Chip and apterous physically interact to form a functional complex during Drosophila development

LIM homeodomain (LIM-HD) proteins play key roles in a variety of developmen tal processes throughout the animal kingdom. Here we show that the LIM-bind ing protein Chip acts as a cofactor for the Drosophila LIM-HD family member Apterous (Ap) in wing development. We define the domains of Chip required for LIM-HD binding and for homodimerization and show that mutant proteins d eleted for these domains act in a dominant-negative fashion to disrupt Ap f unction. Our results support a model for multimeric complexes containing Ch ip and Ap in transcriptional regulation. This model is confirmed by the act ivity of a chimeric fusion between Chip and Ap that reconstitutes the compl ex and rescues the ap mutant phenotype.