09-P021 Atonal regulates Rfx during chordotonal organ development in the Drosophila

base. The anterior cranial base shows an abnormal differentiation of chondrocytes in the mutant, with reduced proliferation and increased terminal differentiation. The main factors responsible to restrict Six2 function to the anterior portion of the cranial base are the tissue-specific transcription of the gene and the presence of compensatory effects from other Six family members, in particular Six1 and Six4. Gain of function experiments indicate that Six2 has a general effect on endochondral bone formation and can affect cartilage development and growth in other body areas. It is likely that Six2 acts by controlling general regulators of chondrocyte differentiation. Our data suggest that Six2 acts to control locally the level of the IGF-axis.