KERNEY, Ryan; Harvard University: An unexpected role for the skeletal regulator Runx2 in anuran development

The runt related transcription factor Runx2 has profound effects on differentiation of the vertebrate skeleton. In zebrafish, chicken, and mouse its mRNA is expressed in early skeletal condensations, and its active protein is critical for the formation of mineralized bone and maturation of cartilage. We have investigated the expression pattern of this gene in two frog species: the metamorphosing Xenopus laevis and direct-developing Eleutherodactylus coqui using both RT-PCR and in situ hybridizations. While skeletal specific mRNA expression patterns are conserved, an additional region of mRNA expression is present in the developing central nervous system of both frog species. Morpholino based gene knock-down experiments reveal an important role for Runx2 in both early neurogenesis and the establishment of the tadpole specific chondrocranium. These novel roles for this transcription factor depart from earlier investigations in other model organisms. Additionally, the timing and distribution of Runx2 mRNA expression differs between E. coqui and X. laevis, in accordance with several developmental differences between these two species with varied developmental modes.