The developmental basis for jaw size variation in evolution and disease

Abstract

Variation in jaw size was critical for the adaptive evolution of vertebrates, yet variation during development is often associated with disease. To test the hypothesis that NC progenitor number and proliferation rates contribute to variation in jaw size, we compared NC development in two birds with distinct jaw size, duck and quail. At stage HH10, duck and quail embryos have substantial differences in brain shape and expression of the brain regionalization genes, Pax6, Otx2, Fgf8, and Krox20. There is no significant difference in Pax7‐postive NC precursors in HH8 duck and quail embryos. But by HH13, duck embryos have nearly twice as many Dlx2‐positive NC in their jaw primordia as do quail, a ratio which is maintained in HH20 embryos. At HH20, quail NC divide 1.4 times faster than duck NC, however, quail embryos also develop 1.6 times faster during this developmental window. After reduction of NC precursors, post‐migratory NC compensate within the jaw primordia to produce a symmetric and relatively normally sized jaw. Importantly, while chick undergo complete compensation, ablated duck embryos form slightly smaller than normal jaws. Our results suggest that modification of multiple aspects of NC cell biology was important to the evolution of large jaw size. Further, our finding of compensatory mechanisms opens avenues for treatment of disease associated with NC progenitors loss.Grant Funding Source: none