Title:
A periodic pattern generator for dental diversity
A periodic pattern generator for dental diversity
Author(s)
Fraser, Gareth J.
Bloomquist, Ryan F.
Streelman, J. Todd
Bloomquist, Ryan F.
Streelman, J. Todd
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Abstract
Background: Periodic patterning of iterative structures is a fundamental process during
embryonic organization and development. Studies have shown how gene networks are employed
to pattern butterfly eyespots, fly bristles and vertebrate epithelial appendages such as teeth,
feathers, hair and mammary glands. Despite knowledge of how these features are organized, little
is known about how diversity in periodic patterning is generated in nature. We address this
problem through the molecular analysis of oral jaw dental diversity in Lake Malawi cichlids, where
closely related species exhibit from 1 to 20 rows of teeth, with total teeth counts ranging from
around 10 to 700.
Results: We investigate the expression of conserved gene networks (involving bmp2, bmp4, eda,
edar, fgf8, pax9, pitx2, runx2, shh and wnt7b) known to pattern iterative structures and teeth in
other vertebrates. We show that spatiotemporal variation in expression pattern reflects adult
morphological diversity among three closely related Malawi cichlid species. Combinatorial epithelial
expression of pitx2 and shh appears to govern the competence both of initial tooth sites and future
tooth rows. Epithelial wnt7b and mesenchymal eda are expressed in the inter-germ and inter-row
regions, and likely regulate the spacing of these shh-positive units. Finally, we used chemical
knockdown to demonstrate the fundamental role of hedgehog signalling and initial placode
formation in the organization of the periodically patterned cichlid dental programme.
Conclusion: Coordinated patterns of gene expression differ among Malawi species and prefigure
the future-ordered distribution of functional teeth of specific size and spacing. This variation in gene
expression among species occurs early in the developmental programme for dental patterning.
These data show how a complex multi-rowed vertebrate dentition is organized and how
developmental tinkering of conserved gene networks during iterative pattern formation can impact
upon the evolution of trophic novelty.
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Date Issued
2008-07-14
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