingual (medial) L
Molars: evolutionary trends: Hominoids max. mand. ( ) ( ): frequently lost ( ) crista obliqua (ridge) Y5 (Dryopithecus) pattern (grooves)
Molars: evol. trends: Cercopithecoids bilophodonty (2 cristae)
Hominoids vs. Cercopithecoids Gorilla Papio
dental development teeth are ectodermal appendages develop through interaction of ectodermal epithelium with underlying mesenchyme (derived from neural crest cells) --> general developmental homology with limb formation --> specific developmental homology with hair, glands, feathers, etc.
limb and tooth development apical ectoderm ridge bromdesoxyuridine fibroblast growth factor ectoderm mesenchym anterior (zone of polarizing activity) sonic hedgehog bone morphogenetic protein medial Freeman (2000) Feedback control of intercellular signalling in development. Nature 408: 313-319 Jernvall (1995) Mammalian molar cusp patterns: Developmental mechanisms of diversity. Acta Zool. Fennica 198: 1 61
http://bite-it.helsinki.fi/ dental development 1 2 3 4 5 6 (crown formation) 7 (root formation)
dental development ectodermal cells neural crest cells http://8e.devbio.com/article.php?ch=13&id=274 (after Thesleff and Sahlberg 1996; photographs from Chai et al. 2000)
dental development: reciprocal signaling between ectoderm and mesenchyme ectoderm mesenchyme enamel knot (signaling center) Jernvall & Thesleff 2000
reiterative signaling (patterning cascade) Jernvall & Salazar-Ciudad 07
reiterative signaling and evolutionary tinkering (early carnivores) (late herbivores) evolution after Jernvall & Salazar-Ciudad 2007
dental development: genetics and morphogenesis gene network proliferation differentiation after Jernvall & Salazar-Ciudad 2007
dental development: gene network EK cells produce: non-ek cells produce: activator activates EK differentiation suppresses proliferation of epithelial cells inhibitor inhibits EK differentiation promotes proliferation of mesenchyme cells EK: enamel knot (transient signaling center)
dental development: gene network model EK differentiation activator BMPs etc. inhibitor FGFs SHH etc. epithelial proliferation mesenchymal proliferation after Salazar-Ciudad & Jernvall, 2002
theoretical basis: Alan M. Turing (1912-1954) reaction-diffusion model of morphogenesis (1952) two different chemical reactions between an activator and an inhibitor different diffusion rates of activator and inhibitor far-from-equilibrium conditions (metabolism): constant feed/removal of reactants input activator inhibitor output
Turing s reaction-diffusion model "I "t = R 1 (I, A) + D I # 2 I I "A "t = R 2 (I, A) + D A # 2 A A + reaction" diffusion" reaction" diffusion" Turing, A.M. (1952). The chemical basis of morphogenesis. " Phil. Trans. Roy. Soc. London B 237: 37 "
RD model and morphogenesis diffusive instability --> pattern formation segmentation of embryos insect wing patterns amphibian/reptilian skin patterns mammalian fur patterns dental cusp patterns à Kondo, S & Miura T (2010). Reaction-diffusion model as a framework for understanding biological pattern formation. Science 329: 1616-1620
RD applets on the web http://cgjennings.ca/toybox/turingmorph/ http://texturegarden.com/java/rd/ http://crossgroup.caltech.edu/stchaos/bar.html http://hopf.chem.brandeis.edu/yanglingfa/pattern/osctu/
dental development pattern formation epithelial cells mesenchymal cells + enamel knot formation morphogenesis cusp formation through differential cell division
morphodynamic model: pattern formation and morphogenesis Salazar-Ciudad I & Jernvall J (2002) A gene network model accounting for development and evolution of mammalian teeth. PNAS 99, 8116 8120
model data and empirical data Salazar-Ciudad I & Jernvall J (2002) A gene network model accounting for development and evolution of mammalian teeth. PNAS 99, 8116 8120
morphodynamics: simultaneous pattern formation and morphogenesis Salazar-Ciudad I, Jernvall J & Newman SA (2003) Mechanisms of pattern formation in development and evolution Development 130, 2027-2037
modeling dental evolution Major transitions in mammalian molar evolution require small changes in the model parameters. The top pair show modeled triconodont and pretribosphenic shapes of lower molar. Salazar-Ciudad & Jernvall (2002)