Lmx1a is a member of the LIM homeodomain containing transcription factors and plays an important role during embryonic development. Specifically, it is required for the proper formation of several structures in the central nervous system, such as the roof plate, the cerebellum, and the inner ear. All these defects may contribute to the neurological phenotype observed in dreher mice, lacking functional Lmx1a protein. Interestingly, this factor was also found to promote midbrain dopaminergic neuron fate. We have introduced Green fluorescent protein (GFP) coding sequences into the Lmx1a locus by homologous recombination, and created knockout mice where GFP recapitulates the Lmx1a endogenous expression pattern.