upregulation is associated with ectopic mandibular cartilage development in amphibians.

BACKGROUND

The emergence of novel structures during evolution is crucial for creating variation among organisms, but the underlying processes which lead to the emergence of evolutionary novelties are poorly understood. The gnathostome jaw joint is such a novelty, and the incorporation of expression into the intermediate first pharyngeal arch may have played a major role in the evolution of this joint. Knockdown experiments revealed that loss of function leads to the loss of the jaw joint, because Meckel's cartilage and the palatoquadrate fuse during development. We used and to further investigate the function of in amphibians. expression levels were upregulated through the use of Ly-294,002 and we investigated the potential consequences of the enhanced expression in amphibians to test the hypothesized joint inducing function of .

RESULTS

We show that Ly-294,002 upregulates expression in vivo. Additionally, ectopic mandibular arch derived cartilages develop after Ly-294,002 treatment. These ectopic cartilages are dorsoventrally oriented rods situated lateral to the palatoquadrate. The development of these additional cartilages did not change the muscular arrangement of mandibular arch-derived muscles.

CONCLUSIONS

Development of additional mandibular cartilages is not unusual in larval anurans. Therefore, changes in the expression during evolution may have been the reason for the development of several additional cartilages in the larval anuran jaw. Furthermore, our observations imply a joint-promoting function of , which further substantiates its hypothetical role in the evolution of the gnathostome jaw joint.